Water resources of the Ipswich River basin, Massachusetts

Abstract

Water resources of the Ipswich River basin are at resent {1960) used principally for municipal supply to about 379,000 person's in 16 towns and cities in or near the river basin. By the year 2000 municipal use of water in this region will probably be more than twice the current use, and subsidiary uses of water, especially for recreation, also will have increased greatly. To meet the projected needs, annual pumpage of water from the Ipswich River could be increased from current maximums of about 12 mgd (million galleons a day) to about 45 mgd without reducing average base flows in the river, provided that the increased withdrawals would be restricted to periods of high streamflow. In addition, considerably more pumpage could be derived from streamflow by utilizing base-flow discharge; however, the magnitude of such use could be determined only in relation to factors such as concurrent ground-water use, the disposal of waste water, and the amount of streamflow required to dilute the pollution load to acceptable levels. Under present conditions, little or no increase in diversion of streamflow would be warranted in the upstream rafts of the basin during the summer and early fall of each year, and only a moderate increase could be made in the lower reaches of the stream during the same period. Annual rainfall in the basin averages about 42.5 inches, and represents the water initially available for use. Of this amount, an average of about 20.5 inches is returned to the a.tmosphere by evapotranspiration. The remainder, about 22 inches, runs off as streamflow in the Ipswich River or is diverted from the basin by pumpage. The average annual stream runoff, amounting to about 47 billion gallons, is a measure of the water actually available for man's use. The amounts of water used by municipalities in recent years are less than 10 percent of the available supply. Large supplies of ground water may be obtained under water-table conditions from the stratified glacial drift that forms .the principal ground-water reservoir of the basin. Stratified drift deposits fill valleys in about 31 percent of the basin. Thicknesses of the deposits are generally less than 50 feet, but at places may be as great as 200 feet. Between 1931 and 1960 recoverable annual recharge to stratified drift aquifers averaged about 10 inches, equal to 42 mgd. The least possible recharge during any of these years was probably more than 41inches, or 25 mgd. Therefore, ground-water withdrawals from the basin could be sustained at a rate at least five times greater than the 1960 rate of 4.9 mgd. In the lower Ipswich basin. withdrawal of ground water could be sustained at a rate eight or nine times greater than the 1960 rate of 1.86 mgd. There are 1 or more favorable sites for further exploration for ground water in each of the 10 communities that occupy the major part of the river ,basin. Small but reliable supplies of ground water for domestic use may be withdrawn from bedrock almost anywhere it. the basin. Ground-water levels show no long-term trend since 1939, and although large fluctuations in water levels occur during each year, the ground-water reservoir at most places in the Ipswich River basin is replenished annually to its full capacity. During parts of most years potential recharge is unable to enter the already-saturated ground-water reservoirs, and most of this 'rejected recharge' enters streams as surface runoff. The chemical quality of both ground and surface water is generally satisfactory for most uses, although excessive concentrations of iron and manganese occur locally, and at places the hardness of the water is objectionable. The surface- and ground-water resources of the basin are closely related. Because most areas favorable for further development of ground water are adjacent to stream channels, large increases in the withdrawal of ground water during low-flow periods will result in reductions of streamflow. The magnitude of t