Floodplain Discipline Report

Transcription

1 Floodplain Discipline Report Duportail Street Bridge Project Benton County, Washington Prepared for: Federal Highway Administration 711 South Capitol Way, Suite 501 Olympia, WA Washington State Department of Transportation P.O. Box Yakima, WA October July 15, 2011

2 This page left blank intentionally for printing purposes.

3 Acronyms BFE BMPs CID CLOMR EA FEMA FHWA FIRMs LOMR NEPA ROW SEPA SR WAC WSDOT USACE Base Flood Elevation Best Management Practices Columbia Irrigation District Conditional Letter of Map Revision Environmental Assessment Federal Emergency Management Agency Federal Highway Administration Flood Insurance Rate Maps Letter of Map Revision National Environmental Policy Act Right of Way State Environmental Policy Act State Route Washington Administrative Code Washington State Department of Transportation United States Army Corps of Engineers i

4 This page left blank intentionally for printing purposes. ii

5 Executive Summary This study analyzes whether there are any substantial effects to the floodplain in the vicinity of the proposed Duportail Street Bridge Project, located in the City of Richland. The project involves the construction of a four-lane bridge between the existing Duportail Street on the south-west side of the Yakima River, to Duportail Street on the north-east side of the river. In addition, intersection improvements at State Route (SR) 240 and Duportail Street will be included, as well as a new roadway (Tanglewood Drive) on the north side of the proposed bridge will be constructed to connect the existing land uses to Duportail Street. Infiltrations trenches and a new waterline, will be constructed. The current Columbia Irrigation Canal drainage will be enclosed under the proposed bridge. The proposed project is located within the legal geographic area of: Township 09 North, Range 28 East, Sections 15 and 16, Benton County, Washington. Existing land use along the project corridor consists of primarily natural open space, multi-family residential, and a few businesses. Refer to the Vicinity Map; Figure 1. A Bridge Hydraulics and Scour Assessment (WEST Consultants, Inc., 2009) written for the project was used as well as regulations, and maps from the City of Richland to identify the existing and potential future floodplain effects within the study area. Two alternatives were analyzed, the No Build and the Preferred Alternative. The No Build was essentially used as a baseline to compare the project effects to, as under the No Build no activities would be taking place, and the status quo is assumed to be maintained. This study shows that proposed bridge will cause a backwater rise of 0.08 feet. The hydraulic and scour assessment (WEST Consultants, Inc., 2009) recommends an estimated median riprap size of 2 feet to protect the right bank. Bank protection alternatives might be riprap, woody debris and vegetation, geo-textiles, and plantings. However, finding measures to protect the entire length of the right bank (as viewed downstream) through the bridge reach against bank erosion and lateral migration would be difficult. Further recommendations in the hydraulic and scour assessment states that the bridge foundation should be designed against significant scour and migration towards the right bank, and that the right bank be monitored after major floods, and if riprap protection were to be included in the design, the hydraulic and scour report recommends heavy-loose rock with a median size exceeding 2-ft to provide a factor of safety for the steep right bank. The proposed new bridge would place piers in the FEMA effective floodway of the Yakima River, and a backwater rise is anticipated, therefore mitigation must be considered. Two possible mitigation measures were analyzed. Based on the assessment, it is recommended that the City submit a Conditional Letter of Map Revision request to the Federal Emergency Management Agency to revise the mapping of the floodplain and floodway of the Yakima River in the bridge reach. Following approval from the Federal Emergency Management Agency, and following bridge construction, the City would then have to submit a Letter of Map Revision to the Federal Emergency Management Agency based on as built bridge drawings. Once the Federal Emergency Management Agency approves the Letter of Map Revision, and City ordinances are changed to reference the revised Flood Insurance Rate Maps, the Federal Emergency Management Agency will make the revised maps effective. iii

6 This page left blank intentionally for printing purposes. iv

7 Table of Contents Acronyms... i Executive Summary... iii 1.0 Introduction Purpose of Report Preferred Alternative No Build Purpose and Need Investigation of Potential Problems Affected Environment Limits of 100 year floodplain Proposed Project Drawings Studies and Coordination Project s Consistency with Existing Watershed and Floodplain Permits Required Current/proposed water resource projects Flood History Existing Structures Foundation Type Scour History Drainage area above encroachment Summary Objectives of the Project Current floodplain use Impacts of all alternatives including the no-build alternative Recommended mitigation References Appendix A: CLOMR Application Appendix B: Permits Required List of Figures Figure 1: Vicinity Map... 3 Figure 2: Limits of the FEMA-Effective and Existing 100-Year Floodplains... 9 Figure 3: Plan View of the Proposed Bridge Figure 4: Cross section of the Proposed Bridge v

8 This page intentionally left blank for printing purposes. vi

9 1.0 Introduction Floodplains are areas prone to periodic inundation and are generally associated with streams, rivers, or lakes. The Federal Emergency Management Agency (FEMA) maps floodplains that have at least a 1 percent probability of flooding in a given year. These floodplains are defined as 100-year floodplains because these areas flood on average once every 100 years. Flood Insurance Rate Maps (FIRMs) indicate FEMA-delineated floodplains. Unless a special critical area study has revised the FEMA floodplain, the zero-rise floodway is the FEMA 100-year floodplain area defined by the Base Flood Elevation (BFE). The Washington Administrative Code (WAC), specifically WAC (1)(h) indicates that abutments, piers, piling, sills, approach fills, etc. associated with new structures should not cause a backwater rise exceeding 0.2 feet in the floodplain. FEMA regulations require that the bridge should cause no rise within the regulatory floodway. The City of Richland does not have a more stringent regulation; therefore it is assumed that new development does not cause a measurable rise (0.1 foot or more) in BFE. 1.1 Purpose of Report The purpose of this Floodplain Discipline Report is to evaluate the Duportail Street Bridge Project for potential effects and benefits the project would have on floodplain resources and identify mitigation measures to address adverse effects as needed. The analysis includes a comparison of how the Preferred Alternative and No Build Alternative would affect the Yakima River floodplain, and an evaluation of consistency with existing city and regional land use plans and development regulations. The report also suggests mitigation measures to relieve negative effects during project construction. The information contained in this discipline report will be used to support the project s Environmental Assessment (EA). Analysis of floodplain effects is required under the National Environmental Policy Act (NEPA) for actions sponsored, funded, permitted, or approved by federal agencies. The State Environmental Policy Act (SEPA) requires analysis of a project s impact on the natural and built environment. 1.2 Preferred Alternative Within the proposed project area the FEMA effective floodplain and floodway are not consistent with the current position of the Yakima River. JUB, Inc.; therefore, conducted a detailed channel and overbank survey of the bridge reach from approximately 500 feet upstream of the proposed bridge crossing to about 1,000 feet downstream. The City of Richland provided some additional overbank survey from approximately 4,000 feet upstream of the proposed bridge to about 4, 000 feet downstream. This data was entered into HEC-RAS hydraulic model in order to calculate the existing 100-year floodplain and floodway of the Yakima River, between the areas 4,000 feet upstream and 3,300 feet downstream. The Bridge Hydraulics and Scour Assessment Detail Report (WEST Consultants, Inc., 2009) analyzed two bridge alternatives. Alternative 1 (4-span bridge 1 ) and Alternative 2 (5-span bridge) were compared against the existing conditions model for the base (100-year) flood. The two bridge alternatives were shown to cause a backwater rise upstream of 0.08 feet for the 4-1 Alternative 1 (4-span bridge) was modified to include an additional span for habitat mitigation after consulting with the US Army Corps of Engineers; however, the requested fifth span is outside both the floodway and the 100- year floodplain so backwater rise was not affected. 1

10 span bridge and 0.09 feet for the 5-span bridge. From this analysis, and considering site and design conditions, Alternative 1 was identified by the design team and City as the Preferred Alternative and will be referred to as the proposed project from now on in this floodplain discipline report. The City of Richland proposes to construct a four-lane bridge over the Yakima River, connecting the existing Duportail Street from its intersection with Queensgate Drive on the south-west side of the river to Duportail Street on the north-east side of the river to its intersection with SR 240. Refer to Figure 1: Vicinity Map. Project activities will include the following: Construction of a four lane bridge; with two 11-foot travel lanes and a 12-foot pedestrian/bicycle path on the upriver side of the bridge. Sidewalks will be installed from Queensgate Drive (southwest of Yakima River) to City View Drive. The northeast segment of Duportail Street will be extended south to connect with the proposed bridge, and will be widened north, to the intersection with Cottonwood Drive; sidewalks will be added where needed to connect with the existing network. Tanglewood Drive will be extended eastward to intersect with Duportail Street north of the proposed bridge and will terminate with a cul-de-sac approximately 700 feet east of the proposed intersection. The intersection of Duportail Street and SR 240 will be upgraded to handle higher traffic volumes. The BNSF railroad tracks running parallel to SR 240 will be raised to the same grade as the intersection of SR 240 and Duportail Street. SR 240 will be widened on both sides of intersection with Duportail Street due to the addition of right turn exit lanes from SR 240 onto Duportail Street. Existing boat launch parking will be relocated and an access road will be constructed to provide access to the proposed boat launch parking area from Tanglewood Drive. An additional access road will be constructed to provide access to the Desert Streams Bible Church from the Tanglewood Drive cul-de-sac; east of Duportail Street. One nature trail will be designated and all remaining disturbed areas, between the left bank of the Yakima River and Tanglewood Drive will be restored. The existing water main crossing within the Yakima River will be replaced. A new water main will be placed along the bridge and the current main will be abandoned in place. The existing Columbia Irrigation District (CID) canal south of the proposed bridge will be enclosed under the proposed bridge. Infiltration trenches will be installed along Tanglewood Drive, Duportail Street, and Riverstone Drive. 2

11 Columbia River Miles 1 in = 0.5 miles Duportail Street Bridge Figure 1: Vicinity Map Duportail Street Bridge Project City of Richland City of Richland June 8, 2011

12 This page left blank intentionally for printing purposes. 4

13 1.3 No Build NEPA requires that the No Build alternative be included and evaluated in this discipline report. This approach is used to establish an existing and future baseline for comparing the effects associated with the proposed project. The No Build Alternative is assumed to maintain the status quo: only routine activities such as road maintenance, repair, and safety improvements would occur within the corridor between now and The No Build Alternative does not include improvements that would increase roadway capacity or reduce congestion on feeder streets to I- 182 or other surface streets in the City of Richland. 1.4 Purpose and Need Purpose The purpose of this project is to alleviate congestion on the I-182 and SR 240 corridors in the city of Richland, to improve emergency vehicle response times to currently underserved areas of town, and improve mobility for bicycle and pedestrian users from the south side of the Yakima River to the north. A new fire station is planned at the approximate location of the intersection of Duportail Street and City View Drive. The proposed new connection over the Yakima River for emergency vehicles using Duportail Street would be a faster, more direct route in some cases. The proposed bridge will contain sidewalks and a bike lane, creating a safe crossing for nonmotorized traffic, as the design speed for the proposed bridge is 35 mph. The proposed new connection over the Yakima River can be used for a more direct route to shopping, employment, or other purposes. An additional north-south crossing in the city of Richland aims to improve mobility, and will substantially reduce the amount of local trips within the SR 240 and I-182 corridor areas. A new waterline will be constructed on the proposed bridge, and the current deteriorating, 36 waterline will be valved out of service and abandoned in place. A previous commitment has been made by the City to replace the waterline and the city has received a grant from the Federal Emergency Management Agency (FEMA) to reduce vulnerabilities to the waterline. Need The City of Richland is planning to serve the growing infrastructure needs of the city particularly emergency vehicle response times and non-motorized transportation by constructing an additional bridge over the Yakima River, connecting Duportail Street south of the Yakima River to Duportail Street north of the Yakima River. In addition, improvements are needed for the city s water pipeline in this area, which is now exposed in places and susceptible to damage or vandalism. There are four existing conditions associated with the roadway that require action to address the above needs: Reduce Emergency Response times on the South Side of the river Improve non-motorized access Improve the city s arterial street network connectivity to reduce the amount of local trips on SR 240 and I-182 Replace Exposed 36-inch waterline 5

14 Reduce Emergency Response times on the South Side of the river Currently, there is only one crossing over the Yakima River in the city of Richland that services the new developments on the south side of the river. There are two other crossings, SR 224 in the north part of Richland, and SR 240 to the south of the city, however to take one of these routes would be lengthy and time consuming. The SR 224 crossing and the I-182 crossing are roughly 3 miles apart, SR 240 crosses just south of I-182. Emergency vehicles needing to get to the other side of the river must choose between crossing to the north, or crossing to the south, which may extend response times to locations located between the existing crossings. Improve non-motorized access The three existing crossings over the Yakima River in the city of Richland do not have designated bicycle or pedestrian access. This restricts non-motorized transportation to remaining on one side of town or the other. Improve the city s arterial street network connectivity to reduce the amount of local trips on SR 240 and I-182 I-182 is currently the only one of three crossings over the Yakima River that services the new developments on the south side of the river. Residential and retail developments southwest of the city center have created a need for more cars to travel over the I-182 Bridge. The I-182 Bridge is increasingly being used as a route for local trips from the city center to the newer developments. The need for local trips to use I-182 is anticipated only to increase as development and population rise. Increasing capacity on the existing crossings of the Yakima River will not solve the problem seen at the choke points in the city of Richland, as the choke points occur on local feeder streets to the main crossing (I-182). The Aaron Drive choke point can be alleviated by approximately 8,500 cars in the year 2012 and by approximately 12,000 cars in 2032 with the proposed bridge, as the current queued cars waiting to get on I-182 take an alternate, more distant crossing in order to continue their local travel. Exposed 36-inch waterline The existing 36-inch waterline that is the sole source of domestic water to all of the residents and businesses in southern Richland crosses the Yakima River near Duportail Street. The waterline is exposed in places as it crosses the river, leaving the waterline susceptible to potential further damage and vandalism. 1.5 Investigation of Potential Problems Flood Hazard The Duportail Road Bridge is within a regulatory (FEMA) floodplain as well as the existing floodplain; calculated using the HEC-RAS hydraulic model. WAC (1)(h) indicates that the bridge should not cause a backwater rise exceeding 0.2 feet in the floodplain. FEMA regulations require that the bridge should cause no rise within the regulatory floodway. The City of Richland does not have a more stringent regulation. Navigational clearance may be an issue at the bridge site, especially at the left (viewed downstream) bank. 6

15 The Yakima River limits access to and from the city center to 3 crossings routes - SR 224 to the north of the project, and I-182 and SR 240 to the south of the project. SR 224 has experienced closures due to flooding. Flood waters in January 2009 inundated one eastbound lane of SR 224 closing it for several days and during the 1996 flood the road was impacted by the flood for a total of 20 days, ten of which days the road was inundated and closed entirely. The elevation of the 1996 flood in the project area was feet. Over six additional floods since the 1970s have also caused transportation issues like the ones described above. The construction of the proposed Duportail Bridge would provide an additional transportation route in the event of SR 224 closure due to floodwaters. Channel Stability There is a steep bank along the right (viewed downstream) bank, and several bars along the left side of the channel. It is clear that the Yakima River is trying to migrate to the right, but is impeded by rock in the steep right bank. Effects on the environment- fish and wildlife, domestic water supplies, recreation Fish passage should not be adversely hydraulically impacted by the replacement of the bridge. Temporary effects to fish and wildlife are likely to occur during construction. A Biological Assessment and Wildlife Discipline report are being prepared to address effects to species in the project area. The existing 36 water transmission line crossing the Yakima River in the project area currently provides 100% of the primary potable water supply for the south Richland community, comprising a population of approximately 16,689 people. The existing waterline, constructed in 1953, was buried below the channel bottom of the Yakima River. However, 50+ years of erosion and scour have now partially exposed the pipe, rendering the pipe highly vulnerable to hydraulic forces, scour and ice flows. The hydraulic analysis and scour report recommended that if the proposed project were replacing the existing buried water main with a new buried pipe, the recommended burial depth should be approximately feet to protect the pipeline from streambed erosion. However, the proposed project includes construction of the water main on the proposed bridge. On the north side of the proposed bridge, there is currently access to several trails, likely used for hiking, bird watching, and access to the river for fishing. As mitigation for this project one trail will be designated through this area and all remaining disturbed areas will be revegetated with native vegetation. Pedestrian access to the riverfront will remain available through the boat ramp. Debris The minimum desired clearance from the low chord of the new bridge to the 100-year design flow water surface elevation, in locations along the bridge where debris is likely to be carried by the river, is 3 feet. Little debris potential exists. The banks are lined with shrubs and small diameter trees. 7

16 2.0 Affected Environment 2.1 Limits of 100 year floodplain Refer to Figure 2 for a map showing the proposed bridge, the limits of the FEMA Effective 100- year floodplain and floodway and the limits of the existing 100-year floodplain and floodway calculated using the HEC-RAS hydraulic model. 2.2 Proposed Project Drawings Refer to Figures 3 and 4 for construction drawings of the proposed bridge including proposed encroachment/structures, a cross-section of the stream, alignment of piers, and skew of crossing. 8

17 Feet 1 inch = 300 feet Legend Proposed Alignment Potential Laydown/Restoration Area - Zero Net Rise Proposed Designated Trail - Zero Net Rise Yakima River FEMA Effective 100-year Floodplain (modeled per FIS 1979) FEMA Effective Floodway (modeled per FIS 1979) "Existing" 100-year Floodplain (modeled per HEC-RAS 2009) "Existing" 100-year Floodway (modeled per HEC-RAS 2009) Figure 2: Limits of the FEMA Effective and "Existing" Floodplains Duportail Street Bridge Project City of Richland July 13, 2011

18 This page left blank intentionally for printing purposes. 10

19

20 This page left blank intentionally for printing purposes. 12

21

22 This page left blank intentionally for printing purposes. 14

23 3.0 Studies and Coordination 3.1 Project s Consistency with Existing Watershed and Floodplain The proposed project is consistent with the existing watershed as it will not change any characteristics of the watershed. As previously mentioned within the proposed project area the FEMA effective floodplain and floodway are not consistent with the current position of the Yakima River. Since these were mapped in 1979 the river has migrated to the south, and in places now lies beyond the floodway limits. The proposed project will result in a 0.08 foot backwater rise, and coordination between the City of Richland and FEMA is recommended to revise the current FEMA mapped floodplain and floodway. A Conditional Letter of Map Revision (CLOMR) has been submitted to the Federal Emergency Management Agency requesting they revise the FEMA designated floodplain and floodway of the Yakima River in the bridge reach to the existing floodplain and floodway calculated using the HEC-RAS hydraulic model in See Appendix A. 3.2 Permits Required A complete list of permits required for the Duportail Street Bridge project can be found in Appendix B. The Duportail Road Bridge is within a regulatory (FEMA) floodplain. State guidelines per the Washington Administrative Code (WAC) WAC (1)(h) indicates that the bridge should not cause a backwater rise exceeding 0.2 feet in the floodplain. FEMA regulations require that the bridge should cause no rise within the regulatory floodway. The City of Richland does not have a more stringent regulation than the FEMA regulations. 3.3 Current/proposed water resource projects A previous commitment has been made by the City to replace a waterline supplying domestic water to residences and businesses in southern Richland. The city has received a grant from FEMA to reduce vulnerabilities to the waterline. The existing 36-inch waterline crosses the Yakima River near Duportail Street. The waterline is exposed in places as it crosses the river, leaving the waterline susceptible to potential further damage and vandalism. The new waterline will be constructed with or without the proposed project, however, with the proposed project; the new waterline will be constructed on the proposed bridge. The current deteriorating, 36 waterline will be valved out of service and abandoned in place. 3.4 Flood History The Yakima River and its tributaries have been heavily altered for the purpose of irrigated agriculture. There are numerous dams and irrigation canals. Irrigation runoff is, in places, returned to the river through canal drains. The irrigation system in the Yakima's watershed causes periods of both severe river dewatering and elevated flows, relative to the historic stream flow regime. An irrigation ditch (CID canal) flows through the project area along the right bank (southwest side) of the Yakima River. This ditch is fed by the Yakima River; a pump station is located approximately 13 miles upstream from the project site. The project proposes to pipe a portion of the CID Canal under the proposed bridge. The canal will be excavated to lay the 15

24 underground pipe. The pipe will be positioned to ensure proper flow of the canal. Since the 1970 s over six flood incidents have caused transportation issues. There are currently only three crossings of the Yakima River, and one of the crossings (SR 224) has been closed several times, (one time lasting 20 days) due to floods. 3.5 Existing Structures There are no existing structures in the project area. 3.6 Foundation Type Construction of the new bridge will be conducted from the temporary work bridge and from both riverbanks. The Duportail Bridge will be 775 feet in length with a minimum foot vertical clearance and a maximum foot clearance over the OHWM of the Yakima River. Construction will occur in three main sequences: 1) drilled shaft, column, cap beams and abutment installation, 2) concrete girder placement and 3) concrete deck construction. Piers 2 & 3 will be waterward of the OHWM, Pier 4 will be approximately 30 feet landward of the OHWM but within the limits of the 100-year floodplain, and Pier 5 will be waterward of the OHWM though it will abut the 100-year floodplain. All four of these piers will be supported by three 8-foot diameter concrete drilled shafts. See Figures 3 and 4 for the plan, elevation and typical cross section of the Duportail Bridge. The southern abutment (Pier 1) will be located on the right bank above the CID canal and the northeast abutment (Pier 6) will be located near the top of the slope of the riverbank. Both the southern abutment and northern abutments are well outside the 100-year floodplain. The Pier 1 abutment will be supported by a spread footing and the Pier 6 abutment will be supported by four 4-foot diameter concrete drilled shafts. 3.7 Scour History The total scour at the bridge consists of three components long-term degradation or aggradation, contraction scour, and pier scour. The potential for long-term bed change in this reach of the Yakima River is considered to be small. If riprap were used for bank protection, we would recommend using heavy loose riprap or larger (about 2-ft material) along the right bank. The left bank is protected by the inside of the bend, and we believe that bank and abutment armoring is not necessary along this side Contraction scour occurring at the bridge is consistent with live-bed scour. The estimated channel velocities in the bridge reach during the 500-year flow could exceed of 12 ft/sec. The channel shear stress is estimated to be 2-4 lb/ft 2, which is at the upper limit for vegetative bank protection. Some bank protection alternatives might be riprap, woody debris and vegetation, and geotextiles and plantings. However, as there is no true abutment to protect, it would be difficult to propose a measure to protect the entire length of the right bank through the bridge reach against bank erosion and lateral migration. Rather, we recommend that the bridge foundation be designed against significant scour and migration towards the right bank, and that the bank be monitored after major floods. 16

25 3.8 Drainage area above encroachment The Yakima River rises to an elevation of 2,449 feet in the Cascade Range at Keechelus Dam, just to the east of Snoqualmie Pass on Interstate 90. The river flows over 200 miles through central and eastern Washington State, where it joins the Columbia River at an elevation of 340 feet about 5.5 miles downstream of the proposed bridge crossing. The Yakima River Basin consists of approximately 6,150 square miles. It is bounded by the Cascade Mountains to the west, the Wenatchee Mountains to the north, the Rattlesnake Hills to the east, and the Horse Heaven Hills to the south. The Yakima River provides irrigation for the dry but fertile land in the valley, and irrigated agriculture is the economic base. Agricultural land totals 1,000 square miles, including irrigated pastures, orchards, grapes, hops, and field crops. A significant portion of Washington apples and cherries are grown in the valley, as well approximately 75% of the hops grown in the United States. Since the late 20th century, the wine industry has grown rapidly in the Yakima Valley, and is designated American Viticultural Area (AVA) location. 4.0 Summary 4.1 Objectives of the Project The proposed project is consistent with, and would assist in implementing, goals and objectives found in the applicable land use plans and regulations. Construction and operation of this project would be compatible with planned development in the study area. The proposed project is designed to improve mobility within the City of Richland by creating an additional crossing of the Yakima River. The long term benefits to the project include improved emergency vehicle response times, and more efficient travel from the city center to outlying residential areas. 4.2 Current floodplain use Much of the floodplain in the vicinity of the project is federally owned and used for recreational purposes. The dead end Duportail Street on the north side of the proposed bridge provides parking and boat-ramp access. There are several trails likely used for hiking and bird watching that can be found along the riverfront. The boat ramp provides access to the river for fishing. As mitigation for this project one trail will be designated through this area and all remaining disturbed areas will be revegetated with native vegetation. Pedestrian access to the riverfront will remain available, and a new boat ramp/access will be constructed with the proposed project. Vehicular access will be better controlled, which has been a concern of the City of Richland, Washington State Fish and Wildlife Department, and the US Army Corps of Engineers. 4.3 Impacts of all alternatives including the no build alternative The Duportail Bridge will require the placement of piers in the floodway of the Yakima River and will impact an approximate 45,000 sq ft of area within the 100-year floodplain; an approximate 500 sq ft area for the placement of piers 2, 3, and 4, and an approximate 44,500 sq ft areas for the construction of a portion of Tanglewood Drive. The project proposes to add 1,105 CY of fill and excavate 615 CY of native materials within the 100-year floodplain. It is; therefore, anticipated the proposed project will result in a backwater rise of 0.08 ft during the 100-year base. 17

26 Backwater rise is anticipated due to the placement of bridge piers in the floodway of the Yakima River. However, the proposed project will have many beneficial effects after construction. Benefits resulting from the proposed project include: improved mobility from the city center to the expanding Queensgate area, faster emergency vehicle response times, an additional crossing of the Yakima River in the event of a flood, the existing deteriorating waterline can be placed on the bridge not buried and susceptible to scour, better access to recreation opportunities on the north side of the project area. The no build alternative would not result in any changes to the floodplain, as no structures would be built. The existing deteriorating waterline will still be replaced; however the only option would be to install it underground. Installing the new waterline underground could potentially lead to the same problems the current waterline is experiencing, scour and ice damage as years pass. 4.4 Recommended mitigation As the proposed project includes installing piers in the floodway of the Yakima River, mitigation is needed for the expected backwater rise. The hydraulic and scour analysis explored two alternatives: (1) consider modifying the river channel to offset the backwater rise, or (2) remap the floodplain and floodway, and following community approval submit a CLOMR to FEMA. When considering modifications to the river channel to offset the expected backwater rise of 0.08 ft during the 100-year base flow for the proposed project (Alternative 1), the areas of potential mitigation were constrained to alternatives on the left overbank (viewed downstream) that did not involve removing the heavy vegetation at the channel banks (generally the areas that show up in brown in aerial photos). Additionally, modification of the steep right bank of the Yakima River had the potential to de-stabilize the bank. Therefore, modifications of the river channel were restricted to consideration of lowering overbank areas either just upstream or just downstream of the propose bridge crossing. The hydraulic and scour analysis simulated a number of alternatives using the, Alternative 1, bridge hydraulic model and none entirely eliminated the backwater rise caused by the proposed bridge. Lowering the left overbank downstream of the proposed bridge did not reduce the upstream backwater rise. While lowering the left overbank just upstream of the proposed bridge crossing could eliminate the backwater rise at the approach section, the hydraulic model showed that it would increase the water surface elevation immediately upstream of the bridge, resulting in a wider floodplain that would have to be remapped for FEMA approval anyway. From the results of the simulations conducted in the hydraulic and scour analysis concluded that the better approach was to submit a CLOMR to FEMA, with community support, to remap the floodplain and floodway of the Yakima River through the bridge reach, and ask FEMA to revise the FIRMs. A copy of the CLOMR application can be found in Appendix A. 18

27 4.5 Cumulative Impacts Cumulative impacts are those effects on the environment which result from the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions regardless of what agency (federal or non-federal) or person undertakes such other actions. Cumulative impacts can result from individually minor but collectively significant actions taking place over a period of time. It is not anticipated that development will occur within the proposed revised 100-year floodplain surrounding the project area. The majority of the land within the currently designated and proposed 100-year floodplain is on USACE owned lands designated as natural open space by the City of Richland and intensive wildlife management lands according to the USACE s McNary Master Plan (FHWA and WSDOT 2011, USACE 1995). Due to these land use designations to date little development has occurred within this area and it is anticipated that little to no development will continue occur within the proposed revised 100-year floodplain surrounding the project area. 19

28 5.0 References City of Richland Comprehensive Land Use Plan. Accessed on June 22, City of Richland GIS Maps. Site visited on July 2, FHWA and WSDOT (Federal Highway Administration and Washington Department of Transportation) Land Use Discipline Report: Duportail Street Bridge Project, Benton County, Washington. January 27 USACE (United States Army Corps of Engineers) Master Plan for the McNary Lock and Dam Project, December 1995 supplement. WEST Consultants, Inc., Bridge Hydraulics and Scour Assessment Detailed Report, April WEST Consultants, Inc., Bellevue, Washington. WSDOT. June, Environmental Procedures Manual, version M Chapter 432, Floodplain. Olympia, Washington. Accessed July 8,

29 Appendix A: CLOMR Application 21

30 This page intentionally left blank for printing purposes. 22

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95 Appendix B: Permits Required 87

96 This page left blank intentionally for printing purposes. 88

97 Permits Required for the Duportail Bridge Project Permit, Approvals and Concurrences NEPA Concurrence Wildlife, Aquatic Resources, and Vegetation Discipline Report Surface Water Discipline Report Geology and Soils Discipline Report 4(f) Discipline Report Visual Impacts Discipline Report Traffic Noise Discipline Report Public Services and Utilities Discipline Report Land Use Discipline Report Environmental Justice Discipline Report Section 7 Concurrence Activity Proposed Action will utilize federal funds, occur on federal lands, and require permit approvals from both the US Army Corps of Engineers and Federal Emergency Management Agency Agency Federal Highway Administration (lead), US Army Corps of Engineers, and Federal Emergency Management Agency US Fish and Wildlife, NOAA Fisheries Section 106 Concurrence Excavation of previously undisturbed areas Department of Archaeology and Historic Preservation Section 10 Permit Approval Regulates the construction of any structure in U S Army Corps of Engineers or over any navigable water of the United States Section 401 Water Quality Certification Required for discharges into waters of the US Ecology associated with the Section 10 permit SEPA Determination Proposed Action will utilize state funds City of Richland NPDES Permit Approval Stormwater Discharge Ecology Hydraulic Permit Approval Use, diversion, obstruction, or change the bed or flow of state waters Shoreline Permit Development within a designated shoreline of City of Richland the state Critical Areas Permit Project action will occur on/in habitat areas City of Richland associated with threatened, endangered, sensitive, or priority species Geologic Hazard Permit Earthwork and/or placement of a structure(s) City of Richland in or within 200 feet of a geologic hazard area Floodplain Development Permit Fill to be placed below the 100-year flood elevation City of Richland CLOMR Conditional Letter of Map Revision Federal Emergency Management Agency 89

98 This page left blank intentionally for printing purposes. 90