CRWR-PrePro Calculation of Hydrologic Parameters

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CRWR-PreProCalculation of Hydrologic
Parameters
Texas Department of Transportation (TxDOT) Water
Resources Modeling Using GIS 2000 - Austin, Texas

• Francisco Olivera, Ph.D.
• Center for Research in Water Resources
• University of Texas at Austin

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Hydrologic Parameters

• Watershed
• Abstractions and routing method
• Parameters
• Stream
• Routing method
• Parameters

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Watershed Abstractionsand Routing Method

• Abstractions rainfall/runoff transformation
• SCS curve number method
• Initial loss constant rate loss
• Routing runoff/flow transformation
• Soil Conservation Service (SCS) synthetic unit
  hydrograph

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Watershed Abstractions
Precipitation (mm/hr)
Runoff (mm/hr)
Soil properties
Runoff f(precipitation, soil properties,
moisture conditions)
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Watershed Routing
Runoff (mm/hr)
Watershed
Flow (m3/s)
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Watershed Routing
Time
Runoff (mm/hr)
Runoff and Flow
Flow (m3/s)
Time
Flow f(Runoff, Watershed hydrologic properties)
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Hydrologic Parameters

• Watershed
• Abstractions and routing method
• Parameters
• Stream
• Routing method
• Parameters

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Watershed

• Area
• Average curve number
• Initial constant rate loss
• Length of longest flow-path
• Slope of longest flow path
• Lag time

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Watershed Abstractions
Average Curve Number
Initial Loss (mm)Constant Loss (mm/hr)
SCS Method
Initial Constant Method
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Elevation Grid
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Flow Length Downstream
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Flow Length Upstream
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Longest Flow-Path
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Flow Length Downstream to the Watershed Outlet
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Hydrologic Parameters

• Flow length downstream to the sub-basin outlet.

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Flow Length Upstreamto the Watershed Divide
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Hydrologic Parameters

• Flow length upstream to the sub-basin divide.
• A NODATA cell is defined at the sub-basin outlets
  before running the flow length function.

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Watershed Longest Flow-Path
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Hydrologic Parameters

• Sub-basin longest flow-path.
• The longest flow-path is the geometric locus of
  the points for which the sum of both flow lengths
  is a maximum.

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Slope of WatershedLongest Flow Path
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Hydrologic Parameters

• Sub-basin lag-time according to the SCS formula

tp sub-basin lag-time (min) LW length of
sub-basin longest flow-path (ft) CN average
Curve Number in sub-basin S slope of the
sub-basin longest flow-path () ?t analysis time
step (min)
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Watershed Lag-Time (SCS)
Flow length upstream and downstream
AverageCurve Number
Lag-time
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Hydrologic Parameters

• Sub-basin lag-time according to 0.6 L/v formula

tp sub-basin lag-time (min) Lw length of
sub-basin longest flow-path (ft) Vw average
velocity sub-basin longest flow-path
(m/s) ?t analysis time step (min)
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Watershed Lag-Time (L/V)
Flow length upstream and downstream
Longest flow-path average velocity
Length of the longest flow-path
Lag-time
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Hydrologic Parameters

• Sub-basin parameters Grid code, area (Km2), unit
  hydrograph model (SCS), length of longest flow
  path (m), slope of longest flow path (fraction),
  average curve number, lag-time (min), baseflow
  (none).

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Hydrologic Parameters

• Watershed
• Abstractions and routing method
• Parameters
• Stream
• Routing method
• Parameters

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Routing Method
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Pure-Lag Method
tlag flow time in the reach I inflow to the
reach Q outflow from the reach

• Flow is delayed a fixed amount of time tlag.

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Muskingum Method
S storage in the reach K flow time in the reach
(Dt lt K lt Dt/2X) X storage parameter I inflow
to the reach Q outflow from the
reach Dt analysis time step

• Flow is delayed a fixed amount of time K, and
  redistributed around its centroid.

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Routing Method
Flow time (Ls/Vs)
Ls/Vs lt Dt
Ls/Vs gt Dt
MuskingumRouting
Pure LagRouting
Ls length of the stream Vs flow velocity in the
stream Dt analysis time step
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Hydrologic Parameters

• Watershed
• Abstractions and routing method
• Parameters
• Stream
• Routing method
• Parameters

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Hydrologic Parameters

• Reach lag-time for Pure Lag routing

tlag reach lag-time (min) Ls length of reach
(m) Vs reach average velocity (m/s)
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Hydrologic Parameters

• Reach lag-time and number of sub-reaches for
  Muskingum routing

K Muskingum parameter K (hr) X Muskingum
parameter X Ls reach length (m) Vs reach
average velocity (m/s) n number of sub-reaches
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Hydrologic Parameters

• Pure lag routing for Ls/60vs lt Dt, otherwise
  Muskingum routing.
• Reach parameters Grid code, sub-basin code,
  length(m), velocity (m/s), routing method (Lag or
  Muskingum), lag time (min), Muskingum X,
  Muskingum K (hr), number of sub-reaches.