Maintenance Dredging of the Odaw River, Ghana Under a Performance Based Contracting Approach
Type:
Presented during:
WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.
Authors:
J. Kemp, J. Gauderis, N. Saidi Mazarou, K. de Wit, L. van der Kamp
Abstract
"Ghana's greater Accra region has perennially suffered from severe flooding during rainy seasons, causing death, displacement of people, and destruction of property: a trend that the government wants to reverse through a long-term dredging plan. The key for reducing flooding is maintenance dredging of the Odaw River and its main tributaries to allow increased water capacity and reduction in flood risk. The problem, however, stems from the required regular undertaking of such maintenance dredging not being completed in an optimal manner. A feasibility study was therefore undertaken to address this, by preparing a ready-to-tender Performance Based Contract (PBC); a first of its kind in Ghana. Data is key to a successful implementation of a PBC. With that in mind an assessment of the annual sedimentation of the main channels was performed and forms a key part of the PBC by helping to determine the performance criteria. It is not viable, practical, or necessary to maintain the river to the original design levels at all times. A certain amount of sedimentation can be allowed but it must be linked to the hydraulic capacity of the different river sections. Based on this philosophy, trigger levels" of allowable sedimentation at different sections of the river were determined based on the hydraulic capacity of the different sections of the river. The performance criteria for the contractor undertaking the maintenance dredging require the riverbed levels to remain within the allowable amount of sedimentation at each section. The PBC also allows the contractor the right to develop commercial activities related to the maintenance dredging (such as re-use of sediment)."
Keywords: Flood alleviation, Performance Based Contract, maintenance dredging