Emergency Action Planning

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Lake Sherwood

Sylvan Lake EAP Case Study

DNR's Perspective

A working group was created that brought together various engineering and geospatial technicians within DNR, emergency managers, and others whose skills were needed to plan and execute a very ambitious multi-year plan to produce inundation maps and EAPs for all 469 HHP dams in the state. Glenn Lloyd, one of the working group leaders, said DNR wanted to move ahead quickly on the statewide mapping and EAP program in part due to two near failures of state regulated dams, one in 2008 and one in 2009. A swift response by DNR Dam Safety engineers and the owners resulted in the dams being saved. Construction equipment was quickly put to work to reroute the spillway flows and keep the dams intact. These incidents coincided with the working group formation and the start of the mapping. They created a sense of urgency to complete EAPs for the dams in and near population concentrations. Lloyd is a civil engineer who was in the dam safety program of the U.S. Army Corps of Engineers for 22 years before joining the Missouri Department of Natural Resources. He has been with DNR 19 years, the last 10 as a dam inspector. He was one of the dam safety team helping emergency manager Mike Daniels and dam owners in Warren County.

Group leader Glenn Lloyd
Group leader Glenn Lloyd

"Mike helped set up the first workshops in Warren County, participated in them to help us educate the dam owners about the importance of EAPs, and then followed up with each dam owner to assist them and finalize their EAPs," Lloyd said. "Mike also joined the DNR dam safety team in presenting an overview of this EAP program at the annual statewide conference of the Missouri State Emergency Management Agency. There and in other meetings he has been a crucial link in explaining the EAP process to other local EMDs.

"While doing all that, Mike continued to work hard with the dam owners in his county to achieve the best compliance rate in the state for a large county with multiple HHP dams.

"DNR approved the EAP for Lake Sherwood Dam on Dec. 29, 2010, so it was almost a year from the initial workshop discussions with the association people to the final approval. Once we had the inundation maps completed and handed them over to Mike and Ed Varno at the workshop, they did the detail work to get the EAP pulled together and work out any further information we felt was needed before DNR could sign off on it.

"Sherwood is one of the early gated communities outside St. Louis, and the city has now grown out to it, so people can live there and still work nearby. It's a very nice place. We have worked with the Sherwood organization well for many years, and they have stayed on top of their dam's needs. Sherwood managers also have their own regular inspection program. If they see something they don't understand or are uncomfortable with, they give us a call. We come out to take a look at it and give them any assistance we can. Lake Sherwood has a history of having a very responsible and concerned organization, and while they aren't the only one like that in Missouri, they certainly are one of the best.

"They have a private engineer with Shannon & Wilson a major regional engineering firm based in St. Louis, but apparently they weren't involved in the EAP development. The engineer helps them with seepage issues. They have done some grouting, but it's mostly to maintain the lake level and control the volume of water seeping, which is through rock and is not a major concern to us. An interesting aspect of Lake Sherwood Dam is that the downstream face is entirely coated in concrete, so seepage should not cause any erosion of the dam face.

"Sherwood has done grouting, which is a form of sand and cement under pressure, every few years to help seal up the seepage points. They recently obtained another construction permit for additional grouting. In dry years they always notice they need to grout again. It can be difficult for the drilling and grouting to hit the precise spot where it is needed. Grouting is usually a needle-in-a-haystack kind of process. At one dam elsewhere in the state they drilled 11 holes and it was the 12th one that finally sealed the seepage.

"Sherwood's upstream dams are less than 35 feet in height, so they normally are not regulated by DNR. But one of them has other characteristics that qualify it as a Class 1 dam (HHP) so it is regulated by state law and fits our requirements for an EAP. The upstream lakes are small enough that if any of them were to breach, Lake Sherwood itself would just hiccup. In fact the toe of that regulated upstream dam is under the surface of Lake Sherwood. If it breached they would lose one of their community roads, but it would not threaten the integrity of the main dam on Lake Sherwood.

"We hope Mike and Ed will schedule a dam break exercise of their EAP, preferably in partnership with the State Emergency Management Agency. It would be a good experience for everyone involved.

"In contrast to Sherwood, we have had some dam owners who are not responsive to our letters and phone calls regarding their need to complete EAPs. As a result we have implemented a Plan B work-around in which we will use the inundation maps and information we have on hand to complete more of the EAP for them. We will send them the EAP and ask if there are any changes they know we should make. We aren't anxious to do their job for them, but it's easier in the long run. It's just the path of least resistance, and this will get the EAPs completed sooner than otherwise. We often are in the same area as those dams on a routine inspection anyway, so taking another hour or two to examine the situation downstream at their dam is not a major issue. Plus, it has given us the side benefit of seeing what exactly is downstream of the dams in more detail – how many homes are there now, where they are, and what could be involved in the event of a dam failure. In some instances we've modified the hazard classification of the dam as a result of knowing what is actually there.

"We are doing a presentation on our EAP program work at Missouri's statewide emergency management conference in April 2015 and have suggested a similar presentation for the Association of State Dam Safety officials for their national meeting in September in New Orleans.

"In 2015 we will be completing the last 60 inundation maps, which are primarily for mine tailings dams. With those we have to apply the technology differently, but when we have those EAPs completed we will schedule the last few dam owner workshops. These tailings dams are mostly in four southeast Missouri counties that each already has EAPs completed for a couple of traditional dams. So a lot of the information on the tailings dams will be the same as we have already documented. The tailings dam EAPs will go fairly quickly because half of them are in one county. The Emergency Management Director there has said she's willing, like Mike Daniels, to sit down with us and get the EAPs done."

Lake Sherwood: Aerial map.
Lake Sherwood: Aerial map.