Quantifying the Importance of Preferential Flow in a Riparian Buffer

Abstract

HighlightsRiparian buffers and vegetative filter strips are uniquely susceptible to preferential flow.An innovative method is proposed to partition infiltration into matrix and macropore domains.Riparian buffer matrix and plot-scale infiltration experiments were simulated with HYDRUS-1D and VFSMOD.Preferential flow accounted for 32% to 47% of infiltration depending on hydrologic conditions.Preferential flow mechanisms should be incorporated into riparian buffer design tools and models.Abstract. Riparian buffers are uniquely susceptible to preferential flow due to the abundance of root channels, biological activity, and frequent wetting and drying cycles. Previous research has indicated such susceptibility and even measured the connectivity of preferential flow pathways with adjacent streams and rivers. However, limited research has attempted to partition the riparian buffer infiltration between matrix and preferential flow domains. The objectives of this research were to develop an innovative method to quantify soil matrix infiltration at the plot scale, develop a method to partition infiltration into matrix and macropore infiltration at the plot scale, and then use these methods to quantify the significance of macropore infiltration at a riparian buffer site. This research further demonstrated the importance of considering preferential flow processes in design tools and models to evaluate riparian buffer effectiveness. Sprinkler and runon field experiments were conducted at an established riparian buffer site with sandy loam soil. Trenches were installed and instrumented with soil moisture sensors along the width of the riparian buffer (i.e., along the flow path toward the stream) for detecting non-uniform flow patterns due to preferential flow. Riparian buffer parameters, including soil hydraulic parameters, were estimated using HYDRUS-1D for the sprinkler experiments and VFSMOD for the runon experiments. This research partitioned the infiltration into matrix and preferential flow domains by assuming negligible exchange of water between the soil matrix and preferential flow pathways in comparison to the magnitude of soil matrix flow. For these experimental conditions with 0.20 to 0.48 L s-1 of runon and initial soil water contents of 0.29 to 0.32 cm3 cm-3, preferential flow accounted for at least 27% to 32% of the total runon water entering the riparian buffer. This corresponded to approximately 32% to 47% of the total infiltration. While increasing the riparian buffer plot soil hydraulic conductivity in single-porosity models can adequately predict the total infiltration and therefore the surface outflow from the buffer, design tools and models should specifically consider preferential flow processes to improve predictive power regarding the actual infiltration processes and correspondingly the non-equilibrium flow and solute transport mechanisms. Keywords: Flow partitioning, HYDRUS, Matrix flow, Preferential flow, Riparian buffer, VFSMOD.

Preferential flow velocity mapping of alluvial soil using temporal electrical resistivity imaging

“…Calculated uid velocity values in this research have datasets that match the models and data generated from more traditional soil monitoring data sources collected onsite [23]. The change in uid velocity values within the macropore ow domains are within reason and would support hydraulic conductivity value variations similar to other literature.…”

“…Guertault et al (2021) calculated soil hydraulic parameters representative of the matrix domain by tting measurements to Van Genutchen parameters. Results from Guertault et al [23] in the same eld location yield hydraulic conductivity values between 23-36 mm/hr. Similar values were obtained using the TERI approach where the results at the base of the soil at 4.5 and 8.5 m share locations with soil moisture probes for the Guertault et al [23] experiment (Table 1; Fig.…”

Perspective: Preferential Flow in Riparian Buffers: Current Research and Future Needs

“…Quantitative data are especially critical to test mathematical formulations to model PF that could be incorporated into hydrologic models used for buffer design and evaluation. Guertault et al (2021) proposed an approach to partition infiltration in a riparian buffer during runoff events between matrix flow and PF using a water budget combining in situ measurements and numerical simulations. The approach was developed and tested in a riparian buffer with sandy soil located in North Carolina.…”