Table of Contents G.1.a Water Resources - Surface Water - Drainage

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1 Table of Contents G.1.a Water Resources - Surface Water - Drainage 1. INTRODUCTION ENVIRONMENTAL SETTING a. Regional Hydrology b. Local Hydrology c. On-site Hydrology ENVIRONMENTAL IMPACTS a. Methodology b. Thresholds of Significance c. Project Design Features d. Project Impacts (1) Project Construction (2) Project Operations (3) Impacts Under No Annexation Scenario CUMULATIVE IMPACTS PROJECT DESIGN FEATURES AND MITIGATION MEASURES a. Project Design Features b. Mitigation Measures LEVEL OF SIGNIFICANCE AFTER MITIGATION Page i

2 Table of Contents List of Tables 88 Existing Catchment Areas & Corresponding Los Angeles River Outfalls Existing 50-Year Flow Rates and Volumes by Catchment Area Proposed Catchment Areas & Corresponding Los Angeles River Outfalls Proposed 50-Year Flow Rates and Volumes by Catchment Area List of Figures 181 Los Angeles Watershed Existing On-site Catchments and 50-year Storm Event Flow Rates Existing Major Drainage Lines and Los Angeles River Outfall Locations Existing On-site Man-made Water Features Proposed On-site Catchment Areas and 50-year Storm Event Flows Proposed On-site Major Storm Drain Lines Page ii

3 IV. Environmental Impact Analysis G.1.a Water Resources - Surface Water - Drainage 1. Introduction This section addresses the potential impacts of the Project with regard to surface water hydrology and summarizes information from the Hydrological Technical Report, prepared by Incledon Consulting Group, March The full text of the technical report is included as Technical Appendix I-1 to this Draft EIR. 2. Environmental Setting a. Regional Hydrology The Project Site is located in the San Fernando Valley, a region bound by the San Gabriel Mountains to the north and the Santa Monica Mountains to the south. The Project Site is located on the southern edge of the San Fernando Valley against the northern slopes of the Santa Monica Mountains. The Project Site is generally bounded by the Los Angeles River Flood Control Channel to the north, the Hollywood Freeway to the south, Barham Boulevard and Hollywood Manor residences to the east, and Lankershim Boulevard to the west. Runoff from the Project Site drains to the Los Angeles River Flood Control Channel located adjacent to the Project Site. The Los Angeles River is concrete lined within the Los Angeles River Flood Control Channel for the majority of its length, including the portion adjacent to the Project Site. The Los Angeles River Watershed covers a land area of over 834 square miles from the eastern Santa Monica Mountains to the San Gabriel Mountains in the west (refer to Figure 181 on page 1336). The upper portion of the watershed is forest and open space, however, the remaining watershed, and area in which the Project Site is located, is highly developed. The Los Angeles River begins in the northwest portion of the County, westerly of Universal City. The Los Angeles River runs easterly past the Project Site within the concrete-lined Los Angeles River Flood Control Channel and continues to flow easterly until turning south and southeast within the City of Burbank. It then flows southerly, passing through downtown Los Angeles and along the I-710 Long Beach freeway, eventually discharging into the Pacific Ocean at the City of Long Beach. Page 1335

4 Source: Los Angeles Regional Water Quality Control Board, Los Angeles River Watershed Map, Figure 181 Los Angeles Watershed Page 1336

5 The Los Angeles River Flood Control Channel is the only regional drainage facility affected by on-site development. The Los Angeles River Flood Control Channel is designed to accommodate 100-year storm event flows. A 100-year frequency storm event is defined as a storm that has a probability of one in one hundred of being equaled or exceeded in any year. Drainage and flood control in the area of the Project Site is regulated by the Los Angeles County Department of Public Works ( County ), and the Department of Public Works ( City ). The County has jurisdiction over regional drainage facilities and drainage facilities within unincorporated portions of the County. The City has jurisdiction over drainage facilities within its area. The County s Hydrology Manual for drainage criteria requires that developed areas have their drainage facilities meet the Urban Flood level of protection. The Urban Flood is defined as runoff from a 25-year frequency design storm falling on a saturated catchment. A 25-year frequency storm event is a storm that has the probability of one in 25 of being equaled or exceeded in any year. The City allows the County Hydrology Manual method be used for 50-year frequency storm for hillside developments. 108 A 50-year frequency design storm event has a probability of one in fifty of being equaled or exceeded in any given year. This report uses the County s Hydrology Manual method for 50-year frequency storm for design storm calculations for all areas of the Project Site. Although the hillside development designation does not apply to the entire Project Site, the 50-year frequency storm is a more conservative measure in determining storm water runoff rates and volumes. b. Local Hydrology The Project Site primarily drains directly to the Los Angeles River Flood Control Channel through an on-site storm drain system. The Los Angeles River Flood Control Channel is under the jurisdiction of the County and the US Army Corps of Engineers. The US Army Corps of Engineers design criterion is that the 100-year storm event is contained within the channel. According to the Federal Emergency Management Agency Flood Insurance Rate Maps, 109 the Los Angeles River Flood Control Channel would accommodate and contain stormwater associated with a 100-year frequency storm event in the vicinity of the Project Site. 110 The Project Site is within Federal Emergency Management Agency Flood Zone C which is defined as an area of minimal flooding. The Project Site is not within a flood protection district as designated by Los Angeles County, or Storm Drain Design Manual. National Flood Insurance Program Flood Insurance Rate Maps C, dated May 4, 1999 and B, dated December 2, The Los Angeles River design criterion is that the 100-year storm event is to be confined within the river channel as determined by the County and the Army Corps of Engineers. Page 1337

6 an area of special flood hazard as designated in the Flood Hazard Map. The Project Site is entirely outside the existing floodplain of the Los Angeles River. Hence, the Project Site is not subject to inundation from 100-year floodwaters. Although most of the Project Site drains directly to the Los Angeles River Flood Control Channel, the southerly portion of the Project Site drains southerly toward the Hollywood Freeway, and a part of the easterly side of the Project Site drains easterly towards Barham Boulevard. Water draining southerly from the Project Site enters into a 39-inch diameter storm drain that is owned and operated by the City 111. This storm drain is located along the north side of the Hollywood Freeway and drains to the west toward Lankershim Boulevard. Near the intersection of Lankershim Boulevard and the Hollywood Freeway, the storm water in the 39-inch storm drain joins with the storm water of a 78-inch diameter storm drain before turning north. This 78-inch storm drain continues to flow north beneath Lankershim Boulevard and it increases in size to an 84-inch diameter for a portion of Lankershim Boulevard before reducing to 78-inch diameter again. This 78-inch diameter storm drain continues along Lankershim Boulevard until it discharges to the Los Angeles River Flood Control Channel. There is also a 48-inch diameter storm drain that flows across Lankershim Boulevard and crosses the northwest corner of the Project Site before discharging into the Los Angeles River Flood Control Channel. Water draining easterly from the Project Site enters into an 18-inch diameter storm drain that is owned and operated by the City. This storm drain flows easterly across Barham Boulevard and then enters into another 78-inch diameter storm drain, which flows northerly along Barham Boulevard and reduces to 75-inch diameter before discharging to the Los Angeles River Flood Control Channel. 112 The existing measured 50-year frequency storm event water flow rate in the reach of the Los Angeles River Flood Control Channel adjacent to the Project Site is 64,773 cubic feet per second (cfs). 113 There is off-site drainage that enters onto the Project Site from locations outside the proposed Project area boundaries. These locations are: (1) the residential area along Blair Department of Public Works, Bureau of Engineering, Navigate LA, Storm Pipes Report, Plan No. D-20085; website: Department of Public Works, Bureau of Engineering, Navigate LA, Storm Pipes Report, Plan No. D-23446; website: Written correspondence provided by Roger Aliaga of the County of Los Angeles Department of Public Works, Water Resources Division, Hydrology Section, on March 26, Page 1338

7 Drive located adjoining the southeast side of the Project Site, and (2) from the Sheraton and Hilton Hotels and 10 Universal City Plaza building areas, both located adjoining the southwest side of the Project Site. The storm drain runoff from these areas accounts for 2.1 percent and 6.5 percent, respectively, of the total existing runoff from the entire Project Site. c. On-site Hydrology A detailed description of the methodology used in this analysis is summarized in Section 3.2 below and described in detail in Appendix I-1, Hydrology, of this Draft EIR. Drainage within the Project Site is divided into small drainage areas, also called catchment areas. Each catchment area along the Los Angeles River Flood Control Channel has one or more outfalls associated with it. Some of the outfalls drain water from more than one catchment area based on existing storm drain lines and drainage patterns. The existing catchment areas and corresponding outfalls are shown on Table 88 on page Figure 182 on page 1341 shows the catchments area boundaries and direction of flow within each catchment area, the 50-year frequency storm event flow, and the outfall numbers. Storm water and runoff from the Project Site flows primarily in three directions as previously discussed above. The southern portion of the Project Site drains southerly toward the Hollywood Freeway and enters into the storm drain system along the north side of the freeway. The eastern portion of the Project Site drains easterly toward Barham Boulevard and enters into the storm drain system along Barham Boulevard. For the northern portion of the Project Site, storm drain lines convey the Project Site s runoff to the north and discharge directly to the Los Angeles River Flood Control Channel through twenty-seven outfalls. For the larger storm drains on the southern and eastern sides of the Project Site, the on-site storm drains convey the runoff from each individual drainage area southerly or easterly and connect to the 39-inch or 18-inch storm drain, respectively. Storm water flows were calculated using the Stormwater Management Model System for Windows based Interface (XP-SWMM) program, per the Los Angeles County Hydrology Manual. 114 The XP-SWMM program was used to calculate the stormwater runoff and peak flow rates for each catchment using inputs determined from physical features of the Project Site and information provided on County hydrologic maps. The peak flow rate is a measure of the highest rate at which storm water leaves the Project Site and enters the Los Angeles River Flood Control Channel during the 50-year, 114 Los Angeles County Hydrology Manual, Chapter 4 Policy on Levels of Protection, January Page 1339

8 Table 88 Existing Catchment Areas & Corresponding Los Angeles River Outfalls Catchment Outfall Number(s) A 15, 16, 17, 18 B 14 C 13 D 11, 12 E 9, 10 F 8 G 7 H 6 I 5 J 3, 4 L 17 M 2, 19 O 1, 20, 21, 22 P 23, 24 Q 24 R 25 S 26 T 25, 26, 27 U 17 V 27 * Differing/missing catchment areas due to relettering and/or physical changes in catchment areas. Source: Incledon Consulting Group, March hour storm event. Storm water volume is the actual amount of water that enters the Los Angeles River Flood Control Channel as a result of the 50-year, 24-hour storm event. As described above, the main storm water flow directions for drainage leaving the Project Site under existing conditions are: easterly towards Barham Boulevard, southerly towards the Hollywood Freeway, and northerly directly into the Los Angeles River Flood Control Channel. For the easterly storm water flows, the existing peak flow rate is 49.8 cubic feet per second and existing storm water volumes are 4.1 acre-feet. For the southerly storm water flows, the existing peak flow rate is cubic feet per second and existing storm water volumes are 25.8 acre-feet. For the northerly storm water flows, the existing peak flow rate is cubic feet per second and existing storm water volumes are acre-feet. The southerly and northerly flows include the storm water flows that enter the Project Site from the off-site Blair Drive community and the hotels and 10 Universal City Plaza building areas. These off-site flows account for 20.6 cubic feet per second of the total peak flow for the Blair Drive community and 64.3 cubic feet per second of the total peak flow for the hotel and 10 Universal City Plaza building areas. For the overall Project Page 1340

9 Page 1341 Source: Incledon Consulting Group, Figure 182 Existing On-site Catchments and 50-year Storm Event Flow Rates

10 Site, the total existing peak flow rate is cubic feet per second and the total existing storm water volume is acre-feet. The existing on-site catchment areas and the flow quantity associated with each onsite catchment area are shown in Figure 182 on page 1341; the major storm drain lines onsite, the direction of flow, and corresponding outfall number(s) showing connections between the Project Site and the Los Angeles River Flood Control Channel are shown on Figure 183 on page The existing flow rates and storm water volumes for the 50-year storm event are shown on Table 89 on page 1344, and discussed below. The Project Site includes six man-made, lined water features, two of which provide a modest benefit for storm water detention, accounting for 3.9 percent of the total existing storm water runoff flow rate. All of the water features are lined with asphalt, concrete or a combination of asphalt and concrete. The water features that provide storm water detention are called Falls Lake and Park Lake and are used for filming and as part of the tram attraction. Falls Lake is primarily empty throughout the course of the year except when used for filming while Park Lake is kept at a level that is almost full. Because of this, Falls Lake provides a larger total benefit of 35.7 cubic feet per second of reduction of peak runoff during the 50-year storm event and Park Lake provides a total benefit of 2.5 cubic feet per second. Runoff and storm drains from the surrounding areas drain into these water features. Drainage from Falls Lake then discharges to a storm drain system that then discharges to the Los Angeles River Flood Control Channel. Drainage from Park Lake flows through an overflow weir and into the storm drain system, which ultimately discharges to the Los Angeles River Flood Control Channel. The other water features, which are also used as part of tram ride attractions, have overflow drains; however, there is no constant inflow and outflow of storm water runoff or drainage from these water features. The existing on-site man-made water features are shown on Figure 184 on page Environmental Impacts a. Methodology The Hydrological Technical Report prepared for the proposed Project evaluated the change in runoff patterns and quantity for the Project Site and the impact of these changes on the existing downstream storm drain capacity. As described above, based on the more conservative of County and City drainage criteria, this report uses the 50-year frequency storm event flows for design storm calculations. Although the CEQA Thresholds Guide provides Development Classifications with typical percentage of imperviousness by zone, it is more accurate to use actual land use areas for this Project so that calculated runoff flow rates Page 1342

11 Page 1343 Source: Incledon Consulting Group, Figure 183 Existing Major Drainage Lines and Los Angeles River Outfall Locations

12 Table 89 Existing 50-Year Flow Rates and Volumes by Catchment Area Catchment Peak Flow Rate (cfs) Volume (ac-ft) A B C D E F G H I J K N/A N/A L M N N/A N/A O P Q R S T U V Total * N/A indicates catchment area not included due to relettering and/or physical changes in catchment areas. Source: Incledon Consulting Group, and volumes reflect actual Project Site conditions. Under the CEQA Development Classifications, the existing and proposed developed portions of the Project Site would be considered 100 percent impervious and the portions of undeveloped hillside would be considered 35 percent impervious. For a Project Site of this size, the impervious percentages based on CEQA Development Classifications would be an oversimplification and possible overstatement of Project Site conditions. Because of this, each catchment area within the Project Site was divided into specific land use categories and impervious percentages assigned based on the land use to determine the amount and flow rates for both the existing and proposed storm water runoff conditions. Determinations as to the potential for flooding of the Project Site by off-site flows are based on the flood designations of the Project Site by Federal Emergency Management Agency and the County and City, as well as observations by the Project s hydrologist Page 1344

13 Page 1345 Source: Incledon Consulting Group, Figure 184 Existing On-site Man-made Water Features

14 concerning off-site flows entering the Project Site. Determinations as to the potential for site-related storm water flows to flood adjacent properties are based on: (1) a conservative assumption that no infiltration and 100 percent runoff occurs on the Project Site under existing and future conditions (in other words, impacts to on-site and off-site drainage facilities are analyzed from the perspective of maximum or peak runoff, and not total volume of runoff over a period of time; peak runoff is more relevant than total volume over time to determining the impact on drainage systems); (2) existing and proposed on-site drainage infrastructure; and (3) observations made by the proposed Project s hydrologist concerning the quantity and disposition of storm water flows which could be generated on, and drain from, the Project Site. In addition, it should be noted that the Project Site is underlain by clayey soils which allow for negligible infiltration during larger storm events where rain first saturates and then runs off the topsoil. The assumptions above are used to identify the capacity requirements of future on-site drainage facilities, and impacts on existing off-site regional drainage facilities. Increases in total non-peak runoff from development are not relevant to the discussion of drainage. The non-peak runoff flow rate varies from 0 cubic feet per second up to the peak rate. Therefore, peak runoff is more relevant than total volume over time to determine the impact on drainage systems. Catchment areas within the Project Site were divided into specific land use categories to determine the amount and flow rates of both the existing and proposed storm water runoff. As previously stated, the City allows the use of the Los Angeles County Hydrology Manual and the Storm Water Management Model system for a Windows-based interface (XP-SWMM) be used to calculate and model storm water runoff. The catchment area, time of concentration, soil type, impervious percentage, and rainfall depth were the inputs used by the XP-SWMM program. These inputs were determined from physical features of the Project Site and information provided on County hydrologic maps. b. Thresholds of Significance Based on the criteria set forth in the CEQA Thresholds Guide (2006), a project would normally have a significant impact on surface water hydrology if it would: Cause flooding during the projected 50-year developed storm event, which would have the potential to harm people or damage property or sensitive biological resources; or Substantially reduce or increase the amount of surface water in a body of water; or Result in a permanent, adverse change to the movement of surface water sufficient to produce a substantial change in the current or direction of water flow. Page 1346

15 In addition, for purposes of this analysis, the Project would be considered to have a significant impact if: Future storm water conveyance facilities are not designed or constructed per applicable County and City standards; or The Project Site is subject to inundation by 100-year floodwaters or other possible flood hazards. c. Project Design Features Project-related activities would require the development of new on-site storm drain facilities to convey stormwater flows from portions of the Project Site where proposed Project activities would alter the existing pattern of runoff. New storm drains would be designed and sized using the Los Angeles County Hydrology Manual method for a minimum 50-year frequency storm event capacity. Table 90 on page 1348 shows the proposed catchments and their corresponding outfall number(s). The proposed locations for the new outfalls, drainage system catchments, direction of flow, and 50-year frequency storm event flow rates that would result from new development are shown in Figures 185 and 186 on pages 1349 and The new on-site storm drains would be 18-inches through 48-inches in size. These new storm drains would be necessary to accommodate modifications to the direction of local storm water flows, drainage areas and patterns resulting from proposed grading of the Project Site. In addition, smaller sized lines would also be installed to convey flows from individual development sites to these larger storm drain facilities. The key changes to the on-site storm drain system are highlighted below. Exact storm drain line sizes may change depending upon the final design for the proposed Project. Development within the proposed Mixed-Use Residential Area would require 36- to 48-inch storm drain lines to drain storm water to the Los Angeles River Flood Control Channel. The 36-inch storm drains would run along the main roadways and residential streets in the proposed development and would increase in size to a single 42-inch storm drain within approximately 300 feet of the Los Angeles River Flood Control Channel. This 42-inch storm drain would increase in size to 48-inch within approximately 150 feet of the Los Angeles River Flood Control Channel. The realignment of Universal Hollywood Drive would require the existing storm drain lines and catch basins to be removed and replaced with 18-inch diameter or larger storm drains and new catch basins, respectively. These new storm drains and catch basins would be located in the new Universal Hollywood Drive alignment. Page 1347

16 Table 90 Proposed Catchment Areas & Corresponding Los Angeles River Outfalls Catchment Outfall Number(S) A 15, 16, 17, 18 B 14 C 13 D 11, 12 E 9, 10 F 8 G 7 H 6 I 5 J 3, 4 L 17 M 19, New Outfall O 1, 20, 21, New Outfall P 23, A New outfall 100-5A Same as above A Same as above A Same as above D D E 25, New Outfall F 26, B A B C 17 * Differing/missing catchment areas due to relettering and/or physical changes in catchment areas. Source: Incledon Consulting Group, March As the proposed Project requires the removal of Falls Lake, to accommodate proposed development within the Mixed-Use Residential Area, the replacement of existing related storm drain facilities with new storm drain lines to redirect discharge into the 36-inch storm drain located in the proposed North-South Road is required. The proposed Project will also include a storm water detention feature to reduce the peak flow rate draining into the Los Angeles River Flood Control Channel. This detention feature will be located in the Mixed-Use Residential Area. The detention system would be designed to reduce the peak flow rate leaving the Project Site under the proposed conditions to a level at or below the peak flow rate leaving the existing Project Site. The detention system would be sized to reduce the peak flow rate by 28.0 cubic feet per second Page 1348

17 Page 1349 Source: Incledon Consulting Group, Figure 185 Proposed On-site Catchment Areas and 50-year Storm Event Flows

18 Source: Incledon Consulting Group, Figure 186 Proposed On-site Major Storm Drain Lines Page 1350 Page

19 and to detain approximately 0.2 acre-feet of volume. The system would be located underground and would consist of either a flow-through or flow-by detention system, or an approved equivalent facility that would provide the same detention volume for peak runoff flow rate. Under the flow-through system, the storm drain line would be increased from 48- inches to 78-inches for an appropriate length to create a reservoir that would limit the flow rate of storm water runoff discharging towards the Los Angeles River Flood Control Channel. The flow-by system would be connected to the 48-inch storm drain and would capture excess storm water runoff in an adjacent detention facility. Under either system, the excess storm water would be contained until the runoff flow rate in the 48-inch storm drain is reduced. For the purpose of the analyses of Project impacts in this analysis, a flow-through detention system was included in Catchment Area A. The exact size and location of the final detention system would be determined prior to construction as final plans for the Project Site buildings are completed. d. Project Impacts (1) Project Construction On-site construction activities may cause short-term hydraulic erosion due to associated grading or construction-related soil disturbance. Grading, removal of existing lakes, development of new roadways, development of drainage improvements and other activities would also alter the Project Site's catchment areas and thus potentially change the Project Site's drainage patterns and directions of flow as noted above. Construction of new drainage facilities would be required in a manner and sequence that would preclude flooding. As discussed in Section IV.G.1.b, Surface Water Quality, during construction, a Storm Water Pollution Prevention Plan and Erosion Control Plan would be implemented to provide for temporary storm water management. These plans would prevent construction from adversely affecting the amount of surface water in a water body. In addition, there would be some construction off-site within the existing River Road to install new connections and up to six new and relocated outfalls to the Los Angeles River Flood Control Channel. All other storm drain facilities would be constructed within the Project site. Construction impacts would be confined to trenching for storm drain lines and removal of existing water features. New storm drains would be constructed to support development and would be in place and functioning as development progresses to serve their respective catchments. Construction under the proposed Project would not subject adjacent properties to proposed Project-related floodwaters because any alteration of flows on-site during construction would be conveyed to existing off-site regional storm drain facilities by temporary flood control improvements established in compliance with responsible agency standards. Therefore, no significant on-site or off-site flood impacts would result during the construction phases of the proposed Project. Page 1351

20 (2) Project Operations Detailed hydrology and hydraulic calculations would be prepared for each Project (as that term is defined in the proposed City and County Specific Plans). The proposed development of the Project Site would require changes and/or modifications to the on-site drainage system. The primary modification to on-site hydrology would be the re-direction of portions of the stormwater runoff that had previously drained easterly or southerly to now drain northerly from the Mixed-Use Residential Area development towards the Los Angeles River Flood Control Channel. Although this is a change to the on-site movement of surface water, new storm drain lines will be constructed using the County Hydrology Manual to adequately handle the change in Project Site drainage patterns. The proposed Mixed-Use Residential development would have a separate drainage system from the other development districts. No off-site storm drains located in Lankershim Boulevard or Barham Boulevard would be changed or replaced as a part of the Project and no off-site drainage facilities would be adversely affected. Notwithstanding, there would be off-site improvements related to the construction of up to six new and relocated outfalls to the Los Angeles River Flood Control Channel. These off-site improvements would occur in the access road to the Los Angeles River Flood Control Channel as storm drains from the Project Site are connected to their respective outfalls. These outfalls may be required due to a potential conflict between existing outfalls and proposed building locations. Further, the Applicant seeks to separate the Mixed-Use Residential Area development storm water runoff from the other Areas. The actual sizes of the new and relocated outfalls would be determined as plans for the Project are further developed, but may range in size from 48-inches to 60-inches in diameter. Construction of a new outfall requires excavating the soil behind the channel wall, sawcutting and removing a portion of the existing channel wall, installing reinforcing steel, and replacing the concrete that was removed, preserving a space into which the new storm drain pipe can be placed. This process is completed by installing the storm drain pipe and replacing the soil. The area of wall removed and replaced is typically not more than 200 square feet for projects of this type. The channel wall, after completion of this process, is as strong or stronger than the wall before the new outfall is constructed. It is also important to note that even if the new/relocated outfalls are not constructed, the overall Project impacts would be the same as those described below. Furthermore, should these new outfalls be constructed, approvals would be required from the Los Angeles County Flood Control District and the U.S. Army Corps of Engineers. The Applicant would submit a Nationwide Permit Pre-Construction Notification (PCN) Form to the South Pacific Division of the U.S. Army Corps of Engineers and a Section 401 Water Quality Certification Application Form to the California Regional Water Quality Control Board, Los Angeles Region, for approval of the new outfalls into the Los Angeles Flood Control Channel prior to construction. Page 1352

21 New storm drains would be constructed using the County Hydrology Manual to adequately handle the change in Project Site drainage patterns. Since all new storm drains would be designed and sized to handle the 50-year frequency storm event (per the Los Angeles County Hydrology Manual), all 50-year frequency storm water flows would be collected and conveyed ultimately to the Los Angeles River Flood Control Channel, and there would be no flooding during a 50-year storm event. Development under the proposed Project would require the construction of specific on-site flood control infrastructure (i.e., smaller than 18 inches in diameter) to convey stormwater flows associated with each development site, or groups of development sites, to the major stormwater infrastructure. Future storm water conveyance facilities would be designed and constructed pursuant to all applicable County and City standards. As stated above, hydrology and hydraulic reports would be prepared for each development area and submitted to the County and/or City for review and approval prior to submittal for grading and building permits. Storm water flows would continue to drain easterly towards Barham Boulevard, southerly towards the Hollywood Freeway and northerly directly to the Los Angeles River Flood Control Channel. The flows would continue to drain either directly through outfalls or via the existing 18-, 39-, and 78-inch storm drains to the south, east, and west of the Project Site, respectively. As with the calculation of existing conditions, the proposed Project storm water flows were calculated using the XP-SWMM program, per the Los Angeles County Hydrology Manual. As shown on Table 91 on page 1354 and discussed below, the peak flow rates and storm water volumes for the 50-years storm event would be as follows for the proposed Project. For the storm water flows that drain easterly, the peak flow rate would be 21.9 cubic feet per second (proposed Catchment Area 200-5B) with a storm water volume of 1.5 acrefeet with the proposed Project. This would be a decrease from the existing easterly peak flow rate (49.8 cubic feet per second) and storm water volume (4.1 acre-feet) discussed previously and as shown on Table 89 on page For the southerly storm water flows, the peak flow rate would be cubic feet per second with a storm water volume of 24.4 acre-feet with the proposed Project (proposed Catchment Areas L, 300-5B, 300-1A and 300-1C). This would be a decrease from the existing southerly peak flow rate and storm water volume discussed above and as shown on Table 89 on page For the northerly storm water flows, the peak flow rate would be cubic feet per second with a storm water volume of acre-feet with the proposed Project. This would be an increase from the existing northerly storm water volume discussed previously and as shown on Table 89 on page Page 1353

22 Table 91 Proposed 50-Year Flow Rates and Volumes by Catchment Area Catchment Peak Flow Rate (cfs) Volume (ac-ft) A B C D E F G H I J K N/A N/A L M N N/A N/A O P A A A A 37.7** D D E F B A B C TOTAL * N/A indicates watershed area not included due to relettering and/or physical changes in catchment areas. ** Includes a 28.0 cubic feet per second reduction in peak flow rate due to storm water detention feature. Source: Incledon Consulting Group, Overall, the catchment areas that drain toward the Hollywood Freeway and Barham Boulevard would have a decrease in peak runoff flow rate and runoff volume with the proposed Project as more catchment areas will drain northerly, directly to the Los Angeles River Flood Control Channel. This redirection of flows northerly is considered beneficial since it will reduce the amount of storm water flowing through City storm drains. As potential runoff is decreasing, the existing off-site storm drain lines draining along the freeway and along Barham Boulevard will not be impacted and will not be modified. No new drainage lines will be constructed off-site for the runoff that drains to the storm drain systems along the Hollywood Freeway and Barham Boulevard. Page 1354

23 With the incorporation of the detention feature as a Project Design Feature, there is no increase in peak flow rate with the proposed Project. In addition, development in the Business, Entertainment, and Studio Areas, with certain exceptions as specified in the County Specific Plan, would incorporate applicable County Low Impact Development Standards Best Management Practices that would reduce the change in flow rates. Peak flow rate measures the highest rate at which storm water is leaving the Project Site and entering the Los Angeles River Flood Control Channel during a storm event. Since there is no increase in peak flow rate with the proposed Project, the Project will not result in a substantial increase in the amount of surface water and would not result in a permanent adverse change to the movement of surface water sufficient to produce a substantial change in the current or direction of water flow. Implementation of the proposed Project would result in an overall increase in the storm water volume generated by the Project Site. Storm water volume is the actual amount of water that enters the Los Angeles River Flood Control Channel throughout the entire storm event. When compared to recorded storm water volumes in the Los Angeles River Flood Control Channel over the past nine years, the 3.2 acre-feet increase in volume with the proposed Project equates to percent of the maximum daily discharge flowing in the Los Angeles River Flood Control Channel (31,339 acre-feet) and percent of the average daily discharge (12,309 acre-feet) 115 flowing in the Los Angeles River Flood Control Channel. This slight increase in storm water volume would not create a substantial increase in the volume of surface water contributed by the Project Site to the Los Angeles River Flood Control Channel and would not result in a permanent adverse change to the movement of surface water sufficient to produce a substantial change in the current or direction of water flow. In addition, development in the Business, Entertainment, and Studio Areas, with certain exceptions as specified in the County Specific Plan, would incorporate applicable County Low Impact Development Standards Best Management Practices that would reduce the change in flow rates. (3) Impacts Under No Annexation Scenario The Project Design Features and Project Impacts would not be affected by annexation, as Project impacts are analyzed using the County Hydrology Manual and method regardless of the portion of the Project Site that is proposed for individual development activities. Further, there is the potential for only a portion of the proposed deannexation/annexation to occur. In this case, the percentage of the Project Site annexed to the City would be less than under the proposed Project, but would greater than under the No Annexation scenario. As with the No Annexation scenario, the project design features 115 Hydrologic Report, March 6, These measured maximum and average discharges were recorded at the Los Angeles River Station F300-R located 1.1 miles up the River at the intersection of Tujunga Avenue and the Los Angeles River. Page 1355

24 and Project Impacts would not be affected by annexation, as Project impacts are analyzed using the County Hydrology Manual and method regardless of the portion of the Project Site that is proposed for individual development activities. 4. Cumulative Impacts The Los Angeles River Flood Control Channel has a catchment area which includes portions of the San Fernando Valley. Cumulative growth within this catchment area could contribute to the increased utilization of the available capacity of the Los Angeles River Flood Control Channel. The proposed Project would result in a net reduction in the quantity of Site-related water currently entering the 39-inch storm drain located along the north side of the Hollywood Freeway. The 78-inch and 84-inch storm drain located along Lankershim, and the 18-inch, 78-inch and 75-inch storm drain lines located along Barham Boulevard. Therefore, the Project s impacts would not be significant on a cumulative basis. Cumulative growth as identified in Section III.B, Related Projects, could subject people and property to flood hazards if located within areas subject to flooding from the 100-year storm event (i.e., Federal Emergency Management Agency Flood Zones A, B, or D) and could subject people and property adjacent to the related projects to flooding if these projects divert or otherwise cause floodwaters to drain onto adjacent properties. It is anticipated that individual buildings and facilities which constitute cumulative growth would be subject to building permit issuance processes which would require design features and characteristics which would reduce potential flood impacts on an individual, and thus, cumulative basis, to acceptable levels. The proposed Project would not contribute to any potentially significant cumulative impacts because it would neither subject on-site persons and property to inundation from 100-year floodwaters, nor would it subject adjacent uses to floodwaters generated on-site. Additionally, the Project Site is not within a flood protection district as designated by Los Angeles County, or an area of special flood hazard as designated in the City of Los Angeles Flood Hazard Map. Therefore, the Project Site would not be subject to inundation by 100-year floodwaters or other possible flood hazards; potential flood hazard impacts would be less than significant during both the construction and operational phases for the proposed Project. The proposed Project in association with other future projects, would not contribute to flooding during the projected 50-year storm event, or have the potential to harm people or damage property or sensitive biological resources. Adherence to the existing requirements of the responsible jurisdictions and Federal Emergency Management Agency concerning development within flood plains would ensure that the proposed Project and other future projects volume and velocity changes would be within the carrying capacity identified by the Army Corps of Engineers for the Los Angeles River Flood Control Page 1356

25 Channel. As Project development, with the incorporation of project design features, would not increase peak flow rates, the Project is not anticipated to have a cumulative effect on the surrounding area. Furthermore, the majority of the areas surrounding the Project Site are developed and consist of highly urbanized developments. Therefore, cumulative impacts related to potential drainage and flood hazards would be considered to be less than significant. 5. Project Design Features and Mitigation Measures a. Project Design Features The following project design features would reduce Project impacts to less than significant level: Project Design Feature G.1.a-1: The Applicant or its successor shall construct new storm drains as needed that shall be designed and sized using the Los Angeles County Hydrology Manual method for a minimum 50-year frequency storm event capacity. Project Design Feature G.1.a-2: The Applicant or its successor shall construct prior to buildout of the Mixed-Use Residential Area an underground storm water detention feature in the Mixed-Use Residential Area. The stormwater detention feature shall be sized to reduce the peak flow rate by 28.0 cubic feet per second and to detain approximately 0.2 acre-feet of volume. The exact size and location of the final stormwater detention feature shall be determined prior to construction as final plans for the Project Site buildings are completed. b. Mitigation Measures Although no significant impacts are anticipated that would reduce or increase the amount of surface water in a body of water; result in a substantial change in the current or direction of water flow having the potential to harm people or damage property or sensitive biological resources; or subject the Project Site to inundation by 100-year floodwaters or other possible flood hazards, the following measure in addition to the identified project design features would be implemented by the Applicant or its successor during the construction phase of the proposed Project: Mitigation Measure G.1.a-1: The Applicant or its successor shall prepare detailed drainage plans for each Project (as that term is defined in the City and County Specific Plans) for review and approval by the Page 1357

26 appropriate responsible agency (i.e., Los Angeles County Department of Public Works or the Department of Public Works) at the time that grading or building permit applications are submitted. These drainage plans shall include detailed hydrologic/hydraulic calculations, as necessary, and drainage improvement plans, and show quantitatively how projected stormwater runoff in each drainage area of the Project site would be conveyed to off-site stormwater conveyance facilities. 6. Level of Significance After Mitigation The proposed Project would incorporate the use of existing and planned stormwater catchment systems and would direct stormwater in a manner that would not result in substantial erosion or flooding within the Project Site or offsite locations. Specifically, the proposed Project would develop new onsite stormwater conveyance facilities in association with the proposed development of the Mixed-Use Residential Area, thereby redirecting existing surface flow from the east and south side of the Project Site northerly to drain into storm drain lines connecting with the Los Angeles River Flood Control Channel. Future storm water conveyance facilities would be designed and constructed per applicable jurisdictional standards, with site-specific system design components to be established and approved by the responsible agencies prior to the issuance of building permits. Stormwater and surface drainage anticipated for the proposed Project during both construction and operational phases would not substantially reduce or increase the amount of surface water in a body of water or result in a permanent, adverse change to the movement of surface water sufficient to produce a substantial change in the current or direction of water flow. The proposed Project would not result in flooding during the projected 50-year developed storm event, or have the potential to harm people or damage property or sensitive biological resources during either the construction or operational phases. Therefore, implementation of the proposed storm drain system improvements, in adherence with the recommended mitigation measures, would result in a less than significant impact for the proposed Project. Page 1358