Ponds and Sponge Cities

You may have admired the pond at the Royal Botanic Garden, Edinburgh. It is an attractive feature, visited by many people including families with small children who especially enjoy the ducks. A recent paper demonstrates that it is much more than an amenity-pond (Krivtsov et al 2020). This pond and the immediately adjacent area have over 100 vascular plant species, 24 phytoplankton taxa and 21 bryophytes. But just as important, the pond also protects the Water of Leith from pollution and flooding, according to the article published recently in the Transactions of the Royal Society.

The research team, headed by Vladimir Krivtsov, use a hydrological model the simulate the effect of the pond, and also the effect of adding a ‘rain-garden’. I hadn’t heard of rain-gardens (see https://en.wikipedia.org/wiki/Rain_garden) but rain-gardens are designed to hold back storm-water for a short period, thus flattening the peak of the run-off. They may also be designed to enhance biodiversity. Nor had I heard of the concept of the ‘sponge city’, the idea that urban areas can be designed to store rain water for a few hours. A sponge city would be biodiverse, with wetland areas; quite the opposite of a concrete city, where the smooth surfaces have no water-retaining properties.

Scotland’s climate is expected to become wetter in winter and drier in summer. There are several ways to design schemes that retain storm-water, but many urban wetlands have been quietly doing this for many years, like the RBGE pond. I recently came across a new water feature on the Braid Burn, at Oxgangs in Edinburgh, designed to hold back the flow into the Braid Burn. It is a haven for wildlife, and much enjoyed by local people.

You can read the complete article (free) by clicking here:


Vladimir has just emailed me to emphasise “the important link between the habitat provided by the pond (including macrophytes), the invertebrates and fish, and the kingfisher which is attracted by those. Kingfishers are of course much loved by the public and birdwatchers (hence increase in amenity value). The bird community is quite rich (see the paper) and  benefits from interzonal effects, as there are woodland and grassland as well as aquatic plants all present in close proximity. In my view, a very fascinating cycle of relationships”.

This morning I visited the Oxgangs pond. Here’s a picture of it. The water level is currently low, and the macrophytes dominate the scene. I would be interested to know how the authorities manage the site (I was dismayed to see a ‘keep out’ sign at the east end of the site).

John Grace 15th May 2020


Krivtsov V et al. 2020 Flood resilience, amenity and biodiversity benefits of an historic urban pond. Phil. Trans. R. Soc. A 378: 20190389.

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