Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Hydrol. Earth Syst. Sci. Discuss., 12, 5427–5463, 2015 www.hydrol-earth-syst-sci-discuss.net/12/5427/2015/ doi:10.5194/hessd-12-5427-2015 © Author(s) 2015. CC Attribution 3.0 License. This discussion paper is/has been under review for the journal Hydrology and Earth System Sciences (HESS). Please refer to the corresponding final paper in HESS if available. Transit times from rainfall to baseflow in headwater catchments estimated using tritium: the Ovens River, Australia I. Cartwright1 and U. Morgenstern2 1School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia 2GNS Science, Lower Hutt 5040, New Zealand Received: 29 April 2015 – Accepted: 20 May 2015 – Published: 11 June 2015 Correspondence to: I. Cartwright (
[email protected]) Published by Copernicus Publications on behalf of the European Geosciences Union. 5427 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract Headwater streams contribute a significant proportion of the total flow to many river systems, especially during summer low-flow periods. However, despite their impor- tance, the time taken for water to travel through headwater catchments and into the 3 5 streams (the transit time) is poorly constrained. Here, H activities of stream water are used to define transit times of water contributing to streams from the upper reaches of the Ovens River in southeast Australia at varying flow conditions. 3H activities of the stream water varied from 1.63 to 2.45 TU, which are below the average 3H activ- ity of modern local rainfall ( 3 TU). The highest 3H activities were recorded following ∼ 3 10 higher winter flows and the lowest H activities were recorded at summer low-flow conditions.