We present a hybrid approach to groundwater transport modeling, “CTRW‐on‐a‐streamline,” that allows continuous‐time random walk (CTRW) particle tracking on large‐scale, explicitly delineated heterogeneous groundwater velocity fields. The combination of a non‐Fickian transport model (in this case, the CTRW) with general heterogeneous velocity fields represents an advance of the current state of the art, in which non‐Fickian transport models or heterogeneous velocity fields are employed but generally not both. We present a general method for doing this particle tracking that fully separates the model parameters characterizing macroscopic flow, subscale advective heterogeneity, and mobile‐immobile mass transfer, such that each can be directly specified a priori from available data. The method is formalized and connections to classic CTRW and subordination approaches are made. Numerical corroboration is presented.

Previous modeling studies of hyporheic exchange induced by moving bedforms have used a moving reference frame, typically corresponding to an individual moving bedform. However, this approach is not suitable for simulating the exchange and accumulation of immobile fine particles beneath moving bedforms, which commonly occurs in sand‐bed streams, as both moving and stationary features must be considered. Here we present a novel simulation framework that may represent arbitrarily shaped, generally aperiodic mobile bedforms within a stationary reference frame. We combine this approach with particle tracking to successfully reproduce observations of clay deposition in sand beds, and the resulting development of a low‐conductivity layer near the scour zone. We find that increased bedform celerity and filtration both lead to a shallower depth of clay deposition and a more compact deposition layer. While increased filtration causes more clay to deposit, increased celerity reduces deposition by flattening hyporheic exchange flowpaths.