Investigation of the thermal regime and subsurface properties of a tidally affected, variably saturated streambed

Abstract

Temperature and moisture content in the variably saturated subsurface are two of the most important physical parameters that govern a wide variety of geochemical and ecological processes. An understanding of thermal and hydraulic processes and properties of transient vadose zones is therefore fundamental in the evaluation of such processes. Here, an investigation of the thermal regime and subsurface properties of a tidally affected, variably saturated streambed is presented. Field and laboratory measurements, as well as a forward numerical model, are jointly employed in the investigation. Temperature, soil moisture, surface level, and water level data were recorded in a transect perpendicular to a tidally driven stream. Frequency‐domain analysis of the subsurface temperature measurements revealed the rapid decay of the tidal temperature driver within the top ∼30 cm of sediment. Several techniques were used to evaluate subsurface thermal and hydraulic properties, including thermal conductivity and the soil water retention curve. These properties were used to constrain a forward numerical model that included coupled treatment of relevant variable saturation thermal and hydraulic physics. Even though the investigated vadose zone is intermittent and relatively shallow ( ≲ 20 cm), the results illustrate how error can be introduced into heat‐transport calculations if unsaturated conditions are not taken into account.

Evaluating a Coupled Phenology‐Surface Energy Balance Model to Understand Stream‐Subsurface Temperature Dynamics in a Mixed‐Use Farmland Catchment

“…Recently, studies of controlling processes have extended from the air/surface water interface to the interface of surface water/groundwater and surface water/streambed (Caissie et al, ; Caissie & Luce, ; Halloran et al, ). In stream reaches where groundwater contribution is significant, heat fluxes from the subsurface can represent a substantial fraction of the stream energy budget (Hannah et al, ).…”

“…Caissie et al () used the vertical one‐dimensional model to estimate the Darcy and streambed heat fluxes. Other researchers have used fully three‐dimensional (3‐D) models (Brookfield et al, ) or cross‐sectional two‐dimensional models (Halloran et al, ) to simulate the integrated surface/subsurface thermal transport. However, due to the computational expense involved in solving fully 3‐D equations, these models were only applied to relatively small portions of a river or a single reach.…”