Storing Freshwater in the Salty Sea: the upsides and downsides of coastal reservoirs to receive and store fresh water

“Storing Freshwater in the Salty Sea” (Asianometry, 22 August 2022)

In this video, the Asianometry host digresses from economics, business and IT issues to one relevant to us all: how and where to capture fresh water needed for drinking, washing and most other human activities and store it in an area large enough to serve major settlements, even cities, without it being affected by salty water or contaminated by pollutants. In the not so distant past, rivers would be dammed with concrete dams that created large artificial lakes as reservoirs but major environmental problems and problems of resettling people, flora and fauna affected by the creation of such lakes resulted. Western nations have more or less stopped building massive concrete dams for these reasons though Turkey still has an enthusiasm for building such dams, often more for geopolitical reasons (such as controlling the Euphrates River flow and thereby controlling the amount of water that reaches nations downstream, such as Syria and Iraq) than for its immediate domestic, agricultural and industrial needs.

In this video, Asianometry investigates the possibility of creating a freshwater lake / coastal reservoir from the sea close to the ultimate consumers. The narrator looks at various examples going back to the Tang Dynasty in China (a primitive reservoir created with stones in Zhejiang province) and more recent and famous examples such as the IJsselmeer, an enclosed inland bay in Zuiderzee in the Netherlands; Plover Cove (constructed 1960 – 1968) in Hong Kong which serves as that territory’s largest freshwater reservoir; the Marina Barrage in Singapore; and Thanneermukkom Bund on Vembanad Lake in Kerala state in southern India. These and other freshwater lakes and bays around the world (especially in China which has many coastal reservoirs) have all had various adverse impacts on their immediate ecosystems and people living and working close by, as do the more traditional concrete dams, so the decision to build either a dam some distance (often considerable) upstream from the users or a coastal freshwater lake close to users will often depend on the costs involved with particular projects and the consequences they are likely to have. The decision also has to be considered against other alternatives to obtaining fresh water such as desalination.

Using various examples of dams and coastal reservoirs (most of them in China and other parts of Asia) to illustrate the advantages and disadvantages of these alternatives to obtaining and storing fresh water in large volumes for cities, the video goes into considerable detail in making the case that each and every proposal for storing fresh water in particular sites is its own special case. What may work for one region in one country may not work in another part of the country. One part of the video addresses the economics involved in proposing and constructing coastal reservoirs as opposed to building traditional concrete dams. Coastal reservoirs can be built from different types of materials (including synthetic materials) but also have the ongoing maintenance costs that traditional concrete dams may not have. Desalination plants have their own particular downsides that may translate into considerable financial costs – but they also have advantages over coastal reservoirs. This leads into a discussion of water quality issues particular to coastal reservoirs such as evaporation, contamination by seawater or brackish water, and pollution from agricultural, industrial and domestic sources. Proximity to population centres may be as much a disadvantage as it is an advantage for coastal reservoirs. As would be expected, the environmental impacts of individual coastal reservoirs are also mentioned in some detail.

The video serves as a useful educational introduction (especially for school and college students) to the idea of coastal reservoirs / freshwater coastal lakes as part of a city’s water use portfolio. As cities grow larger, they need to rely on several sources of fresh water and different methods of obtaining them, and each and every city will need to create its own mix and balance of freshwater sources. Coastal reservoirs can serve both as sources and storages of fresh water and also receive excess fresh water such as might occur during periods of heavy rain and/or flooding. They may have value also as places of recreation and conservation of local ecosystems. The use of attractive visual aids such as maps, graphs, photographs and film help to illustrate and clarify particular issues of fresh water storage and examples of how cities use coastal reservoirs and deal with any problems that arise from their use.