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Lake Sherwood

Sylvan Lake EAP Case Study

Lake Sherwood Dam EAP Case Study

Lake Sherwood team 'pilot tested' the Missouri EAP template and process

Community dam owners, emergency manager and state
engineers pleased with efficiency and results of partnering

Lake Sherwood: Upstream face.
Lake Sherwood: Upstream face.

In 1967, when the current dam was built that would create the 145-acre impoundment at the heart of Lake Sherwood Estates, St. Louis seemed farther away than it does now. The lake hasn't moved and is still 47 miles northwest of the city, but metropolitan sprawl has reached out toward the horseshow cluster of six lakes, five of them interconnected, that comprise the 1,200 acres of woods, water and homes that today are Lake Sherwood Estates.

Typical of St. Louis, there is much history in the Lake Sherwood area. The final home and the original grave site of Daniel Boone and his wife Rebecca are nearby, along with a departure point on the Missouri River for the Lewis and Clark Expedition. Nearby towns include Washington and Marthasville. In 1854, John B. Busch, and older brother of the famous Adolphus Busch, established a brewery in Washington, bottling the first Busch Beer.

The Dam and the Lakes

Lake Sherwood: Downtream face.
Lake Sherwood: Downtream face.

Today, wineries and other attractions dot the land around and east of Lake Sherwood Estates. The Lake Sherwood Dam is designated High-Hazard Potential (HHP) and requires an Emergency Action Plan (EAP) because of the downstream homes, state and Warren County roads and bridges, and other development along a potential inundation area that winds about six miles toward the edge of Marthasville.

Lake Sherwood Estates has six lakes and more than 1,000 property owners. One lake is a mere three acres in size and is separated from the other five, which are connected by conduits and dams. All five lakes are considered part of the Lake Sherwood Dam EAP. At the center of the community is Lake Sherwood. It holds water from a Wolf Creek watershed of nearly 3,000 acres. The lake's normal storage is 2,982 acre-feet of water. The dam is 67 feet high and 1,000 feet long. It is earthen, but with concrete facing on the downstream side.

Lake Sherwood: Area downstream of dam.
Lake Sherwood: Area downstream of dam.

Dams for two of the smaller secondary lakes (Lake Robin Hood and Lake Marian) are not state regulated. A dam on Sugar Hollow Lake is regulated as a Class 1 (HHP) dam and has its own EAP. Were it to breach the water most likely would simply be absorbed by Lake Sherwood, although docks and boats on Lake Sherwood could be damaged by a sudden and potentially hazardous rise of the water level. A failure of one or more of the secondary dams is considered to be of little consequence. Engineers have determined there is virtually no risk of a "cascade" dam failure. Cascading is when a breach of an upstream dam in a system of dams such as at Lake Sherwood Estates causes the failure of one or more downstream dams. When developing hazard classifications for dams, engineers doing breach analysis examine the performance of the entire system if cascading could be a factor in the severity of a dam failure sequence. They will incorporate those possibilities into breach analysis and inundation mapping.

The Lake Sherwood Estates Homeowners Association (HOA) has ownership of the dams and the attendant liabilities. In the nearly 50 years of the dam's existence there has not been a breach or major incident. There has been some seepage typical of many dams of this type in Missouri, and the HOA has had these problems analyzed and addressed by grouting the likely routes of leakage through the rock and earth of the dam. Regularly scheduled inspections and remedial actions by the HOA have made it a model for similar community organizations that own dams.

Lake Sherwood: Dam crest
Lake Sherwood: Dam crest.

Several years ago the homeowner members, directors, and managers of the Sherwood Lake Estates HOA became aware of their liability for any property damage and loss of life if Lake Sherwood Dam were to fail. Their commitment to the EAP process coincided with the launching of a major multi-year initiative by the Missouri Department of Natural Resources (DNR) Dam Safety Program to create breach analysis and inundation maps for each of the state's 469 HHP dams. Providing the dam owners with the analysis and maps – along with developing a uniform, Missouri-specific EAP template for dam owners to use – were the first steps in creation of EAPs for each of the HHP dams, a process expected to complete in 2015 with 100 percent EAP compliance.

The Team

For decades Missouri law specified HHP dam owners were to create EAPs for their dams. In 1990, a provision was added to the state's geologic hazards law requiring inundation maps on all state-regulated dams. Responsibility was assigned to the DNR. But DNR staff and funding shortages meant the law was never fully implemented. If DNR could not do its part of the job, DNR officials reasoned, then dam owners should not be held accountable for EAPs. After all, an EAP without a breach study and inundation maps is not as helpful as it should be. The maps and EAPs issue languished until new geospatial and mapping technologies came along that were less costly and more efficient. DNR dam safety engineers recognized that providing the maps and working with dam owners on EAPs would finally be feasible. Grant funds from the Federal Emergency Management Agency (FEMA) also were important to moving the program forward.

A DNR-led dam safety EAP working group began the new initiative in 2008. The immediate priority was creating maps for dams in the most populous and counties with the most HHP dams. The second priority was to develop a Missouri-specific EAP template. After several of the inundation maps were completed for a particular county, workshops were scheduled to bring together dam owners, local emergency managers, and other stakeholders for education on how to use the maps and the template to finalize the EAP's. The maps were given to each dam owner and their emergency manager, along with the EAP template pre-populated with technical information about the dam from dam construction and inspection records at DNR.

The pilot county for the program was rapidly growing Warren County just west of St. Louis. The county has 125 dams, 28 of which are HHP. Very importantly, Warren County also has a dedicated Emergency Management Director willing to work closely with DNR and dam owners, including Lake Sherwood Estates.

The EAP team that put together the EAP for Lake Sherwood Dam was led by:

  • Ed Varno, Lake Sherwood Estates HOA General Manager.
  • George Schmidt, Lake Sherwood Estates Public Works Director.
  • Michael Daniels, Warren County Emergency Management Director.
  • Glenn D. Lloyd, JR., PE, Dam Safety Engineer, Missouri Department of Natural Resources, Water Resources Center. He led the DNR's EAP team and coordinated with DNR Surface Water Section technicians developing inundation maps.

Additional stakeholders involved included the Marthasville Fire Protection and Ambulance District, the Marthasville Police Department, the Warren County Sheriff's Department, the New Melle Fire Protection District, the Warren County Emergency Operations Center staff, the Warren County Roads & Bridges Department, the Missouri State Highway Patrol, the National Weather Service, and the Missouri State Emergency Management Agency.

Lake Sherwood: Topographic map.
Lake Sherwood: Topographic map.