© J.M. Piwowar 1Geog 409: Advanced Spatial Analysis & Modelling Environmental Modelling

A Drainage Basin Modelling Example

Object: To determine the channel

discharge of a small drainage basin for a given rainfall.

© J.M. Piwowar 2Geog 409: Advanced Spatial Analysis & Modelling Environmental Modelling

A Simple Hydrologic Model

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© J.M. Piwowar 3Geog 409: Advanced Spatial Analysis & Modelling Environmental Modelling

Rainfall

Precipitation less evaporation losses. Assume rainfall falls evenly over the

basin. R = rainfall * surface area

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© J.M. Piwowar 4Geog 409: Advanced Spatial Analysis & Modelling Environmental Modelling

Surface Storage

The amount of rainfall that is detained on the surface.

Assumptions: There is some pre-existing surface

storageOne-half of rainfall is retained in surface

storage. S = S + 0.5*R

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© J.M. Piwowar 5Geog 409: Advanced Spatial Analysis & Modelling Environmental Modelling

Surface-Channel Discharge

The proportion of water in Surface Storage that immediately runs-off.

QSC = surface storage * constant1

Initial Assumption: constant1 = 0.9

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© J.M. Piwowar 6Geog 409: Advanced Spatial Analysis & Modelling Environmental Modelling

Surface-Ground Discharge

The proportion of water in Surface Storage that percolates into the ground.

QSG = surface storage * constant2

Initial Assumption: constant2 = 0.6

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© J.M. Piwowar 7Geog 409: Advanced Spatial Analysis & Modelling Environmental Modelling

Groundwater Storage

The amount of water in the unsaturated soil layers and in the saturated zone below the water table.

Assumptions: There is some pre-existing groundwater

storageOne-half of percolating rainfall is

retained in groundwater storage. G = G + 0.5*QSG

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© J.M. Piwowar 8Geog 409: Advanced Spatial Analysis & Modelling Environmental Modelling

Ground-Channel Discharge

The proportion of water in Ground Storage that seeps back to the surface.

SGC = ground storage * constant3

Initial Assumption: constant3 = 0.3

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© J.M. Piwowar 9Geog 409: Advanced Spatial Analysis & Modelling Environmental Modelling

Channel Discharge

The sum of the water run-offs from the surface and from the ground.

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© J.M. Piwowar 10Geog 409: Advanced Spatial Analysis & Modelling Environmental Modelling Har

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The “Catchwater” Drainage Basin