Hydrological dam safety assessment methods traditionally assume that the reservoir is full while it receives the design flood. In practice, reservoir management strategy determines the probability distribution of reservoir levels at the beginning of flood episodes. In this study we present a method to economically assess the influence of reservoir management strategy on hydrological dam safety and downstream flood risk. The method was applied to a gated-spillway dam located in the Tagus river basin. A set of 100000 inflow hydrographs was generated through a Monte Carlo procedure, reproducing the observed statistics of main hydrograph characteristics: peak flow, volume and duration. The set of 100000 hydrographs was routed through the reservoir applying the Volumetric Operation Method as flood control strategy. Three different scenarios were studied: initial reservoir level equal to maximum normal level, equal to a maximum conservation level and following the probability distribution of initial reservoir levels. In order to evaluate economically the influence of initial variable reservoir level and compare the three scenarios, a global risk index was applied. The index combines the hydrological risk for the dam, linked to the maximum water level experienced in the reservoir while the flood is routed, and the flood risk in the downstream river reach, linked to the discharge releases from the dam. The results highlighted the importance of considering the fluctuation of initial reservoir level for assessing the risk related to hydrological dam safety. Within the case study, the global risk index reduced its value up to 93 % if variable initial reservoir level is accounted, from 1445.6 x103 to 83 x103 euros.
The aims of this study are to quantify the effects of key properties of rainfall time series (frequency, duration, depth, rate and peak, time between events, length of series and precipitation thresholds, among others) on the hydrologic design of sustainable urban drainage systems (SuDS), to test a method for their estimation from daily time series and to quantify their uncertainty. Several typologies of SuDS infrastructures are designed to achieve a target treatment capacity. This target capacity is usually defined according to two methods: treating a percentage of the total volume of rainfall (50, 80, 90, 95, 99%) or treating a percentage of the total number of rainfall events (50, 80, 90, 95, 99%). We considered the city of Madrid as the case study, compiling 58 years of observed data (10-minute time step) and aggregating to daily time series. We obtained the design parameters from the full resolution dataset and then tested a simplified method to estimate them from daily time series of varying length. First, we calculated the design parameters for different storm thresholds (0, 1 and 2 millimeters). Second, we determined the design parameters from the aggregated daily time series by applying a temporal stochastic rainfall generator model (RainSimV3). We estimated the model parameters from daily data and generated 100 series of 58 years at 10-minute time step, and compared the results. Third, we generated 100 series of different lengths (20, 30, 40, 50, 58, 80 and 100 years). Fourth, we generated 100 series of 58 years at 10-minute time step (for each series length). Finally, we analyzed the uncertainty produced by the length of the observed data set. Results showed that, depending on the criteria adopted for the estimation of rainfall design parameters, SuDS structure volumes could vary up to 30 %. Further research includes the analysis of different climate locations.
The study develops a rule operation model for gated spillways which improves the performance of the volumetric evaluation method (MEV). MEV was proposed by Giron (1988) and is largely used in common practice in Spain. The improvement was made by applying a corrective factor to the outflow discharge proposed by MEV method. The choice of the corrective factor was based on a multi-decision environment accounting for the number of improved cases and the amount of improvement. A Monte Carlo simulation environment was created to evaluate the method under a wide range of operating conditions. The environment includes the generation of storms and inflow hydrographs and their routing through the reservoir. The methodology was applied to the Talave basin, in the south-east of Spain. The improved method (called K method) was compared with other methods for the operation of gate-controlled spillways as the MEV and PLEM methods. The results showed that if the corrective factor K is higher than 1 the number of improved cases was significant, while if it is lower than 1 there was not improvement. The analysis of the relation between the return period and the devised method showed that by using the K method the percentage of improvement of both reducing maximum outflows and reducing maximum levels reached in the reservoir is greater for events with higher return periods than for the lower ones.