CRIM uncertainty analysis

The results of investigation into combinations of Catchment Riparian Intervention Measures (CRIMs) have been previously presented. The figure below shows the location of the CRIMs throughout the Uck catchment. Those in red have a positive effect in terms of peak flow reduction. Those in yellow have a negative effect in combination!



Uncertainty analysis was carried out. The 52 positive sites (see previous post and results table) were the focus of this analysis. Essentially the roughness of the channel and floodplain along these reaches was varied in order to show how different levels of roughness effect the peak flow at Uckfield during the (simulated) 2000 flood event.




The key finding from the CRIM Uncertainty Analysis was that similarly fine results in terms of peak flow reduction at Uckfield can be achieved when channel Manning's n is ~0.10, as opposed to the default value for a CRIM of 0.14. This suggests a lower level of channel blockage is required for equally positive results.

HOWEVER, IMPORTANTLY, if channel n is only increased to ~0.10, floodplain roughness MUST be increased to a high level (Manning's n > ~0.16) in order to achieve the best results in relation to downstream peak flow.

Similarly, floodplain roughness can be much lower than 0.16, and providing channel n is high (> ~0.14), similarly fine results can be achieved.

it is important to note that this uncertainty analysis is only carried out for the 52 reaches identified from previous work, and will need to be repeated if different combinations of reach are selected.