Flood Damage Reduction (FDR) Strategy
Flood damage reduction efforts can take many forms, but we will focus on three major options that provide widespread benefits: impoundments, culvert sizing, and land-use change. Each method is useful and when combined can have a major impact on flood control. In selecting alternatives we must analyze the hydrologic characteristics of the basin. Certain areas due to land-use, soil type, topography and location should be treated differently. The Timing Zones map shows three zones: early, middle and late relative flood flow contribution to the Red River Valley in MN and to the Bois de Sioux Watershed. The early zone in the Bois de Sioux Watershed is close to the Bois de Sioux River and water from this area could leave the watershed soon after a storm event while the channel at Wahpeton/Breckenridge can handle the flow. However, this area is in the middle zone of the Red River Basin so downstream impacts on the Red River need to be carefully considered. Waters in the middle and late zones should be slowed and or stored until the downstream areas can handle the increased volume of water. The late zone, in particular, is a great place to implement projects that detain or retain water.
The basic concept of an impoundment is to create a location for water to be stored during an event and then released when downstream areas can better handle it. A nice feature of an impoundment is the ability to design to an appropriate level of storage and be able to manipulate the inflow and outflow of water. Impoundments can also improve water quality by allowing flood waters a place for sediments and nutrients to settle. They may also include other natural resource enhancements (NRE) like wildlife habitat, stream flow augmentation, and improved fisheries.
Culvert sizing implements an inexpensive and fair FDR approach. The old adage, “if everyone contributes a little, we get a lot” applies here. If we can set culvert sizes appropriate to the \hydrologic characteristics of an area, and everyone accepts that they must do their part and store a little water in a large event, a great deal of runoff can be controlled.
Runoff is affected by the type of ground cover it is traveling through. Concrete, bare earth, native prairie, cropland, etc. each effect runoff differently based on their individual characteristics. These affect travel rates, absorbency and ability to filter sediments and nutrients to improve water quality. Restoring natural vegetation in critical areas is a wonderful approach and should be encouraged. However land-use changes cannot solve flooding on its own. This would take too much land out of production by farmers to achieve the needed flood control in the valley.
The current landscape brings runoff down from higher ground into areas, which due to flat terrain, cannot handle it, thus causing widespread flooding. Roads, homes and fields are negatively impacted and damages can be very costly.
The initial response many people have about floodwater is “get it out of here…ASAP” by moving the water to an outlet as fast as possible. However, to remove the floodwater from the watershed means ‘dump’ it on the downstream neighbor…which the downstream neighbor’s response is again “get it out of here…ASAP”…thus ‘dumping’ even more water on their downstream neighbors…and so on…and so on. This response benefits those in the upstream areas, but causes major flooding downstream for others.
Another common issue in the valley is culvert sizing. Many entities (public and private) tend to see things from only one point of view…theirs. Similar to the above mentality, a small culvert blocking any water being ‘dumped’ on them by their upstream neighbors is a good thing; however, larger culverts downstream are a must have. This mentality obviously causes tension between friends, neighbors and even counties, and can eventually lead to lawsuits.
The best response lies in the ability to recognize that flood damage reduction in a fertile region like the Red River Valley is a “shared responsibility” among everyone. From your local farmer, to your state/federal agencies, we need to focus on critical areas that are prone to flooding, while limiting negative impacts on downstream areas. In fact, if done with the “big picture” mentality, the benefits can be felt among communities all the way north to the Hudson Bay.