This document analyzes the hydrology and hydraulics of a site for a 50-year and 100-year storm event. It calculates the total drainage area, soil type, time of concentration, rainfall intensity, runoff coefficient, and peak discharge for the site. It then sizes stormwater conveyance features like a 1'x1' rectangular channel and 4" PVC pipes to safely convey the calculated peak flows through hydraulic calculations using Manning's equation. Attachments include maps, figures, and software output to support the analysis.

1. TABLE OF CONTENTS
SECTIONS
1.0 HYDROLOGY
1.1 TOTAL AREA
1.2 OUTSIDE TRIBUTARY AREA
1.3 SOIL TYPE
1.4 TIME OF CONCENTRATION
1.5 RAINFALL INTENSITY
1.6 RUN OFF COEFFICIENT
1.7 CALCULATION OF PEAK DISCHARGE
2.0 HYDRAULIC CALCULATIONS
2.1 50 YEAR STORM EVENT
2.2 100 YEAR STORM EVENT
ATTACHMENTS
VICINITY MAP
ORANGE COUNTY – HYDROLOGY MANUAL SOILS MAP
ORANGE COUNTY – HYDROLOGY MANUAL – FIGURE D-1
ORANGE COUNTY – HYDROLOGY MANUAL – FIGURE B-3
HYDROLOGY SITE PLAN
HYDROCAD SOFTWARE OUTPUT DATA

2. 1. HYDROLOGY
AREAS
1.1 TOTAL AREA:
Lot Area = 32,354 SF
Total Drainage Areas = 17,532 SF
Total Acres = 0.402 AC
AREA 1 = 3,913 SF
Acres = 0.089 AC
AREA 2 = 13,619 SF
Acres = 0.312 AC
1.2 OUTSIDE TRIBUTARY AREA:
AREA 3 = 14,822 SF
Acres = 0.340 AC
1.3 SOIL TYPE
Soil Type C
-Taken from Orange County Hydrologic Classification of Soils Map (Plate A)
see Appendix
1.4 TIME OF CONCENTRATION
Drainage Areas: A1 & A2
Length (L) of initial area = 179.52 FT
Difference in Elevation for Initial Area (ft) = 10.82 FT
Use Single Family – 1 Acre Lot
Time of Concentration (Tc) (min.) = 5 min. 30 s
Tc was calculated from the Orange county Hydrology Manual Figure D-1 (included)

3. 1.5 RAINFALL INTENSITY
Return Period 50 Years
𝐼(𝑡) = 𝑎𝑡 𝑏
𝐼(𝑡) = (13.521)(5.5)−0.566
𝐼(𝑡) = 5.15 Intensity (in/hr)
Return Period 100 Years
𝐼(𝑡) = 𝑎𝑡 𝑏
𝐼(𝑡) = (15.560)(5.5)−0.573
𝐼(𝑡) = 5.86 Intensity (in/hr)
Values and equations taken from the Orange County Hydrology Manual
(Figure B-3) see attached.
1.6 RUN OFF COEFFICIENT
C = [ai + (
(I−Fp)ap
I
)] Orange County Hydrology Manual
Equation D-3
Where,
C = Runoff Coefficient
I = Rainfall Intensity (inches/Hour)
Fp = Infiltration Rate for Previous Areas (Inches/Hour)
ai = Ratio of Impervious Area to Total Area
Ap = Ratio of Pervious Area to Total Area (ap = 1-ai)
Impervious Area = 12,612 SF
Total Area = 17,532 SF
ai = 0.72
ap = 0.28
Fp = 0.25 in/hr
I (50) = 5.15 in/hr
I (100) = 5.86 in/hr

4. C(50) = [0.72 + (
(5.15−0.25)0.28
5.15
)]
C(50) = 0.986
C(100) = [0.72 + (
(5.86−0.25)0.28
5.86
)]
C(100) = 0.988
1.7 CALCULATE PEAK DISCHARGE (Q)
Q=C(I)(A)
C (Run Off Coefficient) 0.986
I (Rainfall Intensity in/hr A1) 5.15 CFS 0.46 CFS 1.600831
I (Rainfall Intensity in/hr A2) 5.15 GPM 206.4 GPM 718.5
A1 (Area of Section ft^2) 3913 Q(tot)= 2.06 CFS
A2 (Area of Section ft^2) 13619
C (Run Off Coefficient) 0.988
I (Rainfall Intensity in/hr A1) 5.86 CFS 0.52 CFS 1.825223
I (Rainfall Intensity in/hr A2) 5.86 GPM 235.4 GPM 819.2
A1 (Area of Section ft^2) 3913 Q(tot)= 2.35 CFS
A2 (Area of Section ft^2) 13619
50 Years
Area 2
100 Years
Inputs Outputs (Flow Q)
Area 1 Area 2
Inputs
Area 1
Outputs (Flow Q)

5. 2.0 HYDRAULIC CALCULATIONS
Using the Manning’s Equation: 𝑉 =
𝑙
𝑛
∗ 𝑅
2
3 ∗ 𝑆
1
2
Where:
n = Coefficient of Roughness
v = Water velocity down the channel (ft/sec) = flow/Cross Sectional Area
R = Hydraulic radius (ft) = cross sectional area (ft^2)/wetted perimeter (ft)
S = Gradient of channel (ft/ft)
2.1 50 YEAR STORM EVENT
1’ X 1’ Rectangular Channel
INPUT DATA OUTPUT DATA
Flow rate 2.06 CFS Depth of Flow 0.66 ft or 7.92 in
Slope (s) 0.01 FT/FT Max Velocity 3.79 FPS
Manning’s n 0.017 (unfinished PCC) Max Output Flow 2.39 CFS
Shape Channel 1’ Wide Capacity 4.2 CFS
Depth 1 FT Percent full 66%
See Attached HydroCAD Output Data
Depth of Channel > Depth of Flow
12 in > 7.92 in  OK
Design is for two 4” PVC lines
Calculations are for two 4” PVC line therefore flow is input as half from maximum flow from channel
INPUT DATA OUTPUT DATA
Flow rate 1.03 CFS Depth of Flow 0.17 FT or 2.04 IN
Slope (s) 0.67 FT/FT Max Velocity 23.32 FPS
Manning’s n 0.010 Max Output Flow 1.03 CFS
Shape 4” Dia PVC Capacity 2.03 CFS
Depth 4 IN Percent full 51%
See Attached HydroCAD Output Data
Depth of Pipe > Depth of Flow
4 in > 2.04 in  OK

6. 2.2 100 YEAR STORM EVENT
1’ X 1’ Rectangular Channel
INPUT DATA OUTPUT DATA
Flow rate 2.35CFS Depth of Flow 0.74 FT or 8.88 IN
Slope (s) 0.01 ft/ft Max Velocity 3.90 FPS
Manning’s n 0.017 Max Output Flow 2.18 CFS
Shape Channel 1’ Wide Capacity 4.2 CFS
Depth 1 FT Percent full 74%
See Attached HydroCAD Output Data
Depth of Channel > Depth of Flow
12 in > 8.88 in  OK
Design is for two 4” PVC lines
Calculations are for two 4” PVC line therefore flow is input as half from maximum flow from channel
INPUT DATA OUTPUT DATA
Flow rate 1.18 CFS Depth of Flow 0.18 FT or 2.16 IN
Slope (s) 0.67 FT/FT Max Velocity 24.1 FPS
Manning’s n 0.010 Max Output Flow 1.18 CFS
Shape 4” Dia PVC Capacity 2.03 CFS
Depth 4 IN Percent full 54%
See Attached HydroCAD Output Data
Depth of Pipe > Depth of Flow
12 in > 2.06 in  OK