Targeting Conservation Drainage in the Cobb River Ditch
Turbidity and sediment yield from the Le Sueur River watershed to the Minnesota River is a problem. Studies have shown that 200,000 tons/yr come from non-field sources and 25,000 tons/yr come from field sources. With this grant we will develop strategies to reduce sediment yield from the Freeborn County Cobb River Ditch subwatershed.
The Cobb River Ditch drains 30 square miles in the headwaters of the Le Sueur River watershed. The drainage basin has a rolling topography and is dominated by row crop agriculture. At the downstream end of the Cobb River Ditch, moderate sized ravines have formed however small ravines are also evident along the upstream reaches of the ditch. These ravines, as well as the upland crop fields, are sources of suspended sediment load from the Cobb River Ditch.
The project objective is to develop a 5-year implementation plan to manage flow and reduce sediment yield. The effort will provide the needed background and process to extend this systematic approach to the rest of the Cobb River watershed. It is anticipated that transferability of this application from this subwatershed to the other subwatersheds of the Cobb River will be done more efficiently and with greater expectations for outcomes. The information gathered from this area may also have practical application to other similar subwatersheds in the Blue Earth and Le Sueur River basins.
The project objective is to develop a 5 -year implementation plan to manage flow and reduce sediment yield. The effort will provide the needed background and process to extend this systematic approach to the rest of the Cobb River watershed.
Freeborn County and SWCD Staff completed a walk through' survey of this entire ditch system during year one (2011) of this process. Eleven (11) sections of Freeborn Township (T 104 N-R 23 W) or Manchester Township (T 103 N-R 22 W) were visited. Approximately one hundred and forty-eight (148) corrugated metal or plastic surface water outlets, inlets, and culverts were located, identified, and mapped with GPS equipment. Pictures were taken of water clarity, eroded banks, severe slopes, and broken outlets to note areas in need of repair. A Cobb
River Ditch Summary was completed and distributed for GBERBA review during August 2011.