Field Study of Morphological Parameters in Step-Pool Streams

Abbas Torbizadeh,Mohammad Reza Majdzadeh Tabatabai,Ahmad Tahershamsi

doi:10.28991/cej-03091127

Abbas Torbizadeh, Mohammad Reza Majdzadeh Tabatabai + Show 1 more

Open Access

https://doi.org/10.28991/cej-03091127

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Abstract

Nowadays, step-pool formations have attracted a lot of attention, which are distinguished by the successive arrangements of the bed, suitable geometry, and the tumbling flow pattern, which can highly disperse water energy. Field study of a step–pool channel, along with one of the upper reaches of Kamandan River indicated a strong correlation between several morphological parameters of the river such as reach slope, step length, step height, pool depth, local slope, and the like. The length of the reach under the study is 145 meters and has an intermediate morphology based on Montgomery and Buffington’s classification. Therefore, twelve distinct step units were identified for 145 meters upstream while the rest was formed by steep morphology. In the present study, different definitions of wave length were applied to establish the relationships among the above parameters. For instance, the difference between apexes of every two successive step elevation was found to have a considerable relationship with the wavelength with a determination coefficient of 0.9. In addition, bankfull width and depth, along the profile for different cross-sections, were determined to establish a relationship between these parameters and pool spacing. Further, the parameters were applied to create a relationship with step heights.

Highlights

Step-pool channels are considered as a series of stream morphological kinds which change downstream within watersheds
In order to follow the objective of the study, Kamandan River was selected as the case study
The morphology of step-pools has been studied with regard to their hydraulics because their morphologic features are too irregular to be precisely associated with a sequence of artificial structures and too orderly to conclude that the composition of the overall hydraulic behavior is not predictable

Summary

Introduction

Step-pool channels are considered as a series of stream morphological kinds which change downstream within watersheds. Step-pool bed forms were identified at low discharges following the morphological classification of Montgomery and Buffington (1997). In their classification, step-pool streams are identified by longitudinal steps formed by large clasts which separate the pools including finer material. Cascades are typically longitudinal and they are laterally regarded as disordered bed materials including individual boulders separated by small pools [1]. Step-forming clast sizes are typically comparable to annual high flow depths, a stepped longitudinal profile may be developed in steep sand-bedded streams [4]. Chin (1989) suggested that step-pools can be recognized by their staircase-like longitudinal profile resulting from accumulating cobbles and boulders which are located transversely across the channel, alternating with pools including finer material.

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