Design Study 2. CIVE1400: Fluid Mechanics
Design Study Two: River Gaunless Flood Control Dam
Background
Following sever flooding in June 2000 the Environment Agency fast tracked a
flood defence scheme for Bishop Auckland and West Auckland to protect
around 600 homes. Construction works commenced in 2003 and consisted of
2.1km of river training walls and embankment and the construction of a flood
storage area to the west of West Auckland. The dam is approximately 315m
long and contains approximately 90,000m3 of material. The overall scheme
costs were around £9.5m.
The dam is designed to hold back the 1 in 200year flood and by using
“Hydrobrakes” in the flow-through culvert to restrict the outflow so that it will
be equivalent to only a 1 in 2 year event.
Design Brief
Using the site and design data given below, answer the following questions to
evaluate aspects of the design:
1. What is the length of time it will take the reservoir to fill to a level of
127 mAOD from a level of 123 mAOD, if the inflow is the 1 in 200 year flow
rate of 48m3/s and the culverts are both flowing full at velocity of 1m/s?
What would this time be for the 1000 year flood flow?
(Hint: calculate volume available from the table or graph; calculate the net
inflow, then the time to fill this volume.)
2. To prevent erosion of the downstream dam face when there is flow over the
dam the design limit is a velocity of flow of 8m/s. Assuming that the
velocity on the slope is approximately 4 times the velocity over the weir,
calculate the allowable height of flow, H, over the weir crest.
Calculate the height over the crest for the 1000 year flood.
Is the design limit for erosion protection exceeded?
3. An alternative design for the outlet culverts was to pipe the water further
downstream. In this design the pipe would connect to the exit of the
existing culvert and immediately form a bend of 45o. The pipe would reduce
in diameter to 1.5m. What would be the force be on this bend when the
water is flowing at the maximum rate of 1.0m/s and the reservoir surface is
13m above the bend’s entrance?
Assume Atmospheric pressure is equal to 10m of water.
