TECHNICAL MEMORANDUM: SWMM Modeling for Hydromodification ...

TECHNICAL MEMORANDUM:

SWMM Modeling for Hydromodification Compliance of:

Carmax Oceanside

Prepared For:

REC Consultants, Inc.

Prepared by: Luis Parra, PhD, CPSWQ, ToR, D.WRE. R.C.E. 66377

REC Consultants 2442 Second Avenue

San Diego, CA 92101 Telephone: (619) 232-9200

TECHNICAL MEMORANDUM

TO: REC Consultants, Inc.

FROM: Luis Parra, PhD, PE, CPSWQ, ToR, D.WRE, CFM. David Edwards, MS, PE, CFM.

DATE: December 17, 2019 (revised February 26, 2020)

RE: Summary of SWMM Modeling for Hydromodification Compliance for Oceanside Carmax, City of Oceanside, CA.

INTRODUCTION

This memorandum summarizes the approach used to model the proposed commercial site in the City of Oceanside using the Environmental Protection Agency (EPA) Storm Water Management Model 5.0 (SWMM). SWMM models were prepared for the pre and post‐developed conditions at the site in order to determine if the proposed HMP detention facilities have sufficient volume to meet Order R9‐2013‐001 requirements of the California Regional Water Quality Control Board San Diego Region (SDRWQCB), as explained in the Final Hydromodification Management Plan (HMP), dated March 2011, prepared for the County of San Diego by Brown and Caldwell.

SWMM MODEL DEVELOPMENT

The Oceanside Carmax project proposes a commercial auto sales lot on the currently vacant site. Two (2) SWMM models were prepared for this study: the first for the predevelopment and the second for the post‐developed conditions. The project site drains to four (4) Points of Compliance; POC‐1 and POC‐2 are located to the northwest of the site at Plaza Drive, POC‐3 located to the south at Buena Vista Creek and POC‐4 to the east of the site at Thunder Drive. Per Section G1.2 in Appendix G of the 2016 City of Oceanside BMP Design Manual, the EPA SWMM model was used to perform the continuous hydrologic simulation. For both SWMM models, flow duration curves were prepared to determine if the proposed HMP facilities are sufficient to meet the current HMP requirements.

The inputs required to develop SWMM models include rainfall, watershed characteristics, and BMP configurations. The Oceanside Gage from the Project Clean Water website was used for this study since it is the most representative of the project site precipitation due to elevation and proximity to the project site. Per the California Irrigation Management Information System “Reference Evaporation Zones” (CIMIS ETo Zone Map), the project site is located within the Zone 4 Evapotranspiration Area. Thus evapotranspiration vales for the site were modeled using Zone 4 average monthly values from Table G.1‐1 from the 2019 BMP Design Manual. Per the NRCS web soil survey and site specific geotechnical investigation, the project site is situated upon D soils. Soils have been assumed to be compacted in the existing condition to represent the current mass graded condition of the site, while fully compacted in

Oceanside Carmax HMP Memo December 17, 2019 (revised February 26, 2020)

2 W.O.7036‐32

the post developed conditions. Other SWMM inputs for the subareas are discussed in the appendices to this document, where the selection of parameters is explained in detail.

HMP MODELING It should be noted that for POC‐1 the pre‐developed and post‐developed areas tributary to the POC will be equal as there is no diversion of flow in the post developed condition, in addition, the pervious percentage (i.e. 0% impervious due to the pervious surfaces proposed within DMA‐1) assures that there will no change in the FDC at POC‐1. Additionally, areas tributary to POC‐2 (DMA‐2) are part of the green street improvements proposed to Plaza Drive. As such, no HMP analysis is proposed for POC’s 1 and 2.

PRE DEVELOPED CONDITIONS The current site is a single developed lot that is bifurcated by Plaza Drive to the north‐west of the project site. Runoff drains via overland flow to the west of the project site to the existing Plaza Drive, to the south to the adjacent Buena Vista Creek and to the Thunder Drive to the east of the project site. Table 1 below illustrates the pre‐developed areas and impervious percentage accordingly. It should be noted that POC’s 1 and 2 includes the portion of the existing Plaza Drive that is to be improved as part of this project site.

TABLE 1 – SUMMARY OF PRE‐DEVELOPED CONDITIONS

POC DMA Tributary Area, A

(Ac) Impervious

Percentage, Ip(1)

POC‐1 DMA‐1 1.433 0%

POC‐2 DMA‐2 0.216 0%

POC‐3

DMA‐3A 2.085 0%

DMA‐3B 3.520 0%

DMA‐3C 1.279 0%

POC‐4 DMA‐4 0.278 0%

TOTAL ‐‐ 8.812 0% Notes: (1) – Per the 2013 RWQCB permit, existing condition impervious surfaces are not to be accounted for in existing conditions analysis.

DEVELOPED CONDITIONS In developed conditions, runoff from the central project site is drained to one (1) onsite receiving HMP underground detention facility. Once flows are routed via the proposed detention basin, onsite flows are then discharged to the adjacent Buena Vista Creek at POC‐3. A small portion of the project site drains to the receiving curb and gutter within the adjacent Thunder Drive to the east of the project site at POC‐4. Runoff tributary to POC’s 1 and 2 are not analyzed for HMP compliance given that areas and the imperviousness remains constant in both pre and post developed conditions. Plaza Drive will incorporate green street LID principles that will address water quality and HMP requirements accordingly. Table 2 summarizes the post‐developed area and impervious percentage accordingly.


3 W.O.7036‐32

TABLE 2 – SUMMARY OF POST‐DEVELOPED CONDITIONS

POC DMA STRUCTURAL BMP Tributary Area, A

(Ac) Impervious

Percentage, Ip

POC‐1

DMA‐1A SELF‐TREATING 1.082 0.0%

DMA‐1B GREEN STREET

0.129 100%

DMA‐1C 0.229 100%

POC‐2 DMA‐2A

GREEN STREET 0.135 100%

DMA‐2B 0.216 100%

POC‐3 DMA‐3A DETENTION 5.893 85.28%

DMA‐3B SELF‐TREATING 0.993 0.00%

POC‐4 DMA‐4 SELF‐TREATING 0.146 50.4%

TOTAL ‐‐ ‐‐ 8.823 ‐‐ Notes: (1) – The DMA includes Drainage Area D as flows mix and discharge directly at the BMP.

One underground detention system is located within the project site and is responsible for handling hydromodification requirements for the project. In developed conditions, the underground detention basin will comprise of footprint of 6,090 square feet and a depth of 4 feet. The vault will feature an open bottom and an underlying 6‐inch layer of gravel to provide additional storage for retention volume. A riser spillway structure with an outlet slot (see dimensions in Table 4) will be located at the downstream end of the system to control the flows. Flows will discharge from the underground basin via a riser outlet structure within the detention system and then discharge directly to the adjacent Buena Vista Creek. A small self‐treating area (DMA‐3B) confluences directly at this point with the detained flows at POC‐3. The riser structure will act as a spillway such that peak flows can be safely discharged to the receiving POC. Water Quality BMP Sizing

It is assumed all storm water quality requirements for the project will be met by the BMPs detailed in the SWQMP and other BMPs included within the site design. However, detailed water quality requirements are not discussed within this technical memo. For further information in regards to storm water quality requirements for the project (including sizing and drawdown) please refer to the site specific Storm Water Quality Management Plan (SWQMP).

BMP MODELING FOR HMP PURPOSES

Modeling of dual purpose Water Quality/HMP BMPs

One underground detention system will be used for hydromodification conformance for the project site. Tables 3 & 4 illustrate the dimensions required for HMP compliance according to the SWMM model that was undertaken for the project.


4 W.O.7036‐32

TABLE 4 – SUMMARY OF DEVELOPED DUAL PURPOSE BMPs

BMP Tributary Area (Ac)

DIMENSIONS

BMP Area (ft2)

Basin Depth (ft)(1)

Total Volume. (ft3)

Basin 1 5.893 6090 4.2 24,360 Notes:

(1) The depth includes the 6‐inches (0.5’) of gravel beneath the vault surface which has

been reduced to represent the volume of voids available (0.4 X 0.5’ = 0.2’)

TABLE 5 – SUMMARY OF RISER DETAILS:

BASIN Lower Orifice Lower Slot Middle Slot Upper Weir

Diam. (in) Elev.

(ft) B x h (in)

Elev.(1) (ft)

B x h (in)

Elev.(1) (ft)

Length(2) (ft) Elev.(1) (ft)

Basin 1

2 x 2.3125 0.0 36 x 2.5 1.25 45 x 8 2.25 12.0 3.75

Notes:

(2) Invert of the underground system elevation assumed to be 0.00 ft elevation. (3) Overflow length.

FLOW DURATION CURVE COMPARISON

The Flow Duration Curve (FDC) for the site was compared at the POCs by exporting the hourly runoff time series results from SWMM to a spreadsheet.

Q2 and Q10 were determined with a partial duration statistical analysis of the runoff time series in an Excel spreadsheet using the Cunnane plotting position method (which is the preferred plotting methodology in the HMP Permit). As the SWMM Model includes a statistical analysis based on the Weibull Plotting Position Method, the Weibull Method was also used within the spreadsheet to ensure that the results were similar to those obtained by the SWMM Model.

The range between 10% of Q2 and Q10 was divided into 100 equal time intervals; the number of hours that each flow rate was exceeded was counted from the hourly series. Additionally, the intermediate peaks with a return period “i” were obtained (Qi with i=3 to 9). For the purpose of the plot, the values were presented as percentage of time exceeded for each flow rate. FDC comparison at each POC is illustrated in Figures 1 and 2 in both normal and logarithmic scale. Attachment 5 provides a detailed drainage exhibit for the post‐developed condition.

As can be seen in Figure 1, the FDC for the proposed condition with the HMP BMPs is within 110% of the curve for the existing condition in both peak flows and durations. The additional runoff volume generated from developing the site will be released to the existing point of discharge at a flow rate below the 10% Q2 lower threshold for the POC’s. Additionally, the project will also not increase peak flow rates between the Q2 and the Q10, as shown in the peak flow tables in Attachment 1. Discussion of the Manning’s coefficient (Pervious Areas) for Pre and Post‐Development Conditions Typically the Manning’s coefficient is selected as n = 0.10 for pervious areas and n = 0.012 for impervious areas. Due to the complexity of the model carried out in pre and post‐development


5 W.O.7036‐32

conditions, a more accurate value of the Manning’s coefficient for pervious areas has been chosen. Taken into consideration the “Handouts on Supplemental Guidance – Handout #2: Manning’s “n” Values for Overland Flow Using EPA SWMM V.5” by the County of San Diego (Reference [6]) a more accurate value of n = 0.05 has been selected (see Table 1 of Reference [6] included in Attachment 7). An average n value between pasture and shrubs and bushes (which is also the value of dense grass) has been selected per the reference cited, for light rain (<0.8 in/hr) as more than 99% of the rainfall has been measured with this intensity.

DRAWDOWN TIME

To ensure compliance with the 96 hour drawdown requirements per Section 6.4.6 of the Final HMP dated March 2011, drawdown calculations are provided in Attachment 4 of this report. Per the drawdown calculations, the drying time of BMP‐A is approximately 24 hours, satisfying drawdown time requirements.

SUMMARY

This study has demonstrated that the proposed HMP BMPs provided for Oceanside Carmax project site is sufficient to meet the current HMP criteria if the cross‐section areas and volumes recommended within this technical memorandum, and the respective orifice and outlet structure are incorporated as specified within the proposed project site.

KEY ASSUMPTIONS

1. Type D Soils is representative of the existing condition site.

ATTACHMENTS

1. Q2 to Q10 Comparison Tables

2. FDC Plots (log and natural “x” scale) and Flow Duration Table.

3. List of the “n” largest Peaks: Pre‐Development and Post‐Development Conditions

4. Elevations vs. Discharge Curves to be used in SWMM

5. Pre & Post Development Maps, Project plan and section sketches

6. SWMM Input Data in Input Format (Existing and Proposed Models)

7. SWMM Screens and Explanation of Significant Variables

8. Geotechnical Documentation

9. Summary files from the SWMM Model


6 W.O.7036‐32

REFERENCES

[1] – “Review and Analysis of San Diego County Hydromodification Management Plan (HMP): Assumptions, Criteria, Methods, & Modeling Tools – Prepared for the Cities of San Marcos, Oceanside & Vista”, May 2012, TRW Engineering.

[2] – “Final Hydromodification Management Plan (HMP) prepared for the County of San Diego”, March 2011, Brown and Caldwell.

[3] ‐ Order R9‐20013‐001, California Regional Water Quality Control Board San Diego Region (SDRWQCB).

[4] – “Handbook of Hydrology”, David R. Maidment, Editor in Chief. 1992, McGraw Hill. [5] – “City of Oceanside BMP Design Manual”, 2016.

[6] – “Improving Accuracy in Continuous Hydrologic Modeling: Guidance for Selecting Pervious Overland Flow Manning’s n Values in the San Diego Region”, 2016, TRW Engineering.


7 W.O.7036‐32

Figure 1a and 1b. Flow Duration Curve Comparison (logarithmic and normal “x” scale)


8 W.O.7036‐32

Figure 2a and 2b. Flow Duration Curve Comparison (logarithmic and normal “x” scale)


9 W.O.7036‐32

ATTACHMENT 1.

Q2 to Q10 Comparison Table – POC 3

Return Period Existing Condition (cfs) Mitigated Condition (cfs) Reduction, Exist ‐ Mitigated (cfs)

2‐year 3.620 2.935 0.685

3‐year 4.009 3.339 0.670

4‐year 4.543 3.437 1.106

5‐year 4.665 3.826 0.839

6‐year 4.767 4.059 0.708

7‐year 5.038 4.125 0.914

8‐year 5.177 4.264 0.913

9‐year 5.431 4.454 0.977

10‐year 5.813 4.825 0.989

Q2 to Q10 Comparison Table – POC 4

Return Period Existing Condition (cfs) Mitigated Condition (cfs) Reduction, Exist ‐ Mitigated (cfs)

2‐year 0.146 0.086 0.060

3‐year 0.162 0.094 0.069

4‐year 0.183 0.100 0.083

5‐year 0.188 0.104 0.084

6‐year 0.193 0.107 0.086

7‐year 0.203 0.109 0.094

8‐year 0.209 0.113 0.095

9‐year 0.219 0.122 0.098

10‐year 0.235 0.135 0.100

ATTACHMENT 2

FLOW DURATION CURVE ANALYSIS

1) Flow duration curve shall not exceed the existing conditions by more than 10%, neither in

peak flow nor duration.

The figures on the following pages illustrate that the flow duration curve in post‐development

conditions after the proposed BMP is below the existing flow duration curve. The flow duration

curve table following the curve shows that if the interval 0.10Q2 – Q10 is divided in 100 sub‐

intervals, then a) the post development divided by pre‐development durations are never larger

than 110% (the permit allows up to 110%); and b) there are no more than 10 intervals in the

range 101%‐110% which would imply an excess over 10% of the length of the curve (the permit

allows less than 10% of excesses measured as 101‐110%).

Consequently, the design passes the hydromodification test.

It is important to note that the flow duration curve can be expressed in the “x” axis as

percentage of time, hours per year, total number of hours, or any other similar time variable. As

those variables only differ by a multiplying constant, their plot in logarithmic scale is going to

look exactly the same, and compliance can be observed regardless of the variable selected.

However, in order to satisfy the City of Oceanside HMP example, % of time exceeded is the

variable of choice in the flow duration curve. The selection of a logarithmic scale in lieu of the

normal scale is preferred, as differences between the pre‐development and post‐development

curves can be seen more clearly in the entire range of analysis. Both graphics are presented just

to prove the difference.

In terms of the “y” axis, the peak flow value is the variable of choice. As an additional analysis

performed by REC, not only the range of analysis is clearly depicted (10% of Q2 to Q10) but also

all intermediate flows are shown (Q2, Q3, Q4, Q5, Q6, Q7, Q8 and Q9) in order to demonstrate

compliance at any range Qx – Qx+1. It must be pointed out that one of the limitations of both the

SWMM and SDHM models is that the intermediate analysis is not performed (to obtain Qi from

i = 2 to 10). REC performed the analysis using the Cunnane Plotting position Method (the

preferred method in the HMP permit) from the “n” largest independent peak flows obtained

from the continuous time series.

The largest “n” peak flows are attached in this appendix, as well as the values of Qi with a

return period “i”, from i=2 to 10. The Qi values are also added into the flow‐duration plot.

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

2.75

3.00

3.25

3.50

3.75

4.00

4.25

4.50

4.75

5.00

5.25

5.50

5.75

6.00

0.0003 0.003 0.03 0.3

Q (cfs)

Percentage of time exceeded (%)

Oceanside Carmax POC‐3 ‐ Flow Duration Curve

Existing

Proposed

Qx

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

2.75

3.00

3.25

3.50

3.75

4.00

4.25

4.50

4.75

5.00

5.25

5.50

5.75

6.00

‐0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15 0.16

Q (cfs)



Existing

Proposed

Qx

Flow Duration Curve Data for Oceanside Carmax, POC‐3, Oceanside

Q2 = 3.62 cfs Fraction 10 %

Q10 = 5.81 cfs

Step = 0.0551 cfs

Count = 499679 hours

57.00 years

Pass or

Q (cfs) Hours > Q % time Hours>Q % time Post/Pre Fail?

1 0.362 1032 2.07E‐01 942 1.89E‐01 91% Pass

2 0.417 945 1.89E‐01 775 1.55E‐01 82% Pass

3 0.472 855 1.71E‐01 656 1.31E‐01 77% Pass

4 0.527 756 1.51E‐01 573 1.15E‐01 76% Pass

5 0.582 702 1.40E‐01 499 9.99E‐02 71% Pass

6 0.637 658 1.32E‐01 439 8.79E‐02 67% Pass

7 0.692 617 1.23E‐01 405 8.11E‐02 66% Pass

8 0.747 570 1.14E‐01 381 7.62E‐02 67% Pass

9 0.802 530 1.06E‐01 353 7.06E‐02 67% Pass

10 0.858 495 9.91E‐02 339 6.78E‐02 68% Pass

11 0.913 458 9.17E‐02 318 6.36E‐02 69% Pass

12 0.968 432 8.65E‐02 307 6.14E‐02 71% Pass

13 1.023 405 8.11E‐02 291 5.82E‐02 72% Pass

14 1.078 381 7.62E‐02 282 5.64E‐02 74% Pass

15 1.133 351 7.02E‐02 271 5.42E‐02 77% Pass

16 1.188 321 6.42E‐02 257 5.14E‐02 80% Pass

17 1.243 299 5.98E‐02 229 4.58E‐02 77% Pass

18 1.298 281 5.62E‐02 212 4.24E‐02 75% Pass

19 1.353 268 5.36E‐02 199 3.98E‐02 74% Pass

20 1.408 247 4.94E‐02 189 3.78E‐02 77% Pass

21 1.463 235 4.70E‐02 184 3.68E‐02 78% Pass

22 1.518 220 4.40E‐02 177 3.54E‐02 80% Pass

23 1.573 209 4.18E‐02 172 3.44E‐02 82% Pass

24 1.628 202 4.04E‐02 157 3.14E‐02 78% Pass

25 1.683 190 3.80E‐02 152 3.04E‐02 80% Pass

26 1.739 174 3.48E‐02 149 2.98E‐02 86% Pass

27 1.794 155 3.10E‐02 139 2.78E‐02 90% Pass

28 1.849 143 2.86E‐02 126 2.52E‐02 88% Pass

29 1.904 136 2.72E‐02 110 2.20E‐02 81% Pass

30 1.959 125 2.50E‐02 102 2.04E‐02 82% Pass

31 2.014 120 2.40E‐02 93 1.86E‐02 78% Pass

32 2.069 116 2.32E‐02 89 1.78E‐02 77% Pass

33 2.124 113 2.26E‐02 86 1.72E‐02 76% Pass

34 2.179 110 2.20E‐02 79 1.58E‐02 72% Pass

35 2.234 107 2.14E‐02 73 1.46E‐02 68% Pass

36 2.289 100 2.00E‐02 69 1.38E‐02 69% Pass

Detention Optimized

Interval

Existing Condition

Pass or


Detention Optimized

Interval

Existing Condition

37 2.344 94 1.88E‐02 63 1.26E‐02 67% Pass

38 2.399 90 1.80E‐02 55 1.10E‐02 61% Pass

39 2.454 80 1.60E‐02 48 9.61E‐03 60% Pass

40 2.509 73 1.46E‐02 46 9.21E‐03 63% Pass

41 2.564 67 1.34E‐02 43 8.61E‐03 64% Pass

42 2.620 65 1.30E‐02 40 8.01E‐03 62% Pass

43 2.675 63 1.26E‐02 40 8.01E‐03 63% Pass

44 2.730 60 1.20E‐02 40 8.01E‐03 67% Pass

45 2.785 59 1.18E‐02 39 7.81E‐03 66% Pass

46 2.840 57 1.14E‐02 39 7.81E‐03 68% Pass

47 2.895 54 1.08E‐02 35 7.00E‐03 65% Pass

48 2.950 51 1.02E‐02 34 6.80E‐03 67% Pass

49 3.005 47 9.41E‐03 32 6.40E‐03 68% Pass

50 3.060 47 9.41E‐03 31 6.20E‐03 66% Pass

51 3.115 44 8.81E‐03 29 5.80E‐03 66% Pass

52 3.170 42 8.41E‐03 27 5.40E‐03 64% Pass

53 3.225 40 8.01E‐03 24 4.80E‐03 60% Pass

54 3.280 39 7.81E‐03 24 4.80E‐03 62% Pass

55 3.335 38 7.60E‐03 21 4.20E‐03 55% Pass

56 3.390 38 7.60E‐03 17 3.40E‐03 45% Pass

57 3.445 37 7.40E‐03 16 3.20E‐03 43% Pass

58 3.501 37 7.40E‐03 16 3.20E‐03 43% Pass

59 3.556 35 7.00E‐03 15 3.00E‐03 43% Pass

60 3.611 33 6.60E‐03 15 3.00E‐03 45% Pass

61 3.666 30 6.00E‐03 15 3.00E‐03 50% Pass

62 3.721 29 5.80E‐03 15 3.00E‐03 52% Pass

63 3.776 28 5.60E‐03 15 3.00E‐03 54% Pass

64 3.831 28 5.60E‐03 12 2.40E‐03 43% Pass

65 3.886 25 5.00E‐03 12 2.40E‐03 48% Pass

66 3.941 22 4.40E‐03 12 2.40E‐03 55% Pass

67 3.996 22 4.40E‐03 12 2.40E‐03 55% Pass

68 4.051 22 4.40E‐03 12 2.40E‐03 55% Pass

69 4.106 21 4.20E‐03 10 2.00E‐03 48% Pass

70 4.161 21 4.20E‐03 10 2.00E‐03 48% Pass

71 4.216 21 4.20E‐03 9 1.80E‐03 43% Pass

72 4.271 21 4.20E‐03 9 1.80E‐03 43% Pass

73 4.326 20 4.00E‐03 9 1.80E‐03 45% Pass

74 4.382 19 3.80E‐03 8 1.60E‐03 42% Pass

75 4.437 19 3.80E‐03 8 1.60E‐03 42% Pass

76 4.492 19 3.80E‐03 8 1.60E‐03 42% Pass

77 4.547 16 3.20E‐03 8 1.60E‐03 50% Pass

78 4.602 14 2.80E‐03 8 1.60E‐03 57% Pass

79 4.657 13 2.60E‐03 7 1.40E‐03 54% Pass

80 4.712 10 2.00E‐03 7 1.40E‐03 70% Pass

81 4.767 9 1.80E‐03 6 1.20E‐03 67% Pass

Pass or


Detention Optimized

Interval

Existing Condition

82 4.822 9 1.80E‐03 6 1.20E‐03 67% Pass

83 4.877 9 1.80E‐03 6 1.20E‐03 67% Pass

84 4.932 9 1.80E‐03 5 1.00E‐03 56% Pass

85 4.987 9 1.80E‐03 5 1.00E‐03 56% Pass

86 5.042 8 1.60E‐03 5 1.00E‐03 63% Pass

87 5.097 7 1.40E‐03 5 1.00E‐03 71% Pass

88 5.152 7 1.40E‐03 5 1.00E‐03 71% Pass

89 5.207 7 1.40E‐03 5 1.00E‐03 71% Pass

90 5.263 7 1.40E‐03 5 1.00E‐03 71% Pass

91 5.318 6 1.20E‐03 5 1.00E‐03 83% Pass

92 5.373 6 1.20E‐03 5 1.00E‐03 83% Pass

93 5.428 6 1.20E‐03 5 1.00E‐03 83% Pass

94 5.483 6 1.20E‐03 5 1.00E‐03 83% Pass

95 5.538 6 1.20E‐03 5 1.00E‐03 83% Pass

96 5.593 6 1.20E‐03 4 8.01E‐04 67% Pass

97 5.648 6 1.20E‐03 4 8.01E‐04 67% Pass

98 5.703 6 1.20E‐03 4 8.01E‐04 67% Pass

99 5.758 6 1.20E‐03 4 8.01E‐04 67% Pass

100 5.813 6 1.20E‐03 4 8.01E‐04 67% Pass

Peak Flows calculated with Cunnane Plotting Position

Return Period

(years)Pre‐dev. Q (cfs)

Post‐Dev. Q

(cfs)

Reduction

(cfs)

10 5.813 4.825 0.989

9 5.431 4.454 0.977

8 5.177 4.264 0.913

7 5.038 4.125 0.914

6 4.767 4.059 0.708

5 4.665 3.826 0.839

4 4.543 3.437 1.106

3 4.009 3.339 0.670

2 3.620 2.935 0.685

0.00

0.05

0.10

0.15

0.20

0.25

0.0003 0.003 0.03 0.3

Q (cfs)



Existing

Proposed

Qx

0.00

0.05

0.10

0.15

0.20

0.25

‐0.01 0.01 0.03 0.05 0.07 0.09 0.11 0.13 0.15 0.17 0.19 0.21 0.23

Q (cfs)



Existing

Proposed

Qx

Flow Duration Curve Data for Oceanside Carmax, POC‐4, Oceanside

Q2 = 0.15 cfs Fraction 10 %

Q10 = 0.23 cfs

Step = 0.0022 cfs

Count = 499679 hours

57.00 years

Pass or


1 0.015 1037 2.08E‐01 1023 2.05E‐01 99% Pass

2 0.017 968 1.94E‐01 881 1.76E‐01 91% Pass

3 0.019 833 1.67E‐01 776 1.55E‐01 93% Pass

4 0.021 754 1.51E‐01 699 1.40E‐01 93% Pass

5 0.023 703 1.41E‐01 621 1.24E‐01 88% Pass

6 0.026 662 1.32E‐01 542 1.08E‐01 82% Pass

7 0.028 622 1.24E‐01 409 8.19E‐02 66% Pass

8 0.030 564 1.13E‐01 363 7.26E‐02 64% Pass

9 0.032 528 1.06E‐01 340 6.80E‐02 64% Pass

10 0.035 497 9.95E‐02 310 6.20E‐02 62% Pass

11 0.037 462 9.25E‐02 289 5.78E‐02 63% Pass

12 0.039 426 8.53E‐02 239 4.78E‐02 56% Pass

13 0.041 403 8.07E‐02 198 3.96E‐02 49% Pass

14 0.043 380 7.60E‐02 174 3.48E‐02 46% Pass

15 0.046 354 7.08E‐02 158 3.16E‐02 45% Pass

16 0.048 328 6.56E‐02 149 2.98E‐02 45% Pass

17 0.050 298 5.96E‐02 137 2.74E‐02 46% Pass

18 0.052 281 5.62E‐02 119 2.38E‐02 42% Pass

19 0.055 268 5.36E‐02 107 2.14E‐02 40% Pass

20 0.057 247 4.94E‐02 83 1.66E‐02 34% Pass

21 0.059 232 4.64E‐02 76 1.52E‐02 33% Pass

22 0.061 217 4.34E‐02 72 1.44E‐02 33% Pass

23 0.064 209 4.18E‐02 70 1.40E‐02 33% Pass

24 0.066 202 4.04E‐02 64 1.28E‐02 32% Pass

25 0.068 190 3.80E‐02 57 1.14E‐02 30% Pass

26 0.070 169 3.38E‐02 49 9.81E‐03 29% Pass

27 0.072 154 3.08E‐02 48 9.61E‐03 31% Pass

28 0.075 143 2.86E‐02 45 9.01E‐03 31% Pass

29 0.077 137 2.74E‐02 41 8.21E‐03 30% Pass

30 0.079 122 2.44E‐02 39 7.81E‐03 32% Pass

31 0.081 120 2.40E‐02 37 7.40E‐03 31% Pass

32 0.084 116 2.32E‐02 36 7.20E‐03 31% Pass

33 0.086 113 2.26E‐02 33 6.60E‐03 29% Pass

34 0.088 111 2.22E‐02 27 5.40E‐03 24% Pass

35 0.090 106 2.12E‐02 24 4.80E‐03 23% Pass

36 0.092 100 2.00E‐02 22 4.40E‐03 22% Pass

Detention Optimized

Interval

Existing Condition

Pass or


Detention Optimized

Interval

Existing Condition

37 0.095 94 1.88E‐02 22 4.40E‐03 23% Pass

38 0.097 93 1.86E‐02 21 4.20E‐03 23% Pass

39 0.099 80 1.60E‐02 17 3.40E‐03 21% Pass

40 0.101 72 1.44E‐02 14 2.80E‐03 19% Pass

41 0.104 67 1.34E‐02 12 2.40E‐03 18% Pass

42 0.106 65 1.30E‐02 11 2.20E‐03 17% Pass

43 0.108 63 1.26E‐02 9 1.80E‐03 14% Pass

44 0.110 59 1.18E‐02 8 1.60E‐03 14% Pass

45 0.112 59 1.18E‐02 7 1.40E‐03 12% Pass

46 0.115 57 1.14E‐02 7 1.40E‐03 12% Pass

47 0.117 54 1.08E‐02 7 1.40E‐03 13% Pass

48 0.119 51 1.02E‐02 6 1.20E‐03 12% Pass

49 0.121 47 9.41E‐03 6 1.20E‐03 13% Pass

50 0.124 47 9.41E‐03 6 1.20E‐03 13% Pass

51 0.126 44 8.81E‐03 6 1.20E‐03 14% Pass

52 0.128 43 8.61E‐03 6 1.20E‐03 14% Pass

53 0.130 40 8.01E‐03 6 1.20E‐03 15% Pass

54 0.132 39 7.81E‐03 6 1.20E‐03 15% Pass

55 0.135 38 7.60E‐03 6 1.20E‐03 16% Pass

56 0.137 38 7.60E‐03 6 1.20E‐03 16% Pass

57 0.139 37 7.40E‐03 5 1.00E‐03 14% Pass

58 0.141 36 7.20E‐03 5 1.00E‐03 14% Pass

59 0.144 34 6.80E‐03 4 8.01E‐04 12% Pass

60 0.146 33 6.60E‐03 4 8.01E‐04 12% Pass

61 0.148 31 6.20E‐03 3 6.00E‐04 10% Pass

62 0.150 29 5.80E‐03 3 6.00E‐04 10% Pass

63 0.152 28 5.60E‐03 3 6.00E‐04 11% Pass

64 0.155 28 5.60E‐03 3 6.00E‐04 11% Pass

65 0.157 26 5.20E‐03 2 4.00E‐04 8% Pass

66 0.159 22 4.40E‐03 1 2.00E‐04 5% Pass

67 0.161 22 4.40E‐03 1 2.00E‐04 5% Pass

68 0.164 22 4.40E‐03 1 2.00E‐04 5% Pass

69 0.166 21 4.20E‐03 1 2.00E‐04 5% Pass

70 0.168 21 4.20E‐03 1 2.00E‐04 5% Pass

71 0.170 21 4.20E‐03 1 2.00E‐04 5% Pass

72 0.172 21 4.20E‐03 0 0.00E+00 0% Pass

73 0.175 20 4.00E‐03 0 0.00E+00 0% Pass

74 0.177 19 3.80E‐03 0 0.00E+00 0% Pass

75 0.179 19 3.80E‐03 0 0.00E+00 0% Pass

76 0.181 19 3.80E‐03 0 0.00E+00 0% Pass

77 0.184 16 3.20E‐03 0 0.00E+00 0% Pass

78 0.186 15 3.00E‐03 0 0.00E+00 0% Pass

79 0.188 14 2.80E‐03 0 0.00E+00 0% Pass

80 0.190 10 2.00E‐03 0 0.00E+00 0% Pass

81 0.192 9 1.80E‐03 0 0.00E+00 0% Pass

Pass or


Detention Optimized

Interval

Existing Condition

82 0.195 9 1.80E‐03 0 0.00E+00 0% Pass

83 0.197 9 1.80E‐03 0 0.00E+00 0% Pass

84 0.199 9 1.80E‐03 0 0.00E+00 0% Pass

85 0.201 9 1.80E‐03 0 0.00E+00 0% Pass

86 0.204 8 1.60E‐03 0 0.00E+00 0% Pass

87 0.206 7 1.40E‐03 0 0.00E+00 0% Pass

88 0.208 7 1.40E‐03 0 0.00E+00 0% Pass

89 0.210 7 1.40E‐03 0 0.00E+00 0% Pass

90 0.212 7 1.40E‐03 0 0.00E+00 0% Pass

91 0.215 6 1.20E‐03 0 0.00E+00 0% Pass

92 0.217 6 1.20E‐03 0 0.00E+00 0% Pass

93 0.219 6 1.20E‐03 0 0.00E+00 0% Pass

94 0.221 6 1.20E‐03 0 0.00E+00 0% Pass

95 0.224 6 1.20E‐03 0 0.00E+00 0% Pass

96 0.226 6 1.20E‐03 0 0.00E+00 0% Pass

97 0.228 6 1.20E‐03 0 0.00E+00 0% Pass

98 0.230 6 1.20E‐03 0 0.00E+00 0% Pass

99 0.232 6 1.20E‐03 0 0.00E+00 0% Pass

100 0.235 6 1.20E‐03 0 0.00E+00 0% Pass

Peak Flows calculated with Cunnane Plotting Position

Return Period

(years)Pre‐dev. Q (cfs)

Post‐Dev. Q

(cfs)

Reduction

(cfs)

10 0.235 0.135 0.100

9 0.219 0.122 0.098

8 0.209 0.113 0.095

7 0.203 0.109 0.094

6 0.193 0.107 0.086

5 0.188 0.104 0.084

4 0.183 0.100 0.083

3 0.162 0.094 0.069

2 0.146 0.086 0.060

ATTACHMENT 3

List of the “n” Largest Peaks: Pre & Post‐Developed Conditions

Basic Probabilistic Equation:

R = 1/P R: Return period (years).

P: Probability of a flow to be equaled or exceeded any given year (dimensionless).

Cunnane Equation: Weibull Equation:

P.

. P

i: Position of the peak whose probability is desired (sorted from large to small)

n: number of years analyzed.

Explanation of Variables for the Tables in this Attachment

Peak: Refers to the peak flow at the date given, taken from the continuous simulation hourly

results of the n year analyzed.

Posit: If all peaks are sorted from large to small, the position of the peak in a sorting analysis is

included under the variable Posit.

Date: Date of the occurrence of the peak at the outlet from the continuous simulation

Note: all peaks are not annual maxima; instead they are defined as event maxima, with a

threshold to separate peaks of at least 12 hours. In other words, any peak P in a time series is

defined as a value where dP/dt = 0, and the peak is the largest value in 25 hours (12 hours

before, the hour of occurrence and 12 hours after the occurrence, so it is in essence a daily

peak).

List of Peak events and Determination of Q2 and Q10 (Pre‐Development)Oceanside Carmax, POC‐3

T

(Year)

Cunnane

(cfs)

Weibull

(cfs)

10 5.81 5.97 Date Posit Weibull Cunnane

9 5.43 5.61 2.628 2/27/1991 57 1.02 1.01

8 5.18 5.24 2.66 4/28/2005 56 1.04 1.03

7 5.04 5.06 2.71 2/22/1998 55 1.05 1.05

6 4.77 4.83 2.733 8/17/1977 54 1.07 1.07

5 4.67 4.67 2.805 3/1/1991 53 1.09 1.09

4 4.54 4.56 2.824 2/8/1993 52 1.12 1.11

3 4.01 4.03 2.855 4/27/1960 51 1.14 1.13

2 3.62 3.62 2.881 3/19/1981 50 1.16 1.15

2.884 2/14/1998 49 1.18 1.18

2.93 2/12/1992 48 1.21 1.20

Note: 2.931 12/22/1982 47 1.23 1.23

Cunnane is the preferred 2.937 2/22/2008 46 1.26 1.25

method by the HMP permit. 2.98 1/16/1972 45 1.29 1.28

2.984 3/15/1986 44 1.32 1.31

3.072 2/15/1986 43 1.35 1.34

3.079 3/11/1995 42 1.38 1.38

3.098 3/17/1963 41 1.41 1.41

3.144 1/29/1980 40 1.45 1.44

3.164 1/6/2008 39 1.49 1.48

3.183 12/2/1961 38 1.53 1.52

3.2 1/18/1993 37 1.57 1.56

3.244 1/16/1978 36 1.61 1.61

3.311 2/4/1994 35 1.66 1.65

3.432 2/17/1998 34 1.71 1.70

3.501 10/20/2004 33 1.76 1.75

3.552 2/18/1993 32 1.81 1.81

3.556 11/15/1952 31 1.87 1.87

3.596 2/27/1983 30 1.93 1.93

3.62 11/11/1985 29 2.00 2.00

3.651 2/16/1980 28 2.07 2.07

3.665 2/23/1998 27 2.15 2.15

3.716 1/27/2008 26 2.23 2.23

3.765 12/30/1991 25 2.32 2.33

3.849 1/29/1983 24 2.42 2.42

3.851 11/22/1965 23 2.52 2.53

3.889 2/3/1998 22 2.64 2.65

3.903 12/19/1970 21 2.76 2.78

3.93 2/10/1978 20 2.90 2.92

4.082 3/2/1980 19 3.05 3.08

4.309 4/1/1958 18 3.22 3.25

4.498 3/1/1978 17 3.41 3.45

4.518 1/16/1952 16 3.63 3.67

4.521 3/17/1982 15 3.87 3.92

4.599 2/20/1980 14 4.14 4.21

4.656 1/14/1993 13 4.46 4.54

4.664 2/18/2005 12 4.83 4.93

4.674 10/29/2000 11 5.27 5.40

4.752 10/27/2004 10 5.80 5.96

5.006 2/25/1969 9 6.44 6.65

5.087 2/4/1958 8 7.25 7.53

5.304 2/25/2003 7 8.29 8.67

5.895 9/23/1986 6 9.67 10.21

6.339 1/4/1995 5 11.60 12.43

6.584 1/15/1979 4 14.50 15.89

7.019 10/1/1983 3 19.33 22.00

7.263 1/4/1978 2 29.00 35.75

7.807 4/14/2003 1 58.00 95.33

Peaks

(cfs)

Period of Return

(Years)

List of Peak events and Determination of Q2 and Q10 (Post‐Development)Oceanside Carmax, POC‐3

T

(Year)

Cunnane

(cfs)

Weibull

(cfs)


9 4.45 4.63 2.27 11/18/1986 57 1.02 1.01

8 4.26 4.30 2.309 10/20/2004 56 1.04 1.03

7 4.12 4.17 2.311 2/16/1980 55 1.05 1.05

6 4.06 4.06 2.327 1/11/2005 54 1.07 1.07

5 3.83 3.83 2.332 1/13/1997 53 1.09 1.09

4 3.44 3.46 2.349 12/24/1988 52 1.12 1.11

3 3.34 3.34 2.352 12/25/1983 51 1.14 1.13

2 2.94 2.94 2.36 2/18/1980 50 1.16 1.15

2.365 1/20/1962 49 1.18 1.18

2.379 1/6/2008 48 1.21 1.20

Note: 2.38 1/11/1980 47 1.23 1.23



2.435 2/8/1993 44 1.32 1.31

2.436 2/14/1998 43 1.35 1.34

2.443 3/8/1968 42 1.38 1.38

2.45 2/23/2005 41 1.41 1.41

2.486 1/6/1979 40 1.45 1.44

2.52 12/2/1961 39 1.49 1.48

2.524 3/17/1963 38 1.53 1.52

2.556 3/1/1991 37 1.57 1.56

2.576 2/15/1986 36 1.61 1.61

2.586 2/27/1983 35 1.66 1.65

2.593 4/27/1960 34 1.71 1.70

2.768 11/15/1952 33 1.76 1.75

2.849 1/16/1972 32 1.81 1.81

2.888 11/11/1985 31 1.87 1.87

2.891 2/22/2008 30 1.93 1.93

2.935 2/17/1998 29 2.00 2.00

2.992 8/17/1977 28 2.07 2.07

3.04 1/16/1978 27 2.15 2.15

3.078 12/19/1970 26 2.23 2.23

3.107 1/29/1980 25 2.32 2.33

3.148 4/1/1958 24 2.42 2.42

3.172 2/23/1998 23 2.52 2.53

3.204 10/29/2000 22 2.64 2.65

3.295 1/14/1993 21 2.76 2.78

3.332 2/3/1998 20 2.90 2.92

3.346 3/2/1980 19 3.05 3.08

3.368 11/22/1965 18 3.22 3.25

3.371 2/10/1978 17 3.41 3.45

3.388 12/30/1991 16 3.63 3.67

3.399 3/17/1982 15 3.87 3.92

3.532 2/18/2005 14 4.14 4.21

3.808 2/20/1980 13 4.46 4.54

3.826 1/16/1952 12 4.83 4.93

3.826 3/1/1978 11 5.27 5.40

4.059 2/4/1958 10 5.80 5.96

4.064 10/27/2004 9 6.44 6.65

4.216 9/23/1986 8 7.25 7.53

4.331 2/25/1969 7 8.29 8.67

4.904 2/25/2003 6 9.67 10.21

5.538 1/4/1978 5 11.60 12.43

6.497 1/4/1995 4 14.50 15.89

6.767 1/15/1979 3 19.33 22.00

7.246 10/1/1983 2 29.00 35.75

8.029 4/14/2003 1 58.00 95.33

Peaks (cfs)

Period of Return

(Years)

List of Peak events and Determination of Q2 and Q10 (Pre‐Development)Oceanside Carmax, POC‐4

T

(Year)

Cunnane

(cfs)

Weibull

(cfs)


9 0.22 0.23 0.106 2/27/1991 57 1.02 1.01

8 0.21 0.21 0.107 4/28/2005 56 1.04 1.03

7 0.20 0.20 0.109 2/22/1998 55 1.05 1.05

6 0.19 0.20 0.11 8/17/1977 54 1.07 1.07

5 0.19 0.19 0.113 3/1/1991 53 1.09 1.09

4 0.18 0.18 0.114 2/8/1993 52 1.12 1.11

3 0.16 0.16 0.115 4/27/1960 51 1.14 1.13

2 0.15 0.15 0.116 3/19/1981 50 1.16 1.15

0.116 2/14/1998 49 1.18 1.18

0.118 12/22/1982 48 1.21 1.20

Note: 0.118 2/12/1992 47 1.23 1.23



0.12 3/15/1986 44 1.32 1.31

0.124 2/15/1986 43 1.35 1.34

0.124 3/11/1995 42 1.38 1.38

0.125 3/17/1963 41 1.41 1.41

0.127 1/29/1980 40 1.45 1.44

0.128 12/2/1961 39 1.49 1.48

0.128 1/6/2008 38 1.53 1.52

0.129 1/18/1993 37 1.57 1.56

0.131 1/16/1978 36 1.61 1.61

0.134 2/4/1994 35 1.66 1.65

0.139 2/17/1998 34 1.71 1.70

0.141 10/20/2004 33 1.76 1.75

0.143 11/15/1952 32 1.81 1.81

0.143 2/18/1993 31 1.87 1.87

0.145 2/27/1983 30 1.93 1.93

0.146 11/11/1985 29 2.00 2.00

0.147 2/16/1980 28 2.07 2.07

0.148 2/23/1998 27 2.15 2.15

0.15 1/27/2008 26 2.23 2.23

0.152 12/30/1991 25 2.32 2.33

0.155 11/22/1965 24 2.42 2.42

0.155 1/29/1983 23 2.52 2.53

0.157 2/3/1998 22 2.64 2.65

0.158 12/19/1970 21 2.76 2.78

0.159 2/10/1978 20 2.90 2.92

0.165 3/2/1980 19 3.05 3.08

0.174 4/1/1958 18 3.22 3.25

0.182 1/16/1952 17 3.41 3.45

0.182 3/1/1978 16 3.63 3.67

0.182 3/17/1982 15 3.87 3.92

0.186 2/20/1980 14 4.14 4.21

0.188 1/14/1993 13 4.46 4.54

0.188 2/18/2005 12 4.83 4.93

0.189 10/29/2000 11 5.27 5.40

0.192 10/27/2004 10 5.80 5.96

0.202 2/25/1969 9 6.44 6.65

0.205 2/4/1958 8 7.25 7.53

0.214 2/25/2003 7 8.29 8.67

0.238 9/23/1986 6 9.67 10.21

0.256 1/4/1995 5 11.60 12.43

0.266 1/15/1979 4 14.50 15.89

0.283 10/1/1983 3 19.33 22.00

0.293 1/4/1978 2 29.00 35.75

0.315 4/14/2003 1 58.00 95.33

Peaks

(cfs)

Period of Return

(Years)

List of Peak events and Determination of Q2 and Q10 (Post‐Development)Oceanside Carmax, POC‐4

T

(Year)

Cunnane

(cfs)

Weibull

(cfs)


9 0.12 0.13 0.065 8/17/1977 57 1.02 1.01

8 0.11 0.12 0.066 2/8/1993 56 1.04 1.03

7 0.11 0.11 0.066 2/14/1998 55 1.05 1.05

6 0.11 0.11 0.067 12/24/1983 54 1.07 1.07

5 0.10 0.10 0.067 2/22/2008 53 1.09 1.09

4 0.10 0.10 0.068 3/19/1981 52 1.12 1.11

3 0.09 0.09 0.069 1/16/1972 51 1.14 1.13

2 0.09 0.09 0.069 3/1/1991 50 1.16 1.15

0.07 1/29/1980 49 1.18 1.18

0.07 2/15/1986 48 1.21 1.20

Note: 0.07 3/15/1986 47 1.23 1.23



0.073 3/11/1995 44 1.32 1.31

0.073 1/6/2008 43 1.35 1.34

0.074 3/17/1963 42 1.38 1.38

0.075 12/2/1961 41 1.41 1.41

0.075 1/18/1993 40 1.45 1.44

0.075 1/30/2007 39 1.49 1.48

0.076 2/17/1998 38 1.53 1.52

0.079 12/22/1982 37 1.57 1.56

0.079 2/4/1994 36 1.61 1.61

0.08 2/23/1998 35 1.66 1.65

0.08 4/28/2005 34 1.71 1.70

0.083 10/20/2004 33 1.76 1.75

0.084 2/27/1983 32 1.81 1.81

0.085 11/22/1965 31 1.87 1.87

0.085 2/16/1980 30 1.93 1.93

0.086 2/10/1978 29 2.00 2.00

0.086 1/29/1983 28 2.07 2.07

0.086 12/30/1991 27 2.15 2.15

0.086 2/3/1998 26 2.23 2.23

0.086 1/27/2008 25 2.32 2.33

0.088 11/15/1952 24 2.42 2.42

0.088 2/27/1991 23 2.52 2.53

0.09 12/19/1970 22 2.64 2.65

0.091 2/18/1993 21 2.76 2.78

0.092 11/11/1985 20 2.90 2.92

0.095 3/2/1980 19 3.05 3.08

0.097 4/1/1958 18 3.22 3.25

0.099 1/16/1952 17 3.41 3.45

0.099 3/1/1978 16 3.63 3.67

0.1 2/20/1980 15 3.87 3.92

0.1 3/17/1982 14 4.14 4.21

0.103 2/18/2005 13 4.46 4.54

0.104 1/14/1993 12 4.83 4.93

0.106 10/29/2000 11 5.27 5.40

0.107 10/27/2004 10 5.80 5.96

0.108 2/25/1969 9 6.44 6.65

0.111 2/4/1958 8 7.25 7.53

0.117 2/25/2003 7 8.29 8.67

0.138 1/4/1995 6 9.67 10.21

0.143 1/15/1979 5 11.60 12.43

0.147 9/23/1986 4 14.50 15.89

0.155 10/1/1983 3 19.33 22.00

0.159 1/4/1978 2 29.00 35.75

0.171 4/14/2003 1 58.00 95.33

Peaks (cfs)

Period of Return

(Years)

ATTACHMENT 4

AREA VS ELEVATION

The storage provided within the detention basin is located within the basin module in SWMM.

Given that the basin is a vault with a constant area footprint (i.e. the area remains constant as

the depth increases), no stage‐storage calculation is required.

DISCHARGE VS ELEVATION

The orifices have been selected to maximize their size while still restricting flows to conform

with the required 10% of the Q2 event flow as mandated in the Final Hydromodification

Management Plan by Brown & Caldwell, dated March 2011. While REC acknowledges that

these orifices are small, to increase the size of these outlets would impact the basin’s ability to

restrict flows beneath the HMP thresholds, thus preventing the BMP from conformance with

HMP requirements.

In order to further reduce the risk of blockage of the orifices, regular maintenance of the riser

and orifices must be performed to ensure potential blockages are minimized. A detail of the

orifice and riser structure is provided in Attachment 5 of this memorandum.

The LID low flow orifice discharge relationship is addressed within the LID Module within

SWMM – please refer to Attachment 7 for further information.

DRAWDOWN CALCULATIONS

Surface drawdown calculations are provided on the following pages for reference and proof of

draining within 24 hours. It is assumed the basin is full to the invert of the first surface outlet

structure such that the only discharge mechanism available is the LID orifice. The HMS analysis

provided on the following pages indicates the basin is dry within approximately 24 hours.

DISCHARGE EQUATIONS

1) Weir:

/ (1)

2) Slot:

As an orifice: 2 (2.a)

As a weir: / (2.b)

For H > hs slot works as weir until orifice equation provides a smaller discharge. The elevation such that

equation (2.a) = equation (2.b) is the elevation at which the behavior changes from weir to orifice.

3) Vertical Orifices

As an orifice: 0.25 2 (3.a)

As a weir: Critical depth and geometric family of circular sector must be solved to determined Q as a function of

H:

; 2

; 2 ; 8

;

1 0.5 (3.b.1, 3.b.2, 3.b.3, 3.b.4 and 3.b.5)

There is a value of H (approximately H = 110% D) from which orifices no longer work as weirs as critical depth is

not possible at the entrance of the orifice. This value of H is obtained equaling the discharge using critical

equations and equations (3.b).

A mathematical model is prepared with the previous equations depending on the type o discharge.

The following are the variables used above:

QW, Qs, QO = Discharge of weir, slot or orifice (cfs)

CW, cg : Coefficients of discharge of weir (typically 3.1) and orifice (0.61 to 0.62)

L, Bs, D, hs : Length of weir, width of slot, diameter of orifice and height of slot, respectively; (ft)

H: Level of water in the pond over the invert of slot, weir or orifice (ft)

Acr, Tcr, ycr, αcr: Critical variables for circular sector: area (sq‐ft), top width (ft), critical depth (ft), and angle to the center,

respectively.

Outlet structure for Discharge of Detention Basin 1 (note: 0' elevation is assumed as surface invert of 6‐inch gravel layer)

Low orifice: 2.3125 " Lower slot Emergency Weir

Number: 2 Invert: 1.25 ft Invert: 3.750 ft

Cg‐low: 0.62 B 3.00 ft B: 12 ft

Middle orifice: 1 " h 0.208 ft

number of orif: 0 Upper slot

Cg‐middle: 0.62 Invert: 2.25 ft 45.00

invert elev: 0.75 ft B: 3.75 ft

h 0.670 ft

h H/D‐low H/D‐mid Qlow‐orif Qlow‐weir Qtot‐low Qmid‐orif Qmid‐weir Qtot‐med Qslot‐low Qslot‐upp Qemer Qtot Total H Total Q Flow + LID

(ft) ‐ ‐ (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (ft) (cfs) (cfs)

0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

0.100 0.519 0.000 0.018 0.027 0.027 0.000 0.000 0.000 0.000 0.000 0.000 0.027 0.100 0.027 0.027

0.200 1.038 0.000 0.093 0.090 0.090 0.000 0.000 0.000 0.000 0.000 0.000 0.090 0.200 0.090 0.090

0.300 1.557 0.000 0.131 0.159 0.131 0.000 0.000 0.000 0.000 0.000 0.000 0.131 0.300 0.131 0.131

0.400 2.076 0.000 0.160 0.209 0.160 0.000 0.000 0.000 0.000 0.000 0.000 0.160 0.400 0.160 0.160

0.500 2.595 0.000 0.184 0.228 0.184 0.000 0.000 0.000 0.000 0.000 0.000 0.184 0.500 0.184 0.184

0.600 3.114 0.000 0.206 0.232 0.206 0.000 0.000 0.000 0.000 0.000 0.000 0.206 0.600 0.206 0.206

0.700 3.632 0.000 0.226 0.275 0.226 0.000 0.000 0.000 0.000 0.000 0.000 0.226 0.700 0.226 0.226

0.800 4.151 0.600 0.243 0.463 0.243 0.000 0.000 0.000 0.000 0.000 0.000 0.243 0.800 0.243 0.243

0.900 4.670 1.800 0.260 0.964 0.260 0.000 0.000 0.000 0.000 0.000 0.000 0.260 0.900 0.260 0.260

1.000 5.189 3.000 0.276 2.020 0.276 0.000 0.000 0.000 0.000 0.000 0.000 0.276 1.000 0.276 0.276

1.100 5.708 4.200 0.291 2.908 0.291 0.000 0.000 0.000 0.000 0.000 0.000 0.291 1.100 0.291 0.291

1.200 6.227 5.400 0.305 3.049 0.305 0.000 0.000 0.000 0.000 0.000 0.000 0.305 1.200 0.305 0.305

1.300 6.746 6.600 0.318 3.184 0.318 0.000 0.000 0.000 0.104 0.000 0.000 0.422 1.300 0.422 0.422

1.400 7.265 7.800 0.331 3.314 0.331 0.000 0.000 0.000 0.540 0.000 0.000 0.872 1.400 0.872 0.872

1.500 7.784 9.000 0.344 3.439 0.344 0.000 0.000 0.000 1.163 0.000 0.000 1.506 1.500 1.506 1.506

1.600 8.303 10.200 0.356 3.559 0.356 0.000 0.000 0.000 1.517 0.000 0.000 1.873 1.600 1.873 1.873

1.700 8.822 11.400 0.368 3.675 0.368 0.000 0.000 0.000 1.799 0.000 0.000 2.167 1.700 2.167 2.167

1.800 9.341 12.600 0.379 3.788 0.379 0.000 0.000 0.000 2.043 0.000 0.000 2.422 1.800 2.422 2.422

1.900 9.859 13.800 0.390 3.898 0.390 0.000 0.000 0.000 2.260 0.000 0.000 2.650 1.900 2.650 2.650

2.000 10.378 15.000 0.400 4.005 0.400 0.000 0.000 0.000 2.459 0.000 0.000 2.859 2.000 2.859 2.859

2.100 10.897 16.200 0.411 4.108 0.411 0.000 0.000 0.000 2.642 0.000 0.000 3.053 2.100 3.053 3.053

2.200 11.416 17.400 0.421 4.210 0.421 0.000 0.000 0.000 2.814 0.000 0.000 3.235 2.200 3.235 3.235

2.300 11.935 18.600 0.431 4.309 0.431 0.000 0.000 0.000 2.976 0.130 0.000 3.536 2.300 3.536 3.536

2.400 12.454 19.800 0.441 4.405 0.441 0.000 0.000 0.000 3.129 0.675 0.000 4.245 2.400 4.245 4.245

2.500 12.973 21.000 0.450 4.500 0.450 0.000 0.000 0.000 3.275 1.453 0.000 5.178 2.500 5.178 5.178

2.600 13.492 22.200 0.459 4.592 0.459 0.000 0.000 0.000 3.415 2.407 0.000 6.281 2.600 6.281 6.281

2.700 14.011 23.400 0.468 4.683 0.468 0.000 0.000 0.000 3.549 3.509 0.000 7.527 2.700 7.527 7.527

2.800 14.530 24.600 0.477 4.772 0.477 0.000 0.000 0.000 3.679 4.742 0.000 8.898 2.800 8.898 8.898

2.900 15.049 25.800 0.486 4.860 0.486 0.000 0.000 0.000 3.804 6.092 0.000 10.382 2.900 10.382 10.382

3.000 15.568 27.000 0.495 4.946 0.495 0.000 0.000 0.000 3.925 7.551 0.000 11.970 3.000 11.970 11.970

3.100 16.086 28.200 0.503 5.030 0.503 0.000 0.000 0.000 4.043 8.826 0.000 13.372 3.100 13.372 13.372

3.200 16.605 29.400 0.511 5.113 0.511 0.000 0.000 0.000 4.157 9.645 0.000 14.313 3.200 14.313 14.313

3.300 17.124 30.600 0.519 5.195 0.519 0.000 0.000 0.000 4.268 10.400 0.000 15.187 3.300 15.187 15.187

3.400 17.643 31.800 0.528 5.275 0.528 0.000 0.000 0.000 4.376 11.103 0.000 16.007 3.400 16.007 16.007

3.500 18.162 33.000 0.535 5.355 0.535 0.000 0.000 0.000 4.482 11.765 0.000 16.782 3.500 16.782 16.782

3.600 18.681 34.200 0.543 5.433 0.543 0.000 0.000 0.000 4.585 12.391 0.000 17.519 3.600 17.519 17.519

3.750 19.459 36.000 0.555 5.548 0.555 0.000 0.000 0.000 4.736 13.275 0.000 18.566 3.750 18.566 18.566

3.800 19.719 36.600 0.559 5.586 0.559 0.000 0.000 0.000 4.785 13.557 0.416 19.316 3.800 19.316 19.316

3.900 20.238 37.800 0.566 5.661 0.566 0.000 0.000 0.000 4.882 14.104 2.161 21.713 3.900 21.713 21.713

4.000 20.757 39.000 0.573 5.734 0.573 0.000 0.000 0.000 4.977 14.630 4.650 24.830 4.000 24.830 24.830

S t o r a g e ( A C - F T )

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Reservoir "Reservoir-1" Results for Run "Run 1"

Run:Run 1 Element:Reservoir-1 Result:Storage Run:Run 1 Element:Reservoir-1 Result:Pool Elevation Run:Run 1 Element:Reservoir-1 Result:Outflow

Run:Run 1 Element:Reservoir-1 Result:Combined Inflow

ATTACHMENT 5

Pre & Post‐Developed Maps, Project Plan and Detention

Section Sketches

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SAMPLE PROHIBITIVE SIGNAGE

DMA PROPERTIES

LEGEND:

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SECTION A-A: UNDERGROUND DETENTION BASIN

UNDERGROUND DETENTION BASIN (UDB)

SOURCE CONTROL

NOTES

TRASH ENCLOSURE SECTION

” ”

”

” ”TREE WELL DETAIL

ATTACHMENT 6

SWMM Input Data in Input Format (Existing & Proposed Models)

PRE_DEV

[TITLE] [OPTIONS] FLOW_UNITS CFS INFILTRATION GREEN_AMPT FLOW_ROUTING KINWAVE START_DATE 10/01/1951 START_TIME 00:00:00 REPORT_START_DATE 10/01/1951 REPORT_START_TIME 00:00:00 END_DATE 09/30/2008 END_TIME 23:00:00 SWEEP_START 01/01 SWEEP_END 12/31 DRY_DAYS 0 REPORT_STEP 01:00:00 WET_STEP 00:15:00 DRY_STEP 04:00:00 ROUTING_STEP 0:01:00 ALLOW_PONDING NO INERTIAL_DAMPING PARTIAL VARIABLE_STEP 0.75 LENGTHENING_STEP 0 MIN_SURFAREA 0 NORMAL_FLOW_LIMITED BOTH SKIP_STEADY_STATE NO FORCE_MAIN_EQUATION H-W LINK_OFFSETS DEPTH MIN_SLOPE 0 [EVAPORATION] ;;Type Parameters ;;---------- ---------- MONTHLY 0.06 .08 0.11 0.15 0.17 0.19 0.19 0.18 0.15 0.11 0.08 0.06 DRY_ONLY NO [RAINGAGES] ;; Rain Time Snow Data ;;Name Type Intrvl Catch Source ;;-------------- --------- ------ ------ ---------- Oceanside INTENSITY 1:00 1.0 TIMESERIES Oceanside [SUBCATCHMENTS] ;; Total Pcnt. Pcnt. Curb Snow ;;Name Raingage Outlet Area Imperv Width Slope Length Pack ;;-------------- ---------------- ---------------- -------- -------- -------- -------- -------- -------- DMA-3A Oceanside POC-3 2.085 0 363 1 0 DMA-3B Oceanside POC-3 3.52 0 615 1 0 DMA-4 Oceanside POC-4 0.278 0 48 1 0 DMA-3C Oceanside POC-3 1.279 0 223 1 0 [SUBAREAS] ;;Subcatchment N-Imperv N-Perv S-Imperv S-Perv PctZero RouteTo PctRouted ;;-------------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- DMA-3A 0.012 0.05 0.05 0.1 25 OUTLET DMA-3B 0.012 0.05 0.05 0.1 25 OUTLET DMA-4 0.012 0.05 0.05 0.1 25 OUTLET DMA-3C 0.012 0.05 0.05 0.1 25 OUTLET [INFILTRATION] ;;Subcatchment Suction HydCon IMDmax ;;-------------- ---------- ---------- ----------

PRE_DEV

DMA-3A 9 0.01875 0.33 DMA-3B 9 0.01875 0.33 DMA-4 9 0.01875 0.33 DMA-3C 9 0.01875 0.33 [OUTFALLS] ;; Invert Outfall Stage/Table Tide ;;Name Elev. Type Time Series Gate ;;-------------- ---------- ---------- ---------------- ---- POC-3 0 FREE NO POC-4 0 FREE NO [TIMESERIES] ;;Name Date Time Value ;;-------------- ---------- ---------- ---------- Oceanside FILE "OsideRain.prn" [REPORT] INPUT NO CONTROLS NO SUBCATCHMENTS ALL NODES ALL LINKS ALL [TAGS] [MAP] DIMENSIONS -13900.000 2750.000 -5100.000 8250.000 Units None [COORDINATES] ;;Node X-Coord Y-Coord ;;-------------- ------------------ ------------------ POC-3 -9500.000 3000.000 POC-4 -11016.553 2985.714 [VERTICES] ;;Link X-Coord Y-Coord ;;-------------- ------------------ ------------------ [Polygons] ;;Subcatchment X-Coord Y-Coord ;;-------------- ------------------ ------------------ DMA-3A -9509.977 4252.834 DMA-3B -8582.086 4212.925 DMA-4 -11016.553 4043.311 DMA-3C -8302.721 3474.603 [SYMBOLS] ;;Gage X-Coord Y-Coord ;;-------------- ------------------ ------------------ Oceanside -9789.342 5529.932

POST_DEV_1

[TITLE] [OPTIONS] FLOW_UNITS CFS INFILTRATION GREEN_AMPT FLOW_ROUTING KINWAVE START_DATE 10/01/1951 START_TIME 00:00:00 REPORT_START_DATE 10/01/1951 REPORT_START_TIME 00:00:00 END_DATE 09/30/2008 END_TIME 23:00:00 SWEEP_START 01/01 SWEEP_END 12/31 DRY_DAYS 0 REPORT_STEP 01:00:00 WET_STEP 00:15:00 DRY_STEP 04:00:00 ROUTING_STEP 0:01:00 ALLOW_PONDING NO INERTIAL_DAMPING PARTIAL VARIABLE_STEP 0.75 LENGTHENING_STEP 0 MIN_SURFAREA 0 NORMAL_FLOW_LIMITED BOTH SKIP_STEADY_STATE NO FORCE_MAIN_EQUATION H-W LINK_OFFSETS DEPTH MIN_SLOPE 0 [EVAPORATION] ;;Type Parameters ;;---------- ---------- MONTHLY 0.06 .08 0.11 0.15 0.17 0.19 0.19 0.18 0.15 0.11 0.08 0.06 DRY_ONLY NO [RAINGAGES] ;; Rain Time Snow Data ;;Name Type Intrvl Catch Source ;;-------------- --------- ------ ------ ---------- Oceanside INTENSITY 1:00 1.0 TIMESERIES Oceanside [SUBCATCHMENTS] ;; Total Pcnt. Pcnt. Curb Snow ;;Name Raingage Outlet Area Imperv Width Slope Length Pack ;;-------------- ---------------- ---------------- -------- -------- -------- -------- -------- -------- DMA-3A Oceanside BASIN 5.896 85.24 2568 1 0 DMA-3B Oceanside POC-3 0.993 0 432 1 0 DMA-4 Oceanside POC-4 0.146 50.4 63 1 0 [SUBAREAS] ;;Subcatchment N-Imperv N-Perv S-Imperv S-Perv PctZero RouteTo PctRouted ;;-------------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- DMA-3A 0.012 0.05 0.05 0.1 25 OUTLET DMA-3B 0.012 0.05 0.05 0.1 25 OUTLET DMA-4 0.012 0.05 0.05 0.1 25 OUTLET [INFILTRATION] ;;Subcatchment Suction HydCon IMDmax ;;-------------- ---------- ---------- ---------- DMA-3A 9 0.01875 0.33 DMA-3B 9 0.01875 0.33 DMA-4 9 0.01875 0.33 [OUTFALLS] ;; Invert Outfall Stage/Table Tide ;;Name Elev. Type Time Series Gate ;;-------------- ---------- ---------- ---------------- ---- POC-3 0 FREE NO POC-4 0 FREE NO

POST_DEV_1

[STORAGE] ;; Invert Max. Init. Storage Curve Ponded Evap. ;;Name Elev. Depth Depth Curve Params Area Frac. Infiltration Parameters ;;-------------- -------- -------- -------- ---------- -------- -------- -------- -------- -------- ----------------------- BASIN 0 4.2 0 TABULAR BASIN1 6090 0 9 0.265 0.33 [OUTLETS] ;; Inlet Outlet Outflow Outlet Qcoeff/ Flap ;;Name Node Node Height Type QTable Qexpon Gate ;;-------------- ---------------- ---------------- ---------- --------------- ---------------- ---------- ---- OUTLET BASIN POC-3 0 TABULAR/HEAD OUT1 NO [CURVES] ;;Name Type X-Value Y-Value ;;-------------- ---------- ---------- ---------- OUT1 Rating 0 0 OUT1 0.1 0 OUT1 0.2 0 OUT1 0.3 0.027 OUT1 0.4 0.09 OUT1 0.5 0.131 OUT1 0.6 0.16 OUT1 0.7 0.184 OUT1 0.8 0.206 OUT1 0.9 0.226 OUT1 1 0.243 OUT1 1.1 0.26 OUT1 1.2 0.276 OUT1 1.3 0.291 OUT1 1.4 0.305 OUT1 1.5 0.422 OUT1 1.6 0.872 OUT1 1.7 1.506 OUT1 1.8 1.873 OUT1 1.9 2.167 OUT1 2 2.422 OUT1 2.1 2.65 OUT1 2.2 2.859 OUT1 2.3 3.053 OUT1 2.4 3.235 OUT1 2.5 3.536 OUT1 2.6 4.245 OUT1 2.7 5.178 OUT1 2.8 6.281 OUT1 2.9 7.527 OUT1 3 8.898 OUT1 3.1 10.382 OUT1 3.2 11.97 OUT1 3.3 13.372 OUT1 3.4 14.313 OUT1 3.5 15.187 OUT1 3.6 16.007 OUT1 3.75 16.782 OUT1 3.8 17.519 OUT1 3.9 18.566 OUT1 4 19.316 OUT1 4.1 21.713 OUT1 4.2 24.83 BASIN1 Storage 0 6090 BASIN1 4.2 6090 [TIMESERIES] ;;Name Date Time Value ;;-------------- ---------- ---------- ---------- Oceanside FILE "OsideRain.prn" [REPORT]

POST_DEV_1

INPUT NO CONTROLS NO SUBCATCHMENTS ALL NODES ALL LINKS ALL [TAGS] [MAP] DIMENSIONS -13900.000 2750.000 -5100.000 8250.000 Units None [COORDINATES] ;;Node X-Coord Y-Coord ;;-------------- ------------------ ------------------ POC-3 -9500.000 3000.000 POC-4 -11016.553 2985.714 BASIN -9509.977 4143.084 [VERTICES] ;;Link X-Coord Y-Coord ;;-------------- ------------------ ------------------ [Polygons] ;;Subcatchment X-Coord Y-Coord ;;-------------- ------------------ ------------------ DMA-3A -9509.977 4871.429 DMA-3B -8342.630 2995.692 DMA-4 -11016.553 4043.311 [SYMBOLS] ;;Gage X-Coord Y-Coord ;;-------------- ------------------ ------------------ Oceanside -9789.342 5529.932

ATTACHMENT 7

EPA SWMM FIGURES AND EXPLANATIONS

Per the attached, the reader can see the screens associated with the EPA‐SWMM Model in both

pre‐development and post‐development conditions. Each portion, i.e., sub‐catchments,

outfalls, storage units, weir as a discharge, and outfalls (point of compliance), are also shown.

Variables for modeling are associated with typical recommended values by the EPA‐SWMM

model, typical values found in technical literature (such as Maidment’s Handbook of

Hydrology). Recommended values for the SWMM model have been attained from Appendix G

of the 2016 City of Oceanside BMP Design Manual.

Soil characteristics of the existing soils were determined from the NRCS Web Soil Survey and

site specific geotechnical report (located in Attachment 8 of this report).

A Technical document prepared by Tory R Walker Engineering for the Cities of San Marcos,

Oceanside and Vista (Reference [1]) can also be consulted for additional information regarding

typical values for SWMM parameters.

Manning’s roughness coefficients have been based upon the findings of the “Improving

Accuracy in Continuous Hydrologic Modeling: Guidance for Selecting Pervious Overland Flow

Manning’s n Values in the San Diego Region” date 2016 by TRW Engineering (Reference [6]).

PRE‐DEVELOPED CONDITIONS

POST‐DEVELOPED CONDITIONS

Detention Basin

EXPLANATION OF SELECTED VARIABLES

Sub Catchment Areas:

Please refer to the attached diagrams that indicate the DMA and detention BMPs (BMP) sub areas

modeled within the project site at both the pre and post developed conditions draining to the POC.

Parameters for the pre‐ and post‐developed models include soil type D as determined from the NRCS

websoil survey review (attached at the end of this appendix). Suction head, conductivity and initial

deficit corresponds to average values expected for these soils types, according to Appendix G of the

2016 City of Oceanside BMP Design Manual.

For surface runoff infiltration values, REC selected infiltration values per Appendix G of the 2016 City of

Oceanside BMP Design Manual corresponding to hydrologic soil type.

Selection of a Kinematic Approach: As the continuous model is based on hourly rainfall, and the time of

concentration for the pre‐development and post‐development conditions is significantly smaller than 60

minutes, precise routing of the flows through the impervious surfaces, the underdrain pipe system, and

the discharge pipe was considered unnecessary. The truncation error of the precipitation into hourly

steps is much more significant than the precise routing in a system where the time of concentration is

much smaller than 1 hour.

Infiltration:

Per the SWQMP, a factored design infiltration rate of 0.265 in/hr has been applied to the base of the

detention vault.

Overland Flow Manning’s Coefficient per TRWE (Reference [6])

3 Further discussion is provided on page 6 under “Discussion of Differences Between Manning’s n Values” 3

appeal of a de facto value, we anticipate that jurisdictions will not be inclined to approve land surfaces other than short prairie grass. Therefore, in order to provide SWMM users with a wider range of land surfaces suitable for local application and to provide Copermittees with confidence in the design parameters, we recommend using the values published by Yen and Chow in Table 3-5 of the EPA SWMM Reference Manual Volume I – Hydrology.

SWMM-Endorsed Values Will Improve Model Quality

In January 2016, the EPA released the SWMM Reference Manual Volume I – Hydrology (SWMM Hydrology Reference Manual). The SWMM Hydrology Reference Manual complements the SWMM 5 User’s Manual and SWMM 5 Applications Manual by providing an in-depth description of the program’s hydrologic components (EPA 2016). Table 3-5 of the SWMM Hydrology Reference Manual expounds upon SWMM 5 User’s Manual Table A.6 by providing Manning’s n values for additional overland flow surfaces3. The values are provided in Table 1:

Table 1: Manning’s n Values for Overland Flow (EPA, 2016; Yen 2001; Yen and Chow, 1983).

Overland Surface Light Rain (< 0.8 in/hr)

Moderate Rain (0.8-1.2 in/hr)

Heavy Rain (> 1.2 in/hr)

Smooth asphalt pavement 0.010 0.012 0.015 Smooth impervious surface 0.011 0.013 0.015 Tar and sand pavement 0.012 0.014 0.016 Concrete pavement 0.014 0.017 0.020 Rough impervious surface 0.015 0.019 0.023 Smooth bare packed soil 0.017 0.021 0.025 Moderate bare packed soil 0.025 0.030 0.035 Rough bare packed soil 0.032 0.038 0.045 Gravel soil 0.025 0.032 0.045 Mowed poor grass 0.030 0.038 0.045 Average grass, closely clipped sod 0.040 0.050 0.060 Pasture 0.040 0.055 0.070 Timberland 0.060 0.090 0.120 Dense grass 0.060 0.090 0.120 Shrubs and bushes 0.080 0.120 0.180 Land Use Business 0.014 0.022 0.035 Semibusiness 0.022 0.035 0.050 Industrial 0.020 0.035 0.050 Dense residential 0.025 0.040 0.060 Suburban residential 0.030 0.055 0.080 Parks and lawns 0.040 0.075 0.120

For purposes of local hydromodification management BMP design, these Manning’s n values are an improvement upon the values presented by Engman (1986) in SWMM 5 User’s Manual Table A.6. Values from SWMM 5 User’s Manual Table A.6, while completely suitable for the intended application to certain agricultural land covers, comes with the disclaimer that the provided Manning’s n values are valid for shallow-depth overland flow that match the conditions in the experimental plots (Engman,

ATTACHMENT 8

Geotechnical Documentation

Hydrologic Soil Group—San Diego County Area, California

Natural ResourcesConservation Service

Web Soil SurveyNational Cooperative Soil Survey

12/17/2019Page 1 of 4

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472840 472880 472920 472960 473000 473040 473080 473120 473160 473200 473240

472840 472880 472920 472960 473000 473040 473080 473120 473160 473200 473240

33° 11' 1'' N11

7° 1

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33° 11' 1'' N

117°

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33° 10' 52'' N

117°

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33° 10' 52'' N

117°

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N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 11N WGS840 50 100 200 300

Feet0 25 50 100 150

MetersMap Scale: 1:1,980 if printed on A landscape (11" x 8.5") sheet.

Soil Map may not be valid at this scale.

MAP LEGEND MAP INFORMATION

Area of Interest (AOI)Area of Interest (AOI)

SoilsSoil Rating Polygons

A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating LinesA

A/D

B

B/D

C

C/D

D


Soil Rating PointsA

A/D

B

B/D

C

C/D

D


Water FeaturesStreams and Canals

TransportationRails

Interstate Highways

US Routes

Major Roads

Local Roads

BackgroundAerial Photography

The soil surveys that comprise your AOI were mapped at 1:24,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation ServiceWeb Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: San Diego County Area, CaliforniaSurvey Area Data: Version 14, Sep 16, 2019

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Nov 3, 2014—Nov 22, 2014

The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.




12/17/2019Page 2 of 4

Hydrologic Soil Group

Map unit symbol Map unit name Rating Acres in AOI Percent of AOI

LeC2 Las Flores loamy fine sand, 5 to 9 percent slopes, eroded

D 10.1 99.8%

VaB Visalia sandy loam, 2 to 5 percent slopes

A 0.0 0.2%

Totals for Area of Interest 10.1 100.0%

Description

Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms.

The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows:

Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission.

Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission.

Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission.

Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission.

If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes.




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Rating Options

Aggregation Method: Dominant Condition

Component Percent Cutoff: None Specified

Tie-break Rule: Higher




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ATTACHMENT 9

Summary Files from the SWMM Model

PRE_DEV

EPA STORM WATER MANAGEMENT MODEL - VERSION 5.0 (Build 5.0.022) -------------------------------------------------------------- ********************************************************* NOTE: The summary statistics displayed in this report are based on results found at every computational time step, not just on results from each reporting time step. ********************************************************* **************** Analysis Options **************** Flow Units ............... CFS Process Models: Rainfall/Runoff ........ YES Snowmelt ............... NO Groundwater ............ NO Flow Routing ........... NO Water Quality .......... NO Infiltration Method ...... GREEN_AMPT Starting Date ............ OCT-01-1951 00:00:00 Ending Date .............. SEP-30-2008 23:00:00 Antecedent Dry Days ...... 0.0 Report Time Step ......... 01:00:00 Wet Time Step ............ 00:15:00 Dry Time Step ............ 04:00:00 ************************** Volume Depth Runoff Quantity Continuity acre-feet inches ************************** --------- ------- Total Precipitation ...... 402.481 674.360 Evaporation Loss ......... 17.697 29.652 Infiltration Loss ........ 294.999 494.274 Surface Runoff ........... 98.630 165.256 Final Surface Storage .... 0.000 0.000 Continuity Error (%) ..... -2.198 ************************** Volume Volume Flow Routing Continuity acre-feet 10^6 gal ************************** --------- --------- Dry Weather Inflow ....... 0.000 0.000 Wet Weather Inflow ....... 98.630 32.140 Groundwater Inflow ....... 0.000 0.000 RDII Inflow .............. 0.000 0.000 External Inflow .......... 0.000 0.000 External Outflow ......... 98.630 32.140 Internal Outflow ......... 0.000 0.000 Storage Losses ........... 0.000 0.000 Initial Stored Volume .... 0.000 0.000 Final Stored Volume ...... 0.000 0.000 Continuity Error (%) ..... 0.000 *************************** Subcatchment Runoff Summary *************************** -------------------------------------------------------------------------------------------------------- Total Total Total Total Total Total Peak Runoff Precip Runon Evap Infil Runoff Runoff Runoff Coeff Subcatchment in in in in in 10^6 gal CFS -------------------------------------------------------------------------------------------------------- DMA-3A 674.36 0.00 29.65 494.29 165.24 9.35 2.36 0.245 DMA-3B 674.36 0.00 29.65 494.26 165.28 15.80 3.99 0.245 DMA-4 674.36 0.00 29.66 494.35 165.16 1.25 0.32 0.245 DMA-3C 674.36 0.00 29.65 494.28 165.25 5.74 1.45 0.245

PRE_DEV

Analysis begun on: Wed Feb 26 15:40:39 2020 Analysis ended on: Wed Feb 26 15:40:55 2020 Total elapsed time: 00:00:16

POST_DEV

EPA STORM WATER MANAGEMENT MODEL - VERSION 5.0 (Build 5.0.022) -------------------------------------------------------------- ********************************************************* NOTE: The summary statistics displayed in this report are based on results found at every computational time step, not just on results from each reporting time step. ********************************************************* **************** Analysis Options **************** Flow Units ............... CFS Process Models: Rainfall/Runoff ........ YES Snowmelt ............... NO Groundwater ............ NO Flow Routing ........... YES Ponding Allowed ........ NO Water Quality .......... NO Infiltration Method ...... GREEN_AMPT Flow Routing Method ...... KINWAVE Starting Date ............ OCT-01-1951 00:00:00 Ending Date .............. SEP-30-2008 23:00:00 Antecedent Dry Days ...... 0.0 Report Time Step ......... 01:00:00 Wet Time Step ............ 00:15:00 Dry Time Step ............ 04:00:00 Routing Time Step ........ 60.00 sec ************************** Volume Depth Runoff Quantity Continuity acre-feet inches ************************** --------- ------- Total Precipitation ...... 395.344 674.360 Evaporation Loss ......... 47.628 81.241 Infiltration Loss ........ 78.009 133.065 Surface Runoff ........... 276.332 471.355 Final Surface Storage .... 0.000 0.000 Continuity Error (%) ..... -1.676 ************************** Volume Volume Flow Routing Continuity acre-feet 10^6 gal ************************** --------- --------- Dry Weather Inflow ....... 0.000 0.000 Wet Weather Inflow ....... 276.332 90.047 Groundwater Inflow ....... 0.000 0.000 RDII Inflow .............. 0.000 0.000 External Inflow .......... 0.000 0.000 External Outflow ......... 174.386 56.826 Internal Outflow ......... 0.000 0.000 Storage Losses ........... 101.850 33.189 Initial Stored Volume .... 0.000 0.000 Final Stored Volume ...... 0.000 0.000 Continuity Error (%) ..... 0.034 ******************************** Highest Flow Instability Indexes ******************************** All links are stable. ************************* Routing Time Step Summary ************************* Minimum Time Step : 60.00 sec Average Time Step : 60.00 sec

POST_DEV

Maximum Time Step : 60.00 sec Percent in Steady State : 0.00 Average Iterations per Step : 1.00 *************************** Subcatchment Runoff Summary *************************** -------------------------------------------------------------------------------------------------------- Total Total Total Total Total Total Peak Runoff Precip Runon Evap Infil Runoff Runoff Runoff Coeff Subcatchment in in in in in 10^6 gal CFS -------------------------------------------------------------------------------------------------------- DMA-3A 674.36 0.00 90.95 70.90 523.73 83.85 7.04 0.777 DMA-3B 674.36 0.00 26.18 486.48 173.37 4.67 1.13 0.257 DMA-4 674.36 0.00 63.73 239.75 383.00 1.52 0.17 0.568 ****************** Node Depth Summary ****************** --------------------------------------------------------------------- Average Maximum Maximum Time of Max Depth Depth HGL Occurrence Node Type Feet Feet Feet days hr:min --------------------------------------------------------------------- POC-3 OUTFALL 0.00 0.00 0.00 0 00:00 POC-4 OUTFALL 0.00 0.00 0.00 0 00:00 BASIN STORAGE 0.02 2.85 2.85 18823 17:00 ******************* Node Inflow Summary ******************* ------------------------------------------------------------------------------------- Maximum Maximum Lateral Total Lateral Total Time of Max Inflow Inflow Inflow Inflow Occurrence Volume Volume Node Type CFS CFS days hr:min 10^6 gal 10^6 gal ------------------------------------------------------------------------------------- POC-3 OUTFALL 1.13 8.03 18823 17:00 4.675 55.304 POC-4 OUTFALL 0.17 0.17 18823 17:00 1.518 1.518 BASIN STORAGE 7.04 7.04 18823 17:00 83.847 83.847 ********************** Node Surcharge Summary ********************** Surcharging occurs when water rises above the top of the highest conduit. --------------------------------------------------------------------- Max. Height Min. Depth Hours Above Crown Below Rim Node Type Surcharged Feet Feet --------------------------------------------------------------------- BASIN STORAGE 499679.02 2.850 1.350 ********************* Node Flooding Summary ********************* No nodes were flooded. ********************** Storage Volume Summary **********************

POST_DEV

-------------------------------------------------------------------------------------------- Average Avg E&I Maximum Max Time of Max Maximum Volume Pcnt Pcnt Volume Pcnt Occurrence Outflow Storage Unit 1000 ft3 Full Loss 1000 ft3 Full days hr:min CFS -------------------------------------------------------------------------------------------- BASIN 0.096 0 40 17.358 68 18823 17:00 6.90 *********************** Outfall Loading Summary *********************** ----------------------------------------------------------- Flow Avg. Max. Total Freq. Flow Flow Volume Outfall Node Pcnt. CFS CFS 10^6 gal ----------------------------------------------------------- POC-3 2.36 0.17 8.03 55.304 POC-4 1.26 0.01 0.17 1.518 ----------------------------------------------------------- System 1.81 0.18 8.20 56.822 ******************** Link Flow Summary ******************** ----------------------------------------------------------------------------- Maximum Time of Max Maximum Max/ Max/ |Flow| Occurrence |Veloc| Full Full Link Type CFS days hr:min ft/sec Flow Depth ----------------------------------------------------------------------------- OUTLET DUMMY 6.90 18823 17:00 ************************* Conduit Surcharge Summary ************************* No conduits were surcharged. Analysis begun on: Wed Feb 26 15:02:40 2020 Analysis ended on: Wed Feb 26 15:03:07 2020 Total elapsed time: 00:00:27

TECHNICAL MEMORANDUM: SWMM Modeling for Hydromodification ...

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Transcript of TECHNICAL MEMORANDUM: SWMM Modeling for Hydromodification ...