A recently converted culvert bridge in Makueni County, Kenya. The river crossings in Makueni County provide an Interes ng case study: â¢ Recognising the poten ...
The importance of rural roads Physical, social and political isolation are core features of the poverty trap. The concepts of access, services, and participation are at the centre of the development debate. Without reliable roads infrastructure, rural communities struggle to access health and education services or take advantage of markets or employment opportunities. In 2011, one billion people, or 31% of the world's rural population, live isolated from markets and services – defined as living more than 2km from an "all season road" (one that is drivable at all times of the year and within, at most, six hours after rain) by the prevailing means of transport.* Well managed rural roads are a tool for social inclusion, economic development and environmental sustainability. *http://www.worldhighways.com/sections/world-reports/features/rural-roadsimportant-to-global-development/
In Niger, harvesting rainwater from roads is done as a matter of policy.* In Kenya it is done sporadically. Investment in roads much greater than that in agriculture *Source: Meta Meta
*Source: Kenya Rural Roads Authority, Makueni region Swaziland has an area of 17,363km2
• Drainage is key to roads design. • This is especially true of low volume rural roads, as the weather causes more damage than the traﬃc. • Given the ﬁnancial constraints many low-‐income countries operate under, the challenge is to design roads, and especially river crossings, that are less prone to ﬂood damage and require less rouIne maintenance.
Current designs don’t work: Culverts are the most common design for road crossing on LVRRs. However, they are oPen insuﬃcient to cope with peak ﬂoods and require signiﬁcant investments in maintenance. Because in rural areas of developing countries maintenance is oPen inadequate, erosion and fractured road systems result. 80% of roads maintenance costs are spent on emergency repair or reconstruction, often of culvert bridges which wash away. Some common causes of damage to culvert river crossings: 1. Poor construcIon/headwall 2. Culverts get blocked 3. The paved secIon does not accommodate the peak ﬂood and the river spreads and is diverted
Widening of the river
A washed then extended culvert bridge
Source: InternaIonal Labour OrganisaIon
Makueni County example: • In Makueni County there are 7,640 km of unpaved roads with 483 culvert or driP crossings – an esImated total construcIon cost of $225M. • The InternaIonal Labour Oﬃce (ILO) recommends a maintenance budget of 6% to maintain rural road crossings. • The total budget for Makueni County is only $1.1M – meaning that a signiﬁcantly more sustainable and cost-‐eﬀecIve road infrastructure is required to maintain access to services and markets for the rural poor. • This is exempliﬁed by the fact that out of the 483 culvert or driP crossings that 121 (25%) are currently in need of reconstrucIon aPer being washed away, and 362 (75%) are in need of rouIne maintenance. • This proves the inherent weakness of the design in terms of robustness and its high on-‐going maintenance costs.
Why sand dams are an improvement Sand dams are speciﬁcally designed to cope with seasonal river ﬂows, while at the same Ime storing water (rather than channelling it downstream) –making it available for local use. They address four key barriers to food security in drylands: 1. The lack of Ime – driven by the need to collect water from distant sources. 2. The lack of water for small-‐scale irrigaIon and livestock. 3. Poor access to markets and services. 4. The diminished investment in agriculture. Building san dam road crossings at the same height as current road bridges would cost about the same. But – repairs would be minimal and therefore maintenance costs would be much lower – so the lifeIme costs would be much less. Building the san dam road crossing higher would have about the same lifeIme cost as current road bridges – but with the signiﬁcant advantages of supplying year round
A sand dam is a reinforced rubble cement wall built across a seasonal sandy river.
• During the rainy season, a seasonal river forms that carries soil downstream. • The heavier sand accumulates behind the dam, while the lighter silt is carried downstream.
• Within one to four rainy seasons the dam completely ﬁlls with sand. But, up to 40% of the volume behind the dam is water, trapped in the pores between sand parIcles. • Sand dams are the most cost-‐eﬀecIve method of rainwater harvesIng in drylands. A mature sand dam stores up to 40 million litres of water -‐ recharging groundwater and providing people with a safe, reliable and local source of water all year round. • They have virtually zero operaIon and maintenance costs and last for over 50 years. They are widely suited to dryland regions of the world.
• A typical inﬁltraIon gallery, shallow well and hand pump. • On large dams a shallow well can serve 3,000 people. • Water can also be abstracted from scoop holes or from pipes or taps in the dam wall.
More reliable rural roads infrastructure and therefore improved access to markets and services. While the iniIal investment is similar to that of culverts, the long term costs is signiﬁcantly lower due to low maintenance requirements. Sand dams last up over 50 years. The Kenya Rural Roads Authority (KERRA) in Makueni County has built 50 sand dam road crossings since 2007.
The cross secIon of a sand dam road crossing
A suspended sand dam road crossing, innovated by Benson Masila in Makueni County, Kenya.
This sand dam road bridge is near Kako village in Makueni County, Kenya. It is 80m wide and 3m above the bedrock. This dam was built solely to support the rural roads infrastructure. However, following construcIon the increased water storage capacity was recognized and an inﬁltraIon gallery installed to create a municipal water supply that feeds seven village kiosks. Water is pumped at a rate of 50m3/day. Independent evaluaIons found that the signiﬁcantly improved water access impacts the ability of smallholder family farmers to invest in agriculture, as well as improving health and educaIon. A similar sand dam road bridge (Thwake) in Makueni County, Kenya supports three nearby farms to produce Maize, Bananas and Mangoes -‐ even out of season. These examples, and the 48 other sand dam road crossings built in Makueni County, demonstrate the technical feasibility of the innovaIon. However, they were not planned and built for the purpose of water abstracIon, and so inﬁltraIon galleries and abstracIon methods were not integrated in the design. They were also built more like sand dam driPs (with a maximum height of 1.5m above the river bed).
A recently converted culvert bridge in Makueni County, Kenya. The river crossings in Makueni County provide an InteresIng case study: • Recognising the potenIal to capture water for people and agriculture, there has been a conscious deviaIon from building culverts to building driPs. • These driPs are essenIally acIng as sand dams – providing reliable access to markets and services for isolated communiIes, at reduced maintenance cost to the managing authority, as well as improving access to water for people and agriculture.
Ø Culvert bridge cost vs. sand dam cost broadly equal. Ø Opportunity to build higher bridges to maximise other benefits. (ii) Maintenance or repair costs: Our experience of 415 dams shown a 2% failure rate (requiring significant repair). Ø Only 5% sand dams require maintenance and last at least 25 years. Ø Sand dam road crossings would be higher maintenance but 10-20% of culverts. (iii) Environmental and livelihood benefits: Ø Year round water supply averaging 20M litres (20,000m3) yield per year. Supporting people, livestock and irrigation. Ø Reduced soil erosion and land degradation. Ø Natural regeneration of vegetation. Ø Time for farmers to invest in SLM (averaging 2.5 to 5.5 hours a day). Ø
There are many opportuniIes for uIlising roads to harvest water and prevent land degradaIon – in parIcular through improved road crossings. In semi-‐arid drylands, sand dam road crossings are a viable and cost-‐eﬀecIve approach for addressing water insecurity and land degradaIon. Key challenges to take this forward include: 1. CollaboraIon between sectors (roads, water and agriculture) and government ministries. OpportuniIes are: 1. Climate prooﬁng rural roads infrastructure, enhancing aquifer recharge and creaIng dry season water storage builds community based resilience to climate change and are eﬀecIve disaster risk reducIon strategies in dryland regions prone to ﬂood, drought and severe weather events.