Sensitivity of Nutrient Estimations to Sediment Wash-off Using a Hydrological Model of Cherry Creek Watershed, Kansas, USA

This paper presents a hydrological and water quality model for Cherry Creek watershed, located in southeastern Kansas, USA. The Cherry Creek catchment drains approximately 88220 ha and it is a main contributor of water to the Neosho River. Hydrological modeling of the Cherry Creek watershed is performed using the Hydrological Simulation Program Fortran (HSPF). Simulated results for total ammonia (TAM) concentrations occurring at the Cherry Creek watershed outlet for four land use scenarios and a 2-year simulation period, are presented. Sensitivity analysis of total ammonia estimations (TAM=NH

3

+NH

4

) to the unbounded HSPF parameter POTFW is subsequently presented. POTFW represents the ratio of a water quality constituent yield to sediment wash-off outflow. Results showed that small perturbations to a 50 mg/Kg POTFW base value produce the largest normalized sensitivities. Peak sensitivities reached up to 248%, with the -1% perturbation producing the most dramatic sensitivity response in TAM estimations. Results showed a strong relationship between normalized sensitivities to river flow regime. Non-linearities in sensitivity for small ±1% perturbations were detected. These non-linearities are more evident for high stream flow values (strong flood events). For larger perturbations (±60%, ±40%, ±20%, and ±5%) the sensitivity response was shown to be linear.