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Background During the development of the Greenham Common air base the pre-existing whaleback landform was widened to take parallel hard surfaced runways and roadways and, in so doing, removed the heads of a number of wooded spring fed gullies and converted a 5km long rounded hill to a wide level plateau. Water could no longer percolate into the ground and, to control run-off, the whole airbase was divided into catchments leading to thirteen concrete lined rectangular balancing ponds. These ponds retained water after rain and released their content slowly in turn to the various gullies. The Restoration Project required the removal of all of the runways, fuel tanks, roads and other hard areas of the former air base, making many of the concrete ponds redundant. What to do with the concrete ponds The task was to estimate the run-off created from the newly restored landform and discover which of the tanks would be dry and could be removed and which tanks would remain wet and could be converted to wetland wildlife habitat. A further area of the site was to be re-landscaped and new balancing facilities would be needed on a newly established area of grassland. Consideration was also given to preventing erosion within the gullies. Hydro-engineering study To undertake this task a detailed desk study of the airbase surface was made allowing an assessment of the 25 year storm condition of the site to be made. Storm water run-off was calculated, soil infiltrability estimated, pipe capacities assessed and storm water storage requirement calculated. Each pond and its catchment was then visited, measured and photographed. The new condition was then estimated given removal of the extensive hard surfaces so as to discover where the need for balancing would remain. Recommendations It was recommended that of the thirteen concrete ponds, four were required for continued water balancing, eight were no longer required and one was partly required. Two of the ponds needed for continued balancing could be converted to wetland wildlife habitat. Five ponds could be completely removed or converted to wildlife habitat by careful redesign. Redesign options were described together with the needs of each individual pond and the works fully costed. This project was part of a much wider study to assess the vegetation of the airbase and to develop a comprehensive plan for the management of grasslands, heathlands and woodlands on this internationally important cold war heritage and wildlife site. |
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