Pennsylvania Geological Survey, 4th Series, Water Resources Report 47 "Geology and ground-water resources of Monroe County, Pennsylvania" by Carswell, L.D., and Lloyd, O.B., Jr.       Monroe County is on the eastern border of Pennsylvania and includes much of the area popularly called the Poconos. It is an area long used for outdoor recreation and includes a part of the Delaware Water Gap National Recreation Area.      Flow-routing studies were made to evaluate the response of the Lehigh and Delaware Rivers to low-flow augmentative releases from two reservoirs --Francis E. Walter Reservoir and Beltzville Lake--in the Lehigh River basin. Digital routing models that use diffusion-analogy methods to convolute flows with system-response functions were developed to simulate daily flows at selected sites. Model errors, for five sites and for periods of 1 year or more, were mostly between 3 and 12 percent in terms of absolute errors in daily flows and were mostly within 4 percent for flow volumes.       The developed models were satisfactory for predicting hydrographic response at eight sites in the reach from White Haven, Pennsylvania to Trenton, New Jersey. However, abrupt changes in the flow rate of the Lehigh River at the Bethlehem and the Glendon gaging stations could not be adequately replicated with the model. The model tends to underestimate peaks by as much as 30 percent and to overestimate some low flows of short duration by as much as 20 percent. This occurs primarily because inflows from ungaged areas could not be reliably modeled throughout their ranges by use of flow records for gaged streams. The model will underestimate long-duration low flows at the Glendon site for periods when underflows at the gaging stations on Little Lehigh and Monocacy Creeks are significant.       The models were used to route hypothetical releases from Francis E. Walter Reservoir during a low-flow period. The model for the Lehigh River indicated that an added release of 50 ft3/s (cubic feet per second) over a 64-day period during the severe drought in the summer of 1965 would have increased minimum flows for this period at Bethlehem and Glendon by approximately the same amount. A hypothetical release of 200 ft3/s for the period July 20-22, 1965, which is about eight times the actual release in this period, would have been attenuated by about 25 percent when it reached the Bethlehem gage. The synthesized hydrograph for the Bethlehem gage showed such a release would have passed their by July 27. Unresolvable timing errors in the models created an unrealistic hydrographic response for this release at the Trenton gage; but, such a release probably would have passed Trenton by July 29.       In order to time the movement of a release wave more accurately than could be done with the developed model, travel times for the wave of an augmentative low-flow release were obtained by field observations and comparisons of gage-height records. The observed leading edge of an abrupt release of 153 ft3/s from Francis E. Walter Reservoir, which ended a 2-day release at a rate of 48 ft3/s, arrived at the gage below the reservoir in 0.5 hour, at White Haven in 3.7 hours, at the mouth of Pohopoco Creek in about 23.1 hours, at Walnutport in 27 hours, at Bethlehem in 39 hours, and at Glendon in 42 hours.       This release could not be detected in the record for the Trenton gage. Travel time for an augmentative release in the Lehigh River is dependent upon the pre- release discharge, the relative magnitude of the release, and antecedent rain- fall. Relationships are provided for estimating the time of arrival at Walnutport, Bethlehem, and Glendon of the leading edge of waves generated by autmentative releases of 75 to 600 ft3/s. Stage observations on Pohopoco Creek indicated a 2.1-hour travel time between Beltzville Lake and the Lehigh River for the elading edge of a wave produced by a typical augmentative release from this reservoir.       Water resources in the county are derived from precipitation. The Lehigh and Delaware Rivers, bordering the northwestern and southeastern parts, respectively, are the drains for surface-water and groundwater discharge and are essentially unused for water supply.       Water Budgets were calculated for average conditions when annual precipitation is 45 inches. Sixty percent of this, or 27 inches, runs off and 65 percent of that runoff, or 17 inches, moves through the groundwater reservoir. Evapotranspiration varies little between wet and dry years and averages 18 inches.       Bedrock consists of Silurian and Devonian sedimentary rocks, which are intensely deformed by folding in the southeastern third of the county and are moderately deformed in the remainder. During the Pleistocene Epoch, glaciers repeatedly advanced across most of the county. The last of these advances deposited a terminal moraine that expends across the southwestern part of the county. The glaciers eroded preexisting deposits, veneered the upland, and filled valleys with unconsolidated deposits that changed surface-water drainage and altered groundwater gradients.       Water occurs in fractures and solution openings in the consolidated rocks and in intergranular openings in the unconsolidated rocks and weathered calcareous sandstones. Water that reaches the water table moves down the hydraulic gradient to points of discharge, moving both laterally and vertically away from groundwater divides and toward streams. The thickness of the freshwater system is 800 feet or more, both little water is yielded to wells by aquifers more than 500 feet below land surface. Groundwater recharge is 600 to 650 gpm/mi2 (gallons per minute per square mile), and about 1.6 billion gallons per square mile is stored in the groundwater reservoir.       Currently the most productive wells are in consolidated-rock aquifers; however, specific-capacity data suggest that wells in the unconsolidated deposits have potentially larger yields. Well yield is affected primarily by the distribution, size, and interconnection of the water-bearing openings and by topographic location, available recharge, well depth, location within the flow system, pumping rate and duration of pumping, and interference from other pumping wells. Potential yields of properly located, drilled, and developed wells have been calculated for the aquifers. The median yields calculated from specific-capacity data are: from the unconsolidated deposits, 200 gpm; from the Bloomsburg Formation, 100 gpm; and from the Poplar Gap Member of the Catskill Formation, 70 gpm. Median yields of the other units range from 15 to 40 gpm. In general, enough water for domestic use can be obtained throughout the county. Large-scale development and consumptive use of the groundwater will diminish baseflow of the streams.       The temperature of water measured in wells ranges from 44 degrees to 57 degrees F and is largely dependent on altitude of the land surface and depth to the producing zone. Hardness of water in the noncarbonate rocks averages 3 to 4 grains per gallon, or about half that of the carbonate rocks. Water from most of the bedrock aquifers is low in dissolved solids, acidic, and soft. In carbonate rocks, the water tends to be hard and slightly alkaline. Excessive amounts of iron and manganese are encountered in water from the unconsolidated deposits and, locally, from the Catskill and Shawangunk Formations. Return to the Water Resources of Pennsylvania Home Page or go directly to: The URL for this page is http://pa.water.usgs.gov /abstracts/wrr_47.html Please note our privacy statement and disclaimer Accessibility Answers to many common questions can be found on our Frequently Asked Questions (FAQ) page. 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