Emergency Spillways Using Geomembranes

A field study evaluated the design, construction, and operation of a low-cost auxiliary spillway consisting of an earth channel lined with a geomembrane (36-mil Hypalon) protected by an erodible earth cover. The study was conducted at Cottonwood Dam No. 5, Collbran Project, Colorado. The field test installation was completed in the fall of 1985, and an operational test was conducted in the summer of 1986. During the field test, the spillway operated essentially as expected. The soil cover was washed away during the initial flows until the membrane on the bottom of the spillway was exposed. Even though the flow carried much abrasive material, stones, and a few cobbles approximately 100 millimeters in diameter, little or no erosion of the membrane was observed. The overlapped field joints of the membrane functioned well. Future designs should be improved by curved bottom cross sections rather than the usual flat bottom of a trapezoidal section. This would minimize the amount of cover washed away at low flows. The concept could be extended by providing vegetated earth cover that can handle lower floodflows and not require recovering the spillway.-- Bibliography: p. 20