Bed Forms and Sediment Characteristics along the Thalweg on the Tanana River near Nenana, Alaska, USA

Abstract

Sediment sampling and longitudinal river-bottom surveys were conducted along the thalweg on the Tanana River near the city of Nenana, Alaska, USA, to provide basic information for the engineering design requirements of hydrokinetic devices to be deployed in the area. The study reach was located at approximately 64°33'50N and 149°04'W. The Tanana is a large glacier-fed river, with open-water flow conditions from May to October. The river presents a single channel in the study area. Granulometric analyses of sediment moving near the riverbed reveals the coexistence of three distinctive types of sediment along the study reach: 1) nearly uniform fine sand; 2) bimodal distributions containing fine sand and medium gravel; and 3) medium gravel. Preliminary relationships between sediment loads and discharge were developed. Dunes with small superimposed dunes were found along the reach. The basic geometric parameters (i.e., wavelength and height) of dunes were measured, and steepness was calculated. In general, dune wavelength increased with increasing discharge. Dune wavelengths ranged from 41 to 67 m, while small-dune wavelengths ranged from 13 to 16 m. Steepness increased slightly with increasing discharge.