Stefano Casadei

Vulnerability to Drought of a Complex Water Supply System. The Upper Tiber Basin Case Study (Central Italy)

The importance of simulation models to assess the impacts of droughts and the effects of mitigation options on water supply systems is well known. However a common procedure about the exploitation of model results is not established yet. Vulnerability is used to characterize the performance of the system, and it can be a helpful indicator in the evaluation of the most likely failures. In this paper a water allocation model is applied to the water supply system of the upper Tiber Basin (Central Italy) in which both surface waters (rivers, reservoirs) and ground waters (wells, springs) are exploited to feed mainly irrigation and civil users. Drought vulnerability indices are calculated to analyze the performance of the supply system under different climate and management conditions. Water shortage scenarios are simulated as a progressive reduction of mean precipitation, an increase in its standard deviation or a combination of both. The model shows that the safety of the water supply system mainly relies on the reservoirs and that the foreseen increased exploitation of the springs to replace contaminated wells, could be seriously limited by discharge decrease during fall. The vulnerability reduction obtained by a hypothetical augmentation of the storage capacity through additional small reservoirs was positively tested by the model. In conclusion vulnerability indices and synoptic risk maps demonstrated to be useful tools to analyze the model outputs. They provide easy-to-read scenarios to be used in a decision making framework considering negotiating among the main users.

A New Application of Flow Duration Curve (FDC) in Designing Run-of-River Power Plants

The present study evaluates the effects of river run-off regime and hydrological uncertainty on the hydroelectric production of a run-of-river power plant. The mean annual energy from a plant was modeled as a function of run-off regime and design flow, by means of a procedure developed on the mean annual Flow Duration Curves (FDCs) of 15 sample basins in the Umbria Region (Central Italy). Results show that energy output decreases from constant to torrential regimes, following a potential function, and that, the greater the design flow, the greater the rate of decrease. The treatment and validation of these results provided a useful tool for easy identification of optimal design flow, according to the hydrological features of the basin and the target hydroelectric production at the station. Analyses of FDCs with a 20-year return period also showed that the decrease in energy production in dry years and its increase in wet years, compared with the mean annual value, are linearly linked to the design flow. In the present context of possible climate change, this result is presented as the possibility of partially controlling the effects of positive or negative flow rate trends. The results reported here can be applied to any kind of river and hydraulic technology at the power station.

Evaluation of the minimum instream flow of the tiber river basin

This paper discusses various methods for calculating the minimum instream flows for the protection of aquatic life for the purpose of illustrating its increasing complexity. These procedures are the Montana method (Tennant, 1976); the wetted perimeter method (Collings, 1974; Cochnauer, 1976) and the IFIM method (Instream Flow Incremental Methodology; Bovee, 1982). An analysis is then made of some regionalisation criteria based on these methods, from which useful suggestions can be drawn for the development of a procedure to be applied to basins. A method is thus proposed for calculating the recommended flows for protecting the aquatic environment based on simple hydrological variables, such as Q7 10, which can be estimated for a basin on the basis of area A and a Base Flow Index (BFI) which summarises its hydrogeological characteristics. This approach can be used when the field data necessary for more complex methods is not available. These require the defining of the environmental suitability of a watercourse for certain designated reference fish species, according to the flow and the morphology of the channel. The positive results of this approach were verified by Leonard (1990) and this methodology was applied to the Tiber river basin.