Destruction of a Man-Made Lake

It has been well established that destruction of natural habitat can have a variety of negative social, ecological, and cultural effects. What about completely unnatural systems in a place they would never occur naturally? What happens when these are destroyed?  Although not natural ecosystems, they can still be very valuable to the local community.
These issues recently came up in the urban desert near Phoenix, Arizona, when Tempe Town Lake was destroyed by failure of an inflatable dam.

The Salt River originates from snowfall and monsoon rains in the Mongollon Rim and White Mountains of Arizona.  Downstream from Granite Reef Diversion Dam, the river is usually dry due to water withdrawals for human use.  Even before this dam was built, this desert river was probably always unreliable in flow and subject to huge fluctuations in water level.  At the current time it is almost always dry when it passes through the town of Tempe, but when it does flood it can carry a tremendous amount of water.

Many people don't appreciate a dry riverbed, and very few find much value in channelized riverbeds that are dry due to water withdrawals.  As such, in 1999 Tempe Town Lake was created in the channelized riverbed using inflatable dams.


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Tempe Town Lake on Google Maps.

This lake is in no way a natural ecosystem.  It is surrounded by a highly urbanized area and water must be pumped in to counteract evaporation since the river is usually dry.  However, it does provide for recreation, some wildlife habitat, and even fishing in an otherwise dry area.  In a sense the lake does fulfill some ecological functions the river probably did before most of its water was removed, and there are habitat restoration projects occurring in the area.  The lake is quite pretty, in an urban sort of way:


(photo from Wikipedia).

Unfortunately, a lake kept in place by rubber dams is prone to catastrophic failure.  This is exactly what happened last month.  The inflatable dam keeping the lake in place popped!  This unleashed a flash flood into the Salt River, though apparently even the release of a 2 mile long lake into the Salt River did not compare to a good desert flash flood in terms of total amount of water released.  With the lake gone the next morning, people were left with a stinky mud pit (note: it is NOT a bog, as some articles described it, a bog is a very specific and special type of wetland) and a lakeless city.  There has since been a lot of discussion about the loss of this body of water, and what an artificial lake in the desert really means to a community and urban ecosystem.

This lake was not natural per se, but it still served as a way for people to enjoy water and riparian ecosystems that have otherwise been lost in the area.  Per Kris Baxter-Ging ( see comments to this post), the lake will be re-filled behind a new dam in October.  Urban bodies of water are valuable even if not natural, though the source of their water can be a matter of concern in arid areas.  This particular lake is kept full by waters during the flood season, and rarely needs additional water beyond this - in some ways it is like a large rain garden.

Creating urban bodies of water in a form more similar to what would occur in nature allows them to fulfill more functions than a concrete-lined lake (such as higher quality wildlife habitat and increased flood control) and also makes them less likely to break or require extensive maintenance.  In the case of Tempe Town, there were known issues with the dam but it popped before they could be addressed.  In areas like the Sonoran Desert, freshwater lakes are not natural at all, although restoration of desert river habitat is occurring near this lake.  In places like western Pennsylvania and Vermont, lakes or at least beaver ponds are a natural and quite common part of the landscape.

Our lesson for Panther Hollow Lake?  An urban lake is valuable, and Panther Hollow Lake is definitely worth restoring.  When we choose how to restore it, however, I think it will be helpful to look to local nature for inspiration.  Panther Hollow was reported in historic records to contain a small body of water before the lake was built (perhaps a beaver pond).  Restoring Panther Hollow Lake in a way that allows it to act at least partially as a natural pond will allow it to fulfill more functions while offering a site for recreation and also reducing maintenance costs in the long run.  The restoration of Tempe Town Lake provides an opportunity to conduct restoration and maintenance, and the temporary loss of the lake also showed the community just how valuable a resource it is to the community.