GROUND PENETRATING RADAR (GPR) EXPRESSION OF SEDIMENTARY DEPOSITS PRODUCED BY CHANNEL CUTOFFS AND MEANDER STRAIGHTENING AT KILLIAN COVE, CATAWBA RIVER, NORTH CAROLINA

The Catawba River flows through a distinctive, sinuous meander, locally referred to as the “Meck Neck.” Here the river forms a meander couplet, the southern section now being occupied by a reservoir. The northern section of the couplet has a number of arcuate sloughs that have been flooded by elevated waters caused by the reservoir. One of these features - Killian’s Cove - has been examined by topographic analysis, sediment coring, and GPR profiles and grids. Meander straightening is illustrated here by meander scars, abandoned point bars, chute channel fills, and oxbox lakes, some of which are filled with sediment to become channel fills and clay plugs. Abandoned channel fills comprise fining upward sand-to-clay sequences in chutes and silt-to-clay sequences in meander neck cutoff fills. Core samples were acquired along an east-west peninsula at Killian Cove. The maximum depth of coring was 5 meters. The cores provided a stratigraphic section parallel to the current and paleo-channels in the cove. A 150 m 100 MHz GPR profile was driven along the stratigraphic section, and several cross-lines were collected for 3D control. The GPR produced good results to a depth of 15 m, which crossed the sediment/basement contact. Saprolite at the base of the sediments is recognized by a diffuse lower frequency and gradational radar reflection. In the cross-line sections, three paleo-channels were described by southward deepening concave-upward packages of radar sequences. Eight GPR facies were recognized in the sections based on amplitudes, frequencies, and geometries. The GPR facies imply three stratigraphic sequences: (1) An older fining-upward point bar to channel fill sequence (FU1), (2) A younger sequence FU2 in erosional contact with FU1, and (3) A youngest (FU3) sequence that is transitional into modern channel deposits. These three channel packages and the present Catawba River channel indicate that the river has been progressively downcutting as the channel migrated southward.