The contribution of old and new water to a storm hydrograph determined by tracer addition to a whole catchment
✍ Scribed by R. Collins; A. Jenkins; M. Harrow
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 162 KB
- Volume
- 14
- Category
- Article
- ISSN
- 0885-6087
No coin nor oath required. For personal study only.
✦ Synopsis
Two tracer experiments have been carried out at an enclosed catchment in southern Norway. The catchment was brought to steady state with respect to rainfall and runo prior to the tracer addition. A known concentration of lithium bromide was then added to the rainfall for the duration of each event. The tight control on tracer concentration and rainfall amount enabled assessment of the contribution of old and new water to runo, the dominant ¯ow pathways and soil water residence times during a storm event. A signi®cant volume of old' water contributes to runo despite the hydrologically responsive nature of the catchment and several hours of tracer injected rainfall are required before new' water becomes the dominant runo source. After 34 h of tracer injection, `new' water apparently contributes c. 83% to instantaneous ¯ow and c. 55% of the total tracer input to the catchment has been lost in runo. Recovery of the tracer from soil water indicates that the organic soil surface layer is the dominant ¯ow pathway for rainwater through the catchment and that a signi®cant pathway also exists at the soil±bedrock interface. New water is retained in deep pockets of soil for several days. Assessment of the conservative behaviour of the tracer suggests that 10±14% of the input Br À is retained in the soil and the tracer is not conservative. Laboratory experiments indicate that sorption of Br À to organic soil is the likely mechanism of retention. This process is probably concentration dependent and will have occurred predominantly during the initial period of tracer application.