FLOW STRUCTURE AND DEVELOPMENT OF CIRCULAR MEANDER POOLS

Flow structure, bank strength, and scour and fill in one of a series of atypical river bends on Mansfield Creek, Cattaraugus County, New York are studied. These bends are characterized by large, deep, circular pools located at the apices of extremely tight bends. The pattern of flow through the bends is typified by the presence of a large countercurrent occupying approximately half of the pool on the outside of the bend. This differs greatly from the typical river bend in which flow is generally downstream and subparallel to the channel banks throughout the bend. Deposition in the bend also does not follow the conventional pattern, but instead occurs primarily on the concave bank in the form of a concave bank bench. Erosion is concentrated on the convex bank and no point bar deposits exist. Shifting of erosion to the convex bank has been noted elsewhere in the literature in extremely tight bends with ratios of mean radius to mean width of less than 2.0, but not in association with circular meander pools. Several possible theories are suggested that may explain development of the circular meander pools at this site. It is likely that the high, cohesive banks of the study reach are an important factor, slowing channel migration and preventing cutoff chutes from forming, allowing development of highly sinuous meanders.