Flood volume calculation: methods and uncertainties

In the previous update I mentioned the need to calculate the volume of water above the critical flood discharge i.e. the volume of water likely to spill onto the floodplain; a very important calculation when looking at the impact of a flood mitigation measure.

To do this, I essentially need to calculate the area of certain sections of a simulated flood hydrograph - the area under a graph. This is known as integration. The programme I am running my model in, MATLAB, allows this to be done in several different ways. However I am having problems using some of the available methods.

Therefore I am used the trapezoidal rule, which is not likely to give the most accurate estimate of the area of a graph;
http://en.wikipedia.org/wiki/Trapezoidal_rule

The following image is useful for understanding how the trapezoidal rule works
http://en.wikipedia.org/wiki/File:Trapezoidal_rule_illustration_small.svg

As it uses straight lines to approimate a curve, there are inevitably errors in area calculation - moreso than if I can use a similar but more accurate method - and therefore uncertainty in my findings. My aim is therefore to try to figure out how to use an improved method of integration. However, for the moment, the current does allow me to explore the effect of CRIMs on flood volume.

Initial results (for an uncalibrated model) on flood volume to follow soon....