Question

below are the risks of the andersons dam. identify two actions that could be taken by system owners or users to manage these risks. Additionally, explain whether these management actions would eliminate, mitigate, or have little effect on the level of risk that you assessed?

risks of the anderson dam

-The high intensity rainfall may cause the frequent cases of over spilling resulting in over topping of the dam during high intensity earthquake.

-Earth quakes may cause over flooding of dam therby destabilizing its underneath soil resulting in a huge risk to the life of the people and their belongings.

Answer 1

Anderson dam, situated in Santa Clara County, California has been identified susceptible to major risks. A high intensity rainfall could potentially cause over spilling resulting in toppling of the structure, and an earthquake of magnitude 6.6 with the epicenter within the dam could cause destabilization of soils underneath, cause a severe damage/collapse to the dam. At the extreme level, a severe rainfall with earthquake could cause a catastrophe which could lead to an inundation of 30 miles of land downstream. It is therefore required to go for rehabilitation of Anderson dam, in order to avoid any damage to dam and downstream land.

1. First step toward the solution will be to lower the storage level of water in dam. It has already been taken up and the dam is stored only upto 58% percent of its full capacity. A revised study conducted in the dam allowed an additional storage of 11%, hence the dam could now store up to 67% of its total capacity. This method limits the purpose of dam, resulting in shorter storage in the already drought prone area. Hence the measure is a contingency step, aiming before the total solution.

2. The dam could be installed with anchors, that provides additional support to the existing structure. The anchor could be either traditional tie back anchors or restressable anchor heads. Provision of such anchors would be a long term solution, providing anchorage and additional support. Anchorage would substantially mitigate the risks posed.

3. Third step toward the seismic retrofitting that would work on the loose unstabilized soil base. This step would involve strengthening the outlet pipe to convey heavy spillage, increase the concrete spillway height, and stabilizing the upstream embankment shell and strengthening the transition zones to prevent failure due to fault offset during an earthwork. Such a seismic retrofitting along with steps 1 & 2 would possible eliminate the risk posed.