HomeMy WebLinkAboutDrainage Calcs 071723PRE‐CONSTRUCTION
WATERSHED AREA A I25 I100 C25 C100 Q25, CFS Q100, CFS
1 (OFF SITE) 2,162 sf 0.05 ac 7 8.5 0.55 0.62 0.19 0.26
2 (ON SITE) 324,609 sf 7.45 ac 7 8.5 0.55 0.62 28.69 39.27
28.88 39.53
POST‐CONSTRUCTION
WATERSHED AREA A I25 I100 C25 C100 Q25, CFS Q100, CFS
1 (OFF SITE) 2,162 sf 0.05 ac 7 8.5 0.6 0.7 0.21 0.30
2 (ON SITE) 324,609 sf 7.45 ac 7 8.5 0.6 0.7 31.30 44.34
TOTAL 326,771 sf 7.50 ac 7 8.5 0.6 0.7 31.51 44.63
31.51 44.63
DIFFERENCE, PRE VS. POST 2.63 5.10
Post‐Construction:
Drainage Area (A) = 7.50 acre
Runoff Coef. (C25‐post) = 0.60
Runoff Coef. (C100‐post) = 0.70
Intensity (I25) = 7 in/hr
Intensity (I100) = 8.5 in/hr
Discharge Flow (Q25‐post) = 31.51 cfs
Discharge Flow (Q100‐post) = 44.63 cfs
Time of Conc. (tc‐post) = 10.0 min, (HydraCAD)
Allowable Outflow Peak
Discharge Flow (Q25‐pre) = 28.88 cfs
Storage Required
s = 1/2 x (Q25‐post ‐ Q25‐pre) x tb x 60
tb = 2.67 x tp
tp = D/2 + 0.6Tc‐post
D = 3.0 min
tp = 7.5 min
tb = 20.0 min
s = 1,577 cf
11,798 gallons
TOTAL LEAVING PROPERTY
TOTAL LEAVING PROPERTY
DESIGN OF DETENTION TANKS
SITE DEVELOPMENT
MADISON HEIGHTS
PHASE IV
FOR CENTRAL ARKANSAS HOUSING CORPORATION
BY: HARBOR ENVIRONMENTAL, INC.
JULY 14, 2023
Storage Provided
2005.34759 Storage = 2005.3 cf
15,000 gallons
Three (3) 5,000 gallon detention underground tanks
with controlled outlets
Outlet Structure
Outlet Sizing:
D =15in
H = 3.3 ft
Q =3.78D2H0.5
Q = 10.73 cfs per inlet
For Qin (Q25‐pre) = 9.63 cfs, use 1 x 15" opening per tank
Overflow Outlet Sizing:
D = 18 in
H = 3.8 ft
Q =3.78D2H0.5
Q = 16.58 cfs per inlet
For Qout (Q100‐post) = 14.88 cfs, use 1 x 18" opening per tank
Date:C901Harbor5800 Evergreen DriveLittle Rock, AR 72205Ph (501) 663-8800Fax (501) 588-0123www.harborenv.comX XX-XX-XXXXX
Scale:1"=30'Project Number:Drawn By:AHR/AESChecked By:AHR08-12-2022CAHC-22185CENTRAL ARKANSAS HOUSING CORPORATION
PRELIMINARY DRAINAGE REVIEW - PRE-CONSTRUCTION
MADISON HEIGHTS - PHASE IV SCALE: 1" = 30'30'30'0'15'
Harbor5800 Evergreen DriveLittle Rock, AR 72205Ph (501) 663-8800Fax (501) 588-0123www.harborenv.comX XX-XX-XXXXX
Scale:1"=30'Project Number:Drawn By:AESChecked By:AHR11-18-2022CAHC-22185CENTRAL ARKANSAS HOUSING CORPORATION
PRELIMINARY DRAINAGE REVIEW - POST CONSTRUCTION
MADISON HEIGHTS - PHASE IV SCALE: 1" = 30'30'30'0'15'Date:C902