Having seen how the land was shaped, we can turn to look at the present water cycle as it relates to Wintergreen Brook. All the water in the brook comes from the precipitation that falls on the watershed or drainage basin. The average annual precipitation is 46 inches although it can vary between 65 inches and 23 inches. The watershed of Lake Wintergreen is 1.0 square miles. Therefore, on the average 5,280 feet x 5,280 feet x 3.83 feet of precipitation fall which equals 106,867,190 cubic feet of water per year. There are 7.48 gallons in a cubic foot of water, so the average annual precipitation on the watershed of Lake Wintergreen is 799,366,580 gallons.
In an average first order basin east of the Mississippi River, of the precipitation, 91% is infiltrated (taken in by the soil) and 9% is not infiltrated. Of the 91% infiltrated, 8% is subsurface stormflow which is discharged into the stream or lake from minutes to days later, depending on soil type, time of year, vegetation and slope. Twenty-three percent is base flow (enters the water table) and is released to the stream hours to years later. The remaining 60% is evaporated from the soil or transpired by the plants.
Of the 9% not infiltrated, 1% is overland flow and 1% falls on the bodies of water and both end up in the stream or lake very quickly. The other 7% of this evaporates so that a total of 67% of the rainfall is evaporated leaving 33% available to flow down the stream. Thirty-three percent of 799,366,580 gallons equals 263,790,970 gallons of water that should leave Lake Wintergreen annually. (lt is interesting that a lake evaporates about the same amount of water as an equal area of trees.)
One of the activities the students at the Nature Center will do is to measure the rainfall in a simple rain gauge. After each rain or once a week they can calculate how much rain fell on the watershed and the amount that travels each pathway back to the atmosphere. Diagrams will be drawn showing the various flows of precipitation on a cross section of the watershed.
Between 1863 and 1978 Lake Wintergreen provided water for the City of New Haven. The lake was created when an earthen dam was built by Fair Haven Water Co. to flood the bedrock basin. After they had used the water supply for 13 years, the Fair Haven Water Co. was bought out by the New Haven Water Company, which soon bought additional land in the watershed.
By 1920 the company needed additional water which was obtained by bringing water from Belden Brook, north of Wintergreen Brook, into Lake Wintergreen through a diversion pond and a canal. This added a drainage area of .56 square miles to the water supply or an increase of 56% in area. This water could be diverted by the use of a control valve at the gate house at the diversion pond. The canal is easily seen north of the lake where the channel is very straight with a dirt roadway on one side. Left alone, Belden Brook joins Wintergreen Brook one-quarter mile east of the Nature Center.
In 1978 the lake was taken out of the water supply system because strict new Federal standards would have required construction of a filtration plant. This would have been too expensive for the relatively small size of this water source.
In 1980 the spillway and the level of Lake Wintergreen were lowered ten feet at the request of the Corps of Engineers so that the dam could withstand the probable maximum flood which occurs once in 10,000 years.
Prior to the lowering, the lake could store 100 million gallons of water and with the Belden Brook Diversion it could safely supply 800,000 gallons per day to the city.