City Officials Concerned That lake Level Could Affect Water Supply

September 27, 2007
Dwayne Page

With the U.S. Army Corps of Engineers planning to make repairs to Center Hill Dam, Smithville Mayor Taft Hendrixson and other city leaders are concerned about how that might affect the elevation of Center Hill Lake and the intake operation for the city's water supply.

The City of Smithville owns and operates a multiport raw water intake structure located at Center Hill Lake. This intake is the sole source of water for the City of Smithville and the DeKalb Utility District, the city's largest water customer. The intake was constructed in 1967.

In a letter to Joy Broach, Project Planning Branch of the U.S. Army Corps of Engineers, Mayor Hendrixson recently expressed his concerns "The engineering company that designed this structure still serves as the city's consultant and according to their calculations, the absolute minimum lake elevation which will allow this intake to function hydraulically is elevation 618.0 Mean Sea Level (MSL).However, they have cautioned that lake elevations below 620.0 MSL could cause turbulence in the pump well possibly affecting the pumps. In addition, the city's water treatment plant operators report that lake elevations below 623.5 MSL result in poor raw water quality which creates treatment difficulties. For these reasons, we prefer that the Corps of Engineers maintain the elevation of Center Hill Lake at elevation 623.5 or above but understand the importance of Dam repair. If the lake surface is dropped below elevation 620.0 the city's pumps may begin to cavitate and malfunction which will result in the city being out of water."

Tim Dunn, Resource Manager of Center Hill Lake, says repairing the seepage problem at Center Hill Dam may not require the lake elevation to be dropped to the level that would affect water supply for utilities, but there might be a concern because of prolonged dry weather. "We want to make sure we have public water, both for consumption in the homes as well as for fire protection and those types of things, so water supply will be strongly considered in any decisions about lake levels. With the seepage problems, I don't foresee us making any decisions to take the lake down below the existing water intake unless it were a worst case scenario type situation. For normal operations, I don't expect it to have any impact. However, as you know, this summer and early fall we are in a severe drought and there is a possibility that with the drought, at the elevation we are at now on through the fall, we could be looking at fairly low levels this winter toward the end of December down around the low 620's and maybe even as far down as 618 or 619. Hopefully, we will get enough rain that this won't become a reality but if it does I would encourage the water users or water supply folks to consider looking at their drought contingency plans and see what would be required if the drought necessitated the lake going down further than what we would intentionally take the level to. It's something to be aware of and think through, but from the seepage standpoint, I don't expect us going below levels that would affect the water intake."

Dunn says the lake level, as of Wednesday, was at 630 Mean Sea Level. " It is at elevation 630 and that is feet above sea level. To put it into perspective, our normal summer pool elevation is 648, so we're about 18 feet below where we are normally in the middle of the summertime, around Memorial Day. Under our current plan of operation, we are expected to go down to around 623.5 this winter. However, as I mentioned, the drought, with no inflow coming into the lake and with evaporation and minimum releases for water quality and other uses downstream, we may be looking at lower than 623.5. As we go lower, if the drought requires us to go lower, we will work very closely with the other users and the water supply folks to ensure that we know how affective they are able to withdraw water at various elevations and see if there are problems before they occur. Now is the time that communication and working closely together is going to be very important."

Dunn says Corps officials have been in contact with city officials and others who may be affected by the lake elevation. "We have talked with them as well as other stakeholders on the lake as part of our Environmental Impact Statement process. We're doing an Environmental Impact Statement to address possible lake level adjustments, further lowering the lake, and as part of that process we've asked the public and any interested parties to comment on what their impacts may be, and in particular, I have talked with the water supply folks as well as marinas and others who are directly affected by it. We recently talked with the cities and their engineers about exactly what elevations the water intakes could be affected. One of the main things right now is that we want to capture that information and know that we understand and know exactly what the elevations are that are critical to various users so that we can keep that in mind and incorporate that in our decision making process. However, I do want to make sure that the public is aware that public health and safety, which would include water supply, is definitely one of our top priorities."

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