Module 5: Storage Concepts Theodore G. Cleveland, Ph.D., P.E, M. ASCE, F. EWRI October 2013

 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

Watershed –Losses –Transformation –Storage –Routing Precipitation –Meterology, Climate  Runoff  Fraction of precipitation signal remaining after losses Canopy and Depression Storage Reservoir Storage HMS – Basin Component

 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. ~ excess precipitation ~ loss

 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.

 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.

 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

 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

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

 Initial storage (percent of maximum)  Maximum storage (depth)  Storage is satisfied.  Excess can become runoff.

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

 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.

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

 Accounts for storage  Flows are “routed” through a reservoir  Level pool routing  Orifice flow  Weir flow

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

 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

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

 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.

 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

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