SECRETS OF THE SUBSURFACE: SURFACE WATER RECHARGE FROM THE UPPER LOGAN RIVER TO GROUND WATER IN CACHE VALLEY, UTAH

Subsurface recharge into Cache Valley, Utah, from the Bear River Range to the east, which contains over 6,500 feet of carbonate rocks, has been suspected but never estimated or even documented. Four sets of discharge measurements of streams and springs at 14 locations along two segments of the upper Logan River were made during the summer of 2015. Water samples were also taken for chemical analysis, including stable isotopes of hydrogen, oxygen and carbon, during the first and last measurement periods. These data have been used to draw preliminary conclusions concerning the possibility of surface water from the upper Logan River recharging the ground water system in Cache Valley.

Discharge of the Logan River is highest during the peak period of snowmelt runoff in the late spring, and decreases consistently throughout the summer recession period. The upper segment of the river loses water to the ground water system during the peak discharge period, but gains a gradually increasing amount of water from the ground water system later in the summer. The lower segment of the Logan River loses water late in the summer, and probably loses an even greater amount earlier when the discharge is higher. The water from all of the springs and streams is very similar chemically, and is meteoric in origin and spends very little time in the subsurface. These results support the idea that surface water from the upper Logan River in the Bear River Range recharges the ground water system in the adjacent Cache Valley.