Fig. 1  Definition sketch.


HOW TO CALCULATE ONLINE THE NORMAL DEPTH

IN A ROADSIDE DITCH?


Victor M. Ponce

Professor Emeritus of Civil and Environmental Engineering

San Diego State University, San Diego, California


02 March 2024

ABSTRACT.  In this article we show how to calculate the normal depth in a roadsize ditch using ONLINE_SIDE_DITCH, an online calculator developed in 2023 by the Visualab, a hydraulic engineering computational laboratory of the Department of Civil Engineering, San Diego State University, San Diego, California. This design tool may be used to find the geometric dimensions of a roadside ditch, or culvert, given the cognizant hydraulic input variables.

1.  INTRODUCTION

The computation of the normal depth in a roadside ditch is not very straigthforward. The computation requires the iterative use of the Manning equation (Ponce, 2014). A source of possible complexity is that the typical triangular cross-section of the roadsize ditch has different side slopes (Fig. 1). In this article, we expedite the solution by providing an online calculator specifically developed for sizing a roadside ditch.

2.  EXAMPLE

We use the calculator ONLINE_SIDE_DITCH to run the following typical example:

  • Units: SI Units.
  • Discharge Q = 0.08 m3/s.
  • Side slope z1 = 4.
  • Side slope z2 = 0.5.
  • Bottom slope S = 0.005.
  • Manning's n coefficient = 0.015.

3.  RESULTS

REFERENCES

Ponce, V. M. 2014. Fundamentals of Open-channel Hydraulics. Online edition.

Ponce, V. M. 2023. ONLINE_SIDE_DITCH. https://ponce.sdsu.edu/onlinesideditch.php

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