Stage-discharge relations for selected culverts and bridges in the Big Lost River flood plain at the Idaho National Engineering and Environmental Laboratory, Idaho

Information is needed by the U.S. Department
of Energy at the Idaho National Engineering and
Environmental Laboratory to determine the extent
and severity of potential flooding at facilities along
the Big Lost River. Two computer programs—the
Culvert Analysis Program (CAP) and the HECRAS
model—were used to define stage-discharge
relations for 31 culverts and 2 bridge sites in a 10-
mile reach of the river. These relations can be used
to improve surface-water-flow models to evaluate
potential flooding.
Relations between headwater, tailwater, and
discharge through each structure were unique.
Discharge through the culverts as computed by the
CAP ranged from about 0 cubic feet per second to
as much discharge as could be conveyed, and tailwater
elevations ranged from about 0 to 30 feet
above the outlet elevation. Discharge through the
bridges, as computed by the HEC-RAS model,
ranged from nearly 0 to 7,000 cubic feet per second,
and tailwater elevations ranged from nearly 0
to 30 feet above the streambed on the downstream
cross section of each bridge.
Stage-discharge relations provided in lookup
tables in this report can be incorporated into
numerical surface-water-flow models to simulate
the effects of hydraulic structures on flood flows.
One limitation of the CAP and HEC-RAS models
is that changes in flow conditions, such as obstruction
by sediment and debris, are not simulated. If
flow through a hydraulic structure is obstructed by
sediment or debris, then model-simulated discharges
through the structure might be greater than
would be experienced under actual conditions.