This gets the imagination working.
You could imagine this using the running water in the arch and the ambient air temp, or heat harvested from equipment, as the hot and cold sides of a peltier module to generate enough power to keep the batteries of a sensor node powered up. One of those esp8266 boards with temp/humidity sensors weve been discussing.
Would work equaly well with other low energy power generating sources as well.
http://hackarobot.com/energy-harvesting-circuit/
I found it on hackaday.
http://hackaday.com/2015/08/02/i-am-a-battery-harvesting-heat-energy/