Groundwater dynamics along a hillslope: A test of the steady state hypothesis

Abstract

[1] Appropriate conceptual simplifications and assumptions are a central issue for hydrological modeling, especially when those models serve as the foundation for more complex hydrochemical or ecological models. A common and often unexamined assumption in conceptual modeling is that the relation between groundwater levels and runoff can be described as a succession of steady state conditions. This results in a singlevalued, monotonic function between the groundwater levels and runoff. Consequently, the simulated rise and fall in groundwater levels always follow the dynamics of runoff. We tested this assumption with an analysis of detailed groundwater level data along two opposing hillslopes along a stream reach in a Swedish till catchment at Svartberget. Groundwater levels in areas close to the stream followed the dynamics of the runoff. The correlation between groundwater level and runoff decreased markedly for wells farther than approximately 40 m from the stream. The levels were often independent of streamflow: Upslope area groundwater could be rising when riparian groundwater and runoff were falling, and vice versa. There was a high degree of correlation between groundwater levels at similar distances from the stream. The median Spearman rank correlation between wells within 35 m from the stream was 0.86 and for wells located more than 60 m from the stream was 0.96. This indicated that there is a common hydrological pattern even in the upslope area that can be identified and modeled. Despite the widespread acceptance of the steady state assumption previously in this and other study catchments, our study shows that it is not valid for the investigated hillslope site. If the divergence from steady state, with potential ramifications for other processes such as runoff chemistry, is common, then it will be worthwhile to reconsider the appropriate range of applicability for the steady state hypothesis, and the alternatives to that hypothesis.

Riparian zone hydrology and soil water total organic carbon (TOC): implications for spatial variability and upscaling of lateral riparian TOC exports

“…Consequently, other potential flow pathways (such as groundwater recharge to the streambed or overland flow) and biogeochemical processes during transport through the RZ were not taken into account. The effect of alternative flow pathways which could partially bypass the RZ was not assessed in detail, though other studies have confirmed the strong relationship between stream flow and riparian groundwater levels (Seibert et al, 2002). However, periods of potential overland flow as indicated by groundwater levels above surface were relatively limited at most ROK sites (Table 1).…”

The influence of soil moisture on threshold runoff generation processes in an alpine headwater catchment

“…Experimental evidence in mountainous and agricultural catchments has revealed that riparian zones tend to respond differently and almost independently from upslope zones with runoff typically being generated first in riparian areas, and with riparian-hillslope hydrological connectivity increasing under wetter conditions (McGlynn et al, 2004;Wenninger et al, 2004;Ocampo et al, 2006). These different response times reveal distinctly different groundwater dynamics in riparian and upslope zones (Kendall et al, 1999;Seibert et al, 2003;Rassam et al, 2006), leading at times to hysteretic behaviours in the groundwater-runoff relationship (Kendall et al, 1999;McGlynn et al, 2004;Penna et al, 2010). The influence of rapid soil saturation in riparian zones on catchment runoff response has been highlighted in various studies.…”

Riparian Zone Influence on Stream Water Dissolved Organic Carbon Concentrations at the Swedish Integrated Monitoring Sites

“…The flow function, q rip (z), can be derived by differentiating the relationship between stream discharge and groundwater table (GWT) depth (Moldan and Wright 1998;Fölster 2001;Nyberg et al 2001;Seibert et al 2003):…”