Changes

* Trench dimension and spacing in the catchment can then now be calculated. This then has to be checked with local preferences and adjusted accordingly. Trenches in Vietnam were originally designed as rectangular trenches 4m wide by 1m deep, but modified according to requests from local people to trapezoidal trenches 2.5m wide at top and 1m wide at base and 0.75m deep. Trenches should also then be over-dimensioned (exaggerated) to allow long-term runoff volume to be stored despite a lack of maintenance – things like siltation and erosion of the banks will reduce infiltration capacity and volume over time.