Lake Forest reservoir relining and floating cover FIGURES 2-3 Installation underway of double trough system on 28-foot divider wall FIGURE 4 East cell divider wall trough in full service engineer selected a weighted tension cover system. This system uses a series of designed troughs in conjunction with surface floats and ballast weights to supply the required cover tensioning, provide buoyancy in the floating cover and create rainwater collection troughs to drain surface water adjacent to the vertical divider wall. To handle the additional material slack developed in the floating cover from the 28 foot (8.5 m) vertical divider wall during the different reservoir operating levels, a special double trough system was designed and installed. The installation required that large custom-size panels be fabricated in the factory. These panels then needed to be lifted onto the vertical wall on-site to be vertically welded together. The joining of the panels required 3 inch (7.62 cm) wide field seams. The perimeter parapet wall required each fabricated panel to be lifted above the wall for deployment of the factory-produced panels and anchorage to the top of the perimeter wall. The geomembrane liner was anchored at the base of the perimeter wall and the floating cover was anchored to the top of the perimeter wall. The mechanical attachment consisted of stainless steel concrete anchors and stainless steel batten bars with rubber gasket material. The welding on-site was done primarily by thermal wedge and performed in compliance with the Geosynthetics Research Institute GM19 standards, and engineers specified field factory and seam strength requirements. The weight tensioned floating cover system in both reservoir cells also required various additional appurtenances including access hatches, air vents, access stairways, double material over existing concrete stairs on slope and a pump surface water removal system. Figure 2 shows the installation of the divider wall trough system on the west cell. Figure 3 shows the east cell wall 16 Geosynthetics | August September 2023