Material transport from different sources in a network of streams through a catchment

Abstract

A probabilistic model for material transport in a stream network is developed based on geomorphology of the subcatchment and water transit time distribution. A tracer may be a point source or a source distributed over the entire catchment. The tracer particles are transported by advection through streams of different order and also diffuse and react chemically with the sediments lying at the bottom of the streams. Stochastic analysis of travel time is complicated by microscopic exchange processes, which act to retain the tracer in the surrounding medium. These include kinetically controlled exchange with the storage zones, diffusion into the bed sediment, and linear equilibrium sorption. In addition, degradation delays the downstream tracer movement. The sensitivity analysis indicates that for 50% mass arrival the mean arrival time is increased by 3 times for a change in mass transfer parameter, χ*, by 10 times. This increase is further pronounced for higher mass arrivals and higher χ*. The results on a specific application example show that a mere doubling of the uncertain value of diffusive mass transfer rate in the bed sediment reduces the probability that 25% of solute mass arrives at the outlet by ≈90%. The high sensitivity of the probability of the solute mass arrival at the outlet to the uncertain diffusive mass transfer rate implies uncertainty also in predictions of the solute transport process. Thus it can be concluded that the correct estimation of mass transfer rate in the bed sediments within a catchment plays an important role in field‐scale estimation of transport parameters.