ENVIS Technical Report: 77, February 2014
http://www.iisc.ernet.in/ ENVIRONMENT MONITORING IN THE NEIGHBOURHOOD
[WORKBOOK]
http://wgbis.ces.iisc.ernet.in/energy/
Energy and Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560012, India.
*Corresponding author: cestvr@ces.iisc.ernet.in
WATER YIELD IN THE CATCHMENT

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:

  1. Scan the respective topographic map
  2. Use QGIS, Geo-reference or assign the co-ordinates
  3. Digitise waterbody as polygons and Stream network as line features.
    1. Create New features as line or polygon
      Go to Layers, New Shape file Select Line or Polygon feature based on the feature to be delineated, add attributes and save.
    2. Load the new shape files created, click on toggle editing, click on add feature and start delineating the feature, save the edits. And stop toggle editing.
  4. With respect to the water body, digitize its catchmentas polygon feature.
  5. Compute the spatial extent of the catchment. To measure the Area, right click on the catchment layer, click on properties, toggle editing, add column (the same procedure could be adopted to define the attribute), provide the details of the attribute such as attribute name, type such as text, integer or float and then ok.Click on the Field Calculator, click on update field and select the field to be updated (Area). Add the Area Operator to the field calculator expression to estimate the area of the polygon (Catchment). Save Edits and Stop Toggling.
  6. Click on the Open Attribute to obtain the information about the area estimated. [very important: if you have the coordinate system in latitude longitude degree decimal coordinate system, are would be in square degrees, if the coordinate system is UTM then the area would be as square metres. To convert square degrees to hectares multiply the area measured with 1100*1100, and to convert square metres to hectare divide area measured by 10000]. In the above example demonstrated, area is 152.5 Hectares.

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: 

  1. Rainfall data for 15 to 20 years shall be acquired from the agencies such as IMD (Indian Meteorological Department), WRDO, Statistical department etc.
  2. Rain gauge stations inside and near to the basin are identified based on the location of the rain gauge stations.
  3. Annual data is plotted as a graph to understand the dynamics of rainfall over time.

  1. Based on the annual rainfall trend, seasonal variation in the watershed is estimated

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:

  1. The delineated catchment would be in the form of xxx(filename).shp format i.e., as a shape file, first convert the same to kml. Right click on the shape file, click on save as, click on format and select  KEYHOLE MARKUP LANGUAGE (KML) to convert the convert the file to kml, save the file
  2. Double click on the saved ‘kml’ to open the same in Google earth
  3. Within the watershed, start digitising layers as polygons and save as ‘kml’.
  4. Example: Agriculture as a layer, Forest as a layer, water body as a layer etc

  5. ‘kml’ files are imported in QGIS, and converted as shape file (same procedure as step1)
  6. Calculate the are under each landuse using Map calculator tool

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

 

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T.V. Ramachandra
Energy & Wetlands Research Group, Centre for Ecological Sciences,
Centre for Sustainable Technologies,
Centre for infrastructure, Sustainable Transportation and Urban Planning (CiSTUP),
Indian Institute of Science, Bangalore – 560 012, INDIA.
E-mail : cestvr@ces.iisc.ernet.in
Tel: 91-080-22933099/23600985, Fax: 91-080-23601428/23600085
Web: http://ces.iisc.ernet.in/energy
Asulabha K S
Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, INDIA.
E-mail: asulabha@ces.iisc.ernet.in
Bharath H Aithal
Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, INDIA.
E-mail: bharath@ces.iisc.ernet.in
Bharath Settur
Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, INDIA.
E-mail: settur@ces.iisc.ernet.in
Durga Madhab Mahapatra
Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, INDIA.
E-mail: durga@ces.iisc.ernet.in
Gouri Kulkarni
Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, INDIA.
E-mail: gouri@ces.iisc.ernet.in
Harish R. Bhat
Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, INDIA.
E-mail: harish@ces.iisc.ernet.in
Sincy Varghese
Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, INDIA.
E-mail: sincy@ces.iisc.ernet.in
Sudarshan P. Bhat
Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, INDIA.
E-mail: sudarshan@ces.iisc.ernet.in
Vinay S.
Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, INDIA.
E-mail: vinay@ces.iisc.ernet.in

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
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