Ghana Priorities: Urbanisation
The Accra Metropolitan Area (AMA) is suffering from a major urban infrastructure gap. The region’s increasing economic growth has triggered rapid urbanization, characterized by expansion of built-up environment – roads, parking lots, and other structures with impervious surfaces that do not allow water to infiltrate easily so as to replenish the water table. Accra suffers from risks including perennial flooding and exceedingly poor solid waste management (SWM) regimes (Amoako and Frimpong-Boamah, 2015). Inadequacies of drainage systems increase surface runoffs which also increase the risk of flooding. Further, the design capacity of some drains at downstream is not sufficient to safely discharge excess water to the sea. This is worsened by illegal dumping of waste which has become an accepted norm.
Saddled with decreased drains containment capacity due to siltation, solid waste piling up and lack of maintenance, Accra over the decade has suffered from perennial devastating flooding which is bound to increase in the future (Songsore, 2017). This calls for a comprehensive flood risk mitigation strategy, both in terms of tackling the existing hazards and preventing future deterioration, either through conventional measures, which channel water safely to discharging outlets and bio-retention measures, which are natural solutions, designed to absorb the rainwater locally.
Ghana’s developmental challenges are two interrelated enemies - poor environmental sanitation and drainage facilities. These localized, everyday hazards are greatly compounded by global-scale risks associated with the increasing urbanization of poverty (Turok & Scheba, 2018) and climate change dating back to the early 1930s (World Bank, 2019).
Intervention 1: Construction of Pantang and Haasto retention ponds
Retention ponds are ponds designed with additional storage capacity to attenuate surface runoff during rainfall events consisting of a permanent pond area with landscaped banks and surroundings to provide additional storage capacity. The study proposes the construction of retention ponds in the middle and upstream of the Odaw basin to help temporarily store water from peak flood events and gradually release the same following storms.
The analysis covers a time period from 2018 to 2050, with investments occurring in the first year and ongoing operations and maintenance costs thereafter. Costs considered for this analysis were classified into initial investment costs and recurrent costs such as operations, maintenance, and other dis-benefits.
To estimate benefits from the ponds, the study utilizes the existing estimates of flood reduction conducted under the GARID project (World Bank, 2019) and benefits namely (a) direct economic benefits of avoiding or reducing flood damage; and (b) indirect economic benefits gained through less transport and business interruption. Totally, the present value stream of benefits is GHS 284 million of which the expected value of flood reduction benefits is USD 20 million or approximately GHS 91m in 2018 figures.
Intervention 2: Planning for Drain Widening
Even though drains reduce the local probability of flooding, technically deficient drains can result in a faster runoff in upstream areas and subsequently lead to the inundation of downstream in the basin. The intervention envisages constructing new (traditional) drains, especially if placed at bottleneck locations of the Akuapim hills as proposed (ie. Agbogba Happy Home-Alogboshie 13.55 km-stretch). The specification for the storm drain includes increasing its slope (with a steeper runoff) and changing the flow surface (to increase the capacity of the drains).
The construction costs for the storm drain have been assessed at the level of conceptual design, using a bottom-up approach. The estimated cost of the construction of the storm drain was broken down by cost estimates for either dredging or constructing lined concrete of the delineated drainage area. The total upfront investment for the drain is GHS 124 million.
Benefits are based on flood mitigation benefits from the drain - a 12% reduction in possible flood damages, equivalent to GHS 285m at an 8% discount rate. An additional important benefit of investing in a storm drains is the avoided death and illness from enteric diseases, a reduction in diarrheal disease of 30%, and averted productivity losses. The benefits accruing from cases of diarrhea avoided equals GHS 4.3m and increases with GDP growth in accordance with Ghana Priorities assumptions to a total benefit of GHS 72 million till 2050. The aggregated total benefit from this intervention is GHS 379 million.
Intervention 3: Community-based Solid Waste management
The CSM is a multi-sector planning approach geared towards service delivery in marginalized urban neighborhoods: it integrates source separation of waste, collection, recycling/reuse, and disposal; facilitates the incorporation of input from diverse actors and utilizes the concept of urban zoning to enhance the implementation of a decentralized option. Under CSM, areas of high waste generation, like slums, markets, and stadia are identified and segregated. Each “camp” is then contracted out to a service provider who is to undertake constant waste collection and the overall camp management including sweeping, clearing of gutters, and occasional fumigation to expel all rodents.
The analysis is conducted at a ‘camp’ level which we define here as 50,000 people. This is the level at which a given private entity would have the responsibility to ensure operational waste collection services and cleanliness.
The upfront costs include the costs of nine tricycles, three skips, and 6,250 bins for each camp. Upfront costs sum to GHS 1.2m per camp. Ongoing costs are also around GHS 97,000 per month or GHS 1.2m per year (these costs include the cost sweeping, scrubbing of pavement, desilting of drains and gutters, servicing of skip containers and disinfestation. The upfront investments (skips, bins and tricycles) are assumed to last for five years, and operational costs are assumed to increase with real GDP growth over the time period. At an 8% discount rate, the cost of the intervention is around GHS 6.1m per camp over the five-year period.
There are several benefits associated with improved SWM, foremost of which is the removal of waste from the area near the premises. Potential additional benefits include a general cleaner environment within the community, improved health, and reduced flooding. Based on a review we estimate a benefit equivalent to GHS 1.5m per year for a given camp of 12,500 households / 3,125 compounds. Over a 5-year period, the present value of benefits is GHS 6.4m using an 8% discount rate.