100-year storm BASIN 1 (Proposed Condition)

HYDROLOGY BASIN CALCULATIONS
100-year storm
BASIN 1 (Proposed Condition)
In the proposed condition, the drainage runoff from the backyards will be directed towards catch basins/storm drain
pipes which will direct the flow towards the concentration point. The drainage runoff from the frontyards will be directed
towards the gutters on the Private Driveway, Vista De Lamar, and direct the runoff to the concentration point. The
concentration point is the same point as in the existing condition for both runoffs (see the attached Drainage Map 2).
FLOW RATE: Q100 = C * I * A (Rational Method)
AREA:
A = 1.36 Acres (see Drainage Map 2, attached)
C-VALUE:
C = 0.57 (see Table 3-1, Section 4)
TIME OF CONCENTRATION:
TC = Ti
+ Tt
Where:
Initial Time, Ti
Land Use = MDR
Slope = 1 % (See Drainage Map 2, attached)
Ti = 8.4 min (see Table 3-2, Section 4)
And:
Travel Time, Tt
Tt:
Tt is the time it takes the runoff to travel along the landscaped and developed areas
after the initial travel period. Said flow will be assumed to be developed sheet flow. The time it takes the runoff to
travel from the end of the initial travel time to the concentration point is calculated using the velocity and the
distance traveled. The velocity is assumed for each specific condition and the travel distance is obtained from the
Drainage Map 2. See below for calculations:
Assumed Q100 = 3.8 cfs
At:
Q100(Avg) = 3.8 / 2 = 1.9 cfs
Assumed Velocity (V100(Avg)) = 8.3 fps (see Hydraulic Calculations, Section 4)
Then:
Tt = Travel Distance / Velocity = D / V100
Where:
Distance Traveled (D) = 460 ft (see Drainage Map 2, attached)
Then:
Tt = 460 / 8.3 = 55.42 sec = 0.9 minutes
Therefore:
TC = 8.4 + 0.9 = 9.3 minutes
HYDROLOGY BASIN CALCULATIONS
(100-year storm)
BASIN 1 (Proposed Condition) Cont….
INTENSITY CALCULATIONS:
I = 7.44 P6 TC
-0.645 (see Figure 3-1, Section 4)
Where
P6 = 2.8 in (see 100-year Rainfall Isopluvial, Section 4)
Then:
I = 7.44 (2.8) (9.3)-0.645 (see Figure 3-1, Section 4)
Therefore:
I = 4.9 in/hr per Equation
FLOW RATE:
Q100 = C * I * A = 0.57 * 4.9 * 1.36
Q100 = 3.8 CFS