Hydrologic/Watershed Modeling
Design Point
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Glenn Tootle, P.E. , Ph.D.
Department
DepartmentofofCivil
Civiland
andEnvironmental
Architectural Engineering
Engineering
University
University
of Nevada,
of Wyoming
Las Vegas
tootleg@unlv.nevada.edu
tootleg@uwyo.edu
Questions?
 Who has used / developed a hydrologic
model?
 What model(s) did you use?
 Examples
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
Steps to Hydrologic Modeling
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Delineate watershed
Obtain hydrologic and geographic data
Select modeling approach
Calibrate/Verify model
Use model for assessment/prediction/design
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
Urban Watershed
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Design Point
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USGS Quad Map
Digital Elevation Model (DEM)
 Digital file that stores the elevation of the land
surface a specified grid cell size (e.g., 30 meters)
Geographic Data
 Land cover
 Land use
Land Cover
Forest
Oak Woodlands
Mesquite Woodlands
Grasslands
Desertscrub
Riparian
Agriculture
Urban
Water
Barren / Clouds
N
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1992 NALC
5 10 km
Hillshade DEM
STATSGO
EM
Geographic Data
 Soil type/classification
STATSGO
Hydrologic Data
 Meteorological Data
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Temperature
Precipitation
Wind speed
Humidity
 Extrapolation of point
measurements
– Theissen Polygons
– Inverse distance weighting
Hydrologic Data
Streamflow
 Hydrologic Data
Design Point
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– Streamflow
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 Peak discharge
 Daily flow volume
 Annual flow volume
3
– Soil moisture
– Groundwater level
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Modeling Approaches (examples)
TIME SCALE
Empirical
Regression equ’s
Transfer Functions
Simple models
Physically-based
Based on physical
processes
Complicated
Many parameters
Event-based
(minute to day)
Continuous Simulation
(days – years)
Rational Method
SCS Unit Hydrograph
Simple Model
KINEROS
Stanford Watershed
Model
TOPMODEL
SWAT
VIC-3L
TOPMODEL
Basis for Many Hydrologic Models
 Hydrologic Budget (In – Out = ΔStorage)
Transpiration (T)
Evaporation (E)
Precipitation (P)
Streamflow (Q)
Groundwater out (GWout)
Reservoir
Groundwater in (GWin)
Infiltration (I)
Watershed
(P + GWin) – (E + T + I + GWout + Q) = ΔStoragereservoir
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?
Spatial Scaling of Models
Semi-Distributed
Lumped
Parameters assigned to
each subbasin
A3
A1
A2
Parameters assigned to
each grid cell, but cells
with same parameters are
grouped
Fully-Distributed
Parameters assigned to
each grid cell
Stanford Watershed Model
(HSPF)
 Physically-based and continuous simulation
Variable Infiltration Capacity (VIC-3L)
 Continuous simulation and physically-based
 Macroscale hydrologic model that solves full water
and energy balances
VIC-3L Example
Anamoly Three Layers Soil Moisture
( Upper Mississippi Basin)
Anomaly Soil
Moisture (inch)
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0
Jan-50
-100
Sep-63
May-77
Feb-91
Oct-04
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Time (Month)
layer1
layer2
layer3
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
Sensitive Parameters
 Precipitation
 Soil parameters
– Hydraulic conductivity
– Soil water holding capacity
 Evaporation (for continuous simulation)
 Flow routing parameters (for event-based)
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
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?
QUESTIONS