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HEC-RAS study of Simike–Nzovwe drainage

Figure 5. Specific energy distribution along the side drain channel at a selected culvert location
Abbreviations: Crit: Critical depth; EG: Energy grade; WS: Water surface.

Figure 6. Velocity profile along the side drain channel

peak flows but also promotes localized clogging and stresses and localized erosion. Flow transitions at
sedimentation. This outcome is well documented in culvert locations – marked by hydraulic jumps and
the literature, where poor velocity conditions at culvert velocity drops from approximately 7 m/s to <1 m/s –
throats are linked to recurring maintenance needs and contributed to turbulence, sedimentation, and energy
long-term drainage inefficiencies. 44 loss. These findings suggest that the present drainage
design is ineffective in managing flow transitions and
4. Conclusion and recommendations sediment transport, ultimately compromising system
efficiency, increasing maintenance requirements, and
This study employed the HEC-RAS model to evaluate reducing infrastructure resilience.
the hydraulic behavior of a 1.85 km roadside drainage To enhance the hydraulic performance and long-term
system along the Simike–Nzovwe section of the sustainability of the Simike–Nzovwe roadside drainage
TANZAM Highway. The analysis identified critical system, an integrated approach combining engineering
performance limitations associated with both sediment upgrades, ecological design, and advanced modeling
deposition and erosional processes. Subcritical flows is recommended. Optimizing channel geometry by
(Fr <1) upstream of culverts were linked to sediment reducing side slopes from 1:2 to 1:1.5 and increasing
accumulation and frequent blockages, while supercritical longitudinal gradients to 1.5 – 2% can help maintain
flows (Fr >1) on steeper slopes resulted in high shear supercritical flow in targeted sections, minimizing

Volume 22 Issue 4 (2025) 245 doi: 10.36922/AJWEP025190146