Diversions along the Mississippi River
With hundreds of miles of Louisiana rivers passing near cities, commercial fishing areas, ports and other important infrastructure, there needs to be a way to control the river. This need became even more apparent during the Great Flood of 1927 when 26,000 square miles were flooded, 500 people were killed and over 700,000 people were forced to evacuate. In response to this the United States Army Corps of Engineers adopted a policy that expanded levee protection and included floodways and spillways. In doing so, they were establishing river diversions.
A diversion involves the opening up of a control structure along the river to divert (or redirect) a portion of the water. In Louisiana, we have several different types of diversions - both proposed and existing - that are designed to keep communities safe and environmental conditions stable. We will talk about three of them below.
Spillways (flood control diversions) are engineered structures that are used to combat concerns over rising flood waters. Water flows from the river to a receiving basin through gates that can be opened and closed. The Bonnet Carre spillway is an example of a structure which, when opened, diverts water from the Mississippi River to Lake Pontchartrain to reduce the amount of water reaching New Orleans during flood periods.
Freshwater diversions are when river water is used to control environmental conditions in ecosystems along the river. For example, if salinity in a basin begins to get too high, threatening organisms, freshwater from the river can be diverted into the basin to lower salinity levels. At Davis Pond, fresh water, with its accompanying nutrients and sediments, is diverted from the Mississippi River into Barataria Basin. This ensures suitable favorable salinity conditions in the area, combats land loss and increases commercial and recreational fish and wildlife productivity.
A sediment diversion provides a way for engineers to mimic the sediment delivery that occurs during flood conditions in a controlled way. Since a system of levees keeps the Mississippi River in place, the sediment that it carries currently gets dumped into the Gulf of Mexico. Engineers hope to use a diversion with a deeper intake to send sediment-rich waters to nourish vanishing wetlands. The Coastal Protection and Restoration Authority (CPRA) has proposed sediment diversions for lower Barataria Basin and lower Breton Sound.