BEST MANAGEMENT PRACTICES IN THE ARROYO SECO

Transcription

1 BEST MANAGEMENT PRACTICES IN THE ARROYO SECO Francisco Fernandez AECOM

2 Table of Contents Executive Summary Introduction The Arroyo Seco Watershed A Brief History of the Arroyo Seco The Arroyo Seco Foundation Water Issues in the Arroyo Seco Water Quality Depleted Basin and Reliance on Imported Water Habitat Degradation and Wildlife Depletion Existing Plans to Enhance Stormwater Capture, Water Quality and Wildlife Habitat Stormwater Capture Master Plan Upper Los Angeles River Enhanced Watershed Management Program (EWMP) Arroyo Seco Ecosystem Restoration Study Best Management Practices Non-structural BMP s Structural BMP s Bioretention (Rain Gardens) Constructed Wetlands Infiltration Basins Infiltration Trench Media Filters Permeable Pavement Retention Ponds Vegetated Buffer Strip Vegetated Swale Green Streets BMP Ranking Matrix Water Quality Stormwater Capture Habitat Restoration Cost Efficiency... 23

3 3.3.5 Implementation Feasibility BMP Scores Analysis of Outfalls Prioritization Matrix Fifty Year Storm Average Rainfall Area MS4 Permit Sites LA Department of Public Works Testing Sites Prioritization Matrix Results Potential BMPs for the Most Significant Outfalls Altadena Drain Flint Wash W Altadena Drain E Altadena Drain San Rafael Creek North Branch Confluence Seco St Drain Linda Vista Drain Mission St Drain Conclusion and Next Steps References Figure 1 BMP Ranking Matrix Summary... 5 Figure 2 Ten Most Significant Outfalls... 6 Figure 3 Groundwater Basins within the Arroyo Seco Watershed Figure 4 BMP Ranking Matrix Figure 5 Storm Drain Network in Urbanized Arroyo Seco Watershed Figure 6 Catchments Within the Arroyo Seco Watershed Figure 7 50 Year Storm Average Rainfall Scoring Criteria Figure 8 Ranking of Stormwater Outfalls by Average 50 yr Storm Rainfall Figure 9 Drainage Area Scoring Criteria Figure 10 Ranking of Stormwater Outfalls by Area Figure 11 MS4 Permit Sites Within the Arroyo Seco Watershed Figure 12 LA County Public Works Testing Sites Figure 13 Final Ranking of Outfalls Along the Arroyo Seco Channel... 33

4 Figure 14 Proposed BMP Location for Altadena Drain Figure 15 Proposed BMP Location for Flint Wash Figure 16 Proposed BMP Location for W Altadena Drain Figure 17 Proposed BMP Location for E Altadena Drain Figure 18 Proposed BMP Location for San Rafael Creek Figure 19 Proposed BMP Location for North Branch Figure 20 Proposed BMP Location for Confluence Figure 21 Proposed BMP Location for Seco St Drain Figure 22 Proposed BMP Location for Linda Vista Drain Figure 23 Proposed BMP for Mission St Drain... 44

5 Executive Summary With the continual degradation of natural water resources due to anthropogenic activity and current drought conditions, it is becoming of alarming importance for people to protect and ensure the existence of local water resources. Improving the water quality of local streams and rivers would not only create more recreational opportunities for humans but also increase the amount of underutilized resources such as drinking water, produce more wildlife habitat and add aesthetic value of the land. The management of storm water is vital to improving the health of the ecosystem as a substantial amount of water annually flushes through the storm drains, to the rivers, picking up contaminants along the way and making its way to the ocean untreated leading to the degradation of habitats and water quality both locally and downstream. Under the USDA grant, this study was developed for the Arroyo Seco Foundation in order to better understand the utility of BMPs in the Arroyo Seco watershed. Preliminary literature review revealed that throughout its modern history, the Arroyo Seco has faced a variety of challenges which have reshaped its natural watershed. Notable structures that have reshaped the stream s hydrology are Brown Mountain Dam, Devil s Gate Dam and the concrete channel that stretches from the second dam to the Arroyo Seco s confluence with the LA river. These structures along with the increased percentage of impermeable surfaces caused by rapid urbanization have decreased the amount of water that enters the ever depleting Raymond Basin and increased the amount of contaminated stormwater runoff that makes its way into the stream. These conditions have also taken a toll on the native habitats that exist within the watershed and have led to the degradation of an irreplaceable resource. Further research was conducted on a variety of potential BMPs that could be applied in throughout the Arroyo Seco Watershed in order to alleviate the conditions in the watershed. The BMP options that were examined are: 1. Bioretention aka Rain Gardens 2. Constructed Wetlands 3. Infiltration Basins 4. Infiltration Trenches 5. Media Filters 6. Permeable Pavement 7. Retention Ponds 8. Vegetated Buffer Strips 9. Vegetated Swales These BMP s were screened across five different categories: water quality improvement, stormwater capture capability, ability to restore habitat, cost effectiveness and feasibility as they pertain to the specific conditions of the Arroyo Seco watershed. Each BMP was given a score of 1(Low), 3(Moderate) or 5(High) based on its utility in each of the five categories. The scores that a BMP received in every category were then summed in order to give each BMP a total score. Figure 1 below is a summary of the final scores that each BMP received.

6 BMP Type Total Score Bioretention 21 Constructed Wetlands 19 Infiltration Basin 13 Infiltration Trench 13 Media Filter 15 Permeable Pavement 15 Retention Pond 19 Vegetated Swale 17 Vegetated Buffer Strip 17 Figure 1 BMP Ranking Matrix Summary After each BMP was analyzed, the watershed itself was analyzed. Utilizing ArcGIS software, subcatchments for all of the major storm drains and tributaries leading into the urbanized portion of the Arroyo Seco were delineated. Each of these catchments were placed in a ranking matrix that screened through four categories and assigned a score in order to identify which catchments are of higher priority. The four categories used to analyze the catchments were the fifty year storm average rainfall, area and whether or not the outfall of the catchment was considered an MS4 site or a Los Angeles County Public Works Testing Site. The scores that each catchment received across all categories in order to give each catchment a total score. The catchments with the ten highest ranking scores where then prioritized for BMP implementation. Figure 2 below is map of the watershed along with the ten most significant outfalls according to the analysis performed.

7 Figure 2 Ten Most Significant Outfalls The overall task of this study was to propose potential BMPs to the ten most significant outfalls. Next steps include to further analyze the outfalls for flow rates and contaminants and to potentially provide preliminary designs and cost estimates for the proposed BMPs. 1.0 Introduction It is no secret that water, apart from being the building block of life, is also the foundation of civilization. Historically, all major civilizations have been located near a body of water whether it be a lake, a river or the ocean. Waterways provide transportation, irrigation for crops, fish for consumption and ultimately sustain human life and the ecosystem. Living near water however does come with a price. Flooding and other water based natural disasters have destroyed many homes and have claimed many lives throughout history. To combat these natural disasters and reduce the damage that comes from them, societies have taken a variety of measures such as placing flood control dams and channelizing entire rivers. Such is the case for the Arroyo Seco located in Los Angeles County, California. The Arroyo Seco is a relatively dry stream and tributary of the Los Angeles River (LA River) with a tendency to flood ever few years. Devastating flooding in the early 20 th century led to the construction of Devil s Gate Dam

8 and the channelization of the stream downstream of the dam. Since the completion of these flood control structures, the community of the Arroyo Seco has yet to experience such massive flood damage. However, these flood control structures have come at a cost. Substantial wildlife has disappeared from the area and the increase of urbanization has led to the deterioration of the water quality and overall health of the stream. With climate change and drought periods ensueing and the stream along with California s water supply slowly becoming less sustainable, it is of upmost importance for people to radically change the way they manage their resources and develop solutions that both protect human lives from natural disasters and restore the environment while making best use of local resources. Storm water capture and treatment is an increasingly popular practice that allows for the replenishment of groundwater, provides flood attenuation, improvement of water quality and the restoration of the natural environment. Best Management Practices (BMP s) are measures or methods taken to capture storm water and reduce storm water volume at a localized level. Several types of BMP s exist with most falling under the category of either structural BMP s or institutional BMP s. This study proposes the utilization of BMP s as part of an integrated watershed management system for the Arroyo Seco Watershed. The objective of this study is to propose BMP s in the ten most critical outfalls along the urbanized portion of the Arroyo Seco. The BMP s aim to increase groundwater percolation, improve water quality and restore wildlife habitat with the ultimate goal in mind of one day integrating them as part of a naturalized urban stream system. 2.0 The Arroyo Seco Watershed The Arroyo Seco is a 22 mile long stream and a major tributary of the Los Angeles River. The head waters of the stream are located in the San Gabriel Mountains within the Angeles National Forest at elevations of over 6,000 ft. The stream runs through its natural route in the Angeles National Forest down the mountains where it enters the Los Angeles Basin at the foothills in Pasadena near Jet Propulsion Laboratories. Along its urbanized course it passes through the cities of Altadena, Pasadena, La Cañada-Flintridge, South Pasadena, and finally Los Angeles where it meets with the Los Angeles River at its confluence in the neighborhood of Lincoln Heights. The stream is dammed in two locations. Going north to south, the first dam that appears along the stream is Brown Mountain Dam, a debris barrier located in the Angeles National Forest and operated by the US Forest Service (USFS). The second dam that appears going downstream is Devil s Gate Dam which is a flood control dam located in the City of Pasadena just north of the 210 Freeway and operated by the Los Angeles County Flood Control District (LACFCD). South of Devil s Gate Dam the stream becomes channelized and is encased entirely in a concrete channel for the rest of its route except for at two distinct locations. These locations are immediately south of Devils Gate Dam before entering Brookside Golf Course and a section just south of Brookside Park under the Colorado Street Bridge. The stream s watershed drains approximately 47 square miles with about two thirds of that area being located in the mountains. The remainder of the watershed is urbanized and consist primarily residential parcels with sporadic open space which includes parks and golf courses. The stream and its watershed are a

9 historical and cultural landmark that contain some of the most significant locations in the Los Angeles (LA) area. 2.1 A Brief History of the Arroyo Seco The land through which the Arroyo Seco flows was once referred to by the Tongva Native Americans as Hahamogna, a word meaning the land of flowing waters, fruitful valley. Arroyo Seco, which translates from Spanish to literary mean dry stream, was the name given to the stream by Spanish explorer Gaspar de Portola in 1770 as it had been driest stream he had explored to date. Contrary to its name, the Arroyo Seco is actually still known for its frequent flash flooding during major storm events. Historically the stream supported a diverse array of riparian habitat and served as a wildlife corridor marked by Alders, Sycamores, Willows and riparian vegetation. The stream historically provided habitat to several now locally endangered species such as the Arroyo Toad and the anadromous Steelhead Trout. Early Spanish and Mexican settlers learned to tap into the natural perennial springs that occurred throughout the area and pumped the groundwater for agricultural use. The acquisition of California by the United States as well as the Gold Rush of 1948 prompted many settlers from the Eastern US to settle in the area. Increases in population over time slowly began to put a strain on the environment and local water resources. Rising urbanization also began to reshape the natural hydrology of the stream. Subsequent flood events in 1914 and 1916 led to the construction of Devil s Gate Dam in This was the first dam built by the LACFCD. Throughout the 1930s and 1940s, the stream was channelized and encased in concrete. In 1940, the Historic Arroyo Seco Parkway was opened to the public. This was the first freeway in the west coast and was designed to connect downtown Los Angeles with the City of Pasadena. This freeway follows alongside the Arroyo Seco from its confluence all the way up to Lower Arroyo Park in South Pasadena. In 1942, the US Forest Service built Brown Mountain Dam on the Arroyo Seco within the Angeles National Forest. This dam served as a test for other debris barriers in the area. The construction of these structures as well as the increase in urban development have reshaped the hydrology of the watershed. The addition of the aforementioned structures as well as an ongoing increase in urbanization, development and groundwater pumping within the watershed has led to a wide range of water associated issues in the Arroyo Seco as well as the degradation of one of Southern California s most valuable natural resources The Arroyo Seco Foundation The Arroyo Seco is a non-profit organization based in north LA county within the stream s watershed. The Arroyo Seco Foundation was originally founded by Charles Lummis in the early twentieth century as a means of protecting and conserving the Arroyo Seco. The foundation ceased to exist for a while, however it was restarted in the late 1980 s and to this day continues to carry out its original mission of protecting the Arroyo Seco and increasing awareness of our

10 local stream to neighboring communities. This study was developed and completed through the foundation. 2.2 Water Issues in the Arroyo Seco Every watershed faces its own unique set of water issues. The Arroyo Seco has historically been used as an experiment for flood control structures and has suffered severe habitat degradation and impaired water quality. The channelization of the stream and increase in development have increased the amount of impermeable surfaces which in turn has contributed to the depletion of local aquifers. I would suggest explaining the importance of impermeable surfaces in this section, it will set up the next discussion Water Quality The quality of water found in any body of water is essential to sustaining life and maintaining a healthy ecosystem. High development levels and urbanization along with other anthropogenic activities have impaired the quality of water in the Arroyo Seco. Vast amounts of impermeable surfaces throughout the watershed contribute to the increase of contaminated urban runoff and stormwater that enters the stream. Numerous water quality test have been made in the Arroyo Seco by varying agencies including Pasadena Water and Power and the Department of Fish and Game. Several studies such as the Arroyo Seco Watershed Management Program have collected this data from varying sources and concluded that the largest cause of water pollution in the Arroyo is a result of coliform bacteria and trash. These contaminants are typically non-point source pollutants that enter the stream as urban runoff or stormwater runoff through the municipal storm and sewer systems. 303(d) Listing In compliance to the Clean Water Act of 1972, every state agency is responsible for listing every body of water that does not meet adequate water quality standards through the regulation of point source pollution alone. These bodies of water are listed in section 303(d) of the Clean Water Act which is referred to as the 303(d) list. The Arroyo Seco has been listed in the 303(d) list for having exceedances of coliform bacteria and trash consecutively in the years 2002, 2006 and The most recent 303(d) listing reports the Arroyo Seco contains an impaired macroinvertebrate community. The cause however, is unknown and requires further research. The Arroyo Seco occasionally exceeds water quality standards for wet weather Mercury and dry weather Bis (2-ethylhexyl) Phthalate (DEHP), however these exceedances do not occur often enough to require 303(d) listing. Data collected under the Upper LA River Enhanced Watershed Management Plan (EWMP) (you may want to explain who published this paper) suggests that the Arroyo Seco exceeds acceptable amounts of wet weather DEHP with enough frequency to be listed in the 303(d) list but has not been listed. DEHP is used in the production of Polyvinyl

11 Chloride (PVC) and does not have a record for causing harm to humans. It does however, have series of detrimental effects on animals. Total Maximum Daily Loads A body of water that is listed in the 303(d) subjects its governing agency to the development of a Total Maximum Daily Load (TMDL). A TMDL is the numeric quantity of a pollutant that a water of body can receive without deterring water quality standards. Numerous TMDLs have been developed for the Los Angeles River Watershed, which include the Arroyo Seco. The two most relevant to the Arroyo Seco are the LA Watershed River Bacteria TMDL and the LA River Watershed Trash TMDL. The numeric value set forth by the 2010 Los Angeles River Bacteria TMDL for fecal coliform bacteria is 400/100 ml for any single sample or 200/100 ml for the geometric mean of five equally spaced samples taken within a month s time. The 2007 Trash TMDL for the LA River Watershed sets forth a numeric target value of zero for trash. The Arroyo Seco currently exceeds all of these target values. The Upper LA River EWMP was developed precisely for the purpose of meeting TMDL values. JPL Superfund Site Jet Propulsion Laboratory (JPL) is a research and development center managed by the California Institute of Technology (Caltech) under a contract with the National Aeronautics and Space Administration (NASA). Originally opened as a military operation, JPL is now a global leader in robotics and space exploration. This federally funded 176 acre site is situated at the mouth of the Arroyo Seco near Hahamogna Watershed Park on the border of Pasadena and La Cañada Flintridge. This site has been acknowledged to contain hazardous waste that includes rocket fuel that has been disposed of improperly throughout the site which in turn has contaminated the local groundwater supply. In the 1980 s various volatile organic chemicals were detected in the groundwater near JPL, which forced local water companies to close down some of their wells. The U.S. Environmental Protection Agency (EPA) declared the area a superfund site in In 1997, exceedingly high levels of perchlorate were found near the facility. Efforts to clean up the site are still ongoing Depleted Basin and Reliance on Imported Water The Raymond Basin is a 40 square mile groundwater basin located between the San Gabriel Mountains and the San Gabriel Valley Basin. The Arroyo Seco along with Eaton Wash are the primary streams responsible for replenishing the groundwater basin. Historically, the basin has been managed by various governing agencies. The abundance of water near the Arroyo Seco was a cause of attraction for many early settlers. For many years, settlements near the Arroyo Seco relied on local water resources to meet all of their needs. The early Spanish and Mexican settlers would haul water from the stream and local perennial springs and artesian aquifers. As the population increased, the demand for water increased, increasing pumping rates and putting a

12 strain on local resources. The construction of the Owens Valley Aqueduct and the State Water Project has have created a dependence on imported water. As these external sources become victims of climate change and exploitation themselves, they are becoming less reliable. Excessive pumping and increase in impermeable surfaces have led the Raymond Basin to become overdrawn, meaning that less water goes into it compared to water being extracted from it each year. The concrete flood channel and other impermeable surfaces in the watershed limit the amount of water that can percolate into the soil and have also contributed to the depletion of the Raymond Basin. Figure 3 shows the location of the Raymond Basin within the Arroyo Seco watershed. The green outline depicts the Arroyo Seco Watershed. Figure 3 Groundwater Basins within the Arroyo Seco Watershed Habitat Degradation and Wildlife Depletion The increase in development and correspondent degradation of water quality has also led to the loss of much vital wildlife habitat. Though the focus of this report is primarily on water resources, it is essential to note that the protection of wildlife is important to water quality as they are both intertwined into an intricate symbiotic system that depend and rely on each other. A healthy ecosystem is usually a good indicator of healthy water quality, therefore restoring

13 habitat is a vital part of the Arroyo Seco Foundation s goal of restoring a fully functioning natural river system. Habitat Destruction and Fragmentation The Arroyo Seco Watershed was historically home to a variety of species which are now endangered locally or at the federal level, such as the anadromous steelhead trout and the arroyo toad. The dams throughout the stream have impeded fish passage, isolating the fish population in the mountain watershed and virtually exterminating the fish population in the urban watershed. The dams also accumulate large loads of sediments which create flood risks and deprive the lower stream of the rich sediments necessary for fish spawning. Populations of terrestrial species have also been isolated due to the habitat fragmentation that has occurred due to the development of the lower watershed. Invasive Plant Species Several invasive plant species such as the giant reed, pampas grass and tree of heaven have become domesticated in the Arroyo Seco. The Giant reed in particular is notorious for lowering the groundwater table, reducing base flow, creating stream blockage andout competing other valuable native plants. They also offer little to no habitat value. The eradication of invasive species is vital to insuring the water and habitat quality in the Arroyo Seco. 2.3 Existing Plans to Enhance Stormwater Capture, Water Quality and Wildlife Habitat Several studies, control measures, and projects focused on improving storm water capture, water quality, and stream restoration have been proposed for the Los Angeles River Watershed which include projects in the Arroyo Seco. Some of the most recent ones that were reviewed in preparation for this report are the Los Angeles Department of Water and Power s Stormwater Capture Master Plan, the Arroyo Seco Ecosystem Restoration Study conducted by the United States Army Core of Engineers and Upper Los Angeles River Enhanced Watershed Management Program Stormwater Capture Master Plan The Stormwater Capture Master Plan (SCMP) prepared by Geosyntec Consultants for the Los Angeles Department of Power and Water (LADWP) is a group of projects and control measures developed to increase the volume of stormwater that is captured and enhance local water supplies, and reduce the reliance on imported water. Currently 85% of the City of Los Angeles s water supply is imported while only 12% is retrieved from local groundwater supplies. Stormwater is an underutilized resource as only 11% of rainfall is captured and stored annually.

14 The SCMP proposes the use of structural measures, notably BMP s, as means of increasing the amount of stormwater captured to be between 24% and 33% by 2099 within the SCMP study area. The study area consists of any watershed within the City of Los Angeles boundary or that drains into the city s boundary. The study area includes the Arroyo Seco and highlights the infiltration galleries at Garvanza Park within the Arroyo Seco watershed as a model project Upper Los Angeles River Enhanced Watershed Management Program (EWMP) The (ULAR EWMP) is a strategic network of control measures developed by the ULAR EWMP Group in order to improve water quality in the ULAR Watershed and meet TMDL objectives. The ULAR EWMP incorporates regional projects, institutionalized BMP s and green infrastructure to improve water quality and provide other benefits to communities such as recreational opportunities and increased local water supply. The EWMP contains a series of key signature projects to help meet its objective, six of which are located within the Arroyo Seco Watershed Arroyo Seco Ecosystem Restoration Study The Arroyo Seco Ecosystem Restoration Study prepared by the United States Army Core of Engineers Los Angeles District in partnership with Los Angeles County of Public Works is an in depth study that screens the Arroyo Seco Watershed for opportunities to restore key natural hydrologic functions back to the stream. This study contains extensive research on the history of the watershed and its current conditions. The study addresses issues in the watershed by developing measures which fall under broad categories. These categories are habitat restoration, flood and erosion control, recreation, water quality, water conservation and non-structural measures. From these measures, several alternatives were developed as potential future restoration projects. These alternatives are adding fish passage, rearing and forage to the stream, reconnecting the stream with its historical floodplains, eradication of invasive plants with revegetation of the area with native plants, wetland restoration and a no action alternative as well. Sites identified for feasible restoration in this study include Hahamongna Watershed Park, Flint Wash, the Brookside Area and Lower Arroyo Park among several others. 3.0 Best Management Practices BMP s are control measures utilized particularly in managing water pollution. Stormwater BMP s specifically deal with managing contaminated stormwater and urban runoff that is discharged through municipal storm systems intolocal rivers and lakes. BMP s can be either structural (e.g. constructed facility) or institutional (e.g. water management education). BMP s provide a wide variety of environmental benefits such as improved water quality, groundwater recharge, and provision of wildlife habitat as well as opportunities for recreation. The scope of this study involves the identification of which BMP s are most feasible for the Arroyo Seco

15 Watershed. A BMP matrix was used to determine feasibility. Each BMP was analyzed and scored in five categories. The categories include water quality improvement, stormwater capture opportunity, habitat restoration, cost efficiency and feasibility. Each BMP was given a score of 1 (Low), 3 (Moderate) or 5 (High) within the five categories. 3.1 Non-structural BMP s Non-structural BMP s, also known as institutional BMP s, are controls measures that are implemented to reduce the concentration of pollutants in storm water runoff that do not require the construction of a treatment facility. Examples of such BMP s are educational programs that aim to inform the public of habits they can partake in to reduce contaminant loads in runoff such as cleaning up pet waste. A street sweeping program aimed at removing trash and debris is another example of a non-structural BMP. Non-structural BMP s do not necessarily reduce the amount of urban runoff, however if used in conjunction with structural BMP s, they can greatly reduce pollutant loads in runoff. Non-structural BMP s will not be assigned as solutions to the contaminant issues identified for the Arroyo Seco watershed in this report. It is important however, to note the benefits that their implementation in conjunction with other structural BMP s coverd in this reportt. 3.2 Structural BMP s Structural BMP s are constructed facilities that are engineered to reduce urban runoff, capture storm water, and improve water quality or a combination of any. Structural BMP practices also provide other benefits such as providing green space, habitat for wildlife, increased or enhanced park lands, flood attenuation and enhanced scenic aesthetics. This study will primarily focus on the use of structural BMP s and their potential application in the Arroyo Seco watershed. The below subsections will summarize and describe the structural BMP s that are appropriate for retention of stormwater in the Arroyo Seco Bioretention (Rain Gardens) Bioretention BMP s, also known as rain gardens, are a shallow impoundment filled with mulch, soils and native vegetation designed to capture, treat and infiltrate stormwater and urban runoff. These BMP s typically consist of an optional pretreatment buffer strip, a ponding area, a mulch layer, planting soils and a vegetative cover. A buffer strip reduces entering flow rate velocities in order to prevent erosion and protect the bioretention BMP. Stormwater enters the bioretention BMP through curb cuts or other inlets and ponds in the ponding area. The water then percolates within a 72 hour time frame where it is filtered and infiltrated by the soils and vegetation s root system. A variant of bioretention BMP also known as biofiltration also exists. Biofiltration BMP s function similarly to bioretention with the addition of an underdrain in order to reduce stormwater volume at a quicker rate in areas were traditional rain gardens cannot reduce

16 stormwater quickly enough. This underdrain also functions to protect groundwater in areas where groundwater contamination is a concern. Biofiltration BMP s have higher costs than traditional rain gardens. Advantages and Benefits: Efficiently removes a wide variety of pollutants, including coliform bacteria. Highly applicable in most settings including residential areas, ultra-urban areas and stormwater hotspots. Provides a great opportunity for habitat restoration. Properly designed rain gardens should resemble the natural ecosystem and include native species. Provides moderate groundwater recharge in areas where percolation is desired. Disadvantages and Constraints: Not suitable for areas where the water table is located less than six feet from the surface. Not applicable in areas exceeding a 20% slope. Regular maintenance is required in order to prevent sediment from clogging the BMP, prevent erosion, and ensure plant health. May provide habitat for mosquitos and other vectors. Bioretention is relatively expensive when compared to other BMP options Constructed Wetlands A constructed wetland BMP is a man-made marsh designed to capture and treat stormwater and urban runoff. Constructed wetlands can exist either as subsurface flow wetlands or free water surface flow wetlands. Subsurface flow wetlands have bottoms lined with gravel and store water beneath the gravel layer. Free water surface flow wetlands typically come in one of four designs: shallow marsh, extended detention wetland, pond/wetland system, and pocket wetlands. Water is routed into the wetland via an inlet into a shallow pretreatment pool known as a sediment forebay. Coarse sediment is removed in the forebay before water is conveyed into the permanent pool where remaining contaminants are allowed to settle and are removed through natural biological processes. Wetlands can be constructed either online or offline, however an offline wetland is highly preferred as online wetlands pose as a potential hazard for native aquatic life and can become a barrier for fish passage. Advantages and Benefits: Efficiently removes a high variety of pollutants, including coliform bacteria. Reduces peak flow for storm events, hence providing erosion control and flood attenuation. Restores habitat and supports a high diversity of native plants and wildlife. Can create more park space and recreational opportunities. Relatively inexpensive when compared to other BMP options.

17 Disadvantages and Constraints: Requires a consistent base flow in order to maintain water levels. Requires the use of soils with low percolation rates in order to maintain its pools, thus limiting the potential for stormwater capture and reuse. Takes up substantial space, approximately 3-5% of drainage its area, limiting its viability in ultra-urban areas. Can behave as a heat sink to raise the temperature of water which in turn can have adverse effects on cold water fish. Serves as a breeding ground for mosquitos and other vectors Infiltration Basins An infiltration basin is a shallow ditch in the ground that is designed to infiltrate stormwater and urban runoff. Infiltration basins utilize relatively permeable soils to infiltrate and treat water. Grass on the basin s surface improves percolation rates and aids in the treatment of runoff. Basins that are designed to capture large storm events may also contain an inlet and outflow control structures such as an underdrain and/or outlet. The design of a properly functioning infiltration basin is highly soil sensitive and thus require substantial site investigation with geotechnical research. Areas with hydrologic soil types C and D are not ideal for this BMP. A properly sited and designed basin will provide numerous water quality benefits and groundwater recharge. Advantages and Benefits: Efficiently removes a wide variety of pollutants in stormwater, including coliform bacteria. Reduces stormwater loads to provide substantial groundwater recharge and maintain low flows in streams. A properly designed basin will mimic predevelopment hydrology. A large enough basin can provide erosion control and flood attenuation. Disadvantages and Constraints: Requires substantial site investigation and geotechnical studies. Failing to do so can result in failure of the BMP Not suitable in areas where the soil has a low percolation rate. Conversely, areas were the percolation rate is too high can potentially pose a threat to groundwater. Has a high failure rate in comparison to other BMP options. Can be relatively expensive when compared to other BMP options.

18 3.2.4 Infiltration Trench Infiltration trenches are long and narrow trenches that are typically filled with gravel or an alternative medium that are designed to capture and treat stormwater and urban runoff. Alternate designs include a perforated pipe in order to capture and convey larger storm events. Infiltration trenches typically do not contain an outlet structure. Water is contained within the void spaces of the media were it eventually flows into the groundwater table. Trenches can be covered with a thin soil layer that can be planted with grass. In areas that receive high sediment or contaminant loads, a pretreatment BMP such as a vegetated swale or buffer strip may be necessary in order to prevent the trench from clogging and to protect the groundwater from contamination. Advantages and Benefits: Efficiently removes a wide variety of pollutants in stormwater, including coliform bacteria. Effectively reduces stormwater loads and provides high levels of groundwater recharge. Its unobtrusive nature creates little to no impact on site aesthetics. An adequately sized trench will provide erosion control and flood attenuation for high frequency storm events Can be placed in narrow otherwise unusable spaces. Disadvantages and Constraints: May require a pretreatment BMP in order to prevent coarse sediment from entering and clogging the infiltration trench. Not suitable in hydrologic soil types C and D. Extensive site investigation and geotechnical analysis is required prior to the implementation of this BMP. Not suitable for stormwater hot spots. Relatively expensive when compared to other BMP options Media Filters Media filters are engineered structures that contain a layer of media such as sand, peat or compost in order to filter and treat stormwater and urban runoff. Media filters are highly applicable in almost any setting including ultra-urban areas were other BMP s may not be feasible. A media filter typically contains a pretreatment chamber or BMP in order to remove coarse sediments that would otherwise clog the filter. Water is then conveyed from this chamber or BMP into the settling chamber where the media filters out pollutants and then releases the now treated water within 72 hours. Filters can be designed to release water back into the municipal storm sewer system, a nearby body of water or into the groundwater table. Filters can also be designed to be either surface or subsurface filters. Because media filters can vary so vastly in size and design, the costs and attributed benefits vary.

19 Advantages and Benefits: Highly applicable in most settings including ultra-urban settings were other BMP options may not be feasible. Suitable for locations that are deemed as stormwater hotspots. Can provide substantial water quality benefits and groundwater recharge if designed to do so. Subsurface filters have little to no impact on site aesthetics. Subsurface filters also take up less property. Disadvantages and Constrains: Individual filters do not typically treat large drainage areas. Requires regular maintenance to ensure the filter does not clog. Sufficient hydraulic head must be incorporated into the filters design. This may limit the BMP s applications were sufficient hydraulic head cannot be achieved. Can be relatively expensive when compared to other BMP options depending on the design Permeable Pavement Pervious pavements also known as porous pavement or permeable pavements are a type of hard paved surface that allows for on-site infiltration of stormwater and urban runoff into the ground. Typical designs consist of pavement placed above a thick layer of subgrade all of which is above uncompacted soil. An underdrain can also be utilized in highly permeable soils in order to prevent groundwater contamination. The pavements themselves occur in a variety of forms with three common types being porous asphalt/concrete, paving stones and grass pavers. Porous asphalt/concrete has the same visual appearance as traditional asphalt/concrete but contains larger amounts of void space that allows water to infiltrate into the subgrade below. Paving stones are impermeable blocks of stone, brick, or cement which allow water to percolate into the sub grade through the spaces between the blocks which are usually filled with a soil medium. Grass pavers are a unit paver with grass filled cells through which water enters the soil below. Though pervious pavements provide both water quality benefits and groundwater recharge, they are typically used to control peak flow rates during storm events. Advantages and Benefits: Applicable in many urban settings such as parking lots, alleys, sidewalks, driveways, playgrounds and cul-de-sacs. Reduce peak flow rate of storm events. Provide moderate groundwater recharge and water quality improvement. Though initially more expensive than traditional pavements, pervious pavements produce large savings by reducing or eliminating the need for stormwater drainage.

20 Disadvantages and Limitations: Limited to areas with low traffic and light vehicle loadings. Not suitable for stormwater hot spots or areas that receive high sediment loads. Not suitable in areas with steep slopes. More costly than traditional pavements and also require higher skilled labor to install. Requires more stringent care and maintenance than traditional pavements including biannual vacuuming Retention Ponds A retention pond, also known as a detention pond or wet pond, is an impoundment in the ground containing wetland vegetation and a significant depth of water. A pond typically consists of an inflow structure, a sediment forebay, a permanent pool and a controlled outflow. They are usually lined with robust vegetation and have average depths of 3-6 ft. The max depth of a retention pond should not exceed 8 feet. Stormwater and urban runoff are directed into the pond and into its inlet structure where they are treated primarily through settling of particulates and biological uptake from vegetation. A pond can be designed to be either online or offline, however offline ponds are generally preferred. They can also be designed to be seasonal ponds retaining water throught the duration of the rainy season. Advantages and Benefits: Efficiently removes a high variety of pollutants, including coliform bacteria. An adequately sized pond will reduce peak flow, providing flood attenuation and erosion control. Proper vegetation may provide substantial habitat, erosion control, reduce water warming and enhance pollutant removal. Provides ample opportunity for recreation, park space, and serves as a public amenity. Relatively inexpensive when compared to other BMP options. Disadvantages and Constraints: Requires a consistent base flow in order to maintain water levels. Requires more impermeable soils in order to maintain pool, therefore it does not contribute much to groundwater recharge. Can present safety hazards where public access is granted. Water warming caused by the BMP may be harmful to temperature sensitive aquatic species. May serve as a breeding ground for mosquitos and other vectors.

21 3.2.8 Vegetated Buffer Strip A vegetated buffer strip, or simply a buffer strip, is a vegetated surfaces that is designed to reduced and treat sheet flow during storm events. The vegetation in the strip reduces flow velocities and removes particulates via settling and biological uptake. Buffer strips can come in a variety of designs and can utilize a wide selection of vegetation ranging from turf grass, shrubs, native plants, and trees. Depending on the vegetation used, drainage area being treated, permeability of soils, and other factors, the minimum required length and slope for an effective strip may vary. If the required slope and length are not available for the desired design, the BMP may still be utilized however it will not be as effective and provide the same benefits. Check dams and permeable berms can be implemented within the buffer strip in order to further reduce runoff velocities and enhance pollutant removal. An infiltration trench or a curb may be required in order to attain sheet flow within the strip. Failing to do so and allowing concentrated flows toenter the strip may damage the BMP and cause erosion. Buffer strips are typically not used as stand-alone practices and are commonly used as a pretreatment method for other structural BMP s. Advantages and Benefits: Reduces runoff velocities and removes a wide variety of pollutants. Requires very minimal maintenance in comparison to other BMP options. Relatively inexpensive when compared to other BMP options. High costs may be associated with land acquisition. Provides site aesthetics and wildlife habitat with use of proper vegetation. May not take up substantial space and may be squeezed onto roadside curbs and parking lot perimeters. Disadvantages and Constraints: This BMP does not treat large drainage areas. Does not significantly reduce storm volumes or coliform bacteria loadings. Lack of adequate filter length and slope will limit the effectiveness of the BMP. Concentrated flows are likely to damage and erode the BMP, therefore it may require a level spreading structure such as an infiltration trench or curb Vegetated Swale A vegetated swale is a shallow channel that is lined with vegetation at its slopes and bottom and is designed to convey stormwater runoff. Stormwater and runoff velocities are reduced by vegetation as they flow through the swale. The reduced speeds allow for the removal of pollutants and the occurrence of minimal groundwater recharge. Eventually, the water makes its way to the discharge point were it is released into another BMP or into a stormwater conveyance system. Swales can utilize a variety of vegetation in their designs, ranging from turf grass to

22 wetland vegetation. The slope of the swale along with the types of soils and vegetation used influence the effectiveness of the swale and its ability to remove pollutants and infiltrate water. Check dams can additionally be added to a swale to further reduce flow velocities and promote pollutant removal and infiltration. Additionally, a subsurface infiltration trench can be installed beneath the swale in order to further promote groundwater recharge. Swales are not typically used as stand-alone practices and often serve as pretreatment BMP s. Advantages and Benefits: Serve as a cost effective alternative to traditional curbs and gutters. Promotes site aesthetics and greenspace. Can be placed alongside roadways and otherwise unusable spaces. Relatively inexpensive when compared to other BMP options. Disadvantages and Constraints: This BMP does not treat large drainage areas. Various sources have indicated that while swales are efficient at moderately removing other contaminants, they typically have higher effluent levels of coliform bacteria. Improper design may lead to erosion and channelization of the swale. Do not typically function as stand-alone practices and are usually limited to being pretreatment BMP s Green Streets Green streets are a BMP distribution practice that incorporates one or more of the aforementioned structural BMP s in residential neighborhoods in order to improve stormwater capture, improve water quality and promote native habitats. An archetypical green street utilizes several BMP permeable pavement in parking lanes, rain gardens with curb cuts in between the sidewalk and road, infiltration trenches and permeable pavement in driveways and rain barrels in order to capture roof runoff. Properly designed green streets promote natural plants, natural water treatment and groundwater recharge. Because green streets utilize a variety of structural BMP practices, they will not be considered in the BMP ranking matrix. 3.3 BMP Ranking Matrix In order to rank the feasability of each BMP in the Arroyo Seco watershed, a BMP matrix that screened each BMP across five categories was developed. The five categories include include: water quality improvement, stormwater capture opportunity, habitat restoration, cost efficiency and feasibility. After researching each BMP through various sources, each BMP was assigned a

23 score of either 1 (Low), 3 (Moderate) or 5 (High) in each of the five categories. The following sections describe each of the categories and the method used to score each BMP in further detail Water Quality Though not all BMP s are particularly designed with water quality in mind, they all essentially provide water quality improvement to some degree. Water quality improvement refers to a BMP s ability to remove particulate pollutants from stormwater and urban runoff. The California Stormwater Handbook put together by the California Stormwater Quality Association (CASQA) provides information on several BMP s ability to treat a wide variety of contaminants. Other sources such as the International Stormwater Best Management Practice Database Pollutant Category Statistical Report were reviewed in order to determine certain BMP s abilities to remove particular contaminants. Because coliform bacteria is the most problematic contaminant present in the Arroyo Seco channel, the scores in this category were based heavily on each BMP s ability to remove bacteria pollution. BMP s that were highly efficient in removing coliform bacteria were given a score of 5 (High), while BMP s that were moderately efficient or inefficient at removing this contaminant were respectively assigned scores of 3 (Moderate) or 1 (Low) Stormwater Capture Stormwater capture opportunity refers to the amount of water that a BMP can potentially infiltrate and store in the ground. The ability of a specific BMP to capture and store storm water will vary from site to site and most can be modified in design to increase or decrease percolation depending on what is appropriate for that site. Because of this, most BMP s contain some potential to capture stormwater to some degree. However, there are BMP s that due to their inherent design are more limited such as constructed wetlands or retention ponds which require low percolation rates to maintain their function. Other BMP s, such as infiltration basins, are typically designed for the purpose of stormwater capture therefore present more opportunity to replenish groundwater by their inherent design. The Pennsylvania Stormwater Best Management Practices Manual provides descriptions that label each BMP s ability to capture stormwater as either low, moderate and high. This handbook s description as well as the typical design of the BMP were the contributing factors for the scores given to each BMP in this category. BMP s that scored 1(Low) are those that present little to no opportunity for stormwater capture, those that scored 3 (Moderate) are those who potentially present a high or low ability to capture stormwater depending on design and BMP s that received a score of 5 (High) are those that usually provide substantial opportunity for stormwater capture Habitat Restoration

24 The amount of habitat that is introduced by BMP s is dependent of several factors such as the location of the BMP and its design. Due to the fact that individual BMP s can vary in design from location to location, it is not easy to assess how much habitat a specific BMP type will introduce. Some BMP s, for example constructed wetlands, by their intrinsic nature require the utilization of plants that will provide substantial habitat for wildlife. Others such as permeable pavement and infiltration trenches have only limited opportunity to provide habitat for wildlife. BMP s that inherently provide an abundance of plant life and wildlife habitat were given a score of 5 (High) while BMP s that by design provide little to no habitat where assigned a score of 1 (Low). BMP s that do not inherently require substantial plant life and wildlife habitat in order to function but have the potential to be designed to do so where given a score of 3(Moderate) Cost Efficiency BMP s are highly site specific therefor their costs are highly subjective and vary from site to site. Factors that can influence the cost of a BMP are the drainage volume it is designed to treat, permitting costs and land value and the type of plants and materials used. Because of this, sources vary and often conflict on the cost estimates for different BMP s. Several sources were surveyed and the cost of each BMP was compared to other sources in order to reasonably rank each BMP to other types of BMP s in terms of cost effectiveness. Each BMP was then given a cost effectiveness score of either 5 (High), 3 (Moderate) or 1 (Low). Note that a score of 5 indicates inexpensiveness while a score of 1 is associated with high costs. For BMP s whose costs varied greatly among sources but where still relatively inexpensive, a score of 3 was assigned. BMP s that where consistently presented as more expensive where given a score of 1 and BMP s that where generally showed to be inexpensive were given a score of 5. The score of the BMP was also influenced by relative cost in comparison to other BMP options Implementation Feasibility The term implementation feasibility in this report refers to the practical constructability of each BMP. There are various factors that influence the practical application and feasibility of a BMP such as laws, regulations, permitting costs, land acquisition, and public opinion among others. An expansive thorough review of all of these factors was beyond the scope of this study therefore only physical constructability was taken into account for analyzing BMP s in this category. BMP s with numerous design constraints found in the Arroyo Seco watershed were given a score of 1 (Low), while BMP s with only moderate or minimal building and design constraints were respectively assigned scores of 3 (Moderate) and 5 (High) BMP Scores After each BMP was thoroughly reviewed by various sources and scored in each of the five categories, they were placed into a matrix in which the scores where summed up in order to rank the complete utility of the BMP. Below is the final matrix:

25 Figure 4 BMP Ranking Matrix Best Management Practice Ranking Matrix BMP Type Water Quality Stormwater Capture Habitat Restoration Cost Feasibility Total Score Bioretention Constructed Wetlands Infiltration Basin Infiltration Trench Media Filter Permeable Pavement Retention Pond Vegetated Swale Vegetated Buffer Strip Despite the results that this matrix may present, cities and governing agencies may already have their own method of prioritizing BMP types. The city of Los Angele s LID handbook states that BMP s should be prioritized in the following order: 1. Infiltration Systems 2. Stormwater Capture and Use 3. Biofiltration/Bioretention 4. Combination of any of the above Where the first option is not feasible, the next option is selected. If the next option is also infeasible at the specific site, then the next options are selected in sequential order until a feasible solution is found. 4.0 Analysis of Outfalls A majority of the water that makes its way into the Arroyo Seco in the urbanized portion of the watershed enters the channel via municipal storm drains. Rain and urban runoff are conveyed through the terrain s natural and engineered drainage into catch basins. From there, the storm drains direct the water to an outfall along the Arroyo Seco channel. One of the primary tasks of this study was to identify the ten most significant outfalls in terms of how much water and pollutants they contribute to the stream and propose a BMP solution to address water issues pertaining to each of these ten outfalls. ArcGIS tools along with shape files from the LA County GIS Data Portal were utilized in order to map out the storm drain system in the water shed and pinpoint the outfalls along the channel. There are over 30 storm drain outfalls that make their way into the Arroyo Seco channel. Figure 5 is a map of the storm drain network throughout the urbanized portion of the Arroyo Seco Watershed.

26 Figure 5 Storm Drain Network in Urbanized Arroyo Seco Watershed Apart from the MS4 sites along the channel, the Los Angeles County Department of Public Works has also designated eleven testing sites along the stream which it has deemed as significant for determining the general health of the stream. Of these eleven sites, six of them are located directly on an outfall. The LA County GIS Data Portal contained shape files for the drainage areas pertaining the MS4 permit outfalls, however, there were no shape files for other major storm drain systems in the watershed. Also to be noted, the shape file for the Altadena Drain also included the entire mountain portion of the Arroyo Seco Watershed, thus giving a limited understanding of how

27 much water actually drains into the Altadena Drain storm drain system. ArcHydro tools where utilized in order to delineate and develop shape files for the catchment areas pertaining to these non MS4 outfalls and the Altadena Drain. The newly developed catchments along with the ones from the LA County GIS Data Portal were combined in order to obtain a more complete representation of the sub catchments within the watershed. As was done with the BMPs, all of the major outfalls were placed in a matrix in order to prioritize them. Figure 6 Catchments Within the Arroyo Seco Watershed The initial goal of the study was to rank these catchments based on contributing flow and contaminants. However, the available methods and required information for calculating contributing flow proved to be impractical for catchments of this size given the time spent on this study. Also, though there was some water quality data available for some of the outfalls, this data was rather outdated and insufficient to make a proper judgement of how much contaminants each of the catchments contributes to the stream. Since sufficient time and data was not available to

28 properly asses the catchments based on contributing flow and pollutants, a matrix similar to the one used for assessing the BMPs was developed in order to screen each catchment across a variety of relevant categories and rank them based on a final score. 4.1 Prioritization Matrix A matrix was developed as with the BMPs in order to determine which outfalls are of higher priority for BMP implementation. Calculating flow rate for each outfall would have been ideal, however, the time and tools for this project made this task difficult and impractical. Calculating a flow rate for each outfall could present an opportunity for a future project. The prioritization matrix outfalls scored the outfalls based on the fifty year storm average rainfall it receives and its total area. Extra points were given to outfalls corresponding to an MS4 site and/or a testing site Fifty Year Storm Average Rainfall The LA County GIS Data Portal contains a GIS file displaying the isohyets for the fifty year storm average rainfall in LA County. This data represents the rainfall that would occur in a fifty year storm which is the possible largest storm that can statistically happen once in a fifty year time period. This design storm is typically used in hydrologic calculations in the design of hydraulic structures such as BMPs. For this report, it was used to calculate the average fifty year storm rainfall that would occur within the catchment area of each outfall. After calculating the average 50 year storm rainfall for each outfall, the outfalls were subsequently ranked in order from the most amount of rainfall received to the least. The difference between the highest average 50 year storm rainfall and the smallest was then divided by five in order to create intervals that would allow each outfall to be given a score of 1 through 5. Below is a chart displaying the rainfall intervals calculated and their corresponding scores: Average 50 Year Storm Rainfall (in) Is Between: Score Figure 7 50 Year Storm Average Rainfall Scoring Criteria Once the criteria for scoring the outfalls based on their 50 year storm average rainfall was established, each outfall was scored and ranked. The table below gives the results for the final ranking of the outfalls based on the 50 year storm average rainfall:

29 Ranking of Storm Water Outfalls by Average 50 yr Storm Rainfall Rank Drain Rainfall (in) Score 1 Altadnea Drain W. Altadena Drain E. Altadena Drain Ventura St Drain Flint Wash Washington Blvd Drain Rose Bowl Parking Lot Seco St Drain Linda Vista Drain Arroyo Blvd Drain San Rafael Creek Mission St Drain York Blvd Drain Hawthorne St Drain Arroyo Seco Park Drain North Branch Confluence Figure 8 Ranking of Stormwater Outfalls by Average 50 yr Storm Rainfall Area Area was the second criteria used for prioritizing the outfalls along the Arroyo Seco. After delineating catchments for each major outfall, the outfalls were ranked from greatest to least in terms of how much area each one of them drained. The area, in square feet, was simply calculated using ArcGIS s identify tool and then converted into acres. The difference between the largest and smallest drainage area was then divided by five in order to assign scores of 1 through 5 to each outfall. The following is the intervals used to score the outfalls: Area (acres) Is Between: Score Figure 9 Drainage Area Scoring Criteria It is important to note that the area for Flint Wash was not taken into consideration for this calculation. With an area of approximately 4302 acres, including this data point would have skewed the remaining data resulting with the majority of all the outfalls receiving a score of one, hence eliminating a meaningful representation of the drainage areas of the outfalls. Instead, Flint Wash was given an automatic score of five in the area category and all the other outfalls were

30 scored based on the chart above. Below is the final ranking of the outfalls in terms of drainage area acreage: MS4 Permit Sites Ranking of Stormwater Outfalls by Area Rank Drain Area (acres) Score 1 Flint Wash North Branch Altadena Drain W Altadena Drain Confluence E Altadena Drain Linda Vista Drain San Rafael Creek Seco St Drain York Blvd Drain Hawthorne St Drain Ventura St Drain Arroyo Blvd Drain Mission St Drain Arroyo Seco Park Drain Washington Blvd Drain Rose Bowl Parking Lot Figure 10 Ranking of Stormwater Outfalls by Area As part of the 1970 Clean Water Act, the National Pollutant Discharge Elimination System program aims at regulating and reducing contaminants at specific point source locations along major bodies of water. Examples of locations where point source pollutions may occur are industrial settings such as mines and factories, agricultural sites or as is the case in the Arroyo Seco, discharge points for Municipal Separate Storm Sewer Systems (MS4s). An MS4 is a drainage network that consists of storm drains, manholes, catch basins, and/or other man made drainage systems. There are fifteen MS4 permit sites along the main channel of the Arroyo Seco with even more along its tributaries as can be seen in Figure 11 below.

31 Figure 11 MS4 Permit Sites Within the Arroyo Seco Watershed Because these sites are part already part of a nationwide program aimed at reducing pollutants, they were considered to be points of significant importance when analyzing the outfalls hence, catchments whose outfalls correlate with one of these sites were awarded an extra two points in the ranking matrix to give these sites increased priority. Catchments whose outfalls are correlated with an MS4 permit site include: 1. Arroyo Seco Park Drain 2. Hawthorne St Drain 3. Mission St Drain 4. York Blvd Drain 5. Arroyo Blvd Drain 6. San Rafael Creek

32 7. Seco St Drain 8. Rose Bowl Parking Lot 9. Linda Vista Drain 10. Washington Blvd Drain 11. E Altadena Drain 12. W Altadena Drain 13. Ventura St Drain 14. Altadena Drain It is important to note that although the confluence of Flint Wash at the Arroyo Seco is not an MS4 site, Flint Wash was still given MS4 priority due to the fact that multiple MS4 sites are located along the tributary LA Department of Public Works Testing Sites Apart from the MS4 sites along the channel, the Los Angeles County Department of Public Works has also designated eleven testing sites along the stream which it has deemed as significant for determining the general health of the stream. The location of these sites is shown in Figure 12 below.

33 Figure 12 LA County Public Works Testing Sites Due to the significance of these sites, catchments whose outfalls land along one of these sites were also awarded two extra points in order to give these sites extra priority. Of these eleven sites, six of them are located directly on an outfall of the delineated catchments. The catchments whose outfalls lie on a LA County Public Works Testing Site are: 1. Confluence

34 2. North Branch 3. Mission St Drain 4. San Rafael Creek 5. Flint Wash 6. Altadena Drain Prioritization Matrix Results The final ranking matrix sums up the scores that each outfall received in each of the four categories in order to assign the outfall a final score. The outfalls with the ten highest scores where then considered the most significant for this study. Figure 13 below reveals the final scores for all of the analyzed outfalls. Final Ranking of Outfalls Along the Arroyo Seco Channel Rank Drain Rainfall Score Area Score MS4 Site Score Testing Site Score Total Score 1 Altadena Drain Flint Wash W Altadena Drain E Altadena Drain San Rafael Creek North Branch Confluence Seco St Drain Linda Vista Drain Mission St Drain Ventura St Drain Washington Blvd Drain York Blvd Drain Hawthorne St Drain Arroyo Blvd Drain Rose Bowl Parking Lot Arroyo Seco Park Drain Figure 13 Final Ranking of Outfalls Along the Arroyo Seco Channel As revealed by the final matrix, the ten most significant outfalls are the Altadena Drain, Flint Wash, West Altadena Drain, East Altadena Drain, San Rafael Creek, North Branch, the Confluence, Seco St Drain, Linda Vista Drain and Mission St Drain. An important item to take note of is that several catchments such as San Rafael Creek, North Branch and the Confluence which received the same final score were given a different ranking. The rankings for catchments that received equal scores are interchangeable and irrelevant when comparing those catchments to each other. Instead of giving catchments of the same score the same ranking (e.g. San Rafael, Creek, North Branch and the Confluence all receive and equal ranking of 5), each was given a

35 separate ranking so that the top ten ranking catchments would be representative of the ten outfalls with the highest scores. 4.2 Potential BMPs for the Most Significant Outfalls The primary purpose of this study was to assign potential BMPs to the ten most significant outfalls of the Arroyo Seco. The previous section has narrowed down the ten most significant outfalls too: Ten Most Significant Outfalls 1. Altadena Drain 2. Flint Wash 3. W Altadena Drain 4. E Altadena Drain 5. San Rafael Creek 6. North Branch 7. Confluence 8. Seco St Drain 9. Linda Vista Drain 10. Mission St Drain The following sections describe these outfalls in greater detail along with potential BMPs that could be implemented to improve water conditions in each outfall Altadena Drain The outfall of the Altadena Drain is the northern most outfall in the urbanized Arroyo Seco watershed and the first major storm drain system to come into contact with the stream. This storm drain system drains a majority of the norther portion of the city of Altadena. The Altadena Drain drains catchment is geographically one of the largest in the watershed and receives the highest average annual rainfall per fifty year storm. Previous water quality tests have shown that this catchment produces an exceedingly high level of coliform bacteria. All of these qualities make the Altadena Drain ideal for both water quality and stormwater capture BMPs. Bioretention BMPs near and around the Rocking Horse Ranch located in Altadena, CA would be an ideal option for removing coliform bacteria right at the source. Coliform bacteria are largely a result of animal wastes. Placing Bioretention BMPs near a horse stable will likely reduce the amount of bacteria that enters the neighboring drain system. Bioretention BMPs are also ideal for capturing the large amounts of rainfall that fall in this catchment and replenishing the ever dwindling groundwater supply of the Raymond Basin.

36 Figure 14 Proposed BMP Location for Altadena Drain Flint Wash Flint Wash is the largest tributary of the Arroyo Seco in the urbanized portion of the watershed. It alone contains several municipal storm drains which drain out a majority of the city of La Canada Flintridge. The last 4,050 ft of this tributary is a natural stream, however the remainder is enclosed in a flood control channel just like the Arroyo Seco. The Martin McAllister training stable provides a great location for implementing Bioretention BMP s. Animal wastes are a large cause of coliform bacteria and placing bioretention BMP s near and around the horse stables would likely reduce the amount of bacteria that enters Flint Wash and eventually the Arroyo Seco.

37 Figure 15 Proposed BMP Location for Flint Wash W Altadena Drain With a drainage area of 1035 acres and 50 year storm average rainfall of 8.98 inches, the West Altadena drain is easily one of the largest contributors of storm water to the Arroyo Seco. With such a large contributing drainage area, this outfall present enormous opportunity to mitigate storm water and improve water quality. Though the drain system drains the majority of central Altadena, its outfall is located just north of Devil s Gate Dam in Hahamongna Watershed Park in the city of Pasadena, CA. A constructed wetland is a BMP that would fit well with the marsh like riparian habitat present at Hahamongna. They are also proven to improve water quality be greatly reducing the presence of various contaminants in water including coliform bacteria, which is one of the largest water quality issues consistently present in the Arroyo Seco.

38 Figure 16 Proposed BMP Location for W Altadena Drain E Altadena Drain The East Altadena Drain is one of the largest drains in the northern urbanized portion of the watershed. This drain has a catchment area of approximately 763 acres, draining a majority of the southern portion of the city of Altadena. With such a large surface area and an average fifty year storm rainfall of 8.8 in, the East Altadena Drain provides ample opportunity for stormwater capture and treatment BMPs. One such location is John Muir High School which is located just within the city limits of Pasadena near the outfall of the East Altadena Drain. Placing rain gardens and permeable pavement at Muir High School would capture and treat a great deal of stormwater near the outfall of the drain just as it enters the mainline of the stream and help replenish the Raymond Basin. Placing BMP s such as these at a public educational facility will also provide an opportunity to educate young people as well as the rest of the community on sustainable practices and further increase awareness of contemporary local water issues.

39 Figure 17 Proposed BMP Location for E Altadena Drain San Rafael Creek San Rafael creek is a fairly large natural tributary of the Arroyo Seco located in the southwestern portion of the city of Pasadena. San Rafael Creek is one of the last remaining natural tributaries of the Arroyo Seco watershed south of Devil s Gate Dam that has yet to be channelized or turned into a storm drain. Except for the creeks confluence which is incased in concrete, the rest of the stream remains natural. Although this was not one of the typical BMP options that was discussed earlier in the report, the best option for this creek would be to dechannelize and restore its confluence with the Arroyo Seco. Doing so will allow for more ground water infiltration, natural habitat for wildlife and will likely improve the quality of water that enters the Arroyo Seco from San Rafael Creek. Since the confluence is not so large, restoring it can serve as an example project to be studied for larger scale stream restoration projects.

40 Figure 18 Proposed BMP Location for San Rafael Creek North Branch North Branch is the largest tributary in the southern end of the watershed. Once a natural stream, this tributary has been placed underground and converted into a fully operational storm drain system. This tributary flows through several densely populated neighborhoods in north east Los Angeles and has its outfall located in Sycamore Grove Park. Although not discussed in the BMP option, the best option for this outfall would be to daylight the stream meaning, to uncover it and bring it back to the surface. Another viable option would be to convert the neighboring streets into green streets, particularly the small streets that connect to Avenue 50 and York Blvd, since they flow directly into the stream. Studies have indicated that the water in North Branch is high quality stormwater, however placing permeable pavements and rain gardens in the streets surrounding the stream would help continue the trend and keep the stream healthy if it were to ever be daylighted.

41 Figure 19 Proposed BMP Location for North Branch Confluence The confluence referred to in this section is the confluence where the Arroyo Seco meets with the Los Angeles River. Although there is no storm drain that correlates directly with this outfall, there are many small drainage systems the lead directly into the main channel of the Arroyo Seco near and around the confluence. Placing treatment BMP s such as rain gardens and sand filters that integrate with the current drainage system can help to highly reduce pollutants entering the stream in this ultra-urbanized portion of the watershed. In the long run, a complete restoration of the confluence would be the ideal optimal BMP for this catchment. However, lining the streets near the confluence with rain gardens and sand filters might be a quicker, more feasible short term goal that could highly alleviate water conditions at this site and would benefit a future restoration of the confluence as well.

42 Figure 20 Proposed BMP Location for Confluence Seco St Drain With a catchment having an area of about 245 acres, the Seco Street Drain is a fairly large drain that runs along the central portion of Pasadena s Linda Vista community. The drain runs along Linda Vista Ave south of Charles Street and eventually has its outfall in the Arroyo Seco slightly east of Seco Street near the northern end of Brookside Park. The catchment drains mostly residential neighborhoods and a small portion of the San Rafael Hills. With most of its open space being sloped hillside, it is difficult to assess the practicality of BMP s that might require large amounts of open space such as a pond or wetland. The residential neighborhoods however do provide significant opportunities for smaller scale BMPs. Lining the road verges along Linda Vista Avenue with rain gardens would help to capture a plentitude of storm water to replenish the Raymond Basin. This option would also capture many contaminants that occur in residential areas such as metals, nutrients and coliform bacteria right at the source, thus improving the quality of water that enters the drain and eventually the Arroyo Seco.

43 Figure 21 Proposed BMP Location for Seco St Drain Linda Vista Drain The Linda Vista Drain is the storm drain system that drains the northern portion of the Linda Vista neighborhood in the City of Pasadena. With a relatively high average rainfall, this outfall presents itself as a good opportunity for implementing stormwater capture BMPs. The Art Center College of Design, located within this sub watershed, has a relatively large foot print with which can accommodate BMP placement. Replacing its large parking lot with permeable pavements would capture a great deal of storm water while also improving the quality of water that enters the Linda Vista Drain and eventually the Arroyo Seco.

44 Figure 22 Proposed BMP Location for Linda Vista Drain Mission St Drain The Mission Street Drain is a relatively small storm drain system in north east Los Angeles that runs along Mission St, crosses Arroyo Dr and enters the Arroyo Seco in the northern end of Arroyo Seco Golf Course. Although this catchment is relatively small, only having an acreage of 93.9 and a 50 year storm average rainfall of 7.49 inches, it is both an MS4 permit site and a Los Angeles County Public Works testing site, giving it a higher priority status among other small catchments. This catchment is highly urbanized and presents very little opportunity for BMPs that require a large footprint. A good BMP option for this catchment would be to line the northern end of Arroyo Seco Golf Course with infiltration trenches in order to greatly reduce the amount of nutrients that may enter the stream due to the fertilizers used in maintaining the golf course. Although nutrients are currently not the pollutant of largest concern in the Arroyo Seco, they historically have been a problem and properly managing them would help to ensure that the Arroyo Seco continues to stay off the 303(d) list for nutrients.

45 Figure 23 Proposed BMP for Mission St Drain 5.0 Conclusion and Next Steps Water is an essential resource vital to the survival of life. It is essential to implement methods such as BMP s in order to make the most of and protect this invaluable resource. Increasing urbanization and engineered flood protection structures have both contributed to the degradation of one of our most valuable resources. Every rain season, a large percentage of stormwater runs off into the Arroyo Seco untreated and further ailing the condition of the stream. BMPs are a great solution for treating contaminated stormwater runoff as well as storing water into the groundwater basin for later use. As seen throughout the report, the Arroyo Seco provides various opportunities for BMP implementation throughout its vast watershed. Apart from alleviating water conditions in the watershed, these BMPs could also help in restoring habitat that has been lost to urbanization and provide public amenities for local communities. This report has laid out a preliminary foundation for further BMP studies to be carried out in the Arroyo Seco watershed. Further research such as water quality testing near the identified outfalls as well as flow rate measurements can further enhance the results of this report. Further studies should be conducted in order to implement these BMPs in the near future and restore our precious local treasure, the Arroyo Seco.