31 Mar 95
continuous stage-hydrograph of ponding elevations and the
drain outflow for each site. Annual peak values could then be
extracted for graphical display.
Data were used to prepare a CSA for each of the
relationships resulting from the CSA method were very
five subareas. Trial runs of HEC-IFH initially were made on an
comparable with the HEA results, falling between the HEA
expanded memory 386/25 PC using a 10-min time increment.
stage-frequency relationships for blocked and unblocked
These early trials resulted in extremely lengthy run times. Runs
of 8 to 10 hr were typical, with the run aborting before
completion of the CSA due to inadequate computer storage.
The results of the CSA were used to determine the
The acquisition of a 486/33 PC during this phase lessened the
minimum facility, which is shown in Table E-6. Table E-7
problem; however, it was decided to modify the time-step to 1
compares the results of the HEA and CSA for the 100-year
hr to improve the computation performance. The interior
average return period event at one site. Each gravity outlet
inflow hydrographs would not be adequately defined; however,
was analyzed similarly. The hydraulic design details for the
the inflow volume would be acceptable for routing through the
gravity outlets planned for the minimum facility are shown
storage areas and out the gravity outlet(s). Using a 1-hr time
in Table E-8.
step for the 40 years of record resulted in about 3 hr of
computation time for a 486/33 PC. The CSA gave a
CSA Interior Analysis Summary (Minimum Facility)
Comparison of HEA and CSA for the 1-Percent Event