Various instruments in the YEW monitor water levels, flow, and quality. Three V-notch weirs continuously measure the stream discharge at the inlet and outlet of the watershed as well as at the outlet draining the parking garage to the south. Water quality is also monitored at both the inlet and outlet (pictured below).
Two high school interns monitor the V-notch weir at the outlet
In 2014, the Yale Office of Facilities installed groundwater monitoring wells along two transects on the eastern slope of the YEW. Instruments record the groundwater level in the southern set of wells. These measurements will be used to assess water entering and leaving the watershed by all routes.
Monitoring shallow wells from November 1, 2013 to February 1, 2014 showed that groundwater storage increases when there is abundant precipitation (rain and snow), as water fills soil pores. The YEW can hold a large amount of precipitation, releasing this stored groundwater slowly into the stream throughout the winter, spring, and early summer. Groundwater is released gradually to the stream, reducing flooding and increasing low flows between storms.
In 2015, students surveyed downspouts in the YEW watershed. The students found that 50 disconnected downspouts, draining 15,000 sq. feet of roof area, flow onto pervious surfaces such as lawns in the YEW watershed and eventually supply the YEW with surface runoff and groundwater recharge. In a .5 inch storm, 4,485 gallons of water drain from these disconnected downspouts. 76 downspouts currently connected to the New Haven sewer and storm drain system drain 60,000 sq. feet of roof area and could be disconnected to flow into the YEW.
In a .5 inch storm, this means 17,594 more gallons of water draining into the YEW.
The above downspout is connected to the sewer system. This disconnected downspout runs into the YEW.
The map below shows the connected and disconnected downspouts in the YEW. The light blue polygon represents the area of the watershed.
After baseline water data is complete, more downspouts will be disconnected so that they flow into the YEW, instead of into the sewer and storm drain system. These interventions will resupply the YEW’s stream and potentially benefit plant and animal life. In addition, downspout disconnection will reduce the amount of rainwater reaching the sewer system, and therefore reduce flooding and the flow of sewage into receiving waters, such as the Long Island Sound.
As a natural swale, the YEW can reduce the burden on New Haven’s sewer system. The Urban Resources Initiative is leading the construction of “bioswales,” or rain gardens, throughout New Haven. These heavy-duty rain gardens take in water during a storm, like the YEW, and reduce the pollution and flooding that stormwater runoff causes. To learn more about this project, click here. Studying the water cycle in the YEW can inform future green infrastructure projects in New Haven.