Objective: To estimate the water yield in a catchment (of a lake, pond, stream or river).
Catchment (Drainage area, Drainage Basin or Watershed): The area of land draining water into a water body (fig1). Two neighboring catchments are separated by a ridge (highest land that separates two watersheds). The areal extent of a catchment is obtained by tracing the ridge on a Topographical Map (fig2). Based on the spatial extent, catchments are classified given in table 1.
Fig1: Catchment Map
Fig2 : Topographic map indicating different features
Table1: Classification of Catchments in India
Sl.no | Type of Catchment | Area in 1000 Hectares |
1 | Micro-watershed | Less than1 |
2 | Milli-Watershed | 1 – 10 |
3 | Sub-Watershed | 10 – 50 |
4 | Watersheds | 50 – 200 |
5 | Sub-Catchments | 200 – 1000 |
6 | Catchments | 1000 – 3000 |
7 | Basin | 3000 – 25000 |
8 | Region | Greater than 25000 |
Contours: Contours are the imaginary lines on the earth surface with equal elevation. In a topographic map of 1:50000 scale, contours are at every 20 metre interval. Contours with decreasing altitudes with respect to an higher altitude contour indicates hillock, on the contrary increasing contours along a low altitude contour indicates Valley.
Steps involved in Delineating a Catchment:
Similarly, other measurements such as distance, coordinates, centroids etc. along with other vector operations could be made using Calculator TOOL.
Rainfall: Daily Rainfall data at different locations are observed using rain gauges as millimeter and maintained by India Meteorological Department (IMD), Public Works Department (PWD), Water resources Development Organisation (WRDO), Agriculture Department, Revenue Department, Forest Department, etc, and is as depicted in fig.3. Each rain gauge represents rainfall over an area assuming rainfall is uniform in its vicinity
Fig 3: Rain Gauge stations
.
To analyze the rainfall trend and dynamics over a region, seasonal and annual rainfall data for atleast 10 to 20 year.
Steps involved in analyzing rainfall trend in the basin:
Extraction of Land use details from Google Earth: Google earth provides satellite images with high resolution, this could be used to identify different types of land uses in the basin.
Steps involved in extraction of landuse features from Google earth:
Example: Agriculture as a layer, Forest as a layer, water body as a layer etc
Assessment of water yield: Water yield or Surface Runoff is the precipitated water that drains to a water body in a catchment. Surface runoff occurs during monsoon. Factors affecting Runoff are the Slope, Drainage, Land use, Soil Characteristics, Rainfall. The total quantity of water that can be expected in a stream in a given period of time such as monthly, annual etc… is referred to as Runoff Yield.
Runoff Yield (Q) as kilo.cubic metre (Million Litres) is estimated empirically (eq.1) as a function of Rainfall (P) in mm and Area under different land uses (A) in Hectares.
Q = (C*P*A)/100 1
Where Q = Runoff Yield in Million litres
C = Runoff Coefficient of a particular land use
A = Area under land use in Ha
P = Mean Monthly rainfall in mm (average of 10 – 15 years)
Runoff Coefficient under different land use is as specified in table 2.
Land Use | Runoff Coefficient |
Forests | 0.1 – 0.2 |
Plantations | 0.2 – 0.6 |
Agriculture | 0.4 – 0.7 |
Open Spaces, Grasslands | 0.5 – 0.8 |
Built-up | 0.7 – 0.9 |
Rocky Areas | 0.8 - 1.0 |
Water Yield Estimation
Location Description | |||||||||
Catchment Extent | Latitude | Longitude | |||||||
min | min | ||||||||
max | max | ||||||||
Catchment Area in Ha | |||||||||
Annual Rainfall in mm | |||||||||
Land Use | Area in Ha A | Runoff Coefficient C | |||||||
Forests | |||||||||
Plantations | |||||||||
Agriculture | |||||||||
Open Spaces, Grasslands | |||||||||
Built-up | |||||||||
Rocky Areas | |||||||||
Monthly rainfall P in mm | January | February | March | April | May | June | |||
July | August | September | October | November | December | ||||
Seasonal Catchment Yield in Million Litres Q = (C*A*P)/100 | |||||||||
Land Use | January | February | March | April | May | June | |||
Forests | |||||||||
Plantations | |||||||||
Agriculture | |||||||||
Open Spaces, Grasslands | |||||||||
Built-up | |||||||||
Rocky Areas | |||||||||
Gross Yield Q | |||||||||
Land Use | July | August | September | October | November | December | |||
Forests | |||||||||
Plantations | |||||||||
Agriculture | |||||||||
Open Spaces, Grasslands | |||||||||
Built-up | |||||||||
Rocky Areas | |||||||||
Gross Yield Q | |||||||||
Annual Catchment Yield = (Σ Q) | Million Liters |
Citation: Ramachandra T.V. Asulabha K.S., Bharath H. Aithal, Bharath Settur, Durga Madhab Mahapatra, Gouri Kulkarni, Harish R. Bhat, Sincy Varghese, Sudarshan P. Bhat and Vinay S., 2014. Environment monitoring in the neighbourhood., ENVIS Technical Report : 77, February 2014, Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore 560 012.
Contact Address : | |||
Dr. T.V. Ramachandra Energy & Wetlands Research Group, Centre for Ecological Sciences, New Biological Sciences Building, 3rd Floor, E-Wing, Lab: TE15 Indian Institute of Science, Bangalore – 560 012, INDIA. Tel : 91-80-22933099 / 22933503(Ext:107) / 23600985 Fax : 91-80-23601428 / 23600085 / 23600683 [CES-TVR] E-mail : cestvr@ces.iisc.ernet.in, energy@ces.iisc.ernet.in Web : http://wgbis.ces.iisc.ernet.in/energy |