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DES 606 : Watershed Modeling with HEC-HMS

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

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DES 606 : Watershed Modeling with HEC-HMS

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  1. DES 606 : Watershed Modeling with HEC-HMS Module 4 Theodore G. Cleveland, Ph.D., P.E 29 June 2011

  2. 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

  3. Rainfall-Runoff Process • Precipitation • Meterology, Climate • Runoff • Fraction of precipitation signal remaining after losses HMS – Basin Component • Watershed • Losses • Transformation • Storage • Routing Canopy and Depression Storage Reservoir Storage

  4. Canopy (Interception) Storage

  5. ~ excess precipitation ~ loss 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.

  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 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

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

  12. Rainfall-Runoff • As a process diagram: 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 • 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 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.

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

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