Fen Hydrology Study

The Sandhills Task Force and The Nature Conservancy funded a hydrogeological study of the Jumbo Valley and Pullman Valley fens, located in western Cherry County.  The study was part of a Nebraska Environmental Trust grant to restore two drained fens: Jumbo Valley and Pullman Valley. 

Research was conducted by F. Edwin Harvey, James B. Swinehart, and Tina M. Kurtz from Conservation and Survey Division, University of Nebraska-Lincoln.  In April, 2001 their findings were published, entitled "Hydrogeology and hydrochemistry of the Jumbo and Pullman Valley Fens - Cherry County, Nebraska."  Below are key points of the study.

Purpose: To characterize the physical and chemical hydro geology of the Jumbo Valley and Pullman Valley fens. 

Methodology

• The study was initiated in April, 1996 and continued until December, 2000.
• The study installed 104 piezometers within the Jumbo and Pullman Valleys to measure groundwater levels, estimate peat hydraulic conductivity , delineate the flow system and to determine the groundwaters parameter (T, pH), major ion (Ca, Mg, Na, K, HC03, CI, S04 and NO3) and isotope (0180, 02H, and 3H) chemistry.
• The study installed 5 monitoring wells to examine the hydrogeology and hydrochemistry of deeper groundwater system beneath the Jumbo Valley.

• Groundwater levels within the valleys fluctuate seasonally as a result of changes in precipitation and evapotranspiration.
• On average, groundwater levels remained relatively constant from summer to summer during the three year study period.
• Hydraulic conductivity (K) values within the Jumbo Valley peat deposits range between 1.3 X 10-8 to 9 X 10-6 m/s.
• Groundwater flow within the Jumbo Valley is from west to east across valley. Groundwater also flows laterally to the Jumbo Valley from beneath the flanking dunes to the north and south of the valley.
• Groundwater flow within the Pullman Valley is from southwest to northeast across valley, along the valley's axis.
• Groundwater also flows laterally to the Pullman Valley from beneath the flanking dunes to the south and possibly those to the north of the valley.
• Hydraulic gradients are vertically upward into the Jumbo and Pullman Valleys indicating that they are groundwater discharge zones. Locally, small reversals may occur following precipitation events.
• Groundwater flux into the Jumbo Valley was estimated to be approximately 1.6 X 107 m3/yr.
• Groundwaters in both the Jumbo and Pullman Valley fens have very low TDS values ( <250 mg/L ) and are calcium-bicarbonate waters.
• Groundwaters are of meteoric origin (recharged from precipitation) and have not been impacted by evaporation.
• Groundwaters in both the Jumbo and Pullman Valleys were recharged prior to the 1960's except for groundwater discharging along seeps at the southern edge of the Jumbo Valley fen that were recharged in the 1970s or 1980s.
• There does not appear to be a correlation between groundwater chemistry and plant distribution at the spatial and temporal sample intervals used in this study.