The computer-aided development of design criteria for a type of debris-flow check-dam

Debris-flows are very destructive phenomena which can cause material damages and victims: many efforts are devoted by the scientific and technical communities to the modelling and the design of proper countermeasures. The mitigation of the debrisflow effects can be accomplished in three ways: non-structural countermeasures (hazard mapping, insurance policies, regulatory interventions), active structural countermeasures (drainage systems, reforestation), passive structural countermeasures (check-dams, flow-breakers, stilling basins). The passive structural countermeasures consist of proper devices able to intercept the destructive flow, subdividing it into a number of minor flows, thus causing the formation of horizontal- and vertical-axis eddies like the hydraulic jump and, finally, reducing the debris-flow energy. Their design can be accomplished through the determination of the number, shape and size of the flow-breakers, check-dams and stilling basins, which are optimal to cause the loss of energy, and finally the debris-flow to stop; moreover, the design must fulfill the proper structural requirements, because of the loads exerted by the debris-flow on the cited devices. At present, there are not available general design criteria for these passive countermeasures, and physical and mathematical modelling are applied case by case. In this paper a type of check-dam is considered, consisting of a number of square shaped vertical elements, made of concrete or metal. It is shown that the repeated use of a mathematical model of debris-flow, where the momentum and mass conservation equations are discretized through the Finite Volume Method, can supply non-dimensional relations between the relevant design parameters (debris-flow energy losses and total loads exerted on the structures, number and size of the vertical elements) and the dynamical characteristics of the flow (discharge, velocity, height, bed slope). These relations can lead to a better interpretation of the physical model experiments, with decreasing in their implementation costs and, if judicious caution is used, to useful design formulas.