Rainwater Infiltration Model of the Chocaya Basin using Hydrus-1D

Sammanfattning: The objective of this study was to assess the rainwater infiltration process in the unsaturated zone in an alluvial plain. Particularly, this study is focused on the Chocaya basin in central Bolivia. The hydraulic conductivity (Kfs) was obtained from seven in situ measurements of infiltration rate (I) performed by Double Ring Infiltrometer (DRI) test. These seven values were compared to the hydraulic conductivity (Ks) obtained from the empirical models; Hazen equation, Beyer equation and the Rosetta module based on particle size distribution (PSD) data obtained from soil samples. The hydraulic conductivity ranged from 3.4×10-8 to 2.3×10-1 m/s. The obtained soil parameters were implemented with collected meteorological data in Hydrus-1D to simulate the soil water content through a 5m deep soil column. Electrical resistivity tomography (ERT) was used to assess the sub-surface soil structure. The performance of the infiltration model simulating soil water content was compared to in situ observations from soil moisture sensors. The results implied that the hydraulic conductivity obtained from the double ring infiltrometer test and the Rosetta module manage to recreate the soil water content better than values from the Hazen and Beyer equations. The Hydrus-1D models were built to represent the alluvial plain during a 14-months period (2018–2020) to cover a complete rain season and dry season. According to the simulation result, the bottom flux ranges between 0-15 cm yearly through the 5m soil profile. The model results are largely dependent on initial soil water content (θi) and saturated hydraulic conductivity (Ks). This demonstrate the importance of obtaining good field investigation parameters. The study showed that using laboratory-determined soil hydraulic properties to simulate the soil water content at field scale in a stratified soil can produce inaccurate results.