DES 606 :
Watershed Modeling with
HEC-HMS
Module 4
Theodore G. Cleveland, Ph.D., P.E
29 June 2011
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
Rainfall-Runoff Process
•
Precipitation
– Meterology, Climate
HMS – Basin Component
• Watershed
Canopy and Depression Storage
Reservoir Storage
•
Runoff
– Fraction of precipitation
signal remaining after losses
–
–
–
–
Losses
Transformation
Storage
Routing
Canopy (Interception) Storage
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.
~ loss
~ excess
precipitation
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.
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.
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
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
Surface (Depression) Storage
• In HMS part of subbasin properties.
– Simple Surface
– Gridded Surface
Surface (Depression) Storage
• Initial storage (depth)
• Maximum storage
(depth)
– Storage is satisfied.
– Excess can become
runoff.
Rainfall-Runoff
• As a process diagram:
Precipitation
Meterologic properties
Evapotranspiration
Interception Storage
Sub-basin properties
Depression Storage
Infiltration
Loss Model(s)
Excess Precipitation
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.
Reservoir Storage
• In HEC-HMS
reservoirs (and
detention basins)
are treated as a
hydrologic element
in the basin model
Reservoir Storage
• Accounts for storage
• Flows are “routed”
through a reservoir
– Level pool routing
– Orifice flow
– Weir flow
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
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
Reservoir Storage
• The storage relationships are usually
developed external to HEC-HMS
– Like rainfall and external hydrographs, use
external tools to develop the storagedischarge relationships
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.
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
Summary
• Example 4 illustrates the data entry
activities associated with both kinds of
storage.