Improving Urban Runoff Drainage Systems In Shire Indaselassie Town
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Date
2019-03
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Addis Ababa University
Abstract
Storm water discharges are produced when the capacity of the land to retain precipitation is
exceeded and run-off occurs. Run-off will be influenced by rainfall and intensity and duration,
antecedent storms and a number of watersheds, and land use characteristics such as slope, soil
type, and impervious surfaces.
In Shire Enda Selassie city rainfall induced flooding during rainy season is a regular
phenomenon. This may be due to either small size of the drainage canal, an incremental of
rainfall, improper design of self-cleansing velocity or increasing of impervious surfaces of the
catchment. Identifying the main problem associated with the drainage system feasibility and
making the system sustainable is important.
To Simulate the flooding problem in the city using SWMM model which shows the over loaded
conduits as well as junctions then select the preferable depth of flow in conduit or junction
without overflow. Delineation of the area creates by depending on site visiting bounds the region
by flow contributes to the junction or drainage. For one control point the total area contributes
flow is delineated .The total catchment area modeled by SWMM is 56.8 ha, which have 131
junctions, 130 conduits (links) and two out fall considers. For this catchment the total runoff
computed using model is 9.28m3/s whereas calculated by rational method is 7.4m
3
/s. The
network link simulation a result implies around 22.9 % of links is over pressured due to flood.
The total simulation accuracy of the runoff and network systems as assessed by statistical
methods, were RNS, =0.62 and R2 = 0.97. The proposed mitigation measures are modifying the
depth of links for those links. Another case the model cannot simulate the flood problem exists
due to partially blocked the links, so for this problem continuous maintenance is mandatory.
Therefore, the effectiveness of different sustainable drainage systems; Trench filter, swale and
green roof and enlargement of pipe diameters were evaluated for this case study.
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Keywords
Ethiopia, Shire Endaslasse, SWMM model, Sustainable drainage system, Mitigation measures