Hydrologic/Watershed Modeling

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Hydrologic/Watershed Modeling

• Glenn Tootle, P.E.
• Department of Civil and Environmental Engineering
• University of Nevada, Las Vegas
• tootleg_at_unlv.nevada.edu

, Ph.D.
Department of Civil and Architectural
Engineering University of Wyoming tootleg_at_uwyo.edu
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Questions?

• Who has used / developed a hydrologic model?
• What model(s) did you use?
• Examples

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Conceptual Model of Watershed Modeling

• Typical Input
• Topography
• Soil Characteristics
• Land cover
• Land use
• Meteorological data
• Typical Output
• Streamflow
• Subsurface Flow
• Depth to water table

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Steps to Hydrologic Modeling

1. Delineate watershed
2. Obtain hydrologic and geographic data
3. Select modeling approach
4. Calibrate/Verify model
5. Use model for assessment/prediction/design

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What is a Watershed?

• Area that topographically contributes to the
  drainage to a point of interest

Natural Watershed

• Points of Interest
• Road crossing
• Stream gage
• Reservoir inlet
• Wastewater treatment plant
• Location of stream restoration

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Urban Watershed
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USGS Quad Map
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Digital Elevation Model (DEM)

• Digital file that stores the elevation of the
  land surface a specified grid cell size (e.g., 30
  meters)

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Geographic Data

• Land cover

• Land use

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Geographic Data

• Soil type/classification

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Hydrologic Data

• Meteorological Data
• Temperature
• Precipitation
• Wind speed
• Humidity
• Extrapolation of point measurements
• Theissen Polygons
• Inverse distance weighting

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Hydrologic Data
Streamflow

• Hydrologic Data
• Streamflow
• Peak discharge
• Daily flow volume
• Annual flow volume
• Soil moisture
• Groundwater level

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Modeling Approaches (examples)
TIME SCALE TIME SCALE
Event-based (minute to day) Continuous Simulation (days years)
Empirical Regression equs Transfer Functions Simple models Rational Method SCS Unit Hydrograph Simple Model
Physically-based Based on physical processes Complicated Many parameters KINEROS Stanford Watershed Model TOPMODEL SWAT VIC-3L TOPMODEL
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Basis for Many Hydrologic Models

• Hydrologic Budget (In Out ?Storage)

Transpiration (T)
Streamflow (Q)
Evaporation (E)
Groundwater out (GWout)
Reservoir
Precipitation (P)
Groundwater in (GWin)
Infiltration (I)
Watershed
(P GWin) (E T I GWout Q)
?Storagereservoir
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Which Model Should be Used?

• It Depends on
• What time scale are you working at?
• What hydrologic quantity are you trying to
  obtain?
• What data do you have for your watershed?
• How fast of a computer do you have?

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Spatial Scaling of Models
Semi-Distributed Parameters assigned to each grid
cell, but cells with same parameters are grouped
Fully-Distributed Parameters assigned to each
grid cell
Lumped Parameters assigned to each subbasin
A3
A1
A2
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Stanford Watershed Model(HSPF)

• Physically-based and continuous simulation

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Variable Infiltration Capacity (VIC-3L)

• Continuous simulation and physically-based
• Macroscale hydrologic model that solves full
  water and energy balances

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VIC-3L Example
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Calibrating a Model

• Typically the model is calibrated against
  observed streamflow data
• Depending on the model complexity, parameters are
  adjusted until observed streamflow equals model
  streamflow
• Which observed value to use
• Qpeak
• Qvolume
• tpeak

Qpeak
Q
tpeak
Qvolume
t
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Sensitive Parameters

• Precipitation
• Soil parameters
• Hydraulic conductivity
• Soil water holding capacity
• Evaporation (for continuous simulation)
• Flow routing parameters (for event-based)

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Uncertainties

• Precipitation
• Extrapolation of point to other areas
• Temporal resolution of data
• Soils information
• Surveys are based on site visits and then
  extrapolated
• Routing parameters
• Usually assigned based on empirical studies

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Use of Models

• Assessment
• What happens if land use/land cover is changed?
• Prediction
• Flood forecasting
• Design
• How much flow will occur in a 100 year storm?

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QUESTIONS