Developing an Automated Design tool for Open Drainage Channel Case Study: Namatala Catchment, Mbale - Uganda
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Date
2026-06-17
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Busitema University
Abstract
Urban flooding is one of the most destructive consequences of inadequate stormwater infrastructure, particularly in rapidly urbanizing cities of Sub-Saharan Africa. In the Namatala Catchment (330 km2), Mbale City, Uganda, chronic flooding driven by poorly designed open drainage channels has displaced over 6,000 households and caused an estimated UGX 3.4 billion in damage since 2010. These failures persist due to continued reliance on the Rational Method, a peak discharge model fundamentally unsuitable for large, geomorphologically complex catchments, and the absence of any locally calibrated, integrated computational design tool within professional engineering practice. This study develops an automated computational design tool for open drainage channels, implemented as both a MATLAB–SWMM analytical framework and a browser-based web application accessible from any internet-connected device without specialist software. The tool executes a complete seven-step hydrological and hydraulic design pipeline: (i) catchment delineation from SRTM 30 m digital elevation data using ArcGIS; (ii) rainfall frequency analysis via Gumbel Extreme Value Type I (EV-I) distribution fitted to 25 years of NASA POWER daily rainfall data; (iii) Intensity-Duration-Frequency (IDF) curve generation; (iv) peak discharge estimation using the TRRL East African Flood Model as the primary
method, with the Rational Method and SCS Curve Number as secondary comparators; (v) optimal trapezoidal channel sizing via Newton-Raphson iteration of Manning's equation with MATLAB optimisation; (vi) hydraulic constraint verification including Froude number, permissible velocity, and tractive force checks; and (vii) automated accuracy benchmarking against SWMM dynamic wave simulation outputs. Applied to the Namatala Catchment at the 10-year return period, the TRRL model converges in three iterations to a design peak discharge of Q = 63.3 m3/s compared to Q = 427.9 m3/s from the Rational Method (+576% overestimation) and Q = 63.731 m3/s from SWMM dynamic wave simulation (0.68% deviation) confirming near-perfect cross-validation accuracy. The resulting trapezoidal channel iii dimensions across all three design reaches achieve subcritical flow (Fr < 1.0) and comply with all permissible velocity and tractive force thresholds. The browser-based web application, built on React 18, TypeScript, Zustand, and Zod and deployed on the Vercel content delivery network, executes the full pipeline in under two seconds a 240:1 computational efficiency gain over the 48-hour manual design workflow. The tool supports session persistence, interactive IDF visualisations, manual cross-validation, and client-side PDF report generation, and is transferable to other East African ungauged catchments.
The study demonstrates that: (i) the TRRL East African Flood Model is the only valid primary discharge method for the Namatala Catchment; (ii) the Rational Method must be retired from large-catchment drainage practice in Uganda; and (iii) browser-based automated design tools can eliminate the efficiency
and accuracy barriers preventing evidence-based design at scale contributing a validated open-access tool and an empirical basis for national guideline revision.
Keywords: TRRL East African Flood Model; open drainage channel; Namatala Catchment; Manning's equation; SWMM validation; automated design tool; Mbale Uganda; Gumbel EV-I; React web application.
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Undergraduate research report.
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Citation
Anyango, E. K. (2026). Developing an automated design tool for open drainage channel Case study: Namatala Catchment, Mbale - Uganda [Undergraduate Research report]. Busitema University.