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HomeMy WebLinkAboutFinal_Drainage_Report06-Ker-178, PM R6.9 to T9.2 06-0C9401 January 2013 City of Bakersfield California Department of Transportation January 2013 FINAL DRAINAGE REPORT FOR MORNING DRIVE/SR 178 INTERCHANGE PROJECT Project Description: The project would construct a new interchange on SR-178 near the existing Morning Drive/SR-178 intersection, convert the existing two-lane SR-178 roadway with passing lanes to a four- lane freeway, and realign a segment of Morning Drive through the project area crossing over SR-178. Concurrence by: 661-326-3576 Manny Behl Date Telephone City of Bakersfield Concurrence by: 559-243-3507 Sam Wong, P.E. Date Telephone Caltrans Central Region, Hydraulics City of Bakersfield California Department of Transportation January 2013 FINAL DRAINAGE REPORT FOR MORNING DRIVE/SR-178 INTERCHANGE PROJECT IN KERN COUNTY This Drainage Report was prepared under the direction of the following registered civil engineer. The registered civil engineer attests to the technical information contained herein and the engineering data upon which recommendations, conclusion, and decisions are based. _________________________________ ________1/22/13_________ Mike Daly, P.E. Date Registered Civil Engineer City of Bakersfield California Department of Transportation January 2013 i TABLE OF CONTENTS 1 GENERAL 1.1 PROJECT DESCRIPTION ........................................................................................1 1.2 EXISTING DRAINAGE ...........................................................................................1 1.3 LAND USE AND FUTURE LAND USE .................................................................2 1.4 PURPOSE OF THIS REPORT ..................................................................................2 2 HYDROLOGY 2.1 DESIGN STANDARDS AND CRITERIA ...............................................................3 2.2 RAINFALL CHARACTERISTICS ..........................................................................3 2.3 CLIMATE ..................................................................................................................4 2.4 FLOODPLAIN ANALYSIS ......................................................................................4 2.5 GROUNDWATER TABLE ......................................................................................4 2.6 RUNOFF CALCULATIONS ....................................................................................5 3 HYDRAULICS 3.1 DESIGN CRITERIA AND METHODOLOGY ........................................................8 3.2 ROADWAY PROFILE, LAYOUT AND TYPICAL SECTIONS ...........................8 3.3 SPREAD CALCULATIONS.....................................................................................9 3.4 PIPE SIZING CALCULATIONS..............................................................................9 3.5 FLOOD ROUTING (HEC-HMS)..............................................................................9 3.6 RETENTION/DETENTION BASIN DESIGN .........................................................10 3.7 PEAK OUTFLOW.....................................................................................................12 3.8 CROSS CULVERT CALCULATIONS ....................................................................13 3.9 DRAINAGE DITCH CALCULATIONS ..................................................................13 3.10 DRAINAGE FOR CONSTRUCTION STAGING ...................................................14 3.11 ISSUES OF CONCERN AND MITIGATION .........................................................15 4 OTHER AGENCIES 4.1 LOCAL AGENCY COORDINATION .....................................................................16 4.2 UTILITY COMPANY COORDINATION ...............................................................16 5 WATER QUALITY 5.1 PERMANENT BEST MANAGEMENT PRACTICES ............................................17 5.2 TEMPORARY BMPs DURING CONSTRUCTION ...............................................17 6 OTHER CONSIDERATIONS 6.1 COMPATIBILITY WITH FUTURE PROJECTS ....................................................18 7 REFERENCES 7.1 LIST OF REFERENCES ...........................................................................................19 City of Bakersfield California Department of Transportation January 2013 ii LIST OF APPENDICES A. LOCATION MAP B. PROPOSED GEOMETRIC LAYOUT C. PRE-DEVELOPMENT WATERSHED MAP D. POST-DEVELOPMENT WATERSHED MAP E. PROPOSED STORM DRAIN SYSTEM MAP F. IDF CURVES G. NOAA ATLAS 2 RAINFALL DATA H. RUNOFF SUMMARY I. CATCH BASIN RESULTS J. CONDUIT TABLE K. PIPE SUMMARY TABLE L. USDA SOILS MAP M. HEC-HMS SYSTEM SCHEMATICS N. HEC-HMS SUB-BASIN INPUT O. HEC-HMS RESERVIOR STAGE-STORAGE INPUT P. HEC-HMS RESERVIOR STAGE-DISCHARGE INPUT Q. HEC-HMS INFLOW/OUTFLOW HYDROGRAPHS R. CROSS CULVERT ANALYSIS REPORTS S. ROADSIDE DITCH/SWALE CALCULATIONS T. DRAINAGE COORDINATION MEETING MINUTES U. CORRESPONDENCE BETWEEN CITY OF BAKERSFIELD AND CALTRANS V. CORRESPONDENCE BETWEEN CITY OF BAKERSFIELD AND PG&E W. GEOTECHNICAL COMPACTION & PERMEABILITY EXTRACTS Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 1 1. GENERAL 1.1 PROJECT DESCRIPTION The California Department of Transportation (Caltrans), in cooperation with the City of Bakersfield, is proposing to construct a new interchange along State Route 178 at Morning Drive in Bakersfield, California (see Location Map, Attachment 1). The project is located in the northeastern portion of the City of Bakersfield, within central Kern County. The project would construct a new interchange on State Route 178 near the existing Morning Drive/State Route 178 intersection, convert the existing two-lane State Route 178 roadway with passing lanes to a four- lane freeway, and realign a segment of Morning Drive through the project area crossing over State Route 178. The project limits are post mile R6.9 to T9.2. To accommodate the design year traffic forecasts for the Project the ultimate six-lane facility for State Route 178 would be constructed by 2035, through two projects (KER08RTP111 and KER08RTP112) identified in the Kern Council of Governments’ (KernCOG) Destination 2030 Regional Transportation Plan (RTP) Amendment #2, dated September 2009. 1.2 EXISTING DRAINAGE Offsite runoff from the area northeast of the Morning Drive/SR-178 intersection currently flows generally east to the eastern project limit, where it crosses SR-178 and flows to the south. Runoff from the area south of SR-178 and east of Morning Drive currently flows towards SR- 178. After reaching SR-178, runoff flows easterly along the toe of slope and eventually to the south into the Breckenridge Drainage Area. Runoff from the offsite areas west of Morning Drive generally flows to the south, into the Shalimar Drainage Area. Along SR-178 there is an existing high point just west of Morning Drive. East of the high point, the roadway runoff collected by AC dikes generally flows to the east via a piped drainage network. Where AC dikes do not exist, runoff flows freely off the roadway as sheet flow. This onsite runoff is eventually routed to the south into the Breckenridge Drainage Area. West of the high point, the onsite runoff collected with AC dikes generally flows to the west via a piped drainage network and eventually to the south into the Shalimar Drainage Area. Several cross culverts, up to 60 inch diameter, are located along SR-178 and currently convey water from the north to the south. These drainages will be maintained in the proposed project. The existing development south of Auburn Street, including the Canyon Hills Assembly of God Church property, currently discharge runoff across SR-178 and into natural drainage courses to the south of SR-178 through existing cross culverts. Existing drainage facilities and drainage patterns are shown in Appendix C, Pre-development Watershed Map. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 2 1.3 LAND USE AND FUTURE LAND USE The project area included annual grasses and wildflowers which form a dense to sparse ground cover. Preliminary grading has taken place for a large portion of the area to the north of SR-178, east of Morning Drive where a residential development is proposed. Within the project site, land north of SR-178 is primarily vacant with few commercial uses including a church, nursing and education complex while land south of SR-178 is entirely vacant. The City’s General Plan designates the proposed land uses for the project site. Designated uses north of SR-178 include low, low-medium, and high density residential as well as general commercial. South of SR-178, designated uses include low and high-medium density residential, general commercial, mixed use and open space. Planned development in the vicinity of the project site includes additional development of the church property in the northwest quadrant of the project site, which included the realignment of a portion of Auburn Street north of SR-178 and west of Morning Drive. In the northeast quadrant of the project site, a residential development is in the process of being constructed. This development will connect to Morning Drive via the Auburn Street and Morningstar Avenue intersections. Several large residential developments are also planned for construction south of SR-178, west and east of the Morning Drive alignment. Southwest of the project site, a large commercial development is proposed and two residential projects are planned. This development south of SR-178 will be accessed via Morning Drive south to existing Morning Drive near College Avenue. Two large residential developments are planned east of Morning Drive adjacent to and south of SR-178. Traffic from the developments described above, as well as other future growth in the area, is anticipated to use the proposed Morning Drive interchange. 1.4 PURPOSE OF THIS REPORT The purpose of this report is to document the hydrologic, hydraulic and water quality analyses completed during the design of drainage facilities for this project. Calculations for this study are based on the proposed design as shown in Appendix B, Proposed Geometric Layout. Additionally, per Caltrans direction, SR-178 was assumed to have a paved median in order to size structures for future expansion of the roadway. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 3 2. HYDROLOGY 2.1 DESIGN STANDARDS AND CRITERIA This study was completed in accordance with guidelines set forth in the Caltrans Highway Design Manual (HDM), Caltrans District 6 guidelines, and based on input received from the City of Bakersfield. Minutes from coordination meetings with both Caltrans and the City are included in Appendix T, Drainage Coordination Meeting Minutes. The Rational Method was used for storm drain hydraulic calculations as described in Federal Highway Administration (FHWA), Hydraulic Engineering Circular Number 22 (HEC-22). NRCS methods were used to calculate the peak discharges used to size and analyze ditches and cross culverts. While the Rational Method is suitable for use in pipe sizing, its application is limited elsewhere since it is only applicable for relatively small watersheds. Additionally, it is not intended to be used to generate runoff hydrographs or total runoff volume. For this study the Natural Resource Conservation Service (NRCS) methodology was used for the following: · To calculate direct runoff volumes for determination of retention requirements and water quality volumes. · To generate runoff hydrographs for flood/detention routing. · To analyze existing culverts. · To size roadside ditches. · To analyze proposed cross culverts. Per the HDM, the 10-year and 100-year events were considered for the design of cross drainage within the project limits. The 25-year event was used for calculations related to the design of the onsite roadway drainage network. 2.2 RAINFALL CHARACTERISTICS About 90 percent of all precipitation falls from October through April. The 50-year average annual rainfall for the City is about 6.13 inches, classifying it as a desert. Intensity-Duration-Frequency (IDF2000) curves relating storm duration and frequency to rainfall intensity were provided by Caltrans District 6 Hydraulics Department for use in calculations using the Rational Method. IDF curve data for this project is in Appendix F, IDF Curves. The IDF2000 precipitation data was used to determine rainfall depths for use in NRCS runoff calculations. The 100-year, 24-hour event produces 2.76 inches of rainfall. NOAA Atlas 2 precipitation data was used, in accordance with City of Bakersfield criteria, to determine rainfall depths for use in NRCS runoff calculations for Outfall 6 (see Table 3-1) for basin sizing. Final design results in the total volume for the 2.76 inch storm event being retained. A city criterion was initially used due to the runoff retention basin being located outside of State Right-of-Way. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 4 The 100-year, 24-hour event produces 2.43 inches of rainfall for the City design storm event (see Appendix G). 2.3 CLIMATE The City of Bakersfield has a moderate climate with cloudless, warm, and dry summers and mild and semi-arid winters. The average temperature in the City of Bakersfield ranges from 48 degrees Fahrenheit (°F) in December to 83°F in July. There are large climatic variations in the area because of the nature of the surrounding valleys, mountains, and desert areas. 2.4 FLOODPLAIN ANALYSIS According to Federal Emergency Management Agency (FEMA) flood hazard map 06029CIND0A, the project area is located on FIRM Panel 06029C1845E which is not printed and designated as an area not within a flood hazard zone, therefore not at risk of natural flooding from the 100-year storm (September 26, 2008). 2.5 GROUNDWATER TABLE Based on the Log of Test Borings completed for the Fairfax Bridge OC and Oswell Bridge OC, located 0.9 miles and 1.8 miles respectively to the west of site, it’s expected that groundwater would be very deep and would not affect the planned construction activities. Standing Ground Water Surface Level (SGWL) within the project vicinity is estimated to be at least 100 feet. SGWL for wells near the project area range up to 300 feet according to data generated from the Department of Water Resources. The following sources were reviewed to obtain information regarding the depth to groundwater in the vicinity of the site: Water Supply Report: 2001, Kern County Water Agency (KCWA) Depth to Groundwater Map, Spring 2002, prepared by the KCWA State of California Department of Water Resources (DWR) website (http://www.dwr.water.ca.gov) Spring 2000, Lines of Equal Depth to Water in Wells, Unconfined Aquifer, DWR Spring 2006, Lines of Equal Elevation of Water in Wells, Unconfined Aquifer, DWR Borings and preliminary infiltration tests were completed in the vicinity of each of the proposed basin locations (see Figure 3 of District Preliminary Geotechnical Report, dated December 2009). The Preliminary Geotechnical Report prepared for the PA/ED phase of the project indicated that the percolation rate of the soil at the three proposed basin locations generally vary from 0.5 to 5 inches per hour. Borings depths up to 80 ft. did not reveal any groundwater. More recent testing by Earth Mechanics per the report dated August 2, 2012, showed average infiltration rates of 0.20, 0.30 and 0.16 inches per hour for Basins 1, 2 and 3 respectively. This is significantly lower than originally thought, resulting in difficulty attaining ponding depths that drain within the maximum 7 days as required by the City for the 100-year storm event. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 5 2.6 RUNOFF CALCULATIONS As discussed in Section 2.1, the Rational Method was used to determine runoff volumes for the purposes of designing the storm network and examining spread. Watershed areas are shown in Appendix D, Post-development Watershed Map. Runoff calculations for onsite drainage design are included in Appendix H, Runoff Summary NRCS methodology was used to determine total runoff volumes for the pre-development and post development conditions for both the Shalimar and Breckenridge drainage areas. Hydrologic soil groups (HSG) were determined using USDA Soils Maps for the area. Soil data for this project is included in Appendix L, USDA Soils Map. It is understood that Caltrans District 6 Hydraulics, has specific criteria regarding the calculation of runoff for the purposes of sizing retention basins. This criteria requires that retention basins shall retain all on-site runoff for two consecutive 10-year, 24-hour events. The City of Bakersfield guidelines state that retention shall be provided such that there is no net increase in total runoff from the project. Detention/retention ponds shall be sized to store the net increase in runoff volume as a result of the additional impervious area with the proposed project. The design storm event to be used for this is the 100-year, 24-hour event. A letter was written to Sam Wong, Caltrans District 6 Hydraulics from the City of Bakersfield confirming the City’s requirements (see Appendix U). Per the e-mail received from Sam Wong on 2/26/10, Caltrans District 6 Hydraulics has conditionally accepted use of the City’s criteria. In order to ensure no net increase in total runoff from the project, approximately 0.5 acre-feet of runoff should be retained from the Shalimar drainage area and 6.3 acre-feet should be retained from the Breckenridge drainage area. The remaining 2.2 and 36.4 acre-feet of runoff could be released into the Shalimar and Breckenridge City drainage systems respectively (see tables 2-1 thru 2-8). In calculating NRCS runoff volumes, runoff curve numbers were set at 68 for pervious areas. This is consistent with Hydrologic Soil Group B (HSG B) for arid rangelands with cover consisting of desert shrubs. Summaries of watershed areas and runoff volumes for both the pre-development and post- development condition are provided in the following tables. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 6 Pre-Development Table 2-1: Shalimar: Pre-Development Watershed Areas Description Area (SF) Area (AC) HSG Curve Number (CN) Pavement 136038 3.123 N/A 98 Pervious 493535 11.330 B 68 Table 2-2: Shalimar: Pre-Development Total Runoff Volume Calculation P, 100yr-24hr (IN) 2.76 CN 74.5 S 3.4 Ia, (IN) 0.685 Q (IN) 1.080 Area (AC) 14.453 Q (AF) 1.301 Notes: P – accumulated rainfall (potential maximum runoff) (in) Ia - initial abstraction, Ia=0.2*S S – potential maximum retention of rainfall on the watershed at the beginning of the storm (in), S= (1000/CN)-10 Q - volume of accumulated runoff (in), Q= (P-Ia)2/{(P-Ia)+S} Table 2-3: Breckenridge: Pre-Development Watershed Areas Description Area (SF) Area (AC) HSG CN Pavement 739755 16.982 N/A 98 Pervious 34499434 791.998 B 68 Table 2-4: Breckenridge: Pre-Development Total Runoff Volume Calculation P, 100yr-24hr (IN) 2.76 CN 68.6 S 4.6 Ia, (IN) 0.914 Q (IN) 0.540 Area (AC) 808.980 Q (AF) 36.404 Notes: P – accumulated rainfall (potential maximum runoff) (in) Ia - initial abstraction, Ia=0.2*S S – potential maximum retention of rainfall on the watershed at the beginning of the storm (in), S=(1000/CN)-10 Q - volume of accumulated runoff (in), Q=(P-Ia)2/{(P-Ia)+S} Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 7 Post Development Table 2-5: Shalimar: Post-Development Watershed Areas Description Area (SF) Area (AC) HSG CN Onsite-Pavement 342425 7.861 N/A 98 Offsite-Pervious 164003 3.765 B 68 Table 2-6: Shalimar: Post-Development Total Runoff Volume Calculation P, 100yr-24hr (IN) 2.76 CN 88.3 S 1.3 Ia, (IN) 0.265 Q (IN) 1.990 Area (AC) 11.626 Q (AF), Proposed Condition 1.928 Q (AF), Existing Condition 1.301 Minimum Retention Required (AF) 0.627 Notes: P – accumulated rainfall (potential maximum runoff) (in) Ia - initial abstraction, Ia=0.2*S S – potential maximum retention of rainfall on the watershed at the beginning of the storm (in), S=(1000/CN)-10 Q - volume of accumulated runoff (in), Q=(P-Ia)2/{(P-Ia)+S} Table 2-7: Breckenridge: Post-Development Watershed Areas Description Area (SF) Area (AC) HSG CN Onsite-Pavement 2681364 61.556 N/A 98 Offsite-Pervious 31902084 732.371 B 68 Table 2-8: Breckenridge: Post-Development Total Runoff Volume Calculation P, 100yr-24hr (IN) 2.76 CN 70.3 S 4.2 Ia, (IN) 0.844 Q (IN) 0.645 Area (AC) 793.927 Q (AF), Proposed Condition 42.674 Q (AF), Existing Condition 36.404 Retention Required (AF), Volume Based 6.269 Notes: P – accumulated rainfall (potential maximum runoff) (in) Ia - initial abstraction, Ia=0.2*S S – potential maximum retention of rainfall on the watershed at the beginning of the storm (in), S=(1000/CN)-10 Q - volume of accumulated runoff (in), Q=(P-Ia)2/{(P-Ia)+S} Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 8 3. HYDRAULICS 3.1 DESIGN CRITERIA AND METHODOLOGY Runoff from the following storm events were used in the hydraulic analysis: · The 25-year event was used to design the onsite storm water conveyance system. · The 10-year and 100-year events were used to examine cross culvert hydraulics. The proposed design limits spread to the roadway shoulders per HDM guidelines for this type of facility. The storm water conveyance network was designed to maintain existing drainage patterns to the maximum extent possible. Inlet locations were based largely on the geometrics of the proposed roadway and calculated and/or required spread widths. Generally, proposed inlets are positioned at low points, upstream of cross slope reversals in superelevated sections, behind shoulders to drain low areas, and spaced along continuous grades to ensure that the spread criterion is met. Pipe profiles were set to ensure minimum velocities and cover requirements are met. Pipe sizes were established to ensure that the hydraulic grade line (HGL) remains below grate and top elevations for inlets and access holes. HGL calculations are based on the methods described in HEC-22 and include both pipe friction losses and local losses at junctions. Water quality volumes (WQV) were determined as described in the Caltrans Storm Water Quality Handbook - Project Planning and Design Guide (PPDG). Per the PPDG, the CSUS Basin Sizer was used to set the following variables for the WQV calculation: · Unit Basin Storage Volume: 0.33 inches 3.2 ROADWAY PROFILE, LAYOUT AND TYPICAL SECTIONS The proposed project will widen SR-178 to a four-lane freeway from approximately 0.5 mile west of Morning Drive to 1.2 miles east of the existing Morning Drive and then tapering for 0.2 mile to a four-lane conventional highway at the eastern limit of the project near the Canteria Road intersection. The profile of SR-178 will generally follow the existing roadway profile. The crest vertical curve along SR-178 is to be lengthened to meet the sight distance requirements for this facility in the vicinity of the proposed Morning Drive OC. East of Morning Drive the profile is being lowered primarily to reduce the footprint of the project and avoid utility impacts north of SR 178. This profile adjustment also results in reducing the volume of earthwork required and maximizes capacity for drainage conveyance in open ditches within State right of way. The profile grades along SR-178 vary between 0% and 4%. Superelevation rates of 2% are proposed on SR-178 at the eastern end of the project in the vicinity of Canteria Road. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 9 Morning Drive will be realigned and widened to a six-lane roadway from 0.45 miles north to 0.3 miles south of SR-178. Morning Drive would cross over SR-178 with a new overcrossing structure. The profile grades on Morning Drive vary between 0% and 7%. As described in Section 1.1, to accommodate the design year traffic forecasts for the Project the ultimate six-lane facility for State Route 178 would be constructed by 2035 through two future projects. For the purposes of the hydraulic analysis it is assumed that the median is entirely paved to allow for the future widening to 6-lanes and wider shoulders in the median. The proposed layout is provided on the Proposed Geometric Layout exhibit found in Appendix B. 3.3 SPREAD CALCULATIONS Spread calculations were performed in accordance with HEC-22 methodology in order to establish the maximum spacing of inlets along continuous vertical grades. The computer program Storm and Sanitary Sewer Analysis by Autodesk was utilized to model the storm drainage system and calculate the spread. A summary of the spread calculations for each drainage inlet are summarized in the tables provided in Appendix I, Catch Basin Results. The analysis shows that all spreads are less than the shoulder width as required by Table 831.3 of the Caltrans HDM. 3.4 PIPE SIZING CALCULATIONS Pipe sizes were established using HEC-22 methodology. The table provided in Appendix J, Conduit Table, summarizes design parameters for each pipe segment within the storm drain network. HGL calculations include friction losses and local losses at each junction. Losses were modeled by assigning inlet and outlet losses to each pipe segment which ranged from 0.5 to 1.0 based on the junction structure the pipes entered. Appendix K, Pipe Summary provides an output for each pipe segment which includes discharge as well as profiles of various portions of the storm drain system with the hydraulic grade line plotted. The resulting system consists of pipes ranging in size from 18 inches to 36 inches. Riprap aprons, referred to as RSP are provided as outlet protection at each of the outfalls within the storm network and at cross culvert outlets. All pipes longer than 100 feet will have a minimum diameter of 24 inches. All cross culverts are 36 inches to comply with Kit Fox mitigation requirements. 3.5 FLOOD ROUTING (HEC-HMS) U.S. Army Corps of Engineers, HEC-HMS software was used to generate runoff hydrographs for the proposed project. Within the model, the Shalimar and Breckenridge drainage areas were examined as separate basin models. Onsite outfalls and offsite watersheds were input as subbasins within each basin model under existing conditions. Under proposed conditions, individual catch basin watersheds were grouped together to form larger watersheds for use in HEC-RAS. A schematic showing how the watersheds were grouped together is provided in Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 10 Appendix M. NRCS methodology was used to account for infiltration losses within each subbasin. The NRCS unit hydrograph (Type 1 rainfall distribution) was used to model runoff from each sub-basin. Roadside ditches were modeled as reaches using the kinematic routing method. Detention basins were modeled as reservoirs. Additional HEC-HMS Schematic layouts for each basin are also included in Appendix M, System Schematics. HEC-HMS watershed input data is included in Appendix N, Subbasin Input. Detention basins stage storage, stage discharge and the resulting inflow and outflow hydrographs can be found in Appendices O-P. Detention basin inflow and outflow hydrographs were used to ensure that retention requirements for both water quality and the City of Bakersfield storage requirements (per meeting held with City of Bakersfield 7-30-08, see Appendix T) are met. 3.6 RETENTION/DETENTION BASIN DESIGN The locations of the proposed retention and detention basins are shown in Appendix E. Storage volumes were established to meet the greater of the following two conditions: · Per the City of Bakersfield requirements (per meeting held with City of Bakersfield 7-30- 08, see Appendix T), provided storage should retain the net increase in total runoff as a result of the project (Tables 2-6 and 2-8). (In addition please see explanation in Section 2.6 regarding using the City’s design criteria and not District 6 design criteria of retaining all runoff for two consecutive 10-year, 24-hour storms) · Per another meeting with the City of Bakersfield on June 25, 2012, the total 5-year volume shall be retained if there is an increase in total runoff volume downstream of the project. · Per the PPDG, provide storage to detain/retain the water quality volume as described later in Section 5. · The greater of the above required volumes will be met to the extent practicable. Stage-storage relationships were established for each basin. Riser elevations in Detention Basins 1 and 2 were set to reduce the peak discharge to less than existing conditions and reduce the total volume downstream to the extent practicable, which is limited by the City maximum drawdown time in Basin 1. Four inch perforations will be used on the pipe in Basin 1 and set at the elevation which drains within the seven day drawdown time required by the City. Table 3-1 summarizes the required retention based on the City rainfall data for Basin 3. Riser discharge calculations are based on equations for sharp crested weirs and perforation discharge was calculated as orifice flow. Basins 1 and 2, located within Caltrans right-of-way, were additionally designed to meet the maximum drawdown time for the water quality volume (WQV). Caltrans requires the water quality volume to be drained within 96 hours and the City requires the 100- year storm event to drain within 7 days. Table 3-0 summarizes the basins design and constraints. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 11 Table 3-0: Basin Design and Constraints Basin Infiltration Rate (in/hr) 7-Day Drawdown Max Depth (100-yr) (ft) 96-hr Drawdown Max Depth (WQV) (ft) Water Quality Depth / Drawdown Time (ft/days) Depth Below Riser (ft) Depth Below Perforation (ft) 100-yr Drawdown Time at Lowest Outlet Elevation (days) Depth to Retain 5-yr Volume (ft) 1 0.20 2.8 1.6 1.5/3.7 4.6 2.8 7 4.8 2 0.30 4.2 2.4 1.8/3.0 4.2 N/A 7.0 2.7 3 0.16 2.2 1.28 N/A N/A N/A 8.75 1.8 Table 3-1: Outfall OF-6 Runoff, 100-year, 24-hour Event P, 100yr-24hr (IN) 2.43 CN 98.0 S 0.2 Ia, (IN) 0.041 Q (IN) 2.201 Area (AC) 3.638 Q (AF) 0.667 Retention Required (AF) 0.667 The results of the analysis, as summarized in Table 3-0, show that Basin 1 is unable to meet the City maximum drawdown time of 7 days while trying to retain the 5-year storm event volume. The constraint is the result of the depth required to retain the 5-year volume due to the constrained area of the basin. In order to meet the city drawdown time requirement, perforations are provided on the riser pipe at the 2.8 ft maximum depth. With perforations in the riser, there is an increase of 0.2 ac-ft during the 100-year storm event, and no change in runoff volume downstream during the 5-year storm event. There is no increase in peak discharge in either storm event. Basin 1 does, however, meet the Caltrans Water Quality Volume drawdown requirements. Basin 1 is designed to have 2+ feet of freeboard during the 100-year storm event. During storms greater than the 100-year design storm, the riser will serve as the basin outlet. Basin 2 is able to meet all City and Caltrans volume and drawdown requirements. Basin 3, located in the City right-of-way is not subjected to Caltrans requirements. For storm events larger than the 100-year design storm, Basin 2 provides 1+ feet of freeboard in which the riser pipe will serve as a basin outlet. An emergency spillway is also provided which will direct flow to an area inlets and convey flow into the existing 60” stormdrain to the east. The spillway elevation for each basin is shown in Table 3-2. No drainage agreement between Caltrans and the City of Bakersfield is required since this is the historical flow pattern. There is a blue-line shown on the USGS Quadrangle Map, however the City of Bakersfield has replaced the natural creek with a man-made drainage system as defined in their Breckenridge Study Report. The state (Caltrans), as the upstream property owner, has a right to perpetuate the historical flow pattern. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 12 Table 3-2: Basin Spillway Elevation Spillway Elevation (FT) Detention Basin 2 697.00 Basin 3 provides complete retention of the 100-year storm event, though at a depth that will take 8.75 days to drain and require vector control. Basin 3 was designed with 1+ feet of freeboard and flows in excess of the 100-year design storm event will discharge into a future pipe system north along Morning Drive and eastwards along Panorama Drive. Stage-storage input data is included in Appendix O. Stage-discharge input data is included in Appendix P. Inflow/Outflow hydrographs were generated by HEC-HMS for each basin and are included in Appendix Q. The peak inflow and outflow volumes for each basin are shown in Table 3-3 below and were generated using HEC-HMS based on a 100-yr, 24-hour storm event. A comparison of the calculated and required (based on Tables 2-6, 2-8, and 3-1) runoff volume retention is also shown to illustrate the minimum retention requirement for each basin is satisfied. Table 3-3: Basin Summary Detention Basin 1 Detention Basin 2 Retention Basin 3 Total Inflow (AC-FT) 2.1 15.3 0.8 Total Outflow (AC-FT) 1.5 3.7 0.0 Calculated Retention (AC-FT) 0.6 11.6 0.8 Required Retention (AC-FT) 0.6 6.3 0.0 3.7 PEAK OUTFLOW A comparison of existing and proposed peak discharges to the Breckenridge and Shalimar Drainage areas are shown in Table 3-4. The comparison indicates that for all storm events, there will not be a net increase in downstream flow. Table 3-4: Summary of Peak Outflow Shalimar Drainage Area Peak Flow (cfs) Event 2-yr 10-yr 25-yr 50-yr 100-yr Existing 2.7 5.5 8.0 10.0 12.1 Proposed 0.3 0.5 0.9 1.5 2.3 Breckenridge Drainage Area Peak Flow (cfs) Event 2-yr 10-yr 25-yr 50-yr 100-yr Existing 7.1 11.6 21 32.5 46.4 Proposed 0.9 8.2 16.4 25.9 38.0 Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 13 3.8 CROSS CULVERT CALCULATIONS As shown in Appendix E, Proposed Storm Drain System Map, there are two existing cross culverts (XC1 and XC3) which are proposed to be replaced. Culvert XC4 will be replaced with a grate inlet into a 24 inch pipe which discharges into the existing 60” stormdrain system that conveys discharges from the existing detention basin to its north. It has been assumed for this report that the existing system was designed to ultimately convey this runoff. At the time of this report, an existing analysis was not available, and should be further researched to determine if the assumption is true. The two replaced culverts will be replaced with 30” RCP. One additional culvert will be constructed at a new location (PC2) and is also proposed to be a 36” RCP. The 36” minimum height used allows for the Kitt Fox to pass through the culvert while maintaining headwaters within the project right of way. The cross culvert analysis was conducted based on FHWA Hydraulic Design Series Number 5 (HDS-5). Peak flows used in the hydraulic analysis of the culverts were calculated using NRCS methodology by HEC-HMS. Culvert analysis reports are provided in Appendix R. The resulting headwater elevations were examined to ensure 100-year peak flows would not cause flooding problems. Table 3-5 provides a summary of the results. Table 3-5: Cross Culvert Summary-100 year event XC1 PC2 XC3 Existing 1-30 inch CSP DNE 1-60 inch CSP Proposed 1-36 inch RCP 1-36 inch RCP 1-36 inch RCP Construction Replace Existing Replace Existing Replace Existing 100-YR Peak Outflow (CFS) 12.0 12.0 12.5 Computed Headwater Elevation (FT) 800.48 733.45 709.98 Upstream Invert Elevation (FT) 798.61 731.86 708.23 Elevation of Adjacent Road 817.9 735.68 717.29 3.9 DRAINAGE DITCH CALCULATIONS Roadside ditches were configured with triangular cross sections formed between berms and the roadway fill as shown on typical section on the figure in Appendix E, Proposed Storm Drain System Map. Depth and velocity of flow was calculated following the basic principles of open channel flow and Manning’s Equation. Channel geometry was established such that ditches can convey 100 year flows with unlined channels during the 100-year event range from 1.7 to 3.7 feet per second. Table 3-6 summarizes ditch geometry and flow characteristics. Comprehensive calculations are provided in Appendix S, Roadside Ditch/Swale Calculations. Additionally, the northerly offsite ditch was designed to maintain separation between onsite and offsite flows for water quality treatment purposes. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 14 Table 3-6: Ditch Flow Characteristics, 25-year and 100-year event North Channel-100-Year Peak Flows Side Slopes Segment Q100 Slope Velocity Normal Depth Energy Head Freeboard Total Minimum Depth 4:01 45+00 to 30+00 12 2.43 3.13 0.98* 1.13 0.23 1.21 4:01 30+00 to 20+00 12 1.87 2.84 1.03 1.15 0.23 1.26 4:01 20+00 to 18+00 12 1.54 2.64 1.07 1.17 0.23 1.30 South Channel- 100-year Peak Flows Side Slopes Segment Q100 Slope Velocity Normal Depth Energy Head Freeboard Total Minimum Depth 4:01 22+00 to 24+00 5.8 5.81 3.62 0.63 0.84 0.17 0.80 4:01 24+00 to 31+50 5.8 3.37 2.95 0.7 0.84 0.17 0.87 4:01 31+50 to 36+50 5.8 3.15 2.88 0.71 0.84 0.17 0.88 4:01 36+50 to 41+25 5.8 1.99 2.42 0.77 0.86 0.17 0.94 4:01 41+25 to 45+75 12.3 1.53 2.65 1.08 1.19 0.24 1.32 4:01 45+75 to 50+75 12.3 0.74 2.02 1.23* 1.3 0.26 1.49 4:01 50+75 to 58+00 12.3 2.54 3.2 0.98 1.14 0.23 1.21 4:01 58+00 to 62 12.3 0.51 1.76 1.32 1.37 0.27 1.59 *Depth used for culvert tailwater calculation 3.10 DRAINAGE FOR CONSTRUCTION STAGING Interim median inlets will be provided that will convey flow to trunklines along the south side of the road, east of Morning Drive, and to an offset trunkline west of Morning Drive. The placement of the trunklines considered construction of additional lanes in the future. Median drainage may need to include temporary connections to existing systems until the new drainage systems are in place for the westbound portion of the roadway. Existing cross culverts will be replaced or extended to accommodate the widening of SR-178. Construction of the culvert will be phased such that pipe jacking will not be required. Along Morning Drive, north of Auburn Street, the existing drainage system will remain generally the same. New inlets at the intersection of Auburn Street and Morning Drive will be constructed and convey runoff into Basin 3. Impacts during construction should be minor since runoff from the new improvements will be collected into a new drainage system and discharged into a retention basin east of Morning Drive. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 15 3.11 ISSUES OF CONCERN AND MITIGATION An existing stormdrain system was previously constructed with a 60-inch outlet pipe from an existing detention basin to the north, which conveys flow south to a newly constructed trapezoidal earthen channel, known as the Breckenridge Drainage Channel. This system was part of the City in the Hills development located north of SR 178 off of Canteria Drive. The proposed design will collect offsite flow from the area north of SR 178 and convey it to this same 60-inch stormdrain system which has been assumed to have been designed to convey this additional runoff in addition to the detention basin flow. The assumption is based on the Breckenridge Drainage Plan which shows this runoff entering the trapezoidal channel. The infiltration rates of the in-situ material located at the bottom of Basin #1 and #3 are fairly low. As a result of this, Basin 1 is not able to function as an infiltration basin and meet the required City drawdown time and reduction in peak volume. The proposed design included perforations in the riser pipe and will retain only the volume which can be infiltrated in less than 7 days. This results in an increase in 0.2 ac-ft of runoff during the 100-year storm event and reduces the peak discharge. The Caltrans drawdown time for the water quality volume is met. The City stated that if there is to be an increase in volume downstream, that the 5-year volume should be retained. The low infiltration rate also does not allow for this to occur due to limited basin area which results in a depth of ponding greater than the allowable 2.8 ft. The proposed design will provide perforations in the riser pipe to maximize the total volume retained in the basin, however during the 5-year storm event, the same volume of water, 0.6 ac-ft, will be discharged downstream. Other possible mitigation for this would be to over excavate and replace the material soil with a porous material, or use vector control for the 12 days it would take to drain Basin 1 at a depth of 4.8 feet which is required to retain the 5-year storm event. Basin 3 is also unable to infiltrate within the City maximum drawdown time during the 100-year storm event but does during the 5-yeast storm event. Over excavation and vector control are possible solutions for Basin 3 as well. An agreement between Caltrans and the City of Bakersfield is required to apply vector control measures as needed. year Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 16 4. OTHER AGENCIES 4.1 LOCAL AGENCY COORDINATION As discussed earlier, this study and report were completed based on input from the City of Bakersfield (meeting held July 30, 2008), input from Caltrans Hydraulics Staff (meeting held September 2, 2008), and in accordance with the requirements specified in the Highway Design Manual. 4.2 UTILITY COMPANY COORDINATION The location of the retention basin on the west side of the project is in the vicinity of the PG&E transmission towers. The proposed retention basin at this location is configured in such a way that it satisfies PG&E requirements. PG&E has agreed that the basin location does not appear to interfere with their easement rights and have no objections with the proposed location of the basin (see letter in Appendix V). The offsite drainage berm on the east side of the proposed interchange is located in a drainage easement north of the State right-of-way and existing 50 ft. wide utility easement. This berm and offsite ditch will cross the alignment of an existing El Paso/Mojave 30-inch natural gas pipeline. Coordination with PG&E will be continued throughout the design phase to obtain approval. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 17 5. WATER QUALITY 5.1 PERMANENT BEST MANAGEMENT PRACTICES Detention Basins 1 and 2 will serve as permanent treatment BMPs for this project as detention basins. Borings and infiltration tests were completed at each of the proposed basin locations. The Preliminary Geotechnical Report prepared for the PA/ED phase of the project indicated that the percolation rate of the soil at the three proposed basin locations generally vary from 0.5 to 5 inches per hour. Recent percolation tests performed by Earth Mechanics show rates of 0.11-0.36 in/hr. As discussed in Section 3.6, the basins were design such that the water quality volumes will drain within the maximum 96 hours which Caltrans requires. The water quality volume for Basin 1 will drain within 90 hours and Basin 2 will drain within 72 hours. Water quality volumes were determined based on the Caltrans Storm Water Quality Handbook- Project Planning and Design Guide, July 2010 (PPDG). Table 5-1: Shalimar: Water Quality Volume Unit Basin Storage (IN) Volume (CF) Volume (AF) Water Quality Volume 0.33 13927 0.32 Note: Runoff based retention determines detention requirements in the Shalimar Drainage Area Table 5-2: Breckenridge: Water Quality Volume Unit Basin Storage (IN) Volume (CF) Volume (AF) Water Quality Volume 0.33 182362 4.18 Note: WQV determines detention requirements in the Breckenridge Drainage Area. 5.2 TEMPORARY BMPs DURING CONSTRUCTION Selection of appropriate measures to provide temporary erosion/sediment control, and other pollutants are documented in the Storm Water Data Report. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 18 6. OTHER CONSIDERATIONS 6.1 COMPATIBILITY WITH FUTURE PROJECTS Detention Basin 2 was sized to accommodate the runoff volume and water quality requirements associated with the SR-178 Widening Project Phase 1 (EA 06-0F350) which is scheduled to be constructed after the Morning Drive Project. Determination of the runoff from this project was estimated from the Hydrology and Hydraulics Study Report (WRECO January 2012). It is possible that this storage requirement would be reduced if off-site development occurs to the south of SR-178. In the event that the watersheds Offsite-2 and Offsite-3 are developed, the property owner would be required to treat and handle runoff from these watersheds. Morning Drive/SR-178 Interchange Project Drainage Report City of Bakersfield California Department of Transportation January 2013 19 7. REFERENCESS 7.1 LIST OF REFERENCES Meyer Civil Engineering, Inc. 2005. Breckenridge Planned Drainage Area Study, Hydrology Study. March. Bakersfield, CA California Department of Transportation, 2006. Highway Design Manual. Sixth Edition, September, Sacramento, CA. California Department of Transportation, 2007. Storm Water Quality Handbook-Project Planning and Design Guide (PPDG), May, Sacramento, CA. Federal Highway Administration. 2009. Urban Drainage Design Manual, Hydraulic Engineering Circular No. 22 (HEC-22), September, Washington D.C. Geocon Consultants Inc. 2009. District Preliminary Geotechnical Report, Thomas Roads Improvement Program - Morning Drive/SR 178 Interchange Project, December, Sacramento, CA WRECO Hydrology and Hydraulic Study report for SR178 Widening. January 2012. Earth Mechanics. Geotechnical Design Report. August 2012.