Abstract
Normal and critical depths are two important parameters in open-channel design for irrigation and drainage channels. This research is motivated by the lack of analytical solutions to directly compute these depths for most channels, leading to the use of tedious iterative techniques or less accurate approximation methods. This paper presents a computer model to calculate normal and critical depths in trapezoidal, circular, rectangular, and triangular open channels using explicit equations and the Python programming language. The developed model utilized improved explicit equations to provide fast and highly accurate solutions for a range of channel geometries, unlike existing solutions that are limited to certain cross-sections or requires subscription fees. Results demonstrate the model's high precision and stability across multiple channel geometries with maximum relative error (MRE) ≤ 3%, Nash-Sutcliffe Efficiency (NSE) ≥ 0.9873, mean absolute error (MAE) ≤ 0.0143m, and root mean square error (RMSE) ≤ 0.0223m, confirming almost perfect alignment with benchmark solutions. The use of Python makes the model user-friendly, reducing the need for manual calculations and minimizing errors. The model also includes visualizations of the channels to enhance the user experience. Overall, the study provides a practical tool for hydraulic designers and engineers to efficiently determine critical and normal depths in open channel flows.

Key words: Critical depth, normal depth, open channel flows, python, software development.