by Tom Cox, Chair, Lake Level Management Committee

Birch Lake Outlet Structure | Dam Raiders Strike Again | Water Levels Down

Birch Lake Outlet Structure Update

On August 28, Cass County Engineer Dave Enblom convened a meeting at the Hackensack Senior Center for the purpose of updating the public on the status of DNR's 2-year hydrologic study to determine the effect of the Birch Lake Outlet Structure on Ten Mile water levels. Thirty-eight people attended, fifteen of them Ten Mile residents representing thirteen Ten Mile families.

David Ford, Supervisor, Surface Hydrology Unit, DNR Central Office, St. Paul, introduced Dr. Dana Dostert, Surface Water Hydrologist, St. Paul, who made a Power Point presentation covering the century-long history of the outlet structure, the "Thoroughfare" (Boy River) between Ten Mile and Birch, and the hydrological data gathered since last summer. Two of the most interesting discoveries were:

1. that the elevation of the bottom of the river reaches a high point just under the CSAH # 6 bridge - so high, in fact, that at this point there is an effective second "dam" impeding the flow of water out of Ten Mile into Birch Lake, and
2. that over the course of the summer, vegetation in the river increases markedly, so much so as to significantly slow Ten Mile's outflow.

These two facts, among others, result in the observation that "Once Ten Mile levels are high, they take longer to recede than Birch levels partially because Ten Mile Lake is four times greater in surface area than Birch and also because of resistance and restrictions in the channel between the lakes."

Dave Enblom reported that the County was presently soliciting bids on the construction of a new, "clear-span" bridge over CSAH #6. Construction is due to take place this fall, and will have the effect of considerably opening up the channel under the bridge where, presently, the remains of a previous dam, piling caps from the previous bridge and the pilings supporting the present bridge impede water flow themselves and provide ideal conditions for the construction of a beaver dam.
Years ago, Dostert reported, local realtors sponsored the dredging of the river so that they could promote real estate sales on Ten Mile by advertising water access from Ten Mile to the town of Hackensack. Asked whether dredging might be a present-day possibility, Kirk English, DNR Regional Hydrologist, Bemidji, observed that dredging would have fisheries impact and that the question would need to be taken up with DNR's Fisheries Division.

Dostert observed that varying rates of precipitation are the major cause for high and low lake levels. Annual precipitation in seven of the last eight years has been above the 30-year annual mean (27.4"). Year 1999 (31.4") and year 2000 (33.9") are the only two consecutive years of 30" or more of precipitation within the last 30 years. Year 2001 precipitation of 29.6" added to the average cumulative effect. Because of recent years' high precipitation, groundwater levels, which also contribute to lake levels, have increased by more than three feet in this area since 1993.

DNR's study will continue through this next year. DNR hopes to be able to present a final report next summer, with recommendations to Kirk English in the Bemidji office and to the County regarding the future treatment of the Birch Lake Outlet Structure. The goal, insofar as possible, is to have a "fixed weir" structure that will prevent Birch Lake's dropping to unacceptable levels in periods of drought while, in periods of high water, allowing excess water to escape from Birch and Ten Mile without causing hardship downstream through Hackensack, and on Poquet and Pleasant Lakes.

Dam Raiders Strike Again

Where it passes under the CSAH #6 bridge, the Boy River stayed clear of beaver dam activity in early summer, but by the end of July it was clear that the beavers were back, and busy. Bouquets to these intrepid Raiders who descended on the river on Friday, August 9, to rid the stream of dam debris:

With any luck, the new Boy River bridge may obviate the need for the Dam Raiders, though in the worst case the beavers may simply find another, more inaccessible spot to build. This would impede water flow and be much more difficult for the Dam Raiders to remove. Stay tuned!

Water Levels Down This Year

Water in Ten Mile has been lower this summer than last. On May 10, the water was down 3.12 inches from its level on May 1, 2001. On June 8 water stood 10.08 inches lower than it did on June 1 the previous year. By the end of June, however, with summer rains, the difference had decreased to 6 inches, and by the second week in July it had decreased to 3.96 inches.

Last year, after reaching its record high of 1380.22' on June 14, the lake level dropped steadily as the summer wore on, and stood at 1379.60', down 7.44 inches, on September 1. This year on September 4, the level was 1379.58', or about a quarter of an inch lower than last year on roughly the same date.

Walt Kane reports that this year, in late summer, his readings have been disrupted by the dislocation of the DNR gauge in Long Bay due to construction adjacent to the gauge site. The gauge has now been reset, though in a less accessible location, which makes readings more difficult. Meanwhile, in connection with the DNR's ongoing hydrological study, a separate, computerized gauge is sampling the level every ten minutes, and averaging and recording those readings every thirty minutes. This information is far more detailed than we are used to, but it is less convenient for us to obtain than Walt's customary weekly readings for the TMLA. In the near future, our reports will be a little less contemporary than we would prefer.