The power of Constraint Logic Programming (CLP) is in its ability to deal with combinatorial complexity. While simulation calculates the effects of measures, CLP generates good sets of measures that comply with the set of constraints and goals set for the problem. CLP and simulation may be considered complementary.
The intention of this application is to support decision-making in flood prevention by deriving appropriate measure sets from targets and goals to be achieved in a system. It generates good combined measure sets from a database of precalculated measures.
Although the application deals with the consequences of extreme river discharges, the principles of the approach have a much wider scope.
Designing measures
This application applies a constraint which directly represents the hydrodynamic equation. It guards the relation in a river section between cross sectional area (A), roughness (N) and the head difference (dH) over the sections length. The essence of the application is that any reduction of the freedom in one of these three variables directly propagates to the domains of the other variables. So, limiting the possible values for the dH directly translates into limitations of A and N, and vice versa. The values in the domains are thus always consistent with all posted constraints.
The goal is to find values for A and N that are consistent with water levels within the allowed range. Optimisation is directed towards the smallest excavation volume of the river banks, necessary to enlarge A to the required values. This constraint is used in cooperation with the continuity constraints at the section boundaries. This constraint network causes very effective propagation of information.
As a result, the resulting water level is given for every section, as well as values for cross sectional area, excavation depth and roughness.
Solutions are generated quickly (10-20 seconds), but there is much freedom in the problem as it is stated here. More information about realistic limits to cross sectional areas, excavation depths, roughnesses, and some global preferences with respect to scattered or adjacent excavations, etc. would improve the efficiency considerably and would also improve the suitability of the obtained solutions. |
