1. DES 606 : Watershed Modeling with HEC-HMS
Module 5: Storage Concepts
Theodore G. Cleveland, Ph.D., P.E, M. ASCE, F. EWRI
26-28 August 2015

2. Outline for Module 5 Surface Storage Reservoir 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

3. 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

4. Canopy (Interception) Storage

5. Canopy (Interception) Storage
~ excess
precipitation
~ loss
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.

6. 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.

7. 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.

8. Canopy (Interception) Storage
Sophisticated hydrologic abstraction
Likely uncommon in typical engineering hydrological applications, esp. because of the PET feedback
Utility in “scientific investigation”
Measurements are non-existent
While the process undoubtedly occurs, would not be commonly used in Texas, except perhaps East Texas Piney Woods

9. 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

10. Surface (Depression) Storage
In HMS part of sub-basin properties.
Simple Surface
Gridded Surface

11. Surface (Depression) Storage
Initial storage (percent of maximum)
Maximum storage (depth)
Storage is satisfied.
Excess can become runoff.

12. Rainfall-Runoff As a process diagram: Infiltration Precipitation
Meterologic properties
Evapotranspiration
Loss Model(s)
Interception Storage
Depression Storage
Excess Precipitation
Sub-basin properties
Infiltration

13. 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.

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

15. Reservoir Storage Accounts for storage
Flows are “routed” through a reservoir
Level pool routing
Orifice flow
Weir flow

16. 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

17. Reservoir Storage Storage Representations Discharge 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

18. 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

19. HEC-HMS Example 5 – 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.

20. 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

21. Summary
Example 5 illustrates the data entry activities associated with both kinds of storage.