Author(s): Elena Carcano; Daniele Bocchiola
Linked Author(s):
Keywords: Monthly flow duration curve; Environmental release
Abstract: Flow duration curves (FDCs) are an essential tool to assessing the design value of an hydropower plant. At the same time, FDCs can supply reliable information in terms of the optimum environmental flow to be released in order to fulfill biological requirements such as fish reproduction and fish ascends. Generally speaking, a plethora of different criteria has arisen to help engineers and biologists to evaluate the appropriate value of environmental release. Traditional, hydrological, morphological and statistical are some of the available methods which state the minimum flow above considerations on values selected a priori. The last method, through FDCS, associates the environmental flow to a specific duration in time. In this way, the problem of an optimum flow becomes the choice of an appropriate duration or, in other words, of the limit duration a watercourse can naturally sustain before critic conditions. Although the widespread use of FDCs is related to yearly curves (as detailed by Vogel and Fennessey 1994-1995), a mention of monthly curves has been given by Searcy since a remote past (1959). In all their forms of application, in fact, FDCs are always an alternative way of representing hydrogram information. FDCs are built ranking the total series of data in a decreasing order and having rescaled the x axis assigning the maximum value of time t to the lowest observed streamflow. Moreover, Searcy pointed out that, when a sufficiently long record is adopted, the curve represents the cumulative frequency distribution and is of crucial importance as it can be easily updated after each water concession. This work introduces an original method of gaining information from monthly streamflow curves as it aims to compare the mean streamflow datum to the corresponding median value for each month considered. Starting from more than ten year record of data, the procedure builds twelve duration curves for an hydrological homogeneous region (represented by four catchments) and estimates appropriate environmental flows according to the corresponding water availability. Exploring monthly data validates the nowadays recommended variability of the environmental flow release. In a nutshell, the study highlights how a detailed insight of appropriately gathered data allows a better compilation of biological requests.
Year: 2014