In short, “Lake levels were likely affected by residential irrigation in 2012, though groundwater inputs to the lake likely compensated for some of the losses.”
Dr. Nate Bosch, director, Kosciusko Lakes and Streams, Grace College, released the report last week. The study was done by Bosch, Margaret Lee, Amy Bloemendaal and Anna Burke.
“Many Lake Wawasee and Syracuse lake residents contacted us with questions and concerns after the drought we experienced in 2012 and the low lake levels. We produced a figure showing the historical record for lake levels as well as a fact sheet about lake levels to give context to the 18-inch lake level drop … it became clear we needed to conduct a research study on the lake levels and we were encouraged to have several Wawasee and Syracuse lake residents make donations to make the research possible,” said Bosch.
The conclusion to the study notes main causes of changing lake levels are uncontrollable and cannot be controlled by lake managers and property owners, nor can these individuals control how much water leaves the lakes and enters the atmosphere through evaporation. But lake levels can be controlled, such as dam operations when water can go over the spillway. “Lake property owners have control over water lost from the lake due to residential irrigation systems. For future drought events, it may be effective to limit irrigation systems during times of lower lake levels.
“The expansion of agricultural irrigation systems,” according to Bosch, “is something to continue to monitor. If these irrigation systems widely increase, they may start to have a measurable influence on lake levels during drought conditions as well.”
Water budgets for the lakes and watershed were developed. Results show the total inflow into the lakes decreased by 28 percent from 2011 to 2012, while outflow decreased by only 19 percent during the same time. Precipitation was the largest inflow, 42 percent, in 2011 and groundwater was the largest, 51 percent, in 2012. For outflows, Syracuse dam was the largest, 54 percent in 2011 and evaporation was the largest, 54 percent in 2012.
Residential irrigation outflow directly from the lakes was about 11 percent of the total outflow in 2011 and increased to 22 percent of the total outflow in 2012.
Industrial and agricultural irrigation in the watershed was only 1 percent of the outflow in 2011.
“Implications for this study include management consideration of human-controlled lake level influences of the dam outlet and irrigation usage, especially during drought years. However, while humans can control these outflows, inflows of precipitation and stream inputs are uncontrollable such that lake levels can never be fully managed.”
Lake water budget found the average rainfall in 2011 increased from winter through April, fell June through August, then rose the rest of the year. Precipitation was lower in April and May for 2012 and slightly higher in July and August. There was also a difference during the fall each year with higher precipitation in 2011 compared to 2012 and no rain during November 2012. Annual precipitation in the drought year of 2012 was only 54 percent of the annual precipitation in the average year of 2011.
Evaporation was zero during January and February of 2011, slowly increasing during the summer. During May through August the evaporation rate was 34 percent and 54 percent of the annual evaporation respectively for 2011 and 2012. During the winter of 2012 the lakes never completely froze, leading to increased evaporation. During the summer the amount of evaporation was higher with an annual evaporation 28 percent higher compared to 2011.
Rainfall for 2011 was at a normal lever with the amount of water going into the lakes increasing to 2 million cubic meters or m³ for May, decreasing to 200,000 m³ for July and increasing to 2.7 million m³ for December. Stream inflows in 2012 were highest in January at 1.7 million m³, decreasing during the winter until July where the amount was about 70,000 million m³ for each month.
Syracuse dam, the only place surface water directly leaves, had a high amount leaving in January 2011, over 3 million m³. The amount dropped to just over 100,000 m³ each month June through October, rising in November to almost 4 million m³. While 2012 started out nearly the same as 2011, except for March where 21 percent less was leaving and in April, the amount leaving dropped to zero and remained at zero the rest of the year.
Residential irrigation systems, used May through August, averaged 1 to 1.6 million m³ removed from the lake, or 18 percent to 31 percent of the average outflow. During 2012, that usage increased 50 percent.
Groundwater was being returned to the aquifer during the first five months of 2011. During the summer months that water was drawn out to recharge the lake. For the remainder of 2011 the aquifer storage increased.
However groundwater flow for 2012 had a dramatic variation in aquifer storage. From February to July aquifer water was recharging the lake. In June, a maximum of 6.2 million m³ of water was leaving the aquifer. Water continued to leave the aquifer except for January, September, October and December. The total amount of water taken from the aquifer by water wells was 1.1 million m³ of water for all of 2011, 1 percent of precipitation inputs to the watershed. It’s been calculated if 20 farmers were to install major wells in the watershed an additional 4.7 million m³ of water would be taken out of the aquifer, representing about 4 percent of annual precipitation.
Inflows to the lakes were higher in 2011. The 2012 rainfall amount was half the annual precipitation of 2011. With little snow in winter, or rain in the spring, the lake was not able to replenish water lost through evaporation, irrigation and dam outflows. The lack of rain in 2012 also affected stream inlets. The streams delivered less than half the water in 2012 than in 2011.
The study did find lake outflows increased 23 percent in 2012 compared to 2011. “The lakes had less water entering and more leaving, that led to low lake levels.” Evaporation and irrigation took more water out of the lake in 2012 than in 2011. The evaporation increased because of warmer temperatures including the lake not freezing in the winter of 2012.
Residential irrigation systems continued to remove water from the lakes both years. During 2011 5.3 million m³ of water was taken directly out of the lake, the same volume as about 14 inches of lake depth. Under normal conditions, this amount leaving does not cause much concern, but irrigation activities during the drought of 2012 may have “exacerbated low lake level conditions.” In Bosch’s study it shows in the summer of 2012, more than 8 million m³ of water was taken out from lake irrigation, same volume as about 20 inches of lake depth. “In the months that irrigation systems were used, the lake level dropped 17 inches … lake property owners used 50 percent more water on their lawns in 2012 than in 2011 due to the lack of rain.”
The watershed, in which only precipitation is the only input, decreased by 46 percent in 2012 compared to 2011. This impacted the lakes through less water falling directly on the lakes, as well, and indirectly through stream flow.
No water was leaving the area for most of 2012 through the dam, a 64 percent decrease from 2011. The study also shows evapotranspiration from the watershed in 2011 accounted for 65.3 million m³ lost, while in 2012, 64.7 million m³ of water was left in the watershed. While the values changed little between the years, the proportion of precipitation lost to ET increased dramatically during the 2012 drought.
Groundwater in the watershed, taken to be aquifer storage and not part of inflow or outflow from the watershed, varied dramatically from 2011 to 2012. The study states in 2011 33.5 million m³ of water were being transferred into the aquifer under the surface of the watershed, but in 2012 the aquifer lost 6.9 million m³ of water. In 2011 there was enough precipitation and stream flow in the watershed to allow water to remain in the area and flow into the aquifer. In 2012, less water was coming into the watershed from rainfall, while ET and dam outlet losses continued. Wells in the watershed — such as those used by farmers for irrigation — “likely had minimal effect of aquifer storage and therefore the lakes as well.”
The full Wawasee and Syracuse Lakes Water Budget Report can be seen online at water.grace.edu/ under news.