About Lake Detroit Water Levels
Detroit Lake Level Influencers
Precipitation is the ultimate source of the water in Detroit Lake. An annual average of 26 inches of precipitation falls across the approximately 40,000 acres of the Lake’s watershed, including Lake Detroit’s 3000 surface acres. However, the amount of water in the lake’s basin at any time has to do with several factors - how much and when precipitation occurs, how much water flows into the lake from the watershed (from streams, stormwater runoff, and groundwater sources), how much flows out of the lake (by streams, and groundwater interactions) and how much evaporates.
Precipitation variability in timing and amounts - While the average rainfall is 26 inches over the last 30 years in the Lake Detroit area, actual annual precipitation has varied from 18 to 36 inches, with an average departure from the mean of plus or minus about 4 inches (16%). It also is noteworthy that an average of 21 inches (a bit over three-quarters of the annual rainfall) falls during the open water season, but that amount has ranged from 13 to 30 inches.
Surface Flows –1995 to 2009 data show an average annual flow of almost one billion cubic feet entered the lake from its 40,000-acre watershed (which includes Big and Little Floyd Lakes) mostly through the Pelican River. But variability in upstream precipitation patterns generated flows to the lake ranging from 500 million to 1.5 billion cubic feet. During any given period, surface flows out of the lake, approximate the inflows.
Groundwater - A large aquifer underlies all of Detroit’s watershed. It receives water from spring snowmelt and precipitation as well as from regional aquifers extending beyond Detroit’s watershed. Some flowing wells and springs are found in depressions and along streams and Detroit’s lakeshore. These sources provide some flows to the lake, but the volumes and variations are unknown.
Evaporation - Studies have shown that average annual evaporation rates from western Minnesota lake surfaces are very close to the average local annual precipitation rates. However, the evaporation amount at any particular time is tied to temperature and humidity. In a dry mid-summer, evaporation can reduce Lake Detroit levels more than an inch per week.
The Management of Lake Detroit’s Level
Before the late 1880’s, Detroit Lake existed as two adjacent water bodies more or less separated by a low sand barrier. The shallower Little Detroit was sometimes subject to “winterkill” of fish populations because inflows and its shallow depth sometimes failed to provide sufficient oxygen for some species. Little Detroit was connected by the meandering Pelican River which dropped about four-and-a-half feet in elevation to reach Muskrat Lake; Lake Sallie was about one foot lower than Muskrat Lake.
To enable steamboat navigation, in 1888-89 the Pelican River was straightened, its streambed excavated, and an earthen dam and wooden lock/dam system was installed at the outlet between Muskrat and Sallie. The lock/dam facility increased the average water levels in Muskrat and the Pelican River by about four feet and in Detroit Lake by about 1.5 feet, permitting steamboats to move from Little Detroit through the Pelican River, Muskrat to Sallie.
A little later, a channel was dug through the narrow strip of land dividing Big and Little Detroit to permit the steamboats access to a landing serving the railroad in the vicinity of what we now refer to as the Highway 10 Overlook.
Besides facilitating navigation, the increase from natural (pre-1888) levels helped make some shallow shorelines more suitable for swimming and boating. The channel through the sandbar allowed oxygen transfer from Big Detroit thereby reducing winterkill in Little Detroit, but it was no longer possible to use the sandbar dividing the Big and Little Lakes as a cartway.
The local steamboat era ended by the 1920’s with the building of roads and the advent and widespread use of automobiles but the era’s legacy included altered shorelines, biology and depths for Lake Detroit.
In the 1930’s the original earthen dam and wooden lock system enabling navigation from Detroit to Sallie, Melissa and beyond, was replaced with a concrete structure. While it no longer served steamboat navigation, the replacement structure kept Muskrat and Detroit Lakes at higher levels. The dam itself was designed to allow for adjustments to control minor fluctuations in water levels.
Meanwhile, for some decades the City of Detroit Lakes had discharged its untreated sewage to shallow areas of Lake St. Clair, which then extended to the west edge of the city, nearly to the Soo Line railway. To reduce the objectionable odors and potential health hazards, in 1918 a large portion of Lake St. Clair was drained away from city development by ditches to the Pelican River flowing to Muskrat Lake. However, as the city grew, it expanded its public water supply usage and sewage disposal with the result that during dry periods the sewage-augmented flows through the St. Clair ditch were enough to cause the Pelican River to reverse its normal flow towards Muskrat and Sallie, discharging instead to Little Detroit Lake.
During the several dry years of the 1930’s, the City’s solution to the mis-directed sewage problem was in 1935 to erect a “temporary” dam at the outlet of Little Detroit in 1935 to prevent the backflows from the river. The dam also allowed adjustments of Little Detroit’s outflow level, but timely height adjustments were difficult, a circumstance resulting in occasional and unpredictable high levels of water in Detroit Lake. Also, both the temporary dam and the Dunton Lock/Dam facility were subject to unauthorized manipulations of the dam height, either as pranks, or to address dissatisfaction with an existing lake level.
In 1964 the State of Minnesota delegated management of the Dunton Dam to the City of Detroit Lakes. A goal was to manage Detroit levels to address long-standing shoreline owners’ complaints of ice-damage to shorelines as well as to reduce the backflows of sewage to Little Detroit. Winston Larson, longtime City Engineer was given responsibility for the adjustments in dam levels and did so for about 10 years. Later he reported that the attempt to manage water levels was frustrating and the effort was abandoned in the mid-seventies “because it just didn’t work”.
Following mid-1960’s improvements to Detroit’s sewage treatment system that lessened the sewage backflow problem from the Pelican River, and because of growing interest in re-establishing the old navigable waterway from Detroit to Melissa, the “temporary dam” at the Little Detroit outlet to Pelican River was removed.
According to a DNR Report in 1997, the Dunton Dam outlet had been raised and lowered from 1938 to 1997 in a range of about 15 inches, with the lower levels in the 1950’s and higher ones in the latter part of the 1990’s. The DNR data show the dam’s level was a little more than one foot higher in the 1990’s than it was in the 1950’s. There was not much change in the outlet level after 1984.
Dunton Rapids
In the late 1990’s LDA and others continued to advocate for lowering the Dunton Dam outlet to reduce shoreline damage from ice and other highwater effects. Nothing came of those discussions. Instead, as a part of a statewide plan to reduce dam management problems, and to enhance natural fish migrations, the Dunton Rapids outlet was engineered and installed to replicate the flows of the replaced lock and dam.
Did the replacement of Dunton’s dam/lock system with rapids in 2001 alter Detroit water levels? Based upon post-construction measurements, the DNR hydrologists showed that the dam accomplished the project goals which included maintaining flow patterns previously exhibited by the dam. Long-term lake level monitoring records have indicated that average summer high-water levels are higher by about 2 inches since the dam replacement, but seasonal low levels have been almost exactly the same before and after the rapids replaced the dam.
Changeable Lake Levels
The chart displays forty years of the annual season ranges in water levels.
During this period annual level variations ranged from 2 inches to 23 inches with an average of about one foot. Water levels prior to and into the early 1990’s, a period of below-average precipitation, were somewhat lower than since that period, and the ranges somewhat less.
But within those ranges there is a general tendency for Detroit water levels to decline after June. In the last 30 years declines between the 4th of July and Labor Day have been observed in nearly every year, with the average six-inch lake level decrease having much to do with the fact that evaporation rates generally exceed average precipitation rates during this period.
Significant fluctuations in lake levels from year-to-year, and within open-water seasons, have occurred in the past, and will continue.
Dick Hecock, 2024
