Conclusions: it pays off

Key message

  • There are multiple co-benefits in reduced maintenance costs and reduced down-time of roads; in reduced damage to environment; in beneficial use of water or in flood resilience
  • In the on-going green roads for water the sum total of these co-benefits greatly exceeds the additional costs
  • The costs of particularly the adaptive road resilience measures are modest compared to the total infrastructure investments and the cost of protective climate-proofing of roads

In most “roads for water, roads for resilience” applications, there are multiple co-benefits.  By making roads that can serve more purposes than transport, and by making this part of the design and development of roads, it is possible to create roads that (a) reduce the now often substantial collateral damage that uncontrolled road water causes to the landscape around it; (b) are likely to have lower maintenance costs and downtime and are generally better able to withstand weather effects, including those that are caused by climate change; and (c) generate substantial benefits in terms of water harvested with the roads and other beneficial water management functions. In other words, rather than being a source of landscape degradation, they can become instruments for climate-change resilience. Table 13.1. summarizes these triple benefits  using the resilience dividend framework of Tanner et al. (2015).

Table 13.2. Benefits and co-benefits  of the “Green Roads for Water” approach

 Resilience Impact
1Reduced damage in the wake of disaster and unusual eventsReduced cost of road maintenance

Reduced damage due to erosion

Reduced damage due to flooding

Reduced damage due to sedimentation

2Unlocking the economic potentialLess downtime of roads
3Co-benefitsBeneficial use of water harvested from roads


Based on the work in Ethiopia, where the most substantive integrated program is under way, the different resilience dividends were calculated, making use of the multiyear monitoring of erosion, sedimentation, moisture, and groundwater levels near road-water harvesting structures (Woldearegay et al. 2015). The cumulative annual dividend of the roads for the water approach to resilience, as implemented in Ethiopia, is US$16,879 per km (see Table 13.2.). This compares favorably with the direct investments of US$1,800 per km. These investments were largely earthwork measures implemented under the Mass Mobilization watershed campaign. If one were to include the cost of organizing and developing this program, another US$1,800 could be added. Even then a fourfold return to investment is achieved in the first year. It comes as no surprise that the program has spread quickly in the different regions in Ethiopia.

The measures implemented in Ethiopia comprise simple earthworks-based interventions—floodwater spreaders, roadside water ponds and infiltration trenches, many of which are explained in Chapter 2—with no engineering required. It is a minimum but cost-effective package. Other measures may be added that are more encompassing and will require a redesign of the road, for instance using non-vented road drifts (Chapter 8) as sand dams and stream stabilizers; reconsidering the number and locations of road culverts; changing the alignment of the road to optimize runoff capture; or using road embankments for water storage. These will come with their own costs and benefits and as such should be calculated. Indications so far are that such measures do not necessarily add many additional costs and that their costs/benefits may be equally attractive. In several instances, they may make use of the road infrastructure as is and add functionality to it at a very modest additional cost. Several Roads Adaptive and Pro-active Resilience “Plus” measures may even reduce construction costs.

  • An example is the re-use of borrow pits for permanent water storage rather than backfilling them, often done with low-quality soil material (see Chapter 7). This is a considerable cost-saving measure and it creates a local water resource almost for free, especially when site-selection criteria and safety measures are included in upfront planning (van Steenbergen 2017).
  • Another example concerns building roads in flood-prone areas with lower embankments and equipping them with controlled overflow “floodway” structures instead of going for high embankments (see Chapter 11). This reduces costs enormously, as the expenditure on the embankments is considerably less, and prevents roads from washing out in unpredictable locations.
  • A third illustration is the use of culvertless, “non-vented” drifts as road crossings. These come at the same costs as road drifts with culverts but prevent the scouring of rivers and encourage the buildup of sand-water storage immediately upstream of them, combining the function of a road crossing with that of a sand dam (Neal, 2012). Excellent (no date) has made a calculation of costs and benefits and estimates that maintenance costs on culvertless drifts are only 13 percent of the maintenance costs of vented drifts.
  • Fourth is the management of water levels in the coastal lowlands, such as the polders in Bangladesh (see Chapter 4). The only option to do so is to make use of the road network in these areas, expand it wisely, and equip it with appropriate cross-drainage structures.
  • Fifth is the use of road embankments for water storage, as is done in countries as different as Burkina Faso, Portugal, Turkmenistan, Uganda and Yemen. Because the road embankment is already there, the reservoirs can be developed on the basis of sunk costs.
  • The final example is the use of low-cost measures, such as drainage dips, water bars and infiltration bunds, on the widespread network of unpaved roads to guide water to productive uses and prevent damage to those roads that usually are not repaired (see Chapter 9).

Table 15.3. Comparing the costs and benefits from a conventional and inclusive roads resilience approach per kilometer of road in Ethiopia

   Resilience Plus ApproachResilience Basic Approach
CostsPaved roadsUS$1,800US$45,000 1
 Unpaved roadsUS$1,800US$31,200
Resilience Dividend
1Reduced damageReduced cost of road maintenance: unpaved


Periodic: paved

Periodic: unpaved









 Reduced damage due to erosionUS$2,675Negative: considerably more flooding than in base situation
 Reduced damage due to floodingUS$1,762Negative: considerably more flooding than in base situation
 Reduced damage due to sedimentationUS$180
2Unlocking economic potentialLess downtime of roads

Reduced impact from climate change





3Co-benefitsBeneficial use of water harvested from roadsUS$4,500Not there


The cost and benefits of the investment in roads for water-resilience measures may also be contrasted with the Basic Resilience approach. This more conventional approach to resilient roads is described, for instance, by NDF (2014) and Cervigni et al. (2016).

Whereas in the Resilience Plus approach the environment around the road is managed and the road is made part of the landscape, even using roads as a beneficial instrument for water management, in the conventional Protective Resilience approach design specifications of road infrastructure itself are adjusted to make the road better able to withstand adverse weather effects. As discussed this can be justified in many cases as roads are vital for local economies and the cost of disruption is high ( Protecting the road against the impact of climate change can consist of wider paved shoulders, stronger subgrades, and increasing the gravel-wearing thickness by using an improved crushed aggregate, so that there is less infiltration into the subgrade layers (see Table 13.3.). To deal with more intense rainfalls, culverts are adapted so that they can handle larger volumes of water. The cost of this conventional approach to road resilience is high: from US$31,000 to US$45,000 per km – which limits the stretch of roads that can be climate-proofed under this approach. In the case of unpaved roads the costs may be prohibitive.

The other concern is that in this Protective Resilience approach roads may be protected, but the surrounding landscape may be more exposed. Making larger culverts, for instance, to deal with larger flood peaks will create more damage in the area surrounding the road. Moreover, the co-benefits of beneficial water management are also missed: see the last column of Table 13.2.

Another suggestion that is made in the same context is to upgrade unpaved roads to paved roads. This comes at a cost of US$395,000 per km: with 90 percent of roads in Sub-Saharan Africa (SSA) being unpaved, this at best can be implemented in only a few selected locations.

Table 15.4: Examples of design modifications to road infrastructure under conventional Resilience Basic approach (Cervigni, Losos, Chinowsky, & Nuemann, 2016)

Add wider paved shoulder to improve surface drainageIncrease gravel-wearing course thickness to protect subgrade layers
Increase base strengthUpgrade to paved road
Increase protective layer of subgrade layerIncrease culvert size, making for greater flood resistance
Increasing flood design return period by increasing culvert size


There is certainty that road networks will further develop, and the challenge is to integrate inclusive resilience measures in road development from the beginning. In SSA, for instance, road density will still have to catch up. The classified total road-network density stands at 109 respectively149 kms per 1,000 km2 in SSA; or 2.5 resp. 3.4 per 1,000 persons, or 152 kms per 1,000 vehicles. Compare this to a global average road density of 944 km/per 1,000 km2 and it is obvious that there is a large unfulfilled transport need (Foster and Briceño-Garmendia, 2010). On other continents the emphasis is on upgrading roads and having a larger portion of all-weather roads while still expanding the network.

The increase and upgrading of the road networks present considerable opportunities to build in infrastructure productivity from the very beginning. Additional costs are a small fraction of overall road investment. The main cost is in foresight and coordination with other stakeholders: roadside communities, local governments, and other economic sectors.

This Guideline argues for an approach in which resilience improvement and beneficial road water management are part and parcel of the design, development, maintenance and retro-fitting of roads. It is the essence of resilience planning to build systems that are more productive and better able to withstand shocks and stresses. At present, spending on disaster-risk reduction is typically small and isolated rather than integrated in many programs (Watson et al. 2015). Moreover, the emphasis is on preparedness, not on prevention. Drought risks are largely overlooked. This Guideline explains how this should change. It provides practical details on the systematic introduction of the Roads for Water concept in infrastructure programs, and adjusts the design criteria, budgeting systems, and maintenance arrangements. We argue for close cooperation between road authorities and those responsible for agricultural development, water resources management, disaster-risk reduction, and local governments in general. Roads have much to offer in terms of local development and, perhaps unexpectedly, better water management is one prime manifestation of this.

In Chapter 1 we advocated hence the use of Adaptive and Pro-active Approaches to Roads Resilience.  The Adaptive Approach takes the existing roads as the point of departure – making good use of the road infrastructure to introduce measures to manage and control water and make beneficial use of it. This can be the basis for entire road climate retrofitting projects and for campaigns to promote roads for water measures along the roads – implemented by farmers and land owners. Such campaigns consist of motivation, capacity building and coordination, as the example of the Ethiopia programs. Coordination is essential in order that the integrity of the roads is respected and safeguarded and that the benefits of water use are spread wisely, not only to those immediately adjacent to the roads. The threshold to start with Adaptive Approaches is low. The cost per kilometer in Ethiopia were in the order of USD 1800 per kilometer. Other figures come from Kenya, where road water harvesting measures were promoted in the semi-arid counties of Kitui and Machakos and adopted by farmers. The initial average investments for the road water diversion and the land preparation (levelling, terracing) were low, on average USD 421 per farmer. This amount was recouped in less than a year with average of USD 1048 (Kadeni et al, 2019). These benefits then accrued in the subsequent years as well. The benefits were particularly high in short rainy season (as the rainfall is more gentle and a large portion of the run-off can be controlled) and in the drought year (with 30% less of adapting farmers effected than non adopting farmers suffering from droughts).  Similarly, in Bangladesh in the development of water control structures on culvert (see chapter 4) is a low cost Adaptive Reslience measure: it can range from the use of simple sheet iron gate on a pipe culvert to a fully gated structure: the first one having almost now cost, the latter within USD 700 but with the ability to manage water of several hectares of land.

The Pro-Active approach is associated with new road development programs or major rehabilitations and build roads right from the beginning as instruments for climate resilience, landscape management and water management. The cost of the measures are not necessarily much higher (as the example of the non-vented road drifts show), whereas in other cases it needs to be calculated on a case by case basis. Even then integrating the roads with the environment around it may be much more cost effective than merely defending the road against water and climate change, two threats that need not be but can all be part of the same agenda of inclusive green growth. There is moreover scope to make creative approaches on new roads with the development of road side tree planting (Chapter 12) or local forests along the roads offsetting part of the carbon emissions of the indispensable but increasing traffic.