HomeMy WebLinkAboutDrainage Analysis 121125
P.O. BOX 241549 LITTLE ROCK, ARKANSAS 72223 PHONE: (501) 214-9141
December 10, 2025
Mr. Arsanious Hanna, P.E.
City of Little Rock
Planning & Development
723 W. Markham St.
Little Rock, AR 72201
RE: Kanis Commercial Park
Preliminary Drainage Analysis
Mr. Hanna,
This letter is to accompany the submitted Preliminary Plat for the subject project and provides a
summary of the preliminary drainage analysis. The project will consist of 7 commercial lots located off of
Kanis Rd. The project will include paving, drainage, sidewalk, water, sewer, and additional utility
extensions.
The existing site is a clear, undeveloped 14.43-acre parcel with steep to moderate grades. The site drains
both north and south into existing drainage swales/ditches ultimately discharging into a ditch located
along the west/south-west corner of the property.
The rational method was used to determine the existing peak runoff for the watershed. Considering the
existing cover an existing rational coefficient of 0.40 was used for the site. Time of concentrations were
calculated using the TR-55 method. The existing site drains two ways with both outlets ultimately
draining into the existing drainage ditch at the southwest corner of the property. The preliminary
analysis includes two individual drainage basins incorporating both on-site and off-site drainage areas.
These drainage basins are summarized below in Table 1 and are shown on the Preliminary Drainage
Analysis drawing.
EXISTING DRAINAGE AREAS
Release
Point Name Area
(acres)
Composite
Runoff C
Tc
(min.)
Q25
(cfs)
Q100
(cfs)
A
#1
Off-site 1.67 0.71
17
27.78 33.73 On-site 9.35 0.4
#2 Off-site 8.94 0.75 13
46.28 55.94 On-site 5.33 0.4
Total Site Runoff 67.52 81.73
P.O. BOX 241549 LITTLE ROCK, ARKANSAS 72223 PHONE: (501) 214-9141
The existing drainage patterns will largely remain unchanged after construction. Proposed storm
drainage infrastructure will be designed to convey the off-site and on-site run-off to the east drainage
ditch. Detention will be provided on each individual lot as they develop. Detention basins will be sized to
mitigate any additional post-development stormwater runoff per the City of Little Rock Drainage
Manual.
Sincerely,
Jacob White, PE
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX15.0'
25.0'15.0'15.0'10.0'SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS S S S S S S S S S S S S S S S S S S S S S S S S S S S SSSS SSSSSSSS S
W W W W W W W W W W W W W W W W W W W W W W W W W W W W W W WWW
>>>>>>>>>>>>>>>>>>>>DRAINAGE AREA #1
AREA: 11.02 Acre
C: 0.44
TOC: 17 MIN.>>>>>>>>>>>>>DRAINAGE AREA #2
AREA: 14.27 Acre
C: 0.51
TOC: 13 MIN.
FLOW SEGMENT #1
SCS Sheet Flow
L=100 FT
S=3.45%
Travel Time=11.18
FLOW SEGMENT #1
SCS Sheet Flow
L=100 FT
S=8.26%
Travel Time=7.88
FLOW SEGMENT #2
SCS Shallow Concentrated Flow
L=574 FT
S=8.15%
Travel Time=2.08
FLOW SEGMENT #3
SCS Channel Flow
L=700 FT
S=1.49%
Travel Time=3.01
FLOW SEGMENT #2
SCS Shallow Concentrated Flow
L=446 FT
S=5.90%
Travel Time=1.90
FLOW SEGMENT #3
SCS Channel Flow
L=1,446 FT
S=2.97%
Travel Time=3.78
RELEASE POINT A
25 RAHLING CIRCLE, SUITE A-2 LITTLE ROCK, ARKANSAS 72223
PHONE: (501) 214-9141
CIVIL ENGINEERING - CONSULTING SERVICES - LAND SURVEYING
JOE WHITE & ASSOCIATES, INC.