Daylighting Lost Rivers

It has been a very wet year so far; lots of rain. Many parts of the US have had major flooding issues and big storms. When I see the results of these, it reminds me just how important stormwater management is, especially for large, congested cities. When I walk city streets, I often forget about the network of tunnels beneath my feet that keep the roads dry.

But subways and sewers aren't the only things hidden underground. In many cities, rivers and streams actually still exist and flow underneath portions of the city grounds. These waterbodies used to be visible parts of cities, but were buried and/or diverted underground as a result of urban development. In older cities, this was often for public health reasons, as sewage-polluted waters were the cause of sickness and also created terrible odors.

(Image right - Drawing depicting a filther "Father Thames" of the River Thames in Industrial Britain.)

Burying these streams and rivers has had noticeable effects on the environment. City conveyance systems, which replace buried streams and rivers, usually move water to a larger waterbody. This results in more frequent larger flow events to these lakes and rivers. In older cities, water is diverted to combined sewer systems. In these systems, high rainfall events often cause the combined sewage and stormwater to overflow straight into a main waterbody. Higher levels of contamination and nutrients are another adverse effect of urban development because of the number of impermeable surfaces that allow water to pick up various undesirables.

In some instances, the practice of daylighting can reverse the negative effects I just mentioned. Daylighting is the practice of uncovering lost streams and rivers and making them visible again. Often the projects result in more natural restorations, but opening a stream to the light of day between two concrete walls has also been done.

Regardless, the results of successful projects are the same: reduced flooding by increasing hydraulic capacity, water quality improvements through reduced combined sewer overflow, erosion reduction by slowing water velocity, and lower upkeep costs.

Of course, daylighting is not always feasible - the projects can get very expensive and are sometimes not possible based on the location of infrastructure. It cost $19 million dollars and ten years to open up a portion of the Saw Mill River in Yonkers. Pretty pricey, but also pretty nice results.

I first heard about daylighting through a documentary titled Lost Rivers. The practice has been gaining speed in recent years, which is good as I think it would benefit from some more attention and scrutiny. Water is a precious resource that affects so many things, so it is a worthy investment to find better ways to protect it and manage it. All the better if we can manage to do it by unearthing some of these beautiful natural waterways.