Old River Project, Rock-Fill Initial Closure Dam: Hydraulic Model Investigation: Fid-Bau Portal

Old River Project, Rock-Fill Initial Closure Dam: Hydraulic Model Investigation

One element in the plan to control flow from the Mississippi River into the Atchafalaya through Old River is a sand closure dam in Old River. Since high velocities would make it difficult to effect a closure by sand alone, a rock-fill dam is proposed for the initial blockage of flow through Old River. A 1:10-scale model of a 100-ft-wide section of the dam was constructed, both in the dry and during flow, and tested to determine the stability, amounts of seepage through the dam (which would affect velocities at the upstream site of the sand dam), and the effect on seepage of seal blankets on the upstream face. Tests indicated that the proposed cross section for the rock-fill dam would be stable under all conceivable flow conditions regardless of whether the fill had been constructed in the dry or in flowing water. The seepage rate was somewhat greater when the closure dam was constructed in flowing water. In either case, an effective means of reducing seepage flow was the placement on the upstream face of a 4-ft-thick riprap blanket covered with finer material. Use of this seepage-reduction measure resulted in negligible velocities upstream in the vicinity of the sand-fill dam. Tests also indicated the feasibility of using steeper slopes on the upstream and downstream faces of the rock-fill dam. Stability conditions appeared satisfactory with a 1-on-1 upstream slope and a 1-on-2 and 1-on-1 composite downstream slope, which would permit a reduction of about 40 per cent in the volume of rock required.