Integrating%20GIS%20into%20Distributed%20Modeling%20in%20Hydrology

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Integrating GIS into Distributed Modeling in
Hydrology
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Lecture Outline

• Structure of a watershed
• Watershed and stream network delineation
• Integration of TOPMODEL and GIS
• Simulation results from a case study

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Watershed the area enclosed within a drainage
boundary
Drainage divide a line defined topographically
which separates distinct areas of land drainage.
Drainage boundary a closed line drawn along
drainage divides
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Subwatershed a subdrainage area within a
watershed
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A grid defines geographic space as a matrix of
identically-sized square cells. Each cell holds a
numeric value that measures a geographic
attribute (like elevation) for that unit of
space.
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Reach a length of channel considered as a
single hydrologic entity.

• Example a length of river between two tributaries

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Waterbody a volume of water having a horizontal
water surface, which is defined within a specific
area.

• Width is significant when compared to the length.
  
• Examples lake, pond, reservoir, swamp, marsh,
  bay.

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Flow Network a set of connected flowlines
through channel reaches and water bodies
Also called River Network, Stream Network.
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Reach catchment the drainage area locally
defined around a particular channel reach.

• The drainage water from the reach catchment area
  flows to this channel reach before encountering
  any other downstream channel reaches or
  waterbodies.

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Watershed Delineation by Hand
Watershed divide
Outlet
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Digital Elevation Grid a grid of cells (square
or rectangular) in some coordinate system having
land surface elevation as the value stored in
each cell.
Square Digital Elevation Grid a common special
case of the digital elevation grid
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Direction of Steepest Descent
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67
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Slope
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Eight Direction Pour Point Model D8
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Grid Network
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Contributing Area Grid
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Contributing Area gt 10 Cell Threshold
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Watershed Draining to This Outlet
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Watershed and Drainage Paths Delineated from 30m
DEM
Automated method is more consistent than hand
delineation
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Hillslope Modelling
Precipn
ET
dry
Lateral subsurface flow
wet
Streamflow
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TOPMODEL

• The most popular distributed hydrological model.
• Two major advantages Simplicity and the
  possibility of visualizing the predictions of the
  model in a spatial context.

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Assumptions

• The dynamics of the water table can be
  approximated by uniform subsurface runoff
  production per unit area over the area, A,
  draining through a point, and
• The hydraulic gradient of the saturated zone can
  be approximated by the local surface topographic
  slope, tan B

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Topmodel (Based on Beven and Kirkby, 1979 and
later)
Assumption 1. Hydraulic conductivity decreasing
with depth - sensitivity parameter f Assumption
2. Saturated lateral flow driven by topographic
gradient and controlled by depth to water table
(soil moisture deficit). Assumption 3. Steady
state. Saturated lateral flow related to
equilibrium recharge rate. Determines depth to
water table and saturation excess runoff
generation when z lt 0
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• Wetness Index
• wetness index ln(As / tanB), where
• As Contributing Catchment Area in meters
  squared
• B Slope of cell measured in degrees

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Grey Digital Elevation Model
2815 rows 3675 columns 30 m grid
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Order 5 subbasin delineation
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Rain and streamflow gauges
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Pattinson Creek
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Pattinson Creek - Calibration 1990
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Pattinson Creek - Calibration 1990
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Pattinson Creek - Validation 1993/94 with
triangulated rainfall
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Pattinson Creek - Verification 1993
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Are there any questions ?