CRWR-PreProCalculation of Hydrologic Parameters

Francisco Olivera, Ph.D.Center for Research in Water Resources

University of Texas at Austin

Texas Department of Transportation (TxDOT)Water Resources Modeling Using GIS2000 - Austin, Texas

Hydrologic Parameters

Watershed Abstractions and routing

method Parameters

Stream Routing method Parameters

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

Watershed Abstractions

Soil properties

Precipitation (mm/hr)

Runoff (mm/hr)

Runoff = f(precipitation, soil properties, moisture conditions)

Watershed Routing

Runoff (mm/hr)

Flow (m3/s)

Watershed

Watershed Routing

Runoff (mm/hr)

Flow (m3/s)

Time

Ru

noff

an

d F

low

Flow = f(Runoff, Watershed hydrologic properties)

Time

Hydrologic Parameters

Watershed Abstractions and routing method Parameters

Stream Routing method Parameters

Watershed

Area

Average curve number

Initial + constant rate loss

Length of longest flow-path

Slope of longest flow path

Lag time

Watershed Abstractions

Average Curve Number

SCS MethodInitial + Constant

Method

Initial Loss (mm)Constant Loss

(mm/hr)

Elevation Grid

Flow Length Downstream

Flow Length Upstream

Longest Flow-Path

Flow Length Downstream to the Watershed Outlet

Hydrologic Parameters

Flow length downstream to the sub-basin outlet.

Flow Length Upstreamto the Watershed Divide

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.

Watershed Longest Flow-Path

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.

Slope of WatershedLongest Flow Path

Hydrologic Parameters

t5.3,

S67.31

]9)CN/1000[(Lmaxt

5.0

7.08.0w

p

tp: sub-basin lag-time (min)LW: length of sub-basin longest flow-path (ft)CN: average Curve Number in sub-basinS: slope of the sub-basin longest flow-path (%)t: analysis time step (min)

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

Watershed Lag-Time (SCS)

Flow length upstream and downstream

AverageCurve Number

Length and slope of the longest flow-

path

Identification of the longest flow-path

Lag-time

Hydrologic Parameters

t5.3,

V60

L3048.06.0maxt

w

wp

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)

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

Watershed Lag-Time (L/V)

Flow length upstream and downstream

Longest flow-path average velocity

Length of the longest flow-path

Lag-time

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).

Hydrologic Parameters

Watershed Abstractions and routing method Parameters

Stream Routing method Parameters

Routing Method

Pure-Lag Method

Flow is delayed a fixed amount of time tlag.

)t(I)tt(Q lag

tlag: flow time in the reachI: inflow to the reachQ: outflow from the reach

Muskingum Method

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

QIdt

dSandQ)X1(IXKS

S: storage in the reachK: flow time in the reach (t < K < t/2X)X: storage parameterI: inflow to the reachQ: outflow from the reacht: analysis time step

Routing Method

Flow time (Ls/Vs)

Ls/Vs < t

MuskingumRouting

Ls/Vs > t

Pure LagRouting

Ls: length of the streamVs: flow velocity in the streamt: analysis time step

Hydrologic Parameters

Watershed Abstractions and routing

method Parameters

Stream Routing method Parameters

Hydrologic Parameters

s

slag V60

Lt

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

Reach lag-time for Pure Lag routing:

Hydrologic Parameters

s

s

V3600

LK

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

1t

V60/LX2intn ss

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

Hydrologic Parameters

Pure lag routing for Ls/60vs < t, 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.