Multi-criteria assessment of flood hazard in urban drainage systems

The aim of the present work is to provide a simplified but reliable methodology for the estimation of urban flood hazard, based on a hydrologic-hydraulic model and by utilizing Multi-Criteria Decision Analysis (MCDA). A number of manholes are ranked as to their vulnerability to flood on the basis of two different MCDA methods and the relative results are compared. The methodology proposed herein is demonstrated in a part of a subcatchment of a combined drainage network, in Athens, Greece, but it is easy to be implemented in other, both rural and urban, basins. The nodes of the drainage system that are most vulnerable to flood are determined based on eight indices: (i) conveyance (calculated using Manning equation for conduits) (m3 /s); (ii) subcatchment area (m2 ); (iii) subcatchment width (m); (iv) subcatchment average slope (%); (v) Manning coefficient of the impervious part of the subcatchment (s/m1/3); (vi) Manning coefficient of the pervious part of the subcatchment (s/m1/3); (vii) impervious area of the subcatchment (%); and (viii) SCS runoff Curve Number. Four manholes (alternatives) are evaluated with respect to the aforementioned indices (evaluation criteria) as to their vulnerability to flood. The manholes are ranked from the most "risky" to the less "risky". To this end, two different MCDA methods are applied, the Weighted Summation method and the Electre II method, while criteria weights are estimated by using the Analytic Hierarchy Process (AHP) and the respective Saaty scale (Saaty 1977). Both Weighted Summation and Electre II are discrete quantitative methods dealing with quantitative data on the basis of alternative consequences and priorities (weights) assigned to the evaluation criteria (Janssen 1992).