A Stochastic Model of Phosphorus Loading from Non-Point Sources

A stochastic model is presented and applied for Lake Balaton, Hungary to estimate the phosphorus (P) loading from non-point sources. Rainfall events cause surface runoff events and erosion events; all three events are random. P is carried by runoff into the lake in two forms: (1) dissolved P and (2) sediment, absorbed or fixed P. P loading is thus considered as a random variable, whose probability density function (pdf) per event is to be estimated. Pdf of seasonal (e.g. annual) loading is determined as the sum of a random number of random events. The annual mass balance of P stored in lake sediment leads to a first order difference equation, the solution of which can be used to predict the expected P available for release at future times The model is applied for the Tetves subwatershed (70 sq. km.) of Lake Balaton. Preliminary results show that during relatively short runoff events about as much P reaches the lake as during the rest of the year and that more sediment P is produced than dissolved P. Since a considerable variance apppears in the annual amounts of P loading, the use of stochastic models to estimate the loading conditions seems to be most appropriate. The stochastic loading model should be incorporated into a broader control model. Elements of such a control model are given in the form of possible P loading reduction measures; also, economic trade-off between these measures is discussed

Trade-off Between Cost and Effectiveness of Control of Nutrient Loading into a Water Body

A system consisting of a watershed and a water body is considered, and a methodology is presented for selecting the alternative scheme offering the best compromise between economic activity in the watershed and quality of the water body. The general problem is specified for the system of a watershed and a lake endangered by eutrophication. Both economic activity and eutrophication can be characterized by several criteria. The method is applied to actual data from a subwatershed of Lake Balaton, Hungary, where the economic objective is to minimize the sum of costs and losses for the various control measures and the environmental objective is to minimize the amount of P available for algal growth. Both of these objectives are decomposed into several criteria. The action space consists of six pure strategies, namely, the control of (1) point-source pollution, (2) fertilizer, (3) erosion, (4) land use, (5) runoff control, and (6) sediment yield. These six pure actions lead to the definition of eight mixed alternatives. The phosphorus-loading portion of the model is run repeatedly with different stochastic input sequences to account for hydrologic uncertainty and the corresponding environmental objective is expressed as the probability "uj" that alternative "j" results in the largest decrease of P-loading. Model parameters are estimated using available data or published tables and graphs. Compromise programming is used to find a trade-off (or satisfactum solution) that balances the two conflicting objectives. In order to facilitate further application of the methodology, several points are discussed such as the relationship between the lake and its catchment, the error in stochastic simulation, the consideration of various uncertainties, the effect of snowmelt, and possible coupling with detailed lake eutrophication models. Finally, a step-by-step summary of the methodology is given to facilitate application of the model to other cases. Multicriterion decision-making techniques are briefly reviewed in the appendix so that cases with more than two objectives may also be approached

Optimal Flood Levee Designs by Dynamic Programming

An economic optimal development of a levee system along a river is investigated and a dynamic programming (DP) approach is used to find the optima under various conditions. The system consists of a number of levee reaches or stages. A random input of flood wave is regarded at the upstream point of the system. There are two failure modes considered and, consequently, two parameters of the flood wave (state variables) to trigger failure modes in every stage. Stochastic DP is used since the state transition functions (flood routing along the stages) are random functions. Three methods are discussed. In Method I, the expected value of the objective function is taken first, then DP is used as a numerical technique. In Method II, a fixed design flood is chosen as an input under which both optimum cost and policy is determined. In Method III, the value of the expected optimum objective function is calculated. It is shown that the full power of DP cannot be used if Method I is applied. Future research involves comparing the solutions of the three methods

Las políticas del agua en el siglo XXI. Una revisión tras la cumbre de Johannesburgo

[ES] El agua es un factor clave para el desarrollo sostenible. Su importancia para la vida humana, su incidencia en la pobreza, en los desastres naturales y en el funcionamiento de los ecosistemas hacen del agua una de las preocupaciones fundamentales del siglo XXI. Cambio climático, crecimiento de la población, deterioro de la calidad del agua, escasez y competencia sobre el uso de este recurso son retos de suma importancia a los que se enfrenta la humanidad. En consecuencia políticas sensatas, basadas en principios éticos claros, y voluntad política son necesarias para preparar la humanidad a enfrentarse a la crisis del agua. Tres conferencias internacionales del mayor relieve, con sus respectivas declaraciones, son analizadas para explicar la evolución de un proceso que, a partir de la percepción del sentimiento de la opinión pública, trata de buscar acuerdos relativos a una gestión integrada de la política del agua y los correspondientes planes estratégicos. Mientras los acuerdos sobreBogardi, J.; Szöllösi-Nagy, A. (2003). Las políticas del agua en el siglo XXI. Una revisión tras la cumbre de Johannesburgo. Ingeniería del agua. 10(3):259-279. https://doi.org/10.4995/ia.2003.2585OJS25927910

Biologia Futura: integrating freshwater ecosystem health in water resources management

Sustainable water use implies the simultaneous protection of water quality and quantity. Beyond their function to support human needs such as drinking water provision, transportation and recreation freshwater bodies are also habitats. Conceiving them as water users on their own with respective biological, physico-chemical and morphological requirements could help maintaining their healthy state. Healthy freshwater ecosystems are also attractive for high-value human uses. Dwindling per capita availability of water, increasing demands, human well-being and climate change lead to competition for, and pressures on freshwater ecosystems. This has been conceptualized through the modification of the drivers–pressures–state–impacts–responses framework. This distinguishes between pressures, associated with the achievement of human well-being, and stressors, which are defined as the negative effect of excessive pressures or combination thereof on aquatic ecosystems. Guidelines usually specify threshold values to classify water bodies as appropriate for certain utilitarian uses. However, only few guidelines focus on freshwater ecosystem health. Eight guidelines for monitoring of freshwater ecosystem health were analysed in the UNEP-funded project “International Water Quality Guidelines for Ecosystems”. Based on this review, general benchmark values are proposed for key physico-chemical indicators. Furthermore, adaptive pathways towards improved monitoring and protection of the health of freshwater ecosystems are recommended. In this paper, we review the main findings of the report and also review its recent uptake. Water quality guidelines for freshwater ecosystems cannot be conceived without societal consensus and vision. Different climatic, geographical and socioeconomic contexts are to be considered too. Their development is embedded in an adaptive cycle. Its multiple phases and steps indicate a long-term approach including reassessment and potential revisions