Effect of the Hydraulic Characteristics of a Stream Channel and its Surroundings on the Runoff Hydrograph

V Matoušek

doi:10.14311/923

Abstract

The course and magnitude of a rainfall flood depends primarily on the intensity and duration of the rainfall event, on the morphological parameters of the watershed (e.g. its slope and shape), and on how to watershed has been exploited. A flood wave develops in the stream channel that drains the watershed, and it transforms while passing along the channel. This is particularly the case if the water spreads into floodplains and/or storage reservoirs while passing through the channel. This paper addresses an additional effect that has a significant influence on the magnitude and course of the flood wave but has not previously been addressed adequately, namely the effect of the hydraulic parameters of the stream channel itself on the transformation of a flood wave. The paper explains theoretically and shows on a practical example that a smooth channel with a high capacity significantly increases the magnitude and speed of a flood wave.Many flood events are unnecessarily severe just because the watershed is drained by a hydraulically inappropriate channel. The channel is large and smooth and therefore it gathers most of the flowing water during the flood event, producing high water velocity in the channel. As a result, the large and smooth channel accelerates the runoff from the watershed and constrains the spread of water into the floodplain. A high and steep flood wave is developed in the channel, and this floods areas with a limited water-throughput capacity (e.g. urban areas in the vicinity of hydraulic structures) downstream the channel. This paper offers a methodology for evaluating the ability of a channel to convey a flood wave safely and for recognizing whether a regulated channel should be subjected to restoration due to its inability to convey flood waves safely.

Highlights

In the part of central Europe that is the Czech Republic, the effect of an artificial channel of high capacity on the runoff culmination discharge was already under discussion more than a century ago, during implementation of the General Program of River Regulation in the Kingdom of Bohemia, which started in 1903
Nowadays, changing the floodwave hydrograph caused by the spread of water into a floodplain or into a storage reservoir is discussed in standard hydrology textbooks, e.g. [1], [5], together with methods for describing this phenomenon
The paper proposes a methodology for evaluating the flood waves produced by different stream channels

Summary

Introduction

In the part of central Europe that is the Czech Republic, the effect of an artificial channel of high capacity on the runoff culmination discharge was already under discussion more than a century ago, during implementation of the General Program of River Regulation in the Kingdom of Bohemia, which started in 1903. It was claimed that river regulation concentrates water into a river channel and constrains the spread of water into floodplains, resulting in amplification of the flood wave. To suppress this effect, the Program suggested building storage reservoirs on regulated rivers. Transforming the flood wave due to the spread of water into a floodplain or into a storage reservoir is only one part of the problem. The other is the formation of a flood wave due to the channel itself. This effect has not yet been addressed adequately

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