TD 603
Water Resources Management
Lecture 4
Watersheds and Maps
Material used from slides of TD603 Autumn 2013 Prof. Milind Sohoni
TD 603 Water Resources Management Autumn 2014
(last class) Homework
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Mumbai needs 3000 mega-liters/day, which comes
from lakes about 100 km away and about 500 ft
above Mumbai's elevation.
Estimate the number of pipes need to transfer this
water, if the diameter of these pipers is 2m.
V =(1.49 R
2/3
S
1/2
)/ n
TD 603 Water Resources Management Autumn 2014
Watershed
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Definition
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Catchment area/region from which water gets
collected
Defined with ref. to a location
(Rain) Water in the catchment area (watershed) fows
through/to this location
TD 603 Water Resources Management Autumn 2014
Domain decomposition
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The watershed W(x) of point x is
W(x) = {all points y from where surface water fows to x}
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For any x and y,
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W(x) ⊆ W(y) or W(x)∩W(y) is a thin set
TD 603 Water Resources Management Autumn 2014
Thane watershed
TD 603 Water Resources Management Autumn 2014
Ridge lines, flow lines, drainage lines
TD 603 Water Resources Management Autumn 2014
Drainage Systems
source: NREGA watershed manual
TD 603 Water Resources Management Autumn 2014
The Watershed decomposition
TD 603 Water Resources Management Autumn 2014
Watershed classification
source: NREGA watershed manual
TD 603 Water Resources Management Autumn 2014
Watershed Relevance
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?
TD 603 Water Resources Management Autumn 2014
Watershed Relevance
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Volumetric unit for analysis
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Static data
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Dynamic data
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Weather data
Land and water use
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Geology, wells and discharges
Farms, factories, etc.
Objectives
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Water balance, sustainability planning, planning of
interventions and structures.
TD 603 Water Resources Management Autumn 2014
Why watershed (development)?
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Soil erosion reduction
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Silt build up and trapping
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Groundwater recharge
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Storage and surface water capacity
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Soil moisture improvement
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Domain for water balance and planning
P = E + ET + RO + GW + SM + ST
TD 603 Water Resources Management Autumn 2014
Watershed and structures
TD 603 Water Resources Management Autumn 2014
Demarcating watersheds
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Task:
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Draw watershed for a village or a basin or ...
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Enter the toposheets/topographical maps
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Maps
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Direction
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Legend
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Scale
TD 603 Water Resources Management Autumn 2014
Toposheet
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Scaled map of a region
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Basic information: topology (using contours)
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Contour
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Line connecting all points of same elevation
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Vital information for watersheds and planning
Other information in toposheets
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Assets on land
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Drainages, structures
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Roads, Canals, Railway lines, Forests
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Electricity and telephone lines
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...
TD 603 Water Resources Management Autumn 2014
Toposheets classification
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Basic grid 4⁰x4⁰
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1:1,00,0000
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1 in = 16 miles
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Nos. 46, 47 etc.
16 grids of 1⁰x1⁰
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A to P
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1:2,50,000
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1/4 in = i mile
16 grids of 1/4⁰x1/4⁰
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1:50,000
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1 in = 1 mile
46D7
TD 603 Water Resources Management Autumn 2014
Sample Toposheet
TD 603 Water Resources Management Autumn 2014
Demarcating watersheds
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Given a toposheet, how to demarcate a watershed?
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Steps
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1: Identify the point/location w.r.t which the
watershed is to be marked
2. Identify ridges lines and drainages around the
location
3. Use contour lines to draw boundary around the
location
Watershed boundary/Ridge line never crosses
a drainage line
TD 603 Water Resources Management Autumn 2014
Demarcating in action
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Refer to toposheets handed out
Draw watersheds for diferent points marked on the
toposheets
TD 603 Water Resources Management Autumn 2014
Terms
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Watershed
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Catchment area
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Command area
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Ridge-line
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Flow line, drainage
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1st order, 2nd order, 3rd order stream
TD 603 Water Resources Management Autumn 2014
Maps
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(2D) representation of (3D) earth (or sub-parts)
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Displaying useful information
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Essential components
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Direction
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Legend
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Scale
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Information/theme (thematic maps)
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Several maps can be created from basic elevation
data and from satellite images
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Contour, drainage, slope
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Vegetation, geology, rainfall, land-use, soil ...
TD 603 Water Resources Management Autumn 2014
Papagni Watershed
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Papagni river watershed
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2500 sq. km, border district of Andra Pradesh
Study area of Foundation for Ecological Security (
www.fes.org.in)
Extensive use of maps, GIS and data from several
sources
Intersection of several of these maps/layers act as
vital input for development related planning
TD 603 Water Resources Management Autumn 2014
GIS Geographical Information System
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A digital thematic map
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3D representation
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x,y,z
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x,y : latitude and longitude
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z = f(x,y)
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Rainfall, elevation, crop, land-use ...
View is usually 2D
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Layer (thematic information)
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Projection from 3D to 2D
Points, lines, curves, polygons
More in GIS session
TD 603 Water Resources Management Autumn 2014