Report on Urban Stormwater Design: OSD and Easement Drainage UTS

This report presents the design of property drainage for a subdivision, focusing on On-Site Detention (OSD) systems and easement drainage. It includes the design of easement drainage with specifications for overland flow paths and the design of an OSD system using the UPRCT method, covering adjustments for areas not draining to OSD, orifice size calculations, and HED adjustments. The report also checks the adequacy of a 450 rcp pipe size from the OSD to the street's 600 mm rcp, incorporating pit and loss coefficients and providing sample SWMM input data. Key aspects include calculations for storage requirements, peak discharge, weir flow, and the minimization of nuisance by distributing storage. The design adheres to AS 3500.3 standards and includes relevant level information, plan and sections of the OSD, orifice details, sedimentation pits, and inspection pits.

Running head: URBAN STORMWATER DESIGN 1
Urban Stormwater Design
(Report)
Name
Institution

URBAN STORMWATER DESIGN 2
OSD and Easement Drainage
1. Easement Drainage Design;
From, AS 3500.3, 2003, Easement width for:
Stormwater pipe <= 825 = 3.0 m.
Stormwater pipe <= 825 mm diameter and Sewer pipe 225 mm diameter = 4.0 m.
Available Drainage Diameter, = 525 mm,
Adapt Easement Width = 3.0 m
Easement overland flow path; From lot 10 – 9 – 8 -7 – 6 – 5 – 4 – 3 – 2 – Point B.
2. OSD System Design using UPRCT method.
i. Adjutments for area not draining to OSD
Total Site Area =0.5996ha
Initial Storage Requirement 470 x 0.1 =47m3
Storage per area ha 47/0.5996 =78.39m3/ha
Basic PSD = 80 l/s/ha =0.008m3/s
PSD adjustment (Vol/PSD adjustment – from AS 3500.3, 2003
Design Charts with 78.39/ha) = 80l/s/ha

URBAN STORMWATER DESIGN 3
Final PSD 80 x 0.5996 = 47.968l/s
ii. Orifice Size
Peak Discahrge to DCP
Q = CIA/360 (Q- discharge in m3/s, C- runoff coefficient, I – 100 year rainfall intensity mm/hr,
A – Area)
= 0.8 x 224 x 0.5996/360
=0.2984m3/s
= 298.47 l/s
Weir peak flow
Qweir = Inflow to DCP – PSD
= 298.47 – 47.97
=250.5/1000
= 0.2505
Q Weir = CL H3/2
C – Coefficient of weir
H – flow depth over weir in m

URBAN STORMWATER DESIGN 4
L – weir length
0.2505 = 1.6 x 1 x H2/3
H = 0.07256m
Orifice diameter (d)
Q = CA √ 2 g h
C – Orifice discharge coefficient (0.62)
A – area of orifice in m2
g – acc due to gravity 9.81
d – orifice diameter
h – water depth above centre of orifice
d = 2.505 x 0.00635 / √0.5910.5
= 0.0206
=20.6mm
HED Adjustment
HED = PSD x √ h min/h max
=47.968 x √ ¿ ¿)

URBAN STORMWATER DESIGN 5
=44.12l/s
Check with HED exceeds 75% of PSD i.e 35.976, OK
Mean discharge = (44.12 + 47.968) / 2
= 46.044 l/s
Mean discharge/hectare = 46.044/0.5996 =76.79l/s/ha
SSR From Design Charts for PSD 76.9 = 490 m3/ha
Needed storage Volume
Final SSR = 490 x 0.5996
=293.804 m3
Minimize Nuisance by distributing Storage
Using charts for 1 year ARI, percentage of total storage;
0.16 x 293.804 = 47.00 m3
Check 450 rcp pipe size from the OSD to the 600 mm rcp in the street.
Adequate.
Pit and Loss Coefficients
Given full outflow from junction pit, upstream pie flow = Qu, flow out of pit = Qo, flow from
lateral pipes, flow from tank level = Qg and pit loss coefficient = k,

URBAN STORMWATER DESIGN 6
Pit and Loss Coefficients range from 0.5 – 2.5
SWMM sample input data
$RAIN
A1 '1-hour rainfall data for Oolitic, IN'
A2 'Continous data from 1948 to 1999'
* KODEA KODEPR KOVER
B0 0 1 1
* IFORM ISTA IDECID IYBEG IYEND IYEAR ISUM
MIT
NPTS IFILE A NOSTAT
B1 3 9999 1 19490723 19991226 0 1 24
0 0 0.4 1
* THISTO METRIC KUNIT FIRMAT CONV F1 F2 F3
F4 F5 F6 F7
B2 60 0 1 '(2I4,2I2,25I3)' 0.01 1 2 3
4 5 6 7
*
$ENDPROGRA
M

URBAN STORMWATER DESIGN 7
References
STANDARDS AUSTRALIA. (2015). Australian Standard ™ Plumbing and drainage Part 3:
Stormwater drainage. AS 3500.3 .
VICTORIAN BUILDING AUTHORITHY. (2015). Australian/New Zealand Standard Plumbing
and drainage - Part 3: Stormwater Drainage. AS 3500.3 .