Virtually the ent ire effective yield of groundwater in the local bedrock is transmitted through fractures, rather than intergranular pores, as is typical of most geologic regions. The effectiveness of these fractures in transmitting water varies with the rock type and depth below the surface. In the limestone, it is common for the larger fractures to have become enlarged by solution. Most of these openings are joints cutting vertically across the bedding, although numerous bedding-plane partings contribute a great dea l to the permeability. Fractures are distinct and favorable to water flow. Solution by groundwater creates a very heterogeneous permeability within these limestones. Compared to other local bedrock units, limestone's hydraulic properties produce quantitatively more but qualitatively poorer well yields. The increase in fracture size by solution reduces the filtering of pollutants so that tests of the effectiveness of septic systems and well-water purity are essential.
Local shales tend to cru mble when fractured so that clean distinct openings are rare. Because of the interbedded nature of the shales and sandstones it is common to have perching of groundwater along the tops of shale beds. Emergence of groundwater as it seeps along such contacts along the hillsides above the lake shores is extremely common and precludes the effective use of traditional septic systems. Down-dip flow is favored, particularly because the dominant joint direction is roughly parallel to the dip, although this te ndency is obscured in the local area by the comparative lack of down-dip exposure and because the valley drops in elevation roughly equal to the dip.
The hydraulic transmissivity of fractures in bedrock increases by the cube of the effective fracture width. Although this functional relationship does not allow quantitative determination of localized groundwater flow problems because of the heterogeneity of the geologic setting, it is useful in explaining the variation in transmissivity with th e same bedrock unit from place to place. Fracture width increases with weathering and erosional unloading of overlying rocks. The effect of each process decreases rapidly downward from the surface, so that the effective fracture width diminishes downward. Consequently, there is a radical decrease in transmissivity downward below the surface in any fractured bedrock formation, particularly in a rather non-deformed region such as the Otsego Lake watershed. Therefore, groundwater yields diminish with the depth of the contributing bed. As a general rule, if water isn't reached at a depth of roughly 90 m there is poor chance of encountering a usable supply by further drilling.
The valley fill material is more predictable in its yield of water because of its primary intergranular porosity. Unfortunately, the exact nature of the subsurface material is difficult to predict in detail without drilling. Gravel and sand lenses are very common and provide generous yields because of their high permeab ility, but finer grained sediments are even more common and have much lower yields of water. Patterns of gravel and sand bodies can generally be identified from well logs. Stratification of gravel and sand versus silt and clay is common, so that a poor well in the valley fill can generally be improved by deeper drilling and encountering lenses of higher permeability material. The permeability of this material is not seriously affected by increasing depths of overburden.
Deposits of glacial ti ll are distributed over the surface of the area in patches of irregular depth. In general, the thickness of till is greatest on the southern slopes of bedrock hills. This material should be avoided if possible as a site for septic systems and water wells because its permeability is negligible.
Reliable figures for well yield are rare in this area. Most values are given in terms of maximum pumping rate without drying up the well- a measurement that varies according to individual well depths, t echniques for increasing well yield, etc., and provides very little information about the hydraulic character of the rock units in general.
In units of the type exposed in the Otsego Lake area, the following average well yields can be given: 1. Onondoga limestone -40 liters/min (great variation from place to place, depending on size and interconnectivity of solutional openings encountered); 2. Hamilton Group shales -40 liters/min average; 3. Valley sediments -75 liters/min average, as high as 375 liters/min not uncommon.
Water quality varies greatly throughout the watershed because mineralization increases with depth, as rates of water flow become smaller. A typical value for total dissolved solids is about 200 mg/l. Most of this dissolved material is Ca2+ and Mg2+, which renders the water of the area rather hard. For most industrial uses it would be necessary to soften the water obtained from wells both in bedrock and in the valley fill. Iron and manganese are of high enough concentration in local areas to cause a staining problem (up to 1.7 mg/l), in contrast with a normal standard of 0.5 mg/l.
Significant non-point source pollution of ground water is practically negligible in the valley fill material, and by virtue of low population, on the bedrock uplands. However, it is of serious concern where strip development has proceeded along the lake shores. Pollution of the groundwater in the areas where limestone is exposed north of the lake is a concer n. Potential effluents should be avoided and disposing of garbage and animal carcasses in hollows and sinkholes should be discouraged.
CLIMATE (Pack and Hollis, 1973; from Harman et al.,1980; Hollis, 1994)
The Otsego Lake watershed is in a region possessing a humid-continental climate. The prevailing winds are westerly, generally shifting toward the north in winter and toward the south in summer. Otsego Lake is on the eastern border of a region affected by outbreaks of cold, dr y polar air originating in Canada that occur frequently in late fall, winter, and early spring. When these winds are strong and follow trajectories across Lake Ontario, heavy snow squalls often result. In contrast, winds originating over the Gulf of Mexico or adjacent waters are common from May through October and provide the region with warm, humid weather. At times, air flow directly from the Atlantic invades the region, resulting in cool, damp, and cloudy periods.
In the winter months, the area lies in the path of storm systems that move toward the northeastern United States from the west or up along the Atlantic coast from the south. These storms and their associated fronts bring sharp changes in atmospheric conditions within short periods. In summer, storms tend to track north of the State into southern Canada. This produces less variable weather. There are times when rather warm weather in the summer or severe cold in winter may last for as much as a week or longer.
Summers are moderately warm, whereas the winters are long and cold. Temperatures usually rise slowly in the spring, but autumn is pleasant, with warm, sunny days prevalent well into mid- or late October. Precipitation is evenly distributed during the year. Maximum amounts are derived from winter coastal storms and summer thunderstorms. The watershed is located in the "General Appalachian Cloudiness Belt". It receives about 50% of possible sunshine annually, with a minimum of about 40% in winter. The following dat a have been collected from records available in Cooperstown, and are complete from 1854 to the present (Pack and Hollis, 1973; Hollis, 1994).
In the summer, the daily maximum temperature usually ranges from 20E-30EC. A temperature of 32.2EC (90EF) or higher occurs on an average of 5 days per year. Such a temperature has been recorded on as many as 14 days in especially warm seasons, but in two summers out of 10 the temperature fails to reach the 32.2EC (90EF) mark. The highest temperature eve r recorded in Cooperstown is 37.2EC (99EF). It was noted on two successive days, July 9 and 10, 1936. Between early December and early March, a temperature of -18EC (0EF) or colder is observed on an average of 18 days. The number of such days varies from 10 or less in mild winters up to 25 or more in abnormally cold seasons. Low winter temperatures may be expected to range between -9.4EC (15EF) and -3.8EC (25EF) in most years. The lowest temperature on record in the village is -36.7EC (-34EF) on Febru ary 9, 1934.
Annual precipitation averages between 99 and 102 cm. Extremes of precipitation in recent decades have ranged from 72.4 cm in 1964 up to 124.5 cm in 1945 and 1972. The maximum annual total measured at Cooperstown is 147.6 cm, recorded in 1890. Precipitation of 2.5 cm or more in a 24-hour period is likely to occur from six to eight times per year. Rain (5 cm or more) is recorded occasionally; daily amounts in excess of 7.6 cm are rare. Rainfall of 10.2 cm or more in a 24-hour peri od has been recorded on three occasions since 1854, the greatest amount being 12.3 cm on October 5 and 6, 1932.
The area receives an average snowfall of 198 cm per year. This compares with an average of about 254 cm in the extreme northern parts of the watershed and an average of only 152 cm along the southwestern border of Otsego County. Seasonal amounts in Cooperstown, at the south end of the lake, have varied from as little as 81 cm up to a maximum of 354 cm. More than 254 cm (100 in.) has been recorded in 10 winters since 1890, but usually the total has ranged from 152 to 241 cm. The heaviest single snowstorm recorded is 69.9 cm on December 26 and 27, 1969. Measurable snowfall usually begins by mid-November and continues into April, although in exceptional seasons 2.5 cm or more has fallen in the latter half of October and as late as May 10. About four storms yielding 12.7 cm (5 in.) or more of snow may be expected per winter. A snow cover of at least 2.5 cm normally prevails from ear ly December until early April, but in some winters the ground may be bare for short periods.
While wind observations have not been taken on a regular basis, interpolation of records from nearby stations suggest that the prevailing wind is northwest in the winter and early spring with an average velocity of 450 to 670 cm/sec. The prevailing wind shifts to southwest or south in the summer and early fall and averages 360 to 535 cm/sec.
There are about 200 overcast days per year, more tha n half of which normally occur from November through March. About 60 to 70 days of clear skies may be expected per year. The average solar radiation is between 125 and 150 langleys/day in the winter, and between 500 and 550 in the summer (Berman, 1975), which is equivalent to approximately 1000 BTU/ft2/day annually. Thunderstorms occur frequently from May through September. The more intense storms may be accompanied by damaging lightning and wind. Intense rains sometimes occur with thunder storms, but damaging storms of large hail are rare. While heavy snowfall is to be expected, blizzard conditions are not common. The watershed is well removed from the normal path of hurricanes and tropical storms. However, such storms have caused damage in the Lake Otsego area. Major floods are practically unknown.
In late winter or early spring, the occasional combination of heavy rain and melting of a deep snow cover may produce inundation of low-lying areas. Intense rains from summer t hunderstorms may also cause local flash flooding of small creeks and streams around the lake.