GRAIN-SIZE ANALYSIS OF CHANNEL GRAVELS IN HACK AND GOODLETT'S LITTLE RIVER BASIN: A BENCHMARK FOR COMPARISON IN CENTRAL APPALACHIAN WATERSHEDS UNDERLAIN BY THE ACADIAN CLASTIC WEDGE

The Little River basin, VA (41 km²) served as the setting for the seminal work by Hack and Goodlett (1960), in which they developed founding principles of watershed ecology and landscape evolution. As a corollary to their work, this study focuses on grain-size analysis of channel gravels in the Little River as a benchmark for comparison to those 50 km west in the North Fork basin, WV (49 km²). Both study areas are underlain by sandstones of the Acadian clastic wedge (Foreknobs-Hamsphire-Price Fms), which are reflected in the resulting gravel compositions. The lithologic similarity of the two localities serves as a framework for testing models of local bedrock control on gravel production and sediment transport.

Wolman counts of gravel-size were collected at equidistant sampling stations throughout the two channel networks (n ~55 per station, 2-m grid, >5 mm minimum, a-b-c axes tallied). The results of intermediate-axis (D_I) analyses are summarized as follows for the Little River and North Fork, respectively: total no. stations = 36, 33; total no. clasts = 1969, 1790; D₁₆ = 58 mm, 56 mm; D₂₅ = 78 mm, 75 mm; D₅₀ = 139 mm, 130 mm; D₇₅ = 239 mm, 222 mm; D₈₄ = 318 mm, 294 mm; average = 205 mm, 192 mm; mode = 82 mm, 100 mm, Trask sorting = 1.8, 1.7; and avg. five max. clasts per station = 683 mm, 661 mm. Shape analysis reveals that the Zingg disc (~56%) and bladed (~33%) forms are the most frequent occurrences. A positive correlation between the collective average intermediate-axis diameters and five largest clasts per station is described by the equation: D_5max = 4.5(D_avg)-238 (R = 0.91). The spatial distribution of D₅₀ gravel size was also evaluated with respect to sampling position in the drainage networks relative to slope (S, m/m) and drainage area (A_d, km²). Positive correlations between the three parameters are described by equation: S = 0.01(D₅₀/A_d)^0.4 (R = 0.95).

Comparative analysis indicates that the Little River and North Fork are notably similar with respect to gravel-size distributions at the watershed scale, however variations occur within the channel network at the station level, as a function of slope and drainage area. Localized sediment input, transport/storage functions and mix of bedrock lithofacies are interpreted as important factors controlling caliber of channel gravels in central Appalachian landscapes.