LOCAL RIVER MANAGEMENT SCHEMES
(by local I mean, close to King's Lynn)
Thanks to colleague Mr. Stone for these notes...
RIVER NAR
This river flows through Castle Acre.
As it moves through its course, which can be discovered via the NATIONAL WATER ARCHIVE site I referred to on AS Hydrology page
Site Close to Source
Width: 4.6m - gentle slope to banks - trapezoidal shape to channel
Maximum depth: 0.4m
Load: much silt and fine sand, some pebbles up to 3cm in diameter
Site 18km from source
Width: 9.6m - steeper slopes to banks - still trapezoidal shape
Maximum depth: 0.8m max
Discharge 7 times more than at previous location
Load: much silt, some rounded pebbles up to 2cm in diameter
Site 30km from source
Width: 13.8m
Maximum depth: 1.15m
Load: plentiful silt & small rounded pebbles up to 1cm in diameter
Velocity higher than previous locations
Depth increases with distance downstream, but this is not linear
Rapid increase in discharge early on as several small streams feed into the river
Velocity increases with distance from source but again, this change is not linear - slight changes in gradient affect the velocity
Load is getting slightly smaller
Shape of channel is trapezoidal - will be some bank erosion at times of flooding
RIVER WITHAM, Lincolnshire
This is dredged regularly, and the material used to build up the embankments. Risk of rural flooding has been reduced. Meanders have been straightened, with some cut offs being left for water storage.
MISSISSIPPI
Remember that when rivers are shortened, as happened on the Mississippi due to the work of the US Corps of Engineers the water flows faster. As the river is taking less distance to drop the same amount of height, the channel become steeper. This increases river velocity if all other parameters stay the same, so the river therefore has more energy and it uses this energy to erode down.
RIVER NENE, NORTHAMPTON
Used to flood frequently (did so in 1997) Since the 1970s, houses have still been built on the river's floodplain. Flood storage basin at Dunston Mill, and there has been straightening and dredging of the channel. Parts of town have had new flood defences. A new dyke has been built to take storm water from an industrial estate. Washlands scheme to hold water during periods of high flow.
RIVER WELLAND
Passing through Spalding, Lincolnshire. Flood relief channel built with sluice gates to divert water around the town of Spalding.
DEFLECTOR GROYNES built in River RODING, near Thames
These are built from wooden poles and reeds so as to reduce the amount of construction using artificial materials. Flood berms have also been excavated.