Modeling Channel Instabilities and Mitigation Strategies in Eastern Nebraska

Little Salt and West Papillion Creeks in eastern Nebraska have incised and widened, and are threatening saline wetlands (Little Salt Creek) and urban infrastructure (West Papillion Creek) adjacent to the channels. Field studies were carried out to determine erodibility of the cohesive streambed-material, shear strength of the cohesive streambank-material, and channel geometry. Channel evolution simulations with the CONCEPTS model indicate that the modeled reach of Little Salt Creek will degrade over its entire length, varying from 1.5 m at its upstream end to 4.0 m at its downstream end, and that the modeled reach of the North Branch West Papillion and West Papillion Creeks will degrade approximately 2.8 m at its upper end. Near the saline wetlands along Little Salt Creek the average widening at the bank top is 0.6 m. Along the North Branch West Papillion Creek the average widening of the bank top near Fort Street is 1.3 m. Controlling the streambed at bridge crossings along Little Salt Creek prevents channel incision near the saline wetlands. Generally, incision is reduced by about 60 percent. Grade control structures along the upper part of North Branch West Papillion Creek only reduce erosion in their upstream vicinity. Grade control structures would reduce average channel incision by approximately 40 percent. However, maximum channel incision is only reduced by 25 percent.