Dss Watershed Nhrao

8/12/2019 Dss Watershed Nhrao

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GIS based DSS for Watershed Management

Assessment of runoff distribution

N.H.Rao

NAARM


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Problem Definition

Decisions associated with watershed management are centred

around water

Decisions are based on assessment of the hydrologic processes

that occur over itprincipally runoff

Different soil, land slopes, land cover and management practices

affect runoff differently

Resources and processes vary spatially

Large watersheds consist of several subwatersheds connected

hydrologically by a stream network

Decisions require assessments of runoff and its distribution over

the subwatersheds


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To develop a decision support framework for watershed

management based on characterizing the watershed into:

subwatersheds andhomogenous units with respect to subwatersheds,

rainfall, soils and land use

for assessment of runoff and its distribution over thewatershed

Objective


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Defining equation:

Runoff = f(slope, soils, land use, rainfall)

GIS Database Design

Spatial Data layers:

contours (slope) - subwatersheds

soils

land use

rainfall distributionAttribute data: rainfall, soils (hydrologic group)


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Data available

watershed map (KK3 watershed in Mahbubnagar district,

area about 435 sq km) showing stream network, tanks,

settlements in 1:50000 scale

soil map of Mahbubnagar district (1:250000 scale)

SOI toposheets (56 L 6,7,11 which cover the watershed -

1:50000 scale)

Land use land cover map (created in ERDAS1:50000)

Rain gauge station locations in Mahbubnagar district(1:250000 scale)


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Procedure

create spatial database of watershed in ArcGISdigital layers of- boundary

- streams- tanks

- settlements

- contours (merging contours of 3 SOI toposheets and clipping

them with the watershed boundary)

- soils (by clipping from the district soils map with the watershed

boundary)

- rain gauge stations (Thiessen polygonsby clipping from district

rain gauge network map)

delineate watershed into subwatersheds- create Digital Elevation Model (DEM) from contours and streams

- convert grid to coverage

- delineate subwatersheds


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Procedure (contd..)

create homogenous hydrologic response units (HRU) by

overlay of:- subwatersheds

- soils

- land use

- rain gauge station Thiessen polygons

compute runoff from each HRU and subwatershed using

runoff equation for any input rainfall

generate thematic maps of runoff for HRUs, subwatersheds byinteractive input of rainfall data


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Creation of Digital Database of Watershed

Digitizing Watershed map

for

Boundary

Settlements

Water tanks

Stream

Network

Contours Soils Land

Use/Land

Cover

Rainfall

Distribution-

DEM

Flow Direction grid

Sink grid

Watershed delineation

Grid to Coverage Conversion

Sub Watershed Boundary

Hydrological Response Units (CN Unit)

Runoff Computation and Thematic Mapping

Rainfall

data from

database

OVERLAY

Thiessen

Polygons


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Delineation of watershed intosubwatersheds


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Stream


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Derivation of Soil data layer ofwatershed .


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Creating rain gauge station

Thiessen polygons layer ..


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Creating land use land cover data

layer .


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Creating data layer of hydrologic response units

by overlay of data layers:

subwatersheds

soils

Rain gauge station Thiessen polygons

Land use


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Calculation of runoff from each

HRU .


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Soil Group

Land use A B C D

Dense Vegetation 65 75 82 86

Sparse Vegetation 70 79 84 88

Waste Land 71 80 85 88

Water Bodies 100 100 100 100

Curve Number Values

Distribution of curve numbers


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Run off Depth Q (in mm):


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Q=(P0.2S) / [(P0.2S) + S)]

Run off Depth Q (in mm):

S = (25400/CN)254

P = Rain fall Depth in mm

Run off Volume(Cubic Meters):

= ( Q*(Shape_Area)/1000)

From GIS


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Dss Watershed Nhrao

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