DETERMINATION OF VARIATIONS IN STREAMBED CONDUCTIVITY

Streambed conductance per area ranges from 3.9 x 10^-2 /hr to 1.25 /hr for Paint Creek, a river with an average daily discharge of 26.3 m³/s and a drainage area of 2,090 km² in South-central Ohio. The several orders of magnitude change in stream bed conductance is correlated with the time elapsed since a significant flood discharge. Conductance values were determined from the response of ground-water levels in a state observation well about 105 m away from a USGS stream gauge. The gauge and adjacent observation well are in an area where Paint Creek valley is 2.14 km wide and floored with more than 23 m of course glacial outwash forming an extensive and heavily utilized aquifer system.

Determination of realistic streambed conductance values for such alluvial aquifer systems, the sole source of water for much of southern Ohio, is critical because, with increasing water demand, channel infiltration to adjacent public water supplies has increased while travel times between rivers and wells has decreased. Because the channel conductivity determines the path and velocity of water traveling from the rivers to wells, values are essential for calibrating models to assess the impact of surface water quality on ground-water.

Streambed conductance per area was determined from calibrated modeling. This method has several advantages over direct measurement with field permeameters or from channel sediment granulometry because the values are characteristic of a large area and can be determined during flood peaks when streambed conductance per area is difficult or impossible to measure directly.