Hugo Maturana | Geology Reports

USGS2021

A simple low-cost approach for transport parameter determination in mountain rivers

A simplified low-cost approach to experimentally determine transport parameters in mountain rivers is described, with an emphasis on the longitudinal dispersion coefficient ( D L ). The approach is based on a slug injection of table salt (NaCl) as a tracer and specific conductance readings at different locations downstream of the injection spot. Observed specific conductance readings are fit using the advection-dispersion equation with OTIS-P, yielding estimates of cross-sectional area and longitudinal dispersion coefficient for various stream reaches. Estimates of the D L are used to assess the accuracy of several empirical equations reported in the literature. This allowed the determination of complementary transport parameters related to transient storage zones. The empirical equations yielded rather high D L values, with some reaching up an order of magnitude higher to those obtained from tracer additions and OTIS-P. Overall, the proposed approach seems reliable and pertinent for river reaches of ca. 150 m in length.

Coquimbo Region, upper Elqui River↗

USGS2021

Assessment of a conservative mixing model for the evaluation of constituent behavior below river confluences, Elqui River Basin, Chile

Fate and transport modeling of water-borne contaminants is a data demanding and costly endeavor, requiring considerable expes such, it becomes important to know when a complex modeling approach is required, and when a simpler approach is adequate. This is the main objective herein, where a conservative mixing model is used to characterize the transport of As, Cu, Fe, and SO 4 . The study area is divided into three sectors, corresponding to the upstream, middle, and downstream portions of the Elqui River Basin, Chile. In Sector 1, acidic conditions result in the conservative transport of constituents that are sourced from acid rock drainage. In Sector 2, pH increases and transport is influenced by pH-dependent reactions and the subsequent settling of the particulate phase. In Sector 3, there are no additional constituent inputs, and the constituents are conservatively transported downstream. Conservative transport within Sector 3 is confirmed through the development of a regression model that provides monthly estimates of SO 4 load. Whereas SO 4 and Cu concentrations are adequately approximated by the conservative mixing model, estimates of As and Fe concentrations exhibit larger errors, due to the more reactive behavior of these constituents. The fact that the simple, conservative mixing model describes SO 4 transport is a valuable result, as this constituent is known to be one of the primary indicators of mining-related contamination in rivers. The approach could also be a useful starting point for further evaluations of the effects of climate change and hydrological variability on the water quality of rivers.

Elqui River Basin↗