LEED's Certification : Advice Required! - Chennai
Submitted by iwp on February 25, 2009 - 20:45
I am working with a company which is involved in Green Building consultancy in Chennai. As part of our work, we are involved in certification of buildings for LEED- Green Building category. One of the criteria for getting certification involves effective stormwater management. The requirement statement is phrased as follows,
"Implement a stormwater management plan that infiltrates, collects and reuses runoff or evapotranspirates runoff from at least 15% of the precipitation falling on the whole project site both for an average weather year and for the two year, 24-hour design storm"
Currently I am working on two project for Chennai. Here are the problems we are facing
1. What is a "Two year, 24- Hour design storm and how can it be determined?
2. What is the difference between "Average weather year" and " 2 year-24 hour design storm"
3. What would be the intensity of rainfall in mm/hr for Chennai for both "average weather year" and " 2 year-24 hour storm"?
4. Should the detention facilities have sufficient capacity to hold a 24 hour storm run-off?
5. How should the relevant rainwater harvesting structures be designed?
Krithikha Muthukrishnan
Comments
1.
What is a "Two year, 24- Hour design storm and how can it be determined?
Two year 24 hour storm is that rainfall in 24 hours which is expected to be exceeded once in 2 year. It is a probabilistic value.
This is obtained from rainfall frequency analysis from long term rainfall data say for 20 -25 years. The hourly/daily rainfall data for long term period can be obtained from IMD by paying them the requisite fees. Based on that storm frequency analysis is done.
A simple frquency distribution analysis is described in CPHEEO manual/IRC SP 50. The more accurate probability based analysis can be obtained from Applied Hydrology by Van Te Chow or any other good book on hydrology. or there are lot of materials on net.
This space is too small to describe the analysis, which involved some amount of mathematics
2. What is the difference between "Average weather year" and " 2 year-24 hour design storm"
The question is not clear. May be you mean average year 24 hour storm. This is the simple average of a long term rainfall data. 2 year-24 hour design storm is already expected.
3. What would be the intensity of rainfall in mm/hr for Chennai for both "average weather year" and " 2 year-24 hour storm"?
You have to get it by analysis, unless someone is kind enough to disclose their analysed data. you can approach Chennai Metro. I can recall some consultancy study was done in Chennai where IDF curves and storm analysis of different return period.
If I recall correctly IRC SP 50 has given a value of 25 mm/hr for 60 mins duration with frequency of 1 in 1.25 yrs.
4. Should the detention facilities have sufficient capacity to hold a 24 hour storm run-off?
That will be quite a large detention system depending on your catchment area. The size of the detention system is largely dependent on what is your total runoff, how much you can store and how much you can safely discharge.
5. How should the relevant rainwater harvesting structures be designed?
Too generalised question. As you are part of a consultancy service try to find out the answer yourself, from the book Rain Water Harvesting Manual, available in net: http://megphed.gov.in/knowledge/RWHManual.htm
2.
Dear Krithika,
We have studied your query and reply as follows:
1. We are a Ngo based in Delhi and have been providing design for applicants for a token fee to meet with our costs and efforts.
2. We do provide also training and guidance to the applicants, on plan, design, implementation, to operate and for carry out regular maintenance on RWH.
3. Also would provide the mechanism to arrive at and for planning data on potential catchments, zoning of the site and positioning of RWH units, reuse or recharge mechanisms Etc.
These are intricate precise measurements and are assessed to deduce the data to arrive at the RWH system, and the units at the zones Etc. for recharge/ reuse Etc.
4. The contributions in way of token fees received by us help facilitate our providing extension support to needy communities, on awareness and participation, water-conservation, supply and demand side management Etc.
5. We have implemented projects on RWH, WWT, Composting of bio-wastes and appropriate greening of both outdoor and indoor plantation.
We work in schools, colleges, Institutions and Ngos to provide environmental awareness, water-literacy Etc.
6. In this connection , you would be able to cite a water-themed calendar with a relevant fact-sheet in this India Water Portal site . We request you to peruse the same and also pass to interested friends who can become aware on the notings in the calendar and work for the environmental good in communities.
As Holi- “Festival of colurs” is already on we have a slogan- “Play holi- herbal only” - it is good for man and environment.
With well wishes from Vigyan Vijay,
Er. Ajit Seshadri
http://www.vigyanvijay.org
ajit.seshadri@vigyanvijay.org
Er. Ajit Seshadri,Head- Environment, The Vigyan Vijay Foundation
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