Matthew McCartney/IWMI

Integrating grey and green water infrastructure for inclusive sustainable development

Compelling discussion, commentary, stories on agriculture within thriving ecosystems.

In 1957, Karl Wittfogel hypothesized that the emergence of human civilization is linked partially, but importantly, to the management of water to grow food. In this hypothesis, the development of irrigation infrastructure, and the institutions needed to manage that infrastructure, were critical to the development of complex, organized societies in the Middle East and elsewhere.

Today, building large dams, and other water control infrastructure (known as "grey infrastructure"), continues to be a cornerstone of economic growth and development. Investment in grey infrastructure, much of it in low-income countries, is widely acknowledged as essential for achieving the Sustainable Development Goals and adapting to climate change. However, there is also growing recognition that to be sustainable, the development of water infrastructure needs to change.

Interactions between grey infrastructure and the environment

Grey infrastructure is intimately linked to the environment and the landscape in which it is located. And the performance of grey infrastructure is dependent on ecosystem services. For example, the yield of a reservoir (i.e. the total amount of water that can be supplied) is a function not only of the volume of water stored but also the amount and timing of flow from the upstream watershed. The longer that flow extends into a dry season, the greater the yield for a dam of a given size. In other words, the smaller a dam needs to be to guarantee a specified yield.

In a given climate, the amount and duration of flow from a watershed is dependent on a number of catchment characteristics, including topography, soils and geology, but also, importantly, vegetation and the way the land is managed. For example, the runoff from a watershed covered in forest will be very different to that from one where agriculture dominates or one that is urbanized.

Similarly, soil erosion and the speed with which downstream reservoirs fill with sediment is a function of the same characteristics: topography, soils, vegetation and land management. The faster a reservoir fills with sediment, the shorter its operational life. It is estimated that globally some 5% of total reservoir volume has been lost over the years to sedimentation.

In watersheds, human agency affects both land cover and land management so is an important factor influencing the life expectancy of reservoirs and the performance of dams and other grey infrastructure. For this reason, watershed management – the targeted implementation of measures for soil, water and ecosystem conservation – is increasingly recognized as an integral component of sustainable dam management.

Additionally, whilst dams and other grey infrastructure bring many tangible benefits, many ecosystem services are adversely affected when ecosystems are degraded by its construction. For example, dams and irrigation systems alter the timing and volumes of downstream river flows. This typically results in reduced fisheries and, because floods are attenuated, reduced opportunities for "recession agriculture" on flooded land and livestock grazing. Many of the world's deltas, including the Mekong Delta (home to 18 million people), are sinking because silts and sediment from the upper watershed that would naturally replenish them are being trapped behind upstream dams.

The loss of these services is frequently overlooked or inadequately compensated for. As a result, poor people (who are the most reliant on ecosystem services) typically pay the price of development. Globally, it is estimated that since the 1950s, 40–80 million people have been displaced by large dam construction, and many hundreds of millions more have been adversely affected by changes to downstream flows.

An irrigation channel in Myanmar.
Matthew McCartney/IWMI

Blending grey and green infrastructure

Protecting watersheds and aquatic ecosystems (so called "green infrastructure") is increasingly recognized as a cost-effective means to improve water security. The UN, the World Bank and others are therefore promoting green infrastructure to complement grey infrastructure. In addition, the water sector recognizes that grey infrastructure must be built and managed in such a way that it minimizes adverse impacts on critical green infrastructure.

By combining, or "blending", green and grey infrastructure to provide water-related services – including bulk water supply, safe drinking water, waste processing and dilution, erosion control and flood risk reduction – it is possible to get the best of both worlds: infrastructure systems that facilitate sustainable development and conserve ecosystem services, vital for livelihoods and human wellbeing.

There are many encouraging examples. In the Tana River in Kenya, upstream soil and water conservation measures are being implemented in part to conserve downstream hydropower dams. What's more, studies have shown that dams can be operated to preserve the benefits (fisheries, grazing and recession agriculture) of downstream green infrastructure with only small impacts on the primary purpose of the dam, be that hydropower or irrigation.

However, what we really need is not retrospective studies but action to build such considerations into the planning phase of projects. For example, the Itezhi-tezhi dam, built on the Kafue River in Zambia to regulate flow for hydropower production, was the first major dam in Africa constructed with additional storage specifically for the purpose of releasing downstream flow to protect ecosystem and livelihoods. This was a highly progressive intervention when the dam was built in the 1970s.

The need for a more strategic approach

Such blended approaches have yet to properly take root. This is partly down to an absence of comparative economic evaluations, and partly because of questions regarding the approaches' reliability and effectiveness under extremes, and a shortage of technical capacity for implementation. As the global economy continues to expand and climate change begins to bite, continued degradation of green infrastructure undermines the performance of grey infrastructure. This, in turn, undermines future water security and the creation of human benefits.

Simply building more grey infrastructure can no longer be a development imperative. Grey infrastructure is necessary for future development, but is neither economically nor environmentally feasible as the sole approach to sustainable water development. In the water sector, we need to wean ourselves off concrete. We need a strategic transition to better integrate grey–green water management systems that are higher performing, more cost effective and more resilient.


Thrive blog is a space for independent thought and aims to stimulate discussion among sustainable agriculture researchers and the public. Blogs are facilitated by the CGIAR Research Program on Water, Land and Ecosystems (WLE) but reflect the opinions and information of the authors only and not necessarily those of WLE and its donors or partners.

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