Mapping flood extent and understanding mechanisms of surface inundation in areas of impermeable soils using the ANUGA hydrodynamic model: a study from Fredonia, Kansas

Abstract

The present study is one of the first attempts to document the mechanisms and model the flooding within Salt Creek watershed. Available historical data have been analyzed to deduce changes to the physical landscape and the climate within the watershed. An analysis of soil physical properties was done to assess permeability. Real-time measurements of precipitation and water level were collected from the Salt Creek over a course of four months. An ANUGA hydrodynamic model based on variation in precipitation intensity and depth simulated flood extent of three precipitation intensities: 1.12cm/hour, 2.54 cm/hour, and 3.73cm/hour. Historical data shows that Salt Creek watershed has experienced a 7.9% decrease in natural grasslands from 1990 to 2005 and a 15cm increase in average annual precipitation from 1902 to 2016. The precipitation and water level data taken in the field show that there is a 5-7 hour lag time between peak precipitation intensity and peak water level. Particle size analyses (PSA) show that, out of twenty-four soil samples, sixteen (67%) are a silty loam, three (13%) are silty clay loam, two (8%) are very fine sandy loam, with one (4%) each of silt, coarse sand, and coarse sandy loam. Falling-head permeability tests determined an average saturated hydraulic conductivity (Ks) of 0.29µm/s. Associated ponding times for dry soils are ~66% longer than those of wet soils, and ponding times decrease rapidly at precipitation rates in excess of a 2.54cm/hour precipitation intensity. The ANUGA models produced are unable to accurately simulate the flood events, as simulated flood extents are much lower than those from actual flood events. It is hypothesized that the nearby Fall River influences water levels within Salt Creek during large-scale, high-volume precipitation events by pushing excess floodwater into the Salt Creek’s channel. This is likely the result of a constricted floodplain in the Fall River drainage, due to the presence of a limestone formation downstream from the confluence of Salt Creek with the Fall River.