HomeMy WebLinkAboutCDP 2016-0006; MFD-01; HYDROLOGY CALCULATIONS; 2017-04-10Victor Rodriguez-Fernandez, PE.
1283 E Main St., Ste 109, El Cajon, CA, 92021
en~ineervictorrf@aol.com PH: (760) 357-2434
HYDROLOGY CALCULATIONS
for
2637 JEFFERSON ST., Carlsbad
Victor Rodriguez-Fernandez, RCE 35373
APR 11 2017
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4/07/2017
Description
Existing property is a flat 0.25 Acre residential lot draining with about a 1 % slope
towards the West towards an existing multi-family development that is accepting the
existing flows with an exisitng retaining wall. Existing structures and pool to be
demolished. No offsite drainage flows were observed.
The project proposes 4 Apartment Units structure with permeable pavers
driveway and landscaping. There will be an increase of 704 SF the impermeable surface
(from 4152 SF to 4856 SF).
The drainage proposed will be directed towards the same west property line.
There will be no increase of flows by mitigating the imperviousness surfaces increase by
providing permeable pavers and 3" Landscape ponds to increase the Time of
Concentration of the flows and decrease the peak flow.
The expected proposed conditions runoff will be less than the existing conditions
runoff.
Calculations:
EXISTING CONDITIONS
tributary Area= 0.25 Ac (same area as proposed tributary area)
C = 0.55 (Per Table 2)
L=l50' S = 1%
1/2
1.8 X (1.1-0.55) X (150)
Tc -----------------------------12.1 Min (Fig. 3-3) -I= 4.2 (Fig. 3-1)
1/3
(1)
Q 100 =CIA= 0.55 x 4.2 x 0.25 = 0.58 CFS Sheet Flow
PROPOSED CONDITIONS
Tributazy Area = 0.25 Ac
C = 0.70 (Per Table 2)
L1 =200' H2-Hl = 58.3 -56.5 = 1.8'
1/2
1.8 X 0.40 X (200)
S =0.9%
Tc -----------------------------= 10.7 Min (Fig. 3-3)
1/3
(0.9)
The initial To at the 3" Landscape pond# 1 area with initial area of 700 SF, pond volume
286SF@ 3" (V=72CF), assuming 100 yr Intensity of 4.2 in/hr
To= 72CF I (4.2/12) 700 = 0.29 Hrs= 17.6 min
L2 = 150' S = 1% NOT CONSIDERING PAYERS DETENTION TIME
1/2
1.8 X (0.40) X (150)
Tc -----------------------------= 8.8 Min (Fig. 3-3)
1/3
(1)
Total Tc= 10.7 + 8.8 = 19.5 min -I= 3.1 (Fig. 3-1)
Q 100 =CIA= 0.7 x 3.1 x 0.25 = 0.54 CFS Sheet Flow
NO INCREASE OF RUNOFF EXPECTED