The uncertainty effects of design flow on water quality management

Abstract

In water quality management, pollution control strategies have been sought to accord with the assimilative capacity of water bodies so as to preserve water quality. The waste load allocation (WLA) is a useful approach to determine the allowable loading of pollution sources in water quality management. For any WLA, a particular water body condition is needed as a basic scenario under which the relevant parameters are fixed. The particular flow rate is known as design flow and usually set at low flow in order to be protective. The design flow is traditionally a particular deterministic value, such as Q (75), implying that it is expected that the probability of water quality violation is 25% in the long run. However, this long-term expectation might not be realized in individual years due to variability of natural flow. The flow variability will make a WLA plan overoptimistic or over-conservative in different years, suggesting that the deterministic design flow without uncertainty consideration might lead to an ineffective or inefficient decision-making. To address the problem, we explicate the relationship between flow variability, design flow and water quality with different flow distributions to facilitate the understanding of the process of a WLA. In order to manifest the uncertainty effects of design flow, the results from the annual flow duration curve (AFDC) is compared with the conventional flow duration curve (FDC). The AFDC approach is capable of obtaining the uncertainty level of the design flow by generating the confidence interval rather than a fixed value. The effect of different record lengths on design flow determination is estimated as well. Finally, a refined WLA process is proposed with a re-examination of water quality violation to improve the allocation decision under uncertainty. TaHan River Basin in northern Taiwan is used as a case study.

Modelling of hydrological and environmental flow dynamics over a central Himalayan river basin through satellite altimetry and recent climate projections

“…The FDC defines the percentage of time that particular discharge would be equal or exceed for a given catchment (Vogal and Fennessey, 1994). FDCs have worldwide acceptance among researchers for irrigation, water supply, hydroelectric power planning, and understanding water resources problems (Male and Ogawa, 1984; Smakhtin, 2001; Tharme, 2003; Chen and Ma, 2008). Therefore, we had done comparative evaluation of FDCs for observations with future periods under recent climate projections.…”

Water quality evaluation system to assess the status and the suitability of the Citarum river water to different uses

“…To handle the problems in implementing of integrated water quality management are necessary to consider all the related aspects entire the river basin catchments area to ensure the quality of stream water managed will improve gradually. For example, a refined the waste load allocation process is proposed with a re-examination of water quality violation to improve the allocation decision under uncertainty (Chen and Ma 2008). Participatory surface water management is emphasized in order to achieve a holistic and sustainable water management decision-making process (Hartmann et al 2006).…”

Risk analysis of seasonal stream water quality management

“…These models are typically designed on the basis of critical stream conditions such as annual low flows and high summer temperatures (Lence et al 1990), However, the discharge limit based on pre-determined constant conditions is not cost effective doi: 10,2166/wst.2010.538 for rivers with significant seasonal variations in flow (Kao & Bau 1996), Seasonal management programs, which consider the dynamic waste assimilative capacity of a river and allow for different levels of waste treatment during different seasons of the year, have been shown to be more costeffective than non-seasonal uniform treatment programs (Reheis et al 1982;Eheart et al 1987;Rossman 1989;Lence & Takyi 1992;Ng et al 2006;Chen & Ma 2008), Under seasonal discharge programs, allowable discharge rates are indexed to the calendar date, with the expectation that the assimilative capacity of the receiving water body will vary from one period to another. The rate of waste discharge allowed at a given time is determined by considering water quality goals and the acceptable probability of achieving those goals.…”