Experimental application of the concept of Total Maximum Daily Load in the watershed planning under the Water Framework Directive
Author(s)
Santese, Gerardina
Date Issued
February 23, 2010
Type
Doctoral Thesis
Abstract
The Water Framework Directive 2000/60/CE (WFD) was enacted in order to maintain and improve the aquatic environment of the Union. The protection of waters, in terms of quality and quantity, is one of the key aspects of the Directive, which requires the achievement of “good ecological status” for all water bodies by 2015. In many European countries the process of implementation of the WFD has required important changes in the development of the water management plans.
The River Basin Management Plan was indicated as the process to adopt for investigates the current status of the water bodies and define the “Programme of Measures” that permit to reach the objective of “good ecological status”.
This dissertation can be part of the definition process of a “Programme of Measures” for impaired waters through the application of a scientifically based method in order to define the “objective” to achieve, identify the measures to be taken and then evaluate their effectiveness.
The method applied fulfills the requirement of the WFD within the directive to manage both types, punctual and diffuse, of pollution sources causing the deterioration of the ecological status of all European water bodies.
The management of punctual and diffuse sources requires to establish a link between input loads and the water quality standards of the receiving water bodies.
In this dissertation, the use of the concept of the “Total Maximum Daily Load” (TMDL) was applied for an Italian river. The TMDL is an instrument required in the Clean Water Act in U.S.A for the management of water bodies classified impaired. The TMDL calculates the maximum amount of a pollutant that a waterbody can receive and still safely meet water quality standards. It permits to establish a scientifically-based strategy on the regulation of the emission loads control according to the characteristic of the watershed/basin.
The implementation of the TMDL is a process analogous to the Programmes of Measures required by the WFD, the main difference is the analysis of the linkage between loads of different sources and the water quality of water bodies.
The TMDL calculation was used in this study for the Candelaro River, an intermittent Italian river, classified impaired in the first steps of the implementation of the WFD.
The “Load Duration Curves” methodology was adopted for the calculation of nutrient TMDLs due to the more robust approach than the expression based on average long term flow conditions. This methodology permits to establish the maximum allowable loads across to the different flow conditions of a river.
This methodology allowed: to evaluate the allowable loading of a water body; to identify the sources and estimate their loads; to estimate the total loading that the water bodies can receives meeting the water quality standards established; to link the effects of point and diffuse sources on the water quality status and finally to individuate the reduction necessary for each type of sources.
The loads reductions were calculated for total nitrogen, total phosphorus and ammonia.
The measures simulated gave results that show a remarkable ability to reduce the pollutants, for the Candelaro River. This reduction, anyway, is not enough to achieve the objective of water suitable for fish life.
The use of a mathematical model on a watershed scale, the Soil and Water Assessment Tool (SWAT), was applied in order to obtain a daily flow dataset of the Candelaro River and a daily water quality for a longer period than the measured data. The use of the model permitted to obtain a robust assessment of the present and future water quality status overcoming the lack of measured data.
The results highlighted the critical condition of water quality particularly during the dry periods and the necessity to adopt specific measures for each flow conditions, not related to the seasonality, to restore the water surface quality status of the Candelaro River.
Additional information
Dottorato di ricerca in Scienze e tecnologie per la gestione forestale e ambientale
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