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Application:
Improvement in flood defence structures
Customer:
Metcalf
and Eddy Environmental Management
Service:
Physical model study
Problem:
Lower Glendevon Dam Spillway is located in the Ochill hills to the
east of Stirling, Scotland. The capability of the spillway to contain
the summer and winter Probable Maximum Flood (PMF) without overtopping
the spillway walls was in doubt. This was confirmed by a numerical
model study carried out by Metcalf and Eddy, which predicted that
the spillway sidewalls would be overtopped at a change in direction
and gradient. The study concluded that remedial works would be required
to contain the summer and winter PMFs.
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Objectives:
To construct a scale physical hydraulic model of the spillway
structure with surrounding topography and undertake a test programme
to investigate flow conditions generated at high discharges. The
study would also determine the extent of ground protection required
to ensure that the structural integrity of the earth filled dam
was maintained at the elevated flood flows.
Approach:
A 1:35 scale physical model was constructed and tests were undertaken
at different flow rates to assess the hydraulic conditions within
the spillway arrangement. Flows representative of the winter and
summer PMFs (280 and 270m3/s) and the 1 in 10,000 and
1 in 1,000 year flood flows (150 and 84.4m3/s) were used.
Initial tests demonstrated that discharges over the spillway weir
in excess of 34.0m3/s would result in some degree of
overtopping of the sidewalls. As the discharge increased the magnitude
of the flow overtopping the north bank and passing over the downstream
face of the dam would result in severe erosion damage. Modifications
to the physical model were made and a final series of tests completed.
Outcome/Benefits:
As a result of the physical model testing, specific recommendations
were made to improve the existing flood defense structures, including
the addition of a wave run-up wall and the installation of a Reno
matress.
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