Hamilton Pool Project
Espey's Hamilton Pool and its Receiving Watersheds Restoration Project for Travis County has been recognized by the American Council of Engineering Companies (ACEC) of Texas for the 2012 ACEC Texas Engineering Excellence Awards. The distinguished panel of ACEC judges from around the state selected 13 Gold Medal and 8 Silver Medal winning projects from 44 entries based on uniqueness, originality, technical, value to the engineering profession, complexity, and how successfully the project met the needs of the client.
Hamilton Pool is a naturally occurring pool on Hamilton Creek. The natural feature has been a landmark for the Texas Hill Country and Austin area for centuries. In late 2007, the discharge of materials from an upstream residential development in Hays and Travis Counties into the Hamilton Creek watershed polluted and impacted the water quality of Hamilton and Davis Creeks and Hamilton Pool.
In August 2007, Espey Consultants, Inc. (EC) was retained by Travis County to assess the condition of Hamilton Creek and Pool and subsequently develop a remediation and restoration plan. EC provided a detailed assessment of the water quality, physical and chemical analyses, literature review, and a report of findings and recommendations.
EC was then challenged with the task for the direct removal of silt and invasive plant vegetation from six miles of Davis and Hamilton Creeks. Each section of creek provided new and challenging obstacles. The majority of site clean-up was conducted using high-pressure water hoses (via water pumps) to wash the silt deposits down to controlled collection areas or to areas where light-weight dams were pre-installed. Where accessible by rubber track heavy machinery, sediment was collected and removed off site. Hand brooms, shovels, and buckets were used to remove sediment from environmentally sensitive and remote areas.
With Davis and Hamilton Creeks now clean, EC shifted its focus on removing the tremendous amount of sediment that had been deposited into Hamilton Pool. EC designed a removal and restoration plan. EC contracted with commercial underwater divers and specialized filtration equipment to dredge and remove the silt and sedimentation.
Due to limited access, a 90-ton crane was used to lower a barge with attached pump down a 50-foot drop-off into Hamilton Pool. Dive teams working in eight-hour, daily shifts were given the task of suctioning silt deposits from the depths of Hamilton Pool. Once pumped to the barge and back up the cliff, the silt-permeated water was pumped 3,100 feet to a network of mix and filter tanks. A shaker unit was employed for the purpose of removing pebbles and other small material before the water was deposited into mix tanks. Once thoroughly mixed, the silt water was then transferred to filtration tanks at which point the solids and water separation occurred. Once separated, the sediment-free water was pumped back into the Pool via Hamilton Creek. Water quality measurements were taken on a routine basis at designated pool locations, at the shaker unit, and filtration discharge tank to ensure dissolved oxygen, conductivity, and pH readings remained at acceptable safe levels.
Up to nine feet of silt and sediment was removed from the bottom surface of the Pool. Clarity of the water improved from less than a meter to more than four meters in less than a week post sediment removal.