The Water Level

The designs are concepts at this point and the project is still being designed.  The different project options range from no change in water elevations to approximately a 1.6’ drop in the water elevation of the upstream Crissy Lake reservoir.

 The water depth in Crissy Lake is getting shallower over time.  This is mainly happening in north end of the reservoir where the Pomme de Terre River enters.  Sediment carried by the river falls out when it enters the reservoir as flow speed decreases.  This sediment has been accumulating since the dam was constructed in 1939, and is slowly filling in the reservoir.  Initial construction plans from 1935 stated that the average water depth in Crissy Lake was going to be 6 – 7 feet.  Currently, average water depths are 2 – 3 feet.  Comparing photos from 1959 to 2022 below you can see how the north end of the reservoir has narrowed and created more of a stream channel through it.  Over time, we expect this process to continue and slowly create a more natural channel extending south into the shallow areas of the reservoir.  See “Resources” below for additional information on the sediment process above dams.

If the water elevation level is dropped in the upstream reservoir, there would be an opportunity to restore some of the stream channel at the north end of the reservoir.  The area that would be restored is currently less than 1.6’ deep according to a survey done in the spring of 2024 by the DNR.  Restoring it now will mean that we can control where the new stream channel forms, it will create stream habitat with deep pools (5’+ deep) and connected floodplain, we can include more fishing access within the city park and allow for mitigation of the new greenspace to prevent unwanted plants like buckthorn and cattails. This would also restore stream processes where this same sediment that is filling up the reservoir can be deposited in the restored floodplain during flood flows.

Maintaining the water level at the current elevation will not let us control the eventual greenspace.  The sediment will still accumulate in the upstream reservoir, and in time a stream channel will eventually form in additional areas of the reservoir.  Where the new channel forms will be up to the stream.  There would need to be a project in the future to manage buckthorn and cattails that may establish in these riparian areas. 

Other issues with keeping the water level at the current elevation are: increased risk associated with maintaining higher water level; stress on old dam embankment are mostly shifted to County Road 10 embankment; the elevation of County Road 10 may need to be raised to meet navigation requirements for new bridge.

Regardless of the final design for the Crissy Lake Dam project, construction will take place in fall/winter when water elevations and flows are at their lowest, to reduce possibility of a dramatic change in water elevation during construction.