DES 606 : Watershed Modeling with HEC-HMS

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DES 606 Watershed Modeling with HEC-HMS

• Module 4
• Theodore G. Cleveland, Ph.D., P.E
• 29 June 2011

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Module 4 Storage

• Surface Storage
• Treated as abstractions
• Canopy (interception) storage
• Depression storage
• Reservoir Storage
• Treated as hydrologic/hydraulic elements
• Reservoirs (regulated and unregulated)
• Detention basins
• Certain stormwater BMPs

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Rainfall-Runoff Process

• Precipitation
• Meterology, Climate

HMS Basin Component

• Watershed
• Losses
• Transformation
• Storage
• Routing

Canopy and Depression Storage
Reservoir Storage

• Runoff
• Fraction of precipitation signal remaining after
  losses

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HEC-HMS

• Hydrologic Cycle Components in HEC-HMS (circa
  2008)

Snowfall
Evapo- transpiration
Rainfall, P(t)
Snowpack
Snowmelt
Land Surface and Vegetation
Infiltration Loss
Runoff
Runoff
Channels
Reservoirs
Percolation Loss
Discharge, Q(t)
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Canopy (Interception) Storage
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Canopy (Interception) Storage

• Interception is precipitation that does not reach
  the soil, but is instead intercepted by the
  leaves and branches of plants and the forest
  floor.
• The intercepted water generally evaporates and
  leads to loss of that precipitation for the
  drainage basin.

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Canopy (Interception) Storage

• In HMS part of sub-basin properties.
• Simple Canopy
• Gridded Canopy
• HMS gridded implies a GIS type interface
• This course does not directly use gridded
  methods, although introduced in last module.

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Canopy (Interception) Storage

• All precipitation intercepted until storage
  capacity satisfied.
• Excess precipitation then directed to surface
  (depression) storage if any.
• Then excess to runoff component.
• Also considers potential evapo-transpiration
  (PET) as part of the hydrologic cycle.

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Canopy (Interception) Storage

• Sophisticated hydrologic abstraction and likely
  uncommon in typical engineering hydrological
  applications, esp. because of the PET feedback.
• Utility in scientific investigation
• Measurements are likely non-existent.
• While the process undoubtedly occurs, would not
  be commonly used in Texas, except perhaps East
  Texas Piney Woods

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Surface (Depression) Storage

• Depression storage. The volume of water contained
  in natural depressions in the land surface, such
  as puddles. (After Horton, 1935, p. 2)
• In the Green-Ampt model, water ponds at non-zero
  depth hence depression storage is arguably
  important for such infiltration models.
• The interaction of depression storage and
  infiltration is the basis of Hortonian overland
  flow

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Surface (Depression) Storage

• In HMS part of sub-basin properties.
• Simple Surface
• Gridded Surface

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Surface (Depression) Storage

• Initial storage (depth)
• Maximum storage (depth)
• Storage is satisfied.
• Excess can become runoff.

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Rainfall-Runoff

• As a process diagram

Precipitation
Evapotranspiration
Meterologic properties
Loss Model(s)
Interception Storage
Depression Storage
Excess Precipitation
Sub-basin properties
Infiltration
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Reservoir Storage

• Reservoir
• A pond, lake, or basin, either natural or
  artificial, for the storage, regulation, and
  control of water.
• Regulated reservoir
• Outflow controlled by moveable gates and valves.
• Head, and valve settings determine outflow.
• Unregulated reservoir.
• Outflow controlled by fixed weirs and orifices.
• Head and constructed weir height determine
  outflow.

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Reservoir Storage

• In HEC-HMS reservoirs (and detention basins) are
  treated as a hydrologic element in the basin model

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Reservoir Storage

• Accounts for storage
• Flows are routed through a reservoir
• Level pool routing
• Orifice flow
• Weir flow

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Reservoir Storage
Pond with storage, orifice and weir flow.
Orifice flow energy loss model
Weir flow critical depth model
Image from ftp//ftp.crwr.utexas.edu/pub/outgoing/
Robayo/HECHMS.../HEC-HMS.ppt
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Reservoir Storage

• Storage Representations
• Storage vs. Discharge
• Storage vs. Elevation
• Surface Area vs. Elevation
• Discharge Representations
• Spillways, Weirs
• Orifices, Sluice gates
• Pumps
• Dam Breach

Image from ftp//ftp.crwr.utexas.edu/pub/outgoing/
Robayo/HECHMS.../HEC-HMS.ppt
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Reservoir Storage

• The storage relationships are usually developed
  external to HEC-HMS
• Like rainfall and external hydrographs, use
  external tools to develop the storage-discharge
  relationships

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HEC-HMS

• Example 4 Illustrate Reservoir Storage Data
  Entry
• Ash Creek Watershed
• Use the GA runoff generation model
• Will use canopy storage and surface storage to
  illustrate the effects of these components.
• Pretend we will place a small detention facility
  at the outlet
• Develop the storage-discharge curves in Excel
• Enter into HEC-HMS, examine effects.

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Summary

• Storage in HEC-HMS is of two types
• Abstraction Canopy and Depression
• Hydrologic/Hydraulic Reservoir
• Abstraction storage is a sophisticated concept,
  hard to estimate parameters for engineering
  practice its is uncommon.
• Reservoir storage is common, if not fundamental
  in watershed models
• Detention facilities
• BMPs

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Summary

• Example 4 illustrates the data entry activities
  associated with both kinds of storage.