1st
International Conference on Rain Water Cistern Systems
Honolulu, Hawaii,
USA  June 1982
Section
3: Design, Cost, And Policy
Page 102
Hydrographs for RoofTop
Runoff Under Varying Rainfall Conditions
Bhaskar
Datta
Flood Control Dept. Gauhati, INDIA
G.C. Mishra
University of Roorkee, INDIA
Introduction
With increasing population, water supply systems may fail to satisfy the demand
for water. In arid and semiarid regions, especially, the source of water is often
depleted. Rain water collected from roof surfaces and utilized through cistern
systems can augment the usual domestic supply without large expenditures or energy
and can thus meet water shortages.
To design gutters and a cistern system, knowledge of the water surface profile
and flow hydrograph is necessary. The kinematics of flow over roof surfaces can
be determined from available studies of overland flow. Many investigators have
dealt with the problem of overland flow under uniform, excess rainfall either
by using the method of characteristics (Behlke 1957; Henderson 1964; Wooding 1965;
Morgali and Linsley 1965; Abbott 1966; Brakensiek 1966) or by solving the mass
balance equation by assuming a linear relationship between outflow and storage
(Horton 1938; Izzard 1944). Wooding (1965) has dealt with the problem of overland
flow under a constant, uniformly distributed rainfall of finite duration with
an analytical solution for a hydraulic model based on the method of characteristics
for flow over a plane, which is part of a Vshaped catchment. In reality, the
rainfall intensity is not uniform; instead, the distribution is skewed. The typical
time variant design of rainfall distribution patterns described by Rodda, Downing
and Law (1976) for a 10year, 5year and annual return frequencies are shown in
Figure 1. Water surface profiles and flow hydrographs for roof surfaces for such
design storms can be determined for different intervals of time by using the characteristics
equations.
PDF of full document (6pp, 140kb)

Note: The IRCSA proceedings
section is still new and under active management, If you find any problems,
ommissions or corrections please contact
the administrator so we can put things right. 
