Kalamazoo County comprises an area of 572 square miles in the southwestern part of Michigan. It includes parts of the Kalamazoo, St. Joseph, and Paw Paw River basins, which drain into Lake Michigan. The northern two-thirds of the county is drained by the Kalamazoo River and its tributaries. A small area in the western piart of the county is drained by the Paw Paw River, and the rest, by tributaries of the St. Joseph River. Glacial deposits, containing sand and gravel, form an upper aquifer and a lower aquifer underlying large parts of the county. Areas of high transmissibility and thick saturated deposits are sufficiently localized to be considered as separate ground-water reservoirs having limited areal extent and definite hydrologic boundaries.

Ground-water runoff from the basins constitutes a large part of the streamflow. Hydrograph separation shows that ground-water runoff composed 65 and 73 percent of the discharge of Kalamazoo River at Comstock and 75 and 79 percent of the discharge of Portage River near Vicksburg in 1965 and 1966, respectively. Based on the hydrologic budgets for the same years, ground-water recharge was 9.1 and 9.0 inches in the Kalamazoo River basin and 12.2 and 11.6 inches in the St. Joseph River basin.

Ground-water recharge in the Kalamazoo River basin extrapolated for the 34-year period 1933-66 ranged from 4 to 13 inches and averaged 9 inches. In the St. Joseph River basin average recharge was about 9 inches for the same period.

There is a wide range in runoff in the county. Augusta Creek, Portage Creek near Kalamazoo, and Gourdneck Creek have the highest annual runoff and maintain high yields even during periods of deficient precipitation. Spring Brook also reflects large ground-water contributions to streamflow. Storage in these basins could provide additional water during low flows for municipal and industrial needs.

The primary use of lakes in the county is for recreational and esthetic purposes. Maintaining lake levels is therefore of the utmost importance. Levels at Crooked and Eagle Lakes have been maintained by pumping from lower aquifers. Diversion of water from Gourdneck Creek to West and Austin Lakes has helped in maintaining levels. Several relatively undeveloped lakes could be utilized as reservoirs whose storage could be used to augment streamflow or for water supply.

Water in streams is generally of good chemical quality; however, several streams, including the Kalamazoo River downstream from Kalamazoo, have been degraded by municipal and industrial waste disposal. Water in the lakes is generally of good chemical quality with the exception of Barton Lake, which has been degraded by waste disposal.

There is sufficient surface water available in Kalamazoo County to meet requirements for development of large quantities of water. The total available supply (average discharge of a stream) is about 680 mgd (million gallons per day). The dependable supply (7-day Q₂, or average 7-day low flow having a recurrence interval of 2 years) is about 303 mgd. By developing artificial recharge facilities, surface runoff during winter and spring could be utilized to recharge ground-water reservoirs.

Surface-water withdrawal in 1966 was about 58 mgd, of which 33 mgd was withdrawn from the Kalamazoo River. The quantity of water now being withdrawn from the ground and surface sources is small compared to the total that may be obtained in the area through full utilization of these resources.

Mathematical models were used to simulate hydrologic conditions in the ground-water reservoirs and to evaluate maximum drawdowns for periods of little or no recharge. The practical limits of development as determined for the ground-water reservoirs are estimated to be at the following average withdrawal rates: Kalamazoo, 39 .mgd; Schoolcraft, 17 mgd; Kalamazoo-Portage, 24 mgd; and several small reservoirs, 67 mgd. These total 147 mgd. Further development would require additional artificial recharge facilities.

Average ground-water withdrawal in 1966 was about 54 mgd. The Kalamazoo River ground-water reservoir furnished about 28 mgd, the Kalamazoo-Portage ground-water reservoir, about 21 mgd, and the other reservoirs, about 5 mgd. Thus, further development without artificial recharge is estimated to be about 11 mgd in the Kalamazoo River reservoir, 17 mgd in the Schoolcraft reservoir, 62 mgd in the several small reservoirs, and only 3 mgd in the Kalamazoo-Portage reservoir.

The ground water is generally of good chemical quality and is suitable for most uses; however, it is Usually very hard and may contain objectionable amounts of iron. Some deterioration of water quality- has .been observed in several areas because of seepage from stockpiles of industrial minerals.

The presence of many inland lakes, streams having high ground-water runoff, and, in places, relatively undeveloped ground-water reservoirs provides -flexibility in water management.