QUESTION
Preparation of environmental building guidelines for Hyderabad, Andhra Pradesh : Need help in designing a storm water runoff reduction calculator

We are doing a study for HUDA (Hyderabad Urban Development Authority) “Preparation of Environmental Building Guidelines for Hyderabad”. As a part of this project, Im trying to develop a Storm Water Runoff Reduction Calculator which is primarily aimed at comparing the runoff volume reduction between a virgin site storm water run-off base case and the proposed project with SUDS/ LID interventions runoff. The interventions proposed are permeable pavements, drainage swales, infiltration trenches, retention ponds, etc. The scale of operation of this calculator will be at a large site level, community or NEIGHBOURHOOD level and not at the individual building level. I need help with the following points-

•Base-case runoff volume calculator includes deduction of PET and permeation losses from the total runoff volume – I have been able to dig out detailed PET calculators, which Im sure will reduce the user-friendlyness of the calculator. Can I use any minimum value/ percentage as a thumb rule PET+ permeation loss as may be applicable for Hyderabad – for eg: 5% - 7%?

•I understand that the Soil types in Hyderabad are Red Sandy or Black Cotton soils. I have read earlier enquiries giving the infiltration rates of various soil classes- Black cotton soil falls under Silty Clay loam soil category, but I have no idea about the Red sandy soil – information required. In the same breath, I need confirmation whether Runoff coefficient as a determinant for water flow on any particular surface, is it the exact opposite of Infiltration rate or not?

•As mentioned above, my intent is to measure the runoff volume reduction
efficiency of given SUDS/ LID techniques, thorough this calculator. However, I have no information on the efficiency comparables of each of these components or how the efficiency can be calculated. Have been unable to get any similar tool applicable to Indian standards. There is vast data and simulators available online for rooftop rainwater harvesting, but very little on Site level Storm water control – need leads/ literature to help me with this.

Ultimately the tool needs to be user-friendly and least cumbersome so as to increase its stake-holder buy-in. Kindly help with appropriate advice.

Additional information:
We are offering our consultancy for HUDA (now HMDA) for developing Environmental Building Regulations and Guidelines (EBRGs) for the Hyderabad Metropolitan area, along with TERI – New Delhi. The intended end use of the requested information is entirely for the public domain. All the guidelines and calculation tools being developed are for open access to the general public to help them construct green buildings.

 Pallavi Damodara
pallavi@terraviridis.co.uk

by
19 September 2008