Spatial variation of infiltration properties in Paria, Oruro, Bolivia

Abstract: Water is necessary for all life and one of the most important natural resources. The water resources problems were the reason why the project Development of the Altiplano area in Bolivia: a collaboration between Lund University (Sweden) and San Andres University in La Paz (Bolivia) was started. In the project PhD students are investigating the groundwater aquifer Challapampa that supplies the city of Oruro with water. Part of the project is performing a water balance on the groundwater aquifer and includes gathering of infiltration data. To collect infiltration data is a tedious activity thus it is important to investigate ways to relate infiltration properties of a soil to other parameters and by that reduce the requirement of infiltration data. The study addresses the possibilities of decreasing the amount of required infiltration data by investigating relationships between soil parameters e.g. moisture content and hydraulic conductivity. It was realized by studying 91 locations covering an area of around 60 times 60 meters in the village of Paria northeast of the city Oruro, located on the Challapampa aquifer. The study investigates infiltration using a tension disc infiltrometer and soil moisture content at depths of 0-10cm and 10-20cm. The analysis with the tension disc infiltrometer was performed with tensions -100 mm and -50 mm and the data were analyzed using three different methods; developed by Ankeny, et al(1991) and Zhang (1998). In addition the differentiated linearization, developed by Vandervaere et al(2000), was used in conjunction with Zhang (1998). The negative results were discarded because negative results do not have physical meaning according to Vandervaere et al (2000). The data were analyzed in ESRI ArcGIS to produce maps describing the spatial variation of the results. Several different interpolation methods were tested. The amount of negative, and therefore discarded, results accounted for 22% using the constant infiltration rate method by Ankeny et al(1991), 36% for Zhang (1998) and 38% for Zhang (1998) with differentiated linearization. The hydraulic conductivities at the top section of the soil layers were in the range [10-7-10-5]ms-1 with a mean of [2.0-2.8]10-6ms-1 for tension h=-100mm and a mean of [5.8−5.9]10−6 ms−1 for tension h=-50mm. The soil moisture content was in the range of 0.6-50.7% with a mean of 6.6% for 0-10cm depth and [2.1-13.6]% with a mean of 6.5% for 10-20cm depth. The kriging interpolation method was found to be the most suitable due to very high or low results at the borders using other methods. No clear relationships between hydraulic conductivity and soil moisture content were found. Investigation of the physical processes for infiltration should continue so that better instruments or methods could be developed. Also research on substitutes for infiltration should continue because it can create faster measurements with already existing methods and equipment. Furthermore the investigation on the water availability of the Altiplano should continue, including efforts to connect previous studies to new and to make unavailable studies available to the public.