Linking quantified lateral flow gains to catchment attributes in a paired watershed study

Stream to catchment connections are important to understanding the hydrology of a wildland system. Additionally, knowing what role particular catchment attributes play in the contribution of flow to a stream is important for land management decisions. Catchment attribute analysis performed in conjunction with lateral inflow quantification during seasonal discharge recession at higher resolutions (e.g. every 200-700 meters) could contribute more to our understanding of base-flow catchment-stream connections and hydrologic functions. The purpose of this study was to better link catchments to their streams based on catchment attributes and stream flow generation associated with those attributes.; Stream flow at 26 stations and flow gains/losses for 24 stream reaches throughout two paired headwater catchments with differing lithologies was measured synoptically using dilution gauging techniques on three occasions during the summer seasonal discharge recession. Laterally contributing landscape characteristics were determined from digital elevation data and investigated for relationships with the flow gains and losses. Temporal variations in these catchment stream connections were quantified from the synoptic samplings. Additional comparative analysis of streamflow generation during baseflow in these two catchments was done through a qualitative assessment of stream chemistry and geological formations.; Results showed that each stream consisted of gaining and losing reaches rather than a continuum of flow gains moving downstream. Of the landscape characteristics investigated, contributing area was the most dominant explanatory variable in explaining flow gains and losses in one catchment and accounted for as much as 83% of the variation in flow gains. The regression relationship strength and slope deteriorated for the later synoptic samplings in that catchment, suggesting a drying out of hillslopes and a relative increase in hydrologic control by another variable. Lateral contributing area size in the other catchment showed no statistically significant correlations with flow gain/loss, illustrating that traditional landscape relationships with the stream do not hold for catchments with karstic supporting lithology. Stream chemistry patterns for some constituents were explained by catchment lithology patterns; concentrations were significantly (p-value < 0.01) different between the two catchments, suggesting older source water for one of the catchments. This work has highlighted the need to (1) better understand relative importance of different hydrologic controls throughout seasonal recession, and (2) characterize watersheds with respect to lithology prior to making assumptions of chemical and flow generation similarity between adjacent paired catchments of even relatively small size.