291-11 Consequences of Simplification Versus Complexity in Estimating Unsaturated Travel Times in a Multi Layered Soil.

Poster Number 2431

See more from this Division: SSSA Division: Soil Physics
See more from this Session: Soil Physics and Hydrology Student Competition: Lightning Orals With Poster Presentations

Tuesday, November 5, 2013
Tampa Convention Center, East Exhibit Hall

Sara E. Vero1, Tristan G Ibrahim2, Karl G Richards3, Rachel Creamer4, Mark G Healy5 and Owen Fenton2, (1)Agri-Environment, Agri-Food and BioSciences Institute, Belfast, IRELAND
(2)Environment Research Centre, Teagasc, Wexford, Ireland
(3)Environment Soils and Landuse, Teagasc, Wexford, Ireland
(4)Environmental Research Centre, Teagasc, Wexford, Ireland
(5)Civil Engineering, National University of Ireland, Galway, Ireland
Abstract:
An appraisal of unsaturated zone conservative vertical travel times (Ttv) offers a more realistic timescale for expected water quality improvements in response to agricultural mitigation measures. Using actual soil profile data for such estimations is avoided as the standardised laboratory techniques involved are time consuming and laborious (e.g. water retention curve (WRC) data using 0-15 bar pressure plates). Instead estimates of Ttv are often made assuming saturated conditions, using generic values of saturated hydraulic conductivity (ks) and effective porosity (ne). Such an assumption may lead to misleading estimates of Ttv and false assertions with respect to meeting water quality targets. This study estimated Ttv in six layered soil (Ballymacart, Waterford, South Ireland) to 1.25 m depth using different levels of complexity: 1) generic ks and ne values and effective Darcian assumptions were used, 2) modelled ks and ne using the RETC model (input data were soil texture, bulk density and WRC data from pressure plates and centrifuge method (takes 2 days) but still under saturated conditions 3) modelled effective rainfall (ER) values utilising weather data from 1978 to 2007 with modelled and generic ne and 4) modelled soil physical parameters using RETC and Hydrus 1D models under unsaturated conditions. Results showed that the saturated Ttv estimate to 1.25 m depth 8.8 days using generic values (0.010 and 7% for immature till). The saturated equivalent using modelled ks (0.026 m day-1), gradient 1 and ne (40%) was 19.2 days. Using modelled ER of 0.75 m, Ttv of 243 and 42 days, were estimated, respectively. Inputting all available data into Hydrus 1D using unsaturated conditions, Ttv was 467 days. Overall results using actual unsaturated conditions were comparable utilising WTC input data from both pressure plate (taking months) and the centrifuge (taking days) setups. The time and accuracy achieved should encourage others to follow this methodology.

See more from this Division: SSSA Division: Soil Physics
See more from this Session: Soil Physics and Hydrology Student Competition: Lightning Orals With Poster Presentations