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Posted 4/27/2017

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Contact
Project Manager
309-794-5704
cemvr-pm-web@usace.army.mil

Location
The Saylorville Lake Project, Johnston, Iowa, also includes the Big Creek Remedial Works which consists 3 dams, diversion channel, spillway and pump station. The Remedial Works protects Polk City, Iowa.

Description
The Saylorville Lake Project includes the Big Creek Remedial Works which protects Polk City in the Big Creek Valley. The Saylorville Project is a Flood Risk Management Project 8 miles north of the State Capital and Des Moines Metropolitan Area. The Barrier Dam, at the mouth of Big Creek, protects Polk City from Saylorville Lake and the Diversion Dam protects Polk City upstream. The interior drainage forms the Big Creek Ponding Area which water can be evacuated via gravity drainage through an 8-foot conduit.

As a supplement to the gravity conduit, a pumping station was constructed on the protected side of the Barrier Dam to aid in the transmittal of water from Big Creek Ponding Area to Saylorville Lake. The pump station was originally designed to handle the 100-year 4 day precipitation event and pump the ponding area from 848.6 feet down to 836 feet in approximately two weeks. The station was not designed to handle larger events resulting in putting the Polk City sewage lagoons & critical city infrastructure at risk for flooding. When the Saylorville Pool was permanently raised three feet in the early 1980’s to accommodate water supply storage, the window of opportunity to gravity flow water was greatly reduced.

Status
The existing pumping station was not designed to handle the increased rainfall in the watershed, nor the increased runoff which results in a significantly longer time to pump the Big Creek Ponding Area down to normal levels and increases the risks. As a result of the pool raise, gravity drainage is available approximately 6.5% of the time and has a positive head greater than four feet 1% of the time. Significant urbanization and land use changes in the 17 sq. mile Big Creek watershed has increased flow frequency and volume of water entering the ponding area. Rainfall observations show that in several years back to back precipitation events have resulted in run-off volumes that exceed the original design volume. The current pump capacity is inadequate to match inflow volumes & frequency from storm events. Existing pump station is operational with three new 350 h.p. motors and pumps that were re-built in 2015-2016. The supplemental pump station project is designed to be located to the west of the existing station. A new building that would accommodate three additional 500 h.p. motors and pumps. Total capacity of the supplemental station is designed at 200 cfs with discharging of water into the existing 8-foot conduit through the Barrier Dam. This is the #1 ranked deferred maintenance project in the Mississippi Valley Division. Plans and specifications for the Supplemental Pump Station are complete. Construction contract solicitation and award is pending additional funding.

Authority
OM - Operations and Maintenance

Summarized Project Costs

Estimated Federal Cost  $13,100,000
Estimated Non-Federal Cost  $0
Estimated Total Project Cost  $13,100,000 
Allocations Prior to Current FY 2017 Cost  $0
Current FY 2017 Allocation (received to date)  $0
Current FY 2017 Total Capability  $13,100,000 

Major Work Item Current Year
FY 2017:
Plans and specifications for the Supplemental Pump Station are complete. Construction contract solicitation and award is pending additional funding