Developing Uganda’s Urban Paved Areas as Porous Pavements in Support of Africa’s Continental Free Trade Area Implementation.

Abstract

Implementation of Africa’s Continental Free Trade Area requires smooth flow of goods and services. This is constrained by frequent flooding in Kampala and other African Cities. As part of efforts to mitigate floods in Kampala, the government of Uganda has repaired a number of drainage channels. With the ever-increased paving in the urban areas, this increases runoff that cannot be safely accommodated by the drainage channels without flooding. This can be solved by the use of porous pavements.

Porous (permeable) pavements allow water to infiltrate through surfaces that would normally be impermeable, such as asphalt or Portland cement concrete parking lots. Rain may then recharge the groundwater table, and air may pass through to nourish the roots of grass and trees.

Pervious surface treatments reduce the risk of stormwater runoff, retaining the water sub-surface as it gradually infiltrates into the soil; holding the storm water in multiple air voids or cells also assists in pollution control through degradation of hydrocarbons into carbon dioxide and water, and retaining metals in the structure keeps them from the groundwater table.

This paper presents case study findings for a sample porous (permeable) pavement to demonstrate the benefits of using porous pavements as compared to the traditional non-porous design.

The volume of runoff (Q), according to the Soil Classification System (SCS) rainfall runoff relation, depends on the volume of precipitation (P) and the volume of runoff that is available for retention. The actual retention (S) is the difference between the volume of precipitation and runoff. The SCS developed an index, called the runoff curve number (CN), to represent the combined hydrologic effect of soil, land use, agricultural land treatment class, hydrologic condition, and antecedent soil moisture. Curve Numbers for different soil groups are presented in MoWT Road Design Manual, Volume 2 Drainage Manual 2010. CN for paved parking lots, roofs, drive ways, paved with curbs and storm sewers etc. is 98, commercial and business areas (85%) impervious, is 89-95 while for open spaces, lawns, parks can be as low as 39-80. Implying that CN for porous pavements can be as low as 50 giving a reduction in runoff by as much as 50%.