Field and laboratory experiments to investigate infiltration processes and clogging effects from a ponding recharge system at Ban Nong Na, Bangrakum District, Phitsanulok Province, Lower Yom River Basin, Thailand

Paper presented at ISMAR7, Theme - Water Reuse and MAR, Abu Dhabi, UAE, 9-13 October 2010A small-scale field experiment consisting of surface infiltration tests was conducted at Ban Nong Na, located in Bangrakum District, Phitsanulok Province, situated in the Lower Yom River Basin. The shallow groundwater in this area has been heavily pumped for growing rice all year round, and within the past decade static water levels within the gravel, sand and silt aquifers have decreased to a depth of up to ten meters below the ground surface. Research is currently being conducted to investigate the feasibility of managed aquifer recharge by surface ponding methods in the Lower Yom River Basin. This study, which forms one component of the broader project, aims to assess infiltration processes and clogging effects at the laboratory (column) scale and at the small scale (25 m2) in the field. The laboratory experiment consisted of two main components: 1) physical, chemical and biological analyses of raw water and the ambient groundwater and 2) soil column testing under constant head conditions over a period of 100 hours. The field experiment consisted of three main components: 1) characterization of the physical and hydraulic properties of the unsaturated and saturated media 2) pretreatment design considering levels of turbidity removal using synthetic poly and sand filter, and 3) infiltration testing under constant head conditions over a period of 30 hours. These works are intended to provide the design criteria for establishing a larger scale (1,600 m2) pilot recharge system at the study site. Average infiltration rates for the laboratory experiment for source waters with mean turbidities of 0.5 and 100 NTU were found to be 3.27 and 0.15 m/d respectively. The infiltration rate from the field experiment with an average turbidity 50 NTU was 2.53 m/d; a magnitude commensurate with the lab study. Since infiltration rates in excess of 1 m/day are desirable for the pilot trial, the turbidity of the raw canal water used for recharge will be controlled to be less than 50 NTU. Whilst both the laboratory and field experiments were brief and longer test periods needed, more extensive investigations will be performed over the 2010 monsoon season during the full-scale pilot trial