Dilution Method for Measurements of Unsteady Discharges in Mountain Streams

Dilution Method for Measurements of Unsteady Discharges in Mountain Streams

Meijer, D.G.

De Vries, M. (mentor)
Fontijn, H.L. (mentor)
Wang, Z.B. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

1992-02-01

In river engineering problems information on discharges and water levels is essential for many reasons. For irrigation and drinking water purposes it is very important to know how much water can be extracted from a river. Managers of waste water stations need to know how much they can release without exceeding the norms, and information on flood waves in the past help to predict the probability of flood waves in the future. Discharge measurements are therefore necessary. Different methods to measure a river discharge exist, such as the velocity area method, the moving boat method and methods using structures like flumes and weirs. Another method is the dilution method, based on the dilution of a soluble, non-disintegrating substance, to be released in the river. For steady flows, the principles of this method are rather simple, and recommendations on how to perform the measurements already exist (ISO Handbook). However, for unsteady flows, this method is much more complicated, and even its applicability is questionable. Studies on this topic, in which rivers were schematised as prismatic channels have already been carried out. In the present study the practice is the central issue. The applicability of the dilution method is investigated for mountain rivers with irregular cross-sections, big rocks and unsteady discharges. In chapter 2 the principles of the dilution method are explained, and the studies made thus far are outlined, as well as the approach in the present study. In chapter 3 the basic equations for the motion of water and transport processes, necessary for a transport model that can deal with the typical problems of an irregularly shaped mountain river, are formulated. A numerical scheme is derived in chapter 4, resulting into a flow-and-transport-simulating computer program (FATS). Dilution discharge measurements are simulated in imaginary rivers under flood wave conditions . The river discharge is then a time dependent upstream boundary condition, and a few measurements (water levels, concentrations) are generated. In chapter 5 a numerical procedure is developed (FINDQ) to compute the upstream river discharge, which uses only these measurements without any further information on characteristic river parameters. Determination of these parameters is an identification problem, which is solved using the DUD procedure. The quality of the discharge determination can be estimated by comparing the result with the original upstream boundary condition in FATS, supposed to be 'true'. Finally, in chapter 6, attention is paid to the field work and equipment required to obtain real measurements for the discharge determination. Using the FINDQ-DUD algorithm, the river discharge as a function of time can then be computed to a certain degree of accuracy, which is the eventual aim of this study.

river management
mountain rivers
discharges

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Student theses

master thesis

(c) 1992 Meijer, D.G.