HomeMy WebLinkAboutApn I3 - HydrologyAPPENDIX I3
Hydromodification Study
Hydromodification Study
For
Otay Ranch
Village 8 West
Chula Vista Tract No. 09-XX
John A. Hayes, P.E.
R.C.E. # 58003
Expiration Date: June 30, 2014
Prepared For
Otay Land Company, LLC
1903 Wright Place, Suite 220
Carlsbad, CA 92008
(760) 602-3777
Prepared By
Hale Engineering
7910 Convoy Court
San Diego, CA 92111
(858) 715-1420
Date: August 26, 2011
i H.E. Job No. 08020
Table of Contents
1 Vicinity Map ..................................................................................................... 1
2 Introduction..................................................................................................... 2
3 Hydromodification Method and Criteria ........................................................... 3
3.1 Hydromodification Methodology: ............................................................... 3
4 Hydromodification Results ............................................................................. 4
4.1 Pre-Developed Condition .......................................................................... 5
4.2 Developed Condition ................................................................................. 6
5 Conclusions .................................................................................................... 7
Appendices
Appendix 1 Hydro-Modification Pre-Developed Land Use Exhibit
Appendix 2 Hydro-Modification Post-Development Land Use Exhibit
Appendix 3 San Diego Hydrology Model (SDMH) Program Results
Appendix 4 Outlet Structure Details and Calculations
Appendix 5 HEC-HMS routing results
1 H.E. Job No. 08020
1 Vicinity Map
2 H.E. Job No. 08020
2 Introduction
The proposed project is located within the Otay Watershed, specifically the Otay
Valley Hydrologic Area. Village 8 West is a 320-acre SPA (Special Planning
Area) portion of the larger Otay Valley Parcel of the City of Chula Vista currently
used for light agrarian and grazing purposes. An existing reservoir occupies a
central portion of the property. The Otay Valley Parcel is the largest parcel of
Otay Ranch, comprising 9,449 acres bounded by Telegraph Canyon Road on the
north, Heritage Road and the Otay Landfill Site on the west, Brown Field on the
south, and Lower Otay Lake on the east.
The northern portion of the proposed project will ultimately drain to Wolf Canyon
via two of five proposed storm drain systems. The other three storm drain
systems drain the remainder of the project to the Otay River southerly of the
southern boundary of the proposed project.
The discharge to the Otay River is downstream of the Otay reservoir. The first
Otay dam failed in an event which degraded the downstream Otay River. Per the
Final Hydromodification, the lower Otay River Valley is listed as a river reach
that is exempt from hydromodification analysis (see section 6, page 6.6, table 6.1
of the Final HMP dated March 2011, Therefore no calculations for
hydromodification or storage routing have been performed for discharge into
Otay River. Within this report are the necessary hydromodification calculations
required for the design of the detention basin proposed per the project.
The design of the backbone storm drain system is performed in a separate
hydrologic analysis. Refer to the "Preliminary Drainage Study for Otay Ranch
Village 8 West" for the project storm drain design.
3 H.E. Job No. 08020
3 Hydromodification Method and Criteria
Clear Creek Solution, Inc’s San Diego Hydrology Model (SDHM) software
program is adapted from Western Washington Hydrology Manual (WWHM)
Version 3, but has been modified to represent San Diego County hydrology and
enhanced to be able to size other types of control measures and low impact
development (LID) techniques for flow reduction as well.
3.1 Hydromodification Methodology:
The SDHM software architecture and methodology is the same as that
developed for BAHM (Bay Area Hydrology Model) and WWHM and uses HSPF
as its computational engine. Like BAHM and WWHM, SDHM is a tool that
generates flow duration curves for the pre- and post-project condition and then
sizes a flow duration control pond/basin or vault and outlet structure to match the
pre-project curve.
The HSPF hydrology parameter values used in SDHM are based on calibrated
watersheds. SDHM incorporates the rain gage data provided on the Project
Clean Water website; the Lower Otay rain gage data is used in the calculations
provided within this report. SDHM runs HSPF to generate an hourly runoff time
series from the available rain gauge data over a number of years. Stormwater
runoff is computed for both pre-project and post-project land use conditions.
Then, SDHM routes the post-project stormwater runoff through the proposed
stormwater. SDHM uses the pre-project peak flood value for each water year to
compute the pre-project 2- through 100-year flood frequency values1. The post-
project runoff 2- through 100-year flood frequency values are computed at the
outlet of the proposed stormwater facility. The model routes the post-project
runoff through the stormwater facility. As with the pre-project peak flow values,
the maximum post-project flow value for each water year is selected by the
model to compute the developed 2- through 100-year flood frequency. The pre-
project 2-year peak flow is multiplied by 10% to set the lower limit of the erosive
flows, in accordance with the current HMP performance criteria2. The pre-project
10-year peak flow is the upper limit. A comparison of the pre-project and post-
project flow duration curves is conducted for 100 flow levels between the lower
limit and the upper limit. The model counts the number of hours that pre-project
flows exceed each of the flow levels during the entire simulation period. The
model does the same analysis for the post-project mitigated flows.
1 The actual flood frequency calculations are made using the Weibull ranking procedure described in
Bulletin 17B (United States Water Resources Council, 1981).
2 In SDHM, this low flow limit is a user-defined variable, to allow flexibility pending potential changes in
regulatory requirements.
4 H.E. Job No. 08020
4 Hydromodification Results
The SDHM program results are included in Appendix 3. The computed flow rates
for the Wolf Canyon discharge point of compliance are as follows:
Storm Event
2-Year 5-Year 10-Year 25-Year
Pre-Project Flow (cfs) 28.6 39.0 55.6 93.0
Post-Project Flow (cfs) 17.1 31.8 40.1 63.9
The post-project flows shown above are calculated based on the inclusion of a
detention basin with the following design parameters:
Total Storage Volume = 23.3 Acre-feet
Depth = 24’ feet
Side Slope = 2:1 (Horizontal: Vertical)
Outlet Structures See Section 4
SSD (Stage, Storage, Discharge) Table provided in report
Developed flows calculated for the various return periods using the
Modified Rational Method (per County of SD Hydrology manual) are
higher than those calculated by HSPF. The higher flow values were
routed through the basin using HEC-HMS 3.3 to verify capacity. The
results are provided in this report. (See Section 5)
No manual infiltration assumed.
5 H.E. Job No. 08020
4.1 Pre-Developed Condition
In the pre-developed condition, a 183.6-acre drainage area outlets at the point of
compliance of Wolf Canyon. This basin is composed of the northern portion of
Village 8 West and a portion of Otay Ranch Village 7. In the pre-developed
condition, the northern portion of Village 8 west is undeveloped while the tributary
portion of Otay Ranch Village 7 contains a high school and associated roadways.
Land uses of the pre-developed drainage area breakdown as follows:
C, D, Grass, Site (10-20%) = 31.4 acres
C, D, Dirt, ST (10-20%) = 94.0 acres
C, D, Urban, Flat (0-5%) = 20.0 acres
Roads, Mod (5-10%) = 14.3 acres
Roof Area = 5.0 acres
Hardscape, Flat (0-5%) = 18.9 acres
See Appendix 1 Hydro-Modification Pre-Developed Land Use Exhibit for the
locations of the various land use types in the drainage area.
As described in Section 3, design data from Project Clean Water was used with
Clear Creek Solution, Inc’s San Diego Hydrological Model (SDHM) software in
the hydromodification analysis of the Pre-Developed Condition.
6 H.E. Job No. 08020
4.2 Developed Condition
In the developed condition, a 202.6-acre drainage area outlets at the point of
compliance of Wolf Canyon. This basin is composed of the northern portion of
Village 8 West and a portion of Otay Ranch Village 7. In the developed condition,
the northern portion of Village 8 west is developed with graded pads for future
development and associated paved roadways and the tributary portion of Otay
Ranch Village 7 shall continue to house the existing high school and associated
roadways. Land uses of the developed drainage area breakdown as follows:
C, D, Grass, Site (0-5%) = 2.5 acres
C, D, Grass, Site (10-20%) = 32.4 acres
C, D, Grass, Site ( > 20%) = 12.0 acres
C, D, Urban, Flat (0-5%) = 37.0 acres
Roads, Mod (5-10%) = 36.2 acres
Roof Area = 12.6 acres
Hardscape, Flat (0-5%) = 18.9 acres
Parking, Flat (0-5%) = 51.0 acres
See Appendix 2 Hydro-Modification Development Land Use Exhibit for the
locations of the various land use types in the drainage area.
As described in Section 3, design data from Project Clean Water was used with
Clear Creek Solution, Inc’s San Diego Hydrological Model (SDHM) software in
the hydromodification analysis of the Developed Condition.
7 H.E. Job No. 08020
5 Conclusions
This Hydromodification Study contains analyses for the 2-, 10-, 25-, and 50-year,
storm events. These analyses are used in the design and sizing of the proposed
detention basin upstream of the Wolf Canyon point of compliance. This basin is
for flow control only; see the Water Quality Technical Report for storm water
runoff treatment BMP’s. With the inclusion of the proposed detention basin, post-
project flow rates at the point of compliance of the Wolf Canyon discharge shall
be less than pre-project rates for the 2-, 5-, 10-, and 50-year storms.
SECTION 1
SECTION 2
SECTION 3
SDHM2011
PROJECT REPORT
___________________________________________________________________
Project Name:V8 WEST-park
Site Name :V8W
Site Address:LA MEDIA
City :Chula Vista
Report Date :8/1/2011
Gage :LWR OTAY
Data Start :10/01/1959
Data End :09/30/2004
Precip Scale:1.00
Version :2011/06/22
___________________________________________________________________
PREDEVELOPED LAND USE
Name :Basin 1
Bypass:No
GroundWater:No
Pervious Land Use Acres
C D,Grass,Ste(10-20) 31.4
C D,Dirt, St(10-20%) 78.3
C D,Urban,Flat(0-5%) 20
Impervious Land Use Acres
Roads,Mod(5-10%) 14.3
Roof Area 5
Sidewalks,Flat(0-5%) 18.9
___________________________________________________________________
Element Flows To:
Surface Interflow Groundwater
___________________________________________________________________
Name :Existing Park Area
Bypass:No
GroundWater:No
Pervious Land Use Acres
C D,Dirt, St(10-20%) 15.7
Impervious Land Use Acres
___________________________________________________________________
Element Flows To:
Surface Interflow Groundwater
___________________________________________________________________
MITIGATED LAND USE
Name :Basin 1
Bypass:No
GroundWater:No
Pervious Land Use Acres
C D,Grass,Ste(10-20) 32.4
C D,Urban,Flat(0-5%) 37
C D,Grass,Flat(0-5%) 2.5
C D,Grass,Very(>20%) 12
Impervious Land Use Acres
Roads,Mod(5-10%) 36.2
Roof Area 12.6
Sidewalks,Flat(0-5%) 18.9
Parking,Flat(0-5%) 51
___________________________________________________________________
Element Flows To:
Surface Interflow Groundwater
SSD Table 1 SSD Table 1
___________________________________________________________________
Name :SSD Table 1
Depth:24 ft.
Element Flows To:
Outlet 1 Outlet 2
Culvert 1
___________________________________________________________________
SSD Table Hydraulic Table
Stage Area Volume
(ft) (ac) (ac-ft) Manual NotUsed NotUsed NotUsed NotUsed
0.000 0.557 0.000 0.000 0.000 0.000 0.000 0.000
1.000 0.590 0.573 0.657 0.000 0.000 0.000 0.000
2.000 0.624 1.180 0.929 0.000 0.000 0.000 0.000
3.000 0.659 1.822 1.137 0.000 0.000 0.000 0.000
4.000 0.695 2.499 1.313 0.000 0.000 0.000 0.000
5.000 0.732 3.212 1.468 0.000 0.000 0.000 0.000
6.000 0.770 3.963 1.608 0.000 0.000 0.000 0.000
7.000 0.808 4.752 1.737 0.000 0.000 0.000 0.000
8.000 0.848 5.580 1.857 0.000 0.000 0.000 0.000
9.000 0.889 6.448 1.970 0.000 0.000 0.000 0.000
10.000 0.930 7.357 3.390 0.000 0.000 0.000 0.000
11.00 0.972 8.309 4.035 0.000 0.000 0.000 0.000
12.00 1.016 9.303 7.175 0.000 0.000 0.000 0.000
13.00 1.060 10.34 8.708 0.000 0.000 0.000 0.000
14.00 1.105 11.42 15.19 0.000 0.000 0.000 0.000
15.00 1.151 12.55 26.32 0.000 0.000 0.000 0.000
16.00 1.198 13.73 50.60 0.000 0.000 0.000 0.000
17.00 1.246 14.95 63.01 0.000 0.000 0.000 0.000
18.00 1.295 16.22 89.67 0.000 0.000 0.000 0.000
19.00 1.345 17.54 128.8 0.000 0.000 0.000 0.000
20.00 1.395 18.91 176.0 0.000 0.000 0.000 0.000
21.00 1.447 20.33 229.8 0.000 0.000 0.000 0.000
22.00 1.501 21.80 304.6 0.000 0.000 0.000 0.000
23.00 1.556 23.33 435.4 0.000 0.000 0.000 0.000
___________________________________________________________________
Name :Culvert 1
Discharge Structure
Riser Height: 0 ft.
Riser Diameter: 0 in.
Element Flows To:
Outlet 1 Outlet 2
___________________________________________________________________
Name :Lot A: Park
Bypass:No
GroundWater:No
Pervious Land Use Acres
C D,Grass,Flat(0-5%) 10.4
Impervious Land Use Acres
Roads,Flat(0-5%) 5.6
___________________________________________________________________
Element Flows To:
Surface Interflow Groundwater
Culvert 2 Culvert 2
___________________________________________________________________
Name :Culvert 2
Discharge Structure
Riser Height: 0 ft.
Riser Diameter: 0 in.
Element Flows To:
Outlet 1 Outlet 2
___________________________________________________________________
___________________________________________________________________
ANALYSIS RESULTS
Flow Frequency Return Periods for Predeveloped. POC #1
Return Period Flow(cfs)
2 year 28.552977
5 year 38.963207
10 year 55.647814
25 year 92.968818
Flow Frequency Return Periods for Mitigated. POC #1
Return Period Flow(cfs)
2 year 17.108301
5 year 31.799082
10 year 40.11682
25 year 63.861616
___________________________________________________________________
___________________________________________________________________
POC #1
The Facility PASSED
The Facility PASSED.
Flow(cfs) Predev Mit Percentage Pass/Fail
2.8553 1891 1871 98 Pass
3.3886 1409 1489 105 Pass
3.9218 1125 1027 91 Pass
4.4551 980 800 81 Pass
4.9883 837 702 83 Pass
5.5216 770 635 82 Pass
6.0548 691 589 85 Pass
6.5881 616 521 84 Pass
7.1214 533 443 83 Pass
7.6546 460 394 85 Pass
8.1879 409 334 81 Pass
8.7211 374 285 76 Pass
9.2544 336 256 76 Pass
9.7876 311 234 75 Pass
10.3209 275 216 78 Pass
10.8542 249 201 80 Pass
11.3874 227 189 83 Pass
11.9207 208 179 86 Pass
12.4539 198 171 86 Pass
12.9872 186 163 87 Pass
13.5205 179 157 87 Pass
14.0537 164 149 90 Pass
14.5870 154 140 90 Pass
15.1202 146 130 89 Pass
15.6535 137 126 91 Pass
16.1867 130 118 90 Pass
16.7200 126 113 89 Pass
17.2533 117 108 92 Pass
17.7865 111 99 89 Pass
18.3198 108 92 85 Pass
18.8530 104 87 83 Pass
19.3863 100 83 83 Pass
19.9195 94 83 88 Pass
20.4528 92 75 81 Pass
20.9861 86 69 80 Pass
21.5193 79 67 84 Pass
22.0526 74 60 81 Pass
22.5858 73 56 76 Pass
23.1191 68 52 76 Pass
23.6523 63 50 79 Pass
24.1856 62 48 77 Pass
24.7189 58 47 81 Pass
25.2521 54 44 81 Pass
25.7854 52 42 80 Pass
26.3186 49 41 83 Pass
26.8519 45 38 84 Pass
27.3852 44 37 84 Pass
27.9184 43 35 81 Pass
28.4517 41 34 82 Pass
28.9849 38 34 89 Pass
29.5182 36 34 94 Pass
30.0514 32 31 96 Pass
30.5847 31 30 96 Pass
31.1180 30 28 93 Pass
31.6512 28 23 82 Pass
32.1845 25 22 88 Pass
32.7177 23 21 91 Pass
33.2510 22 18 81 Pass
33.7842 21 18 85 Pass
34.3175 21 17 80 Pass
34.8508 19 15 78 Pass
35.3840 18 14 77 Pass
35.9173 18 13 72 Pass
36.4505 18 12 66 Pass
36.9838 17 12 70 Pass
37.5171 17 12 70 Pass
38.0503 16 12 75 Pass
38.5836 16 12 75 Pass
39.1168 15 10 66 Pass
39.6501 13 9 69 Pass
40.1833 13 9 69 Pass
40.7166 13 9 69 Pass
41.2499 13 9 69 Pass
41.7831 12 9 75 Pass
42.3164 12 9 75 Pass
42.8496 12 9 75 Pass
43.3829 12 9 75 Pass
43.9161 11 9 81 Pass
44.4494 11 9 81 Pass
44.9827 11 8 72 Pass
45.5159 11 8 72 Pass
46.0492 11 8 72 Pass
46.5824 11 8 72 Pass
47.1157 10 8 80 Pass
47.6489 10 8 80 Pass
48.1822 10 8 80 Pass
48.7155 9 8 88 Pass
49.2487 9 8 88 Pass
49.7820 9 8 88 Pass
50.3152 9 8 88 Pass
50.8485 9 8 88 Pass
51.3818 9 7 77 Pass
51.9150 9 7 77 Pass
52.4483 9 6 66 Pass
52.9815 8 5 62 Pass
53.5148 8 5 62 Pass
54.0480 8 5 62 Pass
54.5813 8 5 62 Pass
55.1146 8 5 62 Pass
55.6478 6 4 66 Pass
_____________________________________________________
___________________________________________________________________
Water Quality BMP Flow and Volume for POC #1
On-line facility volume:0 acre-feet
On-line facility target flow:0 cfs.
Adjusted for 15 min:0 cfs.
Off-line facility target flow:0 cfs.
Adjusted for 15 min:0 cfs.
___________________________________________________________________
Perlnd and Implnd Changes
No changes have been made.
___________________________________________________________________
This program and accompanying documentation is provided 'as-is' without warranty of any kind. The entire risk regarding the
performance and results of this program is assumed by the user. Clear Creek Solutions, Inc. disclaims all warranties, either
expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event
shall Clear Creek Solutions, Inc. be liable for any damages whatsoever (including without limitation to damages for loss of
business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to
use this program even if Clear Creek Solutions, Inc. has been advised of the possibility of such damages.
SECTION 4
STAGENO.AREA(ACRES)STORAGE(ACFT)(UsingEndArea)
00.556747050
10.589917040.573332045
20.62400991.180295515
30.659025641.821813285
40.694964252.49880823
50.731825733.21220322
60.769610093.96292113
70.808317324.751884835
80.847947425.580017205
90.88850046.448241115
100.929976257.35747944
110.972374978.30865505
121.015696569.302690815
131.0599410310.34050961
141.1051083811.42303432
151.1511985912.5511878
161.1982116813.72589294
171.2461476514.9480726
181.2950064816.21864967
191.3447881917.538547
201.3954927718.90868748
211.4471194220.32999358
221.5007887921.80394768
231.5555640223.33212409
241.6114451324.91562866
1"
=
4
0
'
SECTION 5
Computed Results
Computed Results
Computed Results
Computed Results
Computed Results