When and How Did Conditions Change in the Watershed?
Precipitation and Runoff
A hydrologic break point identified in 1990 showed precipitation and runoff increasing throughout the year, when compared to pre-1990, with the greatest increases during the summer growing season. The fall had greater increases in seasonal runoff when compared to increases in precipitation (see graph below).
Precipitation has also increased 19% over the past 30 years compared to the prior century, with 5.4 inches of increased average annual precipitation.
The main take-away is that we see more water flowing through our rivers in each season, accelerating already unstable conditions throughout the watershed.
Beginning in the 1950s, land use in the watershed began to shift from a diverse mix of crops, including early season varieties, to one dominated by row crop production, which concentrates water use in the summer months.
Increased tiling of wet soils, drainage projects, land use alterations, and past wetland loss have reduced the ability to store water on the lands or in the soils. Approximately 47% of the watershed has been tile drained and 90% of wetlands have been drained.
Source: DNR Hydrology and Connectivity Report