Storage (RS)

Storage-discharge routing can be used to define either channel or reservoir routing. When this routing option is specified the appropriate data items are dimmed and additional radio buttons are used to determine whether channel or reservoir routing is to be used.

The following parameters must be defined regardless of the storage routing option specified.

NSTPS - Number of steps to be used in the storage routing. Typically this is approximately equal to (reach length) / (average velocity * time interval (NMIN) ). NSTPS is usually equal to 1 for a reservoir.
ITYP - The next parameter RSVRIC can be entered in one of three different ways:

STOR - Storage in acre-feet (1000 cu m).
FLOW - Discharge in cfs (cms).
ELEV - Elevation in feet (m).

RSVRIC - Storage, discharge, or elevation as defined by ITYP corresponding to the desired starting condition at the beginning of the first time period as specified on the IT record in the Job Control dialog.

Channel Routing

If the channel routing option is specified, the Define button will access a dialog which allows you to choose between Normal depth and Modified-Puls methods. If Normal depth is specified, the following parameters must be defined for the RC record.

Manning's coefficients - Manning roughness coefficients for the channel and left and right overbanks.
Length - The length of the river reach.
Slope - The slope of the river reach.
Max Elevation - The maximum elevation for which storage and outflow values are to be computed.

In addition to these parameters an eight point cross section must be defined using the XY Series Editor. The first two points define the left overbank, the third point defines the left bank, the fourth and fifth points define the channel itself, the sixth point defines the right bank, and the last two points define the right overbank.

If the modified-Puls method is chosen the volume (SV) outflow (SQ) relationship must be defined. Both records are defined using the XY Series Editor.

Reservoir Routing

If the reservoir routing option is specified then one method for volume and one method for outflow must be defined.

Known volume - Define a known volume (SV) record using the XY Series Editor. Optionally, you can define the elevations (SE) which correspond to the known volumes.
Computed volume - By defining an area (SA) elevation (SE) relationship the volume can be computed automatically by HEC-1. Both records are defined using the XY Series Editor.

If a TIN has been used to define the watershed a storage capacity curve can be generated and the information used to set up the volume/elevation (SV, SE) or area/elevation (SA, SE) data. See Storage Capacity Curves for more information.

The available methods for outflow include:

Known outflow - Define a known outflow (SQ) record using the XY Series Editor.
Computed Weir Spillway - A combination of data records are used to define spillway characteristics (SL, SS, ST). Parameter description for these different records are as follows:

Low-Level Outlet (SL)

ELEVL - Center line elevation of downstream end of low-level outlet.
CAREA - Cross-sectional area in square feet (square m) in the low-level outlet orifice equation.
COQL - Discharge coefficient in orifice outlet equation.
EXPL - Exponent of head in orifice equation.

Spillway Characteristics (SS)

CREL - Spillway crest elevation. This value must be less than the highest elevation on the SE card for HEC-1 to run properly.
SPWID - Spillway length.
COQW - Discharge coefficient in the spillway weir flow equation.
EXPW - Exponent of head in the weir spillway flow equation, usually equals 1.5.

Dam Overtopping (ST)

TOPEL - Elevation of the top of the dam at which overtopping begins.
DAMWID - Length of the top-of-dam which is actively being overtopped.
COQD - Discharge coefficient in the weir equation.
EXPD - Exponent of head in the weir equation.