VARIABLES AFFECTING MEANDER BEND MIGRATION OF REGULATED STREAM, KANSAS RIVER, USA

The rate of lateral migration of large alluvial rivers is often reduced by the presence of large dams and reservoirs. Studies often cite flow regulation, and in turn the reduction of high-energy flows acting on banks, as the primary cause of this measured reduction. However, other factors are certainly at play, such as the rate and frequency of drops in water level. An abrupt drop in water level can create a situation in which significant volumes of saturated bank material are suspended above the water line. Under such conditions, saturated banks no longer experience the confining pressure of the river, are heavier, and possess a positive pore pressure with reduced static friction. Other variables such as precipitation, irrigation schedule, bank profile, bank material pore pressure, dam release schedule and river stage, freeze-thaw cycles, and seasonality of high flow events have also been known to affect bank erosion rates. The present study will examine a 750-meter length of bank on a single meander bend of the Kansas River for 1.5 years, to include two wet seasons. Although downstream of two large dams, this bank displays significant rates of erosion, as much as 5 m per year in 2015. Many of the above variables are being analysed with multiple regression against the rates of bank erosion. Data is collected in the field using tensiometers and a total station. Other data is acquired from nearby weather stations and stream gage records. The primary factors responsible for changes in bank retreat will be presented as preliminary 1-year results.