The relationship between water transit time and geomorpholoy in PinLin

The passage of water through a watershed implies the residence time of water within the system that closely related to water resource recharge, the rate of chemical weathering, the speed of pollutant degradation, or agricultural practices. Currently, the evaluation of transit time requires a combination of sampling data and model calculations. However, the models cannot be finely adjusted for different influencing factors, and the input data relies on on-site sampling.This study selected 19 sub-watersheds in Pinglin area of Taiwan to collect stable isotope data for transit time modeling. Storage selection model was used to calculate the transit time, and regression methods were then employed to assess the relationship between watershed transit time and various geomorphic indices. In study period 2013 to 2015, result indicated that the mean transit time of discharge 19 outlet range from 240 to 508 days, and young water fraction account for 10% to 23%, close to the value of other headwater chatchment in northen Taiwan. Area, flowpath length, and high above the nearest drainage (HAND) geomorphic indices were calculates, range from 1.09 to 196 km², 57.5 to 68.3m respectively, and the area proportion of the relief from nearest drainage under 5m range can up to 6.6%.