final drainage report for morning...

06-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


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


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


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


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.


City of Bakersfield


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.


City of Bakersfield


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.


City of Bakersfield


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.


City of Bakersfield


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.


City of Bakersfield


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}


City of Bakersfield


January 2013

7

Post Development

Table 2-5: Shalimar: Post-Development Watershed Areas


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


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}


City of Bakersfield


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.


City of Bakersfield


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


City of Bakersfield


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.


City of Bakersfield


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.


City of Bakersfield


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


City of Bakersfield


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.


City of Bakersfield


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.


City of Bakersfield


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


City of Bakersfield


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.


City of Bakersfield


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.


City of Bakersfield


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.


City of Bakersfield


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.

final drainage report for morning...

Documents