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Fig. 1   Cataract Canyon, Green river, Utah.


HOW TO CALCULATE ONLINE SEDIMENT DISCHARGE

BY THE COLBY METHOD?


Victor M. Ponce

Professor Emeritus of Civil and Environmental Engineering

San Diego State University, San Diego, California


08 March 2024

ABSTRACT.  Knowledge of sediment transport discharge and concentration is a requirement in the design of hydraulic conveyance structures. In this article, we present an online calculator of sediment load (sediment discharge and sediment concentration) by the Colby 1964 method. The method is known to be particularly accurate for the calculation of sediment load in alluvial streams. An example of the calculation using ONLINECOLBY rounds up the experience.

1.  INTRODUCTION

Knowledge of sediment transport discharge and concentration is a requirement in the design of hydraulic conveyance structures. Applications are in flood control and associated hydraulic structures. Currently, there are quite a few methods available for the calculation of sediment discharge; however, none are so convenient, straight forward, and predictable as the Colby 1964 method (Colby, 1964; Ponce, 2014a). In this article, we present an online calculator of sediment load (sediment discharge and sediment concentration) by the Colby 1964 method. The method is known to be particularly accurate for the calculation of sediment load in alluvial streams. An example of the calculation using ONLINECOLBY rounds up the experience.

2.  THE COLBY METHOD

The Colby (1964) method for the calculation of sediment discharge, herein referred to simply as the "Colby method," is a methodology to calculate the discharge of sands. The method is based on Colby's earlier work (Colby and Hembree, 1955; Colby, 1957; Ponce, 2014b). It relies heavily on the relationship between sediment discharge and mean velocity, with flow depth and channel width as additional parameters. Secondary parameters are water temperature, bed material size, and wash load concentration (Fig. 2).

Ponce (2014c)

Fig. 2   Relation between two classifications of sediment load.

3.  USE OF THE ONLINE CALCULATOR

The online calculator ONLINECOLBY was developed in 2020 at the Visualab, Department of Civil, Construction, and Environmental Engineering, San Diego State University, San Diego, California. We run the calculator with the following input data:

  • Units [Select one]:   

    		•
       SI Units (metric)

  • Mean velocity v (m/s):   

    		•
       1

  • Mean flow depth d (m):   

    		•
       2

  • Channel width B (m):   

    		•
       10

  • Water temperature T (°C):   

    		•
       20

  • Bed material size d50 (mm):   

    		•
       0.5

  • Wash load concentration Cw (ppm):   

    		•
       300

Output from the calculator is shown below. The discharge of sands, or sediment discharge, is: Qs = 488.1839 M. Tons per day; the concentration of sediment is: Cs = 0.2825 kg/m3.

REFERENCES

Colby, B. R., and C. H. Hembree. 1955. Computations of Total Sediment Discharge, Niobrara River Near Cody, Nebraska. U.S. Geological Survey Water-Supply Paper 1357, Washington, D.C. https://ponce.sdsu.edu/colby_and_hembree_1955.pdf

Colby, B. R. 1957. Relationship of unmeasured discharge to mean velocity. Transactions, American Geophysical Union, 38(5), Oct., 708-717. https://ponce.sdsu.edu/colby1957agu.pdf

Colby, B. R. 1964. Discharge of sands and mean velocity relations in sand-bed streams. U.S. Geological Survey Professional Paper 462-A, Washington, D.C. https://ponce.sdsu.edu/usgsprofessionalpaper462A_colby1964.pdf

Ponce, V. M. 2014. Engineering Hydrology: Principles and Practices. https://ponce.sdsu.edu/enghydro/index.html

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