The dependable yield of the present Hemlock system has previously been estimated at 31 mgd, assuming, however, that the entire Hemlock Lake drainage area of 48.0 square miles is tributary to the lake and that no leakage losses occur.
There is a stream, Yohon Creek, at the head or south end of the drainage basin of Springwater Creek near Wayland, draining an area of 2.20 square miles, shown on the U.S. Geological Survey map as tributary to Springwater Creek and thence to Hemlock Lake. This stream has been diverted at a point just north of the village of Wayland at some time in the past and its runoff now passes into Canaseraga Creek. The runoff from this area is over 1 mgd.
There is also a not inconsiderable amount of leakage or seepage through the present Hemlock Lake dam, particularly near the west end of the dam.
In 1913 a diversion dam was constructed on Canadice Outlet at the location of the former Beam mill dam, together with a 5-foot (inside) diameter diversion conduit, 3,800 feet long, leading from the intake dam to an inlet weir in Hemlock Lake. The conduit is of reinforced concrete, with 9-inch wall thickness, and throughout a portion of its length the invert is below the normal level of Hemlock Lake. Under certain conditions water can flow back from Hemlock Lake into the conduit. According to the record plans of the conduit, poor foundation material was encountered in places, particularly about 300 feet from Hemlock Lake, where peat and other woody material occurred at the bottom of the trench and hand-mixed concrete was used.
This conduit was not put into use until 1919 and apparently has been entered and some repairs made to leaky joints on one occasion.
In August 1942 the writer noticed that the soil was saturated and water standing on the ground on the conduit route about 300 feet from Hemlock Lake, where the poor foundation material was encountered. Following up the conduit another location was found where the grass was killed and the soil surface washed, ,and the writer was informed that earlier in the season, when the water in Hemlock Lake was higher, water had flowed out above the conduit and flowed over the ground until it was absorbed at a little distance from the conduit. On a later visit, with Hemlock Lake at a lower level saturation of the soil at sta. 35.00, nearest Hemlock Lake, had disappeared. Similar conditions occurred in 1943.
The 36-inch section of conduit I from Hemlock dam to air valve no. 45 was abandoned in 1934 and the conduit blocked off at the dam and also just north of Hemlock village. About 100 feet south of the highway at Hemlock village, a large stream of clear water was found entering Hemlock Outlet from the east and excavation showed that it came from the rock trench in which Conduit 1 is laid. It appears that considerable leakage takes place from the Canadice diversion conduit under two conditions:
1. As a result of back-water and upward pressure from Hemlock Lake, Particularly when Hemlock Lake is at a high level, and only at times when Hemlock Lake is above the lip of the inlet weir of the Canadice diversion conduit, elevation 392.00. The leakage occurs mostly near the Hemlock Lake end of the conduit and is mostly Hemlock Lake water.
2. Much larger leakage occurs for shorter intervals near the head of the diversion conduit at times when diversion from Canadice Outlet is taking place and the conduit is flowing full, and particularly if Hemlock Lake is than at a high level. This water is mostly Canadice Lake water. The abandoned portion of Conduit I crosses underneath the Canadice diversion conduit not far from the point where the heaviest leakage occurs. This abandoned portion of Conduit I apparently contains numerous openings through the pipe walls or joints and acts as an interception gallery, so that a considerable part of the leakage from the Canadice diversion conduit enters Conduit I and is carried downstream to Hemlock village, where the flow is blocked off and the grade of the conduit creates a sufficient pressure to force the water out of leaks in Conduit I and it enters Hemlock Outlet. Because of its variability and the fact that Hemlock Outlet also receives a certain amount of ground-water, a precise determination of the amount of this leakage loss, which has certainly taken place since 1934, has not been made. It is, however, that the total loss of water from Yohon Creek diversion and from leakages as above described has averages at least 2 mgd running back at least to 1935 and part of it much longer. As a check on this estimate a balance-sheet for the present Hemlock Lake system for the 10-year period 1933-1942, has been made up as follows: