Flood Reduction, Dams, & Levees
Nuclear Power Station Extreme Rainfall Event
As a result of the Fukushima accident, nuclear power plants are now reviewing their infrastructure and operational procedures to minimize their risk should this, or a similar event occur near their plant. A team of experts was assembled for this five-day Value Planning study to ensure the safety of a nuclear power station during an extreme rainfall event. One of the major objectives of the study was to develop a plan for intervention that minimized actions required of plant personnel.
Flood Risk Management Project
The design concept for this flood mitigation project included a concrete ogee-crested spillway founded on piling, a fish passage, and a portion of the diversion channel with a low flow channel. Each of the disparate elements was addressed independently presenting significant design challenges. This Value Planning study facilitated an efficient transfer of knowledge from the largely private sector feasibility team to the in-house design team while developing a coherent, integrated design.
Auxiliary Water Supply
A potential situation had been postulated that both of the13.5 MW Kaplan (fish) turbines are inoperable for a year creating the need for a back-up water supply to ensure there is no disruption to fish migration. The back-up water system would feed the auxiliary water system, which is fed by the discharge from the two turbines. To provide the back-up water supply, the proposed design was to mine a hole through the concrete portion of the dam to install a 10-foot diameter steel pipe to supply 1,400 cfs to the auxiliary water supply. The pipe will be routed to the existing, and currently abandoned, fish lock approach channel where a seven-foot diameter cone valve will dissipate the head differential. The fish approach channel will be modified to accommodate the discharge from the cone valve and to dissipate the remaining energy before transferring the flow through six (6) six-foot diameter pipes into the auxiliary water supply chamber (AWSC). From the Value Engineering study several constructability risks and potential risks to the long term stability of the dam were identified; the team provided alternatives to mitigate these risks while achieving a more cost effective design concept.
Industrial Park Receives 500 Year Flood Protection
The Dodson Industrial District is a unique mix of industrial, commercial, and retail businesses in the southeast area of Kansas City, MO. It may be the oldest, organized district in the City, dating back well before World War II. The Blue River, generally, is the southern boundary of the district. At one point, the oxbow of the river was cut off, diverting the river to its present course, leading the City to establish a landfill site in the former oxbow.
Due to the excessive and sudden flooding associated with this area, the US Army Corps of Engineers along with the City of Kansas City began a four-phase construction program to build a 1.29 mile levee and flood wall system to reduce the flooding risk for this area.
There were two major cost drivers in this project; foundation preparation and sanitary sewer relocation. Nearly 50% of the project cost was related to foundation preparation due to the old uncontrolled landfill area and the undetermined amount of buried trash. The value team provided a solution that would achieve a positive seepage cutoff and reduce the large volume of excavation and disposal cost associated with removing this buried material, the Value Team recommended the use of a slurry cutoff wall that would improve the seepage control and minimize the required excavation.
Additionally the Value team provided solutions that would avoid the gravity sewer in the toe of the levee and protect the water main levels.
Raw Water Reservoir
SVS conducted a Value Engineering Study on this dam and reservoir project to create raw water storage to feed a planned 15 MGD water treatment plant (WTP) located nearby. The project includes the construction of a 315 meter long roller compacted concrete (RCC) gravity dam. The crest elevation is approximately 30 meters above the invert of the nearby river at elevation 103.5 meters. The normal operating pool will be at elevation 100.0 meters with a maximum flood pool at elevation 102.0 meters. The study resulted in 15% of the project budget in savings.
Stream Work Value Study Saves over 90%
Through team leadership provided by SVS, the value engineering team was able to reduce the project cost of this $42 million project to $3 million. The studied project includes a three-mile reach of a creek through a pristine upper-scale subdivision in the heart of Kansas City, which causes frequent flooding to homes in excess of $500,000. Using natural stream design methods, the value engineering team was able to remove all but one home from the 100-year flood plain and reduce the construction cost from $42 million to $3 million, a savings of over 90%.
Emergency Levee Repair
In order to repair the damages suffered in the prolonged 2011 flooding along Council Bluffs, Iowa levee system, 28.5 miles are to be restored. Also damaged were a short section of wall, pump stations, relief wells, and interior drainage consisting of pipes through the levee, flap gates, and gatewells. As a result of the flood, the structure of the Veterans Memorial Highway pump station failed, damaging the pipeline through the levee. The levee was scoured and eroded in many locations and the grass on the upstream face was killed by prolonged inundation. Two key scope items include the restoration of the damaged pump stations and repairs to Veterans Memorial Highway.
Since the levees must be repaired before the following spring floods, much of the value teams’ efforts were focused on supporting the on-going work and shortening construction duration. Many of the value team’s ideas implemented involved revising the methods of contracting to expedite construction, and to improve the robustness and life cycle of the levee system structures.
Rough River Dam
Rough River Dam, a 1590-foot long earthen dam, is part of a three-dam complex providing flood protection to the Green River Basin of Kentucky. Based on the Screening Portfolio Risk Assessment, this dam is rated as a Class II (urgent unsafe or potentially unsafe). The comprehensive risk assessment cited the potential for seepage and piping failure modes and recommended expedited action to remedy these potential risks.
This project entails construction of a complete cutoff wall with foundation grouting and the construction of a conduit filter. This action is intended to reduce the potential risk to well within tolerable guidelines.
The Value team recommended alternatives which offered the potential to reduce the project cost by over 75% while reducing the potential for seepage and piping failure modes to well within tolerable guidelines. One alternative included construction of a tunnel in the rock along the axis of the dam with seepage barriers in lieu of a cutoff wall with foundation grouting.
Eastbank Pump Station
This flood reduction project consists of providing a new floodwall between the pump stations and the lake using a T-wall design, extension of the discharge tubes/pipes, and addition of 12-foot wide sluice gates on the horizontal pumps discharges. In addition, new breakwater structures will be added to two of the four existing pump stations at this facility. The pump stations house multiple horizontal pumps with 11-foot diameter impellers powered by 3,100 HP diesel engines.
The value engineering study resulted in recommendations to add additional capacity to the floodwalls and eliminate the breakwaters and to replace a mechanical slide gate for each of the sluice gates with one set of stop logs for each pump station. The new floodwall was also moved further away from the pump station to allow continued operation of the pump stations during construction. These recommendations saved $30 million and several months of construction without sacrificing any of the functional performance requirements for the project.
Urban Flood Reduction
This Creek Basin has had a long history of severe flooding, often extensive damage along an important commercial corridor in a large city in the midwest. The project’s purpose was to provide 100-year flood protection to the community by increasing the flood conveyance capacity of the creek.
The original concept plan was to increase the channel cross section through a combination of excavation, retaining walls, and flood walls in the upper reach of the creek, maintain the middle reach as the natural channel, and convert the lower reach into a vertical walled channel. To accommodate the widened creek cross section in the upper reach, two bridges including a railroad bridge were to be replaced. However, due to certain constraints, both new bridges would still have hydraulic concerns.
The value team challenged the traditional thinking and searched for innovative solutions – solutions that had not been previously considered. In doing so, the team focused on improving the performance of the required functions. As a result of implementing the team’s recommended value alternatives, a natural stream design was incorporated into the upper and middle reaches of the creek to improve conveyance and increase long-term stability of the creek. The implementation of the value alternatives improved: aesthetics, channel conveyance, railroad alignment, public safety, stability of the railroad bridge and actually simplified the entire project. Beyond these enhancements to function performance, the value team was able to achieve a $28 million savings on this project. More importantly, the local sponsor is extremely satisfied and feels that they now have a much improved project.