ETL 1110-2-367
31 Mar 95
(1) The base condition for evaluating pumping capacity is
with-project conditions stage-frequency relationships for the
with the selected gravity outlet configuration in place. Several
pumping plans.
pumping station plans are evaluated against the base plan, each
f.
Economic analysis of pumping station plans. The
with an incremental increase in pumping capacity.
following paragraphs describe the procedures for performing the
(2) The pump operation criteria must be defined. Pump-
economic analysis of pumping stations.
on and pump-off elevations must be determined so that the
pumps operate prior to the start of damages. Pump-on
(1) The cost engineering team member provides cost
elevations are usually set below flood stage with pump-off
estimates of several pumping station plans or sizes as were
elevations usually set at 0.3 to 0.6 m (1 to 2 ft) below pump-on
specified and evaluated. The stage-damage relationships
elevations. If a levee stability problem exists when the exterior
previously provided by the economist are still applicable.
river reaches a certain stage, the pump-off elevation must be set
for a higher stage. Two or more pump units generally make up
(2) An economic analysis is required for all pumping
total pumping capacity. Several units that can be operated in
stations to determine the NED (USACE 1990a) pump capacity.
phases to step up to the total capacity may be more effective
The cost engineering team member provides cost estimates of
than one or two large-capacity pumps. Pump cycling can
each pumping station analyzed using HEC-IFH and the
become a problem with a few large pumps and limited
economist provides stage-damage relationships by damage
conveyance capability to the pumping station. Limited flow
category for existing and potential future with-project
delivery capacity to the station or flow surges in sewer systems
conditions. The expected annual damage for each plan or
or at locations close to an upper basin with a very short time of
pumping station capacity is determined by the study economist
concentration can cause cycling problems. Varying the capacity
using the computed stage-frequency relationships and the stage-
of the pump units and the on-off elevations minimizes pump
damage relationships.
cycling times.
(3) The operation and maintenance costs of pumping
(3) HEC-IFH can use up to ten pumping units for each
stations are significant and an important factor, especially from
interior pumping plan specified by the PUMP module. All
the local sponsor's standpoint. HEC-IFH provides data such as
pumping units are assumed to be located at the primary outlet
the maximum pump head and the average annual days pumped.
location. The PUMP module input is summarized in Chapter 3
These data are evaluated by the electrical/mechanical engineer
for CSA, and in Chapter 7 of the HEC-IFH user's manual. The
to determine electrical or fuel costs, and to assist in pump
operating data entered for the CSA and HEA is slightly
selection.
different. For CSA, different values of pump start and stop may
be defined for each calendar month of the year. For HEA, a
(4) A plan comparison array as shown in Table 5-1 is
single pump start and stop elevation is defined for use during the
developed to aid in identifying the economically optimal or NED
entire analysis.
plan. The data for benefits and annual costs for each plan versus
pump station capacity are then plotted to pick the economically
(4) The CSA and HEA may both be used to evaluate the
optimal plan as illustrated in Figure 5-5. Other environmental,
pumping station design and to derive the existing and future
social impacts, performance, operation, and safety information
Table 5-1
Economic Evaluation of Pumping Station Capacity
Expected
Average
Average
Average
Annual
Annual
Annual
Net
Damage
Benefits
Cost
Benefits
B/C
Plan
(00)
(00)
(00)
(00)
Ratio
Levee + Minimum Facility
952
-
-
-
-
Plus 80 m3/s (100 cfs) pump
632
320
400
-80
0.80
Plus 155 m3/s (200 cfs) pump
328
624
510
+114
1.22
Plus 230 m3/s (300 cfs) pump
185
767
650
+117
1.18
Plus 385 m3/s (500 cfs) pump
46
906
980
-74
0.90
5-10
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