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The recent surge of rainfall prompted Army and public works engineers to find immediate solutions to flooding and the threat of sinkholes forming on Sand Hill.
Last month, two separate rainfall incidents caused flooding and created sinkholes in the Sand Hill area, including flooding of a barracks parking area and along 2nd Armored Division Road, and the development of a sinkhole near the newly constructed building in the 30th Adjunct General Headquarters.
Subject matter experts from the Directorate of Public Works and the Army Corps of Engineers are working with the contractor to repair the damage and implement preventive measures as quickly as possible, said Randy Lemoine, civil engineer for the DPW Engineering Division.
Lemoine said newly installed pipes from the construction of the dining facility resulted in a longer traveling distance, shallower pipe slope and multiple bends that have diminished the storm drains hydraulic efficiency and capacity, causing debris to be caught in the bends. This resulted in water backing up and coming out of the catch basin. The flooding was worsened by elevation of the DFAC and surrounding ground, which blocked the emergency overland floodway and resulted in about two feet of water ponding in the nearby parking lot.
We have a drainage system that starts at 2nd Armored Division Road and goes south to a drainage ditch that goes underneath the railroad tracks, Lemoine said. When they built the (dining facility) next to the starship, it was built over where that pipe is located. The designer placed a structure at the upstream end and diverted the water through a new pipe around the DFAC.
The building next to the DFAC has a separate storm drainage system that discharges to a different location. As an immediate action, were going to put a new catch base in the parking lot that was flooded and the seperate drainage system will give it an alternate way to get out.
Long-term action involves a watershed study to estimate future flow volumes to determine the appropriate size of new pipe and emergency flow system to discharge water at a different location away from the dining facility and toward the nearby Opossum Creek, Lemoine said.
As for sinkholes, Lemoine said the combination of rainfall with eroding dirt can lead to the collapse of land and structures around it. Until the repairs are made, it is possible the sinkholes adjacent to the 30th Adjunct General headquarters will enlarge with future rainfalls. This could cause damage to the detention basin outfall and discharge pipe, requiring a complete rebuilding of the detention outfall.
Over at the 30th AG, that is a typical textbook case of what we call piping, he said. When you put a pipe in a (anti-seepage) collar, the intent is for the water to go inside of the pipe. If you dont have good compaction of the dirt around it, water may want to go along the outside of it and in this case, it did and eroded the soil away.
The Army Corps of Engineers and public works will meet with contractors of the building for the best solution, Lemoine said.
We will review the proposed repair and make sure it is an adequate fix, he said. Our concern is that we dont jeopardize the building nearby. We have some concern because there is construction going on immediately downstream that could be a hazard to that building if we dont get this reconstructed properly.
For now, Lemoine said drivers should avoid flooded roads and keep distance from dangerous areas.
Everyone should avoid driving where the road is covered with water because it only takes a few inches of water going across the roadway to push your car off of the road, he said. Its safer to just stay away from it.