RWRE–A WEB BASED OPEN SOURCE GIS TOOL FOR ROOF WATER RUNOFF ESTIMATION

In rural areas of low rainfall, roof top rainwater harvesting is an ideal method for collecting rainwater because it helps not only in meeting at least a part of the water requirement but also prevents storm runoff and flooding during heavy rains. Individual houses and buildings are the best units for collecting the roof water. In this work an interactive web-based GIS tool named RWRE (Roof Water Runoff Estimator) has been developed to estimate the runoff from the rooftops of the buildings. REWE tool was designed using open source geospatial development tools like Geoserver and OpenLayers. The developed tool provides a polygon drawing tool to delineate the rooftop of individual buildings. The area of rooftop of each building is listed. The runoff coefficient for each building is also taken as input. The annual average rainfall is required to calculate the total amount of water available from the rooftops of all the delineated buildings. For the testing and development of RWRE, the municipal area of Bhopal city of Madhya Pradesh was taken. This tool can be configured to be used for any rural or other area and can be of great help in planning and designing of the roof water harvesting structures as it quickly and accurately estimates the volume of water available from the buildings.


Introduction
Rainwater harvesting is an age old technique of collection of rain water from localised catchments and storing it in reservoirs or tanks or infiltration of surface water to subsurface water.The process of collecting and storing runoff from rooftops is called roof water harvesting. In residential areas roof top rainwater harvesting is an ideal method for collecting rainwater because it not only helps in meeting some part of water requirement but also reduces storm water runoff and flooding of roads during heavy rainfall. Individual houses and buildings are the best units for collecting the roof water.
Rooftop water harvesting has many advantages over the various other techniques of water harvesting.Some of the advantages of rooftop rainwater harvesting are mentioned below: a) Rooftop rainwater harvesting is a suitable option for augmenting groundwater recharge/storage in areas, where natural recharge is reduced considerably due to less availability of land for percolation of rainwater.

b)
Rooftop rainwater harvesting can be used to add to the domestic requirements in rural areas.
c) The water collected from the roof tops use to be soft, bacteriologically safe and free from organic matter, because the roof catchments are usually cleaner as compared to the ground level catchments.

d)
Collecting water from rooftops helps to improve the quality of groundwater by dilution.
e) The rainwater harnessed from the rooftops can be utilised at the time of water scarcity.
f) The structures required for harvesting rainwater are simple, economical and eco-friendly.  Radhakrishna (2007), isolated attempts at rain water harvesting will not produce desired results, but a concrete action plan will be required to be drawn and implemented, making it a mass movement for water harvesting. OpenLayers.

Runoff Calculation
The volume of water available from the rooftop harvesting can be calculated by following formula:

W = T x A x R
Where, W is the volume of water available from rooftop water in liters, T is total area of the roof in Sq. m., A is the annual rainfall in mm and R is the coefficient of runoff. Roof area should be measured on the map i.e. the area projected on a horizontal surface.
Runoff coefficient for any catchment is the ratio of the volume of water that runs off a surface to the volume of rainfall that falls on the surface (Rainwater Harvesting and Utilisation Book 2). It accounts for the fact that all the rainfall falling on a catchment cannot be collected. The nature of roofing material can greatly affect the quality and quantity of runoff water. Impervious roofing materials with smoother and cleaner surfaces contribute to better quality and quantity of water. The runoff coefficient of untreated ground sloping less than 10 per cent will be in range of 0 to 0.3 and with rocky natural pavement will be in range of 0.2 to 0.5 (Pacey, 1989

4) HTML and CSS
The framework of application using the above mentioned tools is given in Figure 1  GeoServer is an open source software server written in Java. GeoServer allows users to share and edit geospatial data. It is designed for inter-operability and it can publish data from any major spatial data source using open standards.
GeoServer allows users to view and edit geospatial data as Web Map Service (WMS) and Web Feature Service (WFS). In this application both WMS and WFS were used.

Apache
Tomcat is an open source Javabased web and servlet container, used to host Java-based applications (Khare, 2012). Its major function is to respond to the requests from the clients i.e. web browsers. Apache Tomcat can easily link to GeoServer.

OpenLayers is one of the most important components of RWRE. OpenLayers is an open
source client side JavaScript library for making web maps, viewable in nearly any web browser (Hazzard, 2011). It is based on AJAX (Asynchronous Java Script and XML) technology.
OpenLayers is a client side library and it does not require any special server side software or settings. It can be used even without downloading anything. OpenLayers makes it easy to put a dynamic map in any web page (Openlayers.org).OpenLayers was used in this application to write all the map related functions.

Scope of the Work
The scope of our work is aimed at developing an easy to use web based GIS tool, which can be used as to compute the volume of

Functioning of Application
The application runs in a web browser and is quite easy to uses.The developed application RWRE provides the following functionalities:   volume from polygon is also stored.

Conclusion
The developed application can be used for the runoff estimation from the rooftops of the buildings of a residential or commercial area.
It can be used in rural areas to estimate the roof water runoff from the large buildings like cold