An Engineering Design of the Drainage Crossing at St. Lawrence Road in Rubaga Division
Abstract
This report presents results on the engineering design of the existing drainage crossing along St.
Lawrence road in Ndeeba, Rubaga division Kampala district, based on Road Design Manual
Volume II: Drainage Design 2010, Kampala Drainage Master Plan 2016 T2 – Design Standards
for Stormwater Facilities and The Manual for Hydraulic Design of Highway Culverts Third
Edition.
The existing crossing was a 600mm concrete pipe culvert which is not of sufficient hydraulic capacity to carry storm water across the road from Nabunya channel into Kabaka’s lake. The effect
was flooding which led to washing out of St. Lawrence road, interruption of traffic flow, pollution
of the lake, and slipperiness. In order to mitigate the flooding, a box culvert was designed after
assessment of the hydrology of the area. The designed culvert is a box culvert of two barrels each
with a width of 3.5m and height of 1.7m spanning 10.5m, with reinforcement ofT12 and T16 high
tensile bars.
Culvert failure can occur for a wide variety of reasons including maintenance, environmental, and
installation-related failures, functional or process failures related to capacity and volume causing
the erosion of the soil around or under them, and structural or material failures that cause culverts
to fail due to collapse or corrosion of the materials from which they are made. Therefore, before
the culverts are constructed, the design and the review data must be checked always during the
design stage.
Ongoing culvert function without failure depends on proper design and engineering
considerations being given to load, hydraulic flow, surrounding soil analysis, backfill and bedding
compaction, and erosion protection. Improperly designed backfill support around culverts can
result in material collapse or failure from inadequate load support.