Application of groundwater temperature data for the determination of vertical groundwater velocities in the Chiang Mai basin, Thailand

Abstract

Groundwater recharge is an important factor in assessing groundwater resource. Recharge rate is required for groundwater modelling. In this research the groundwater temperature method is used for quantifying recharge rates and identification of recharge area in Chiang Mai basin. Temperature-depth profiles were obtained from 20 monitoring wells in Chiang Mai Basin during dry season of 2007. The results of this study, most of the wells located in recharge zone except only four wells were in discharge zone. The overall recharge rates of the top units of all recharge wells range from 1.62-32.81 cm/yr with an average of 14.0 cm/yr. The average value is approximately 12 % of the annual rainfall (116 cm/yr). As for the recharge rate in different geological units, the top units of wells in young alluvial deposits (Qcp) give the average recharge rate of 6.07 cm/yr whereas those in low terrace deposits (Qcr) give the average recharge rate of 10.72 cm/yr and those in high terrace deposits (Qcm) give the average recharge rates of 23.13 cm/yr. The wells in discharge zone may indicate groundwater discharge into the river and/or excessive exploitation of groundwater in the municipal or agricultural areas and/or heat source underneath in relation to NE-SW active basement faults parallel to the eastern basin edge and to Mae Tha active fault zone about 10 kms toward the eastern side of the basin.