Old River: Structures Required

The positive control of flow diversion from the Mississippi River into the Atchafalaya River Basin through the Old River requires structures that will permit the retention of the adopted flood-control plan. The preceding stipulation dictates a maximum discharge capacity of not less than 700,000 cu ft per sec for the project-flood stage. Also mandatory is the provision for sufficient capacity at lesser stages to make unnecessary the increased frequency of operation of the downstream Morganza (La.) Floodway and the Bonnet Carre (La.) Floodway. For medium stages the structures must have a capacity that is equivalent to the natural diversion capacity of the Old River in order that channels may be developed through the lower Atchafalaya River Basin, where such flows will result in bankfull stages. To meet navigation requirements, a waterway traversing the closure dam must be provided. The foregoing requirements are fulfilled in the design of the low-sill structure and the overbank structure described herein, and in the appurtenant channels, levees, closure dam, and navigation lock for which planning is under way.