Fill‐and‐Spill: A Process Description of Runoff Generation at the Scale of the Beholder

Abstract

The famous French mathematician Henri Poincaré said that "Science is built up of facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house" (Poincaré, 1902). Our perceptual understanding of runoff processes sometimes appears as a heap of facts (or observations), with many of them dating back to the First International Hydrological Decade and the following years, when key observations were made regarding translatory flow (Hewlett & Hibbert, 1967), saturation excess overland flow (Dunne & Black, 1970), saturated wedges (Weyman, 1973), old water effusion (Martinec, 1975), the importance of topographic convergence (Anderson & Burt, 1978) and preferential flow (Mosley, 1979). Since then, field hydrologists have continued to document more and more runoff responses in more and more areas.What we have learned from these myriad studies is that (i) runoff processes are scale dependent, making the "up-scaling" of field-based process observations very difficult to nearly impossible, (ii) runoff concepts developed for humid areas (e.g., the variable source area concept) often do not apply in semi-arid and arid areas, and (iii) runoff responses are non-linear (thresholds, hysteresis, etc.) because regardless of whether the dominant flowpaths occur at the surface as overland flow or as subsurface stormflow within the soil or subsoil or saprolite or bedrock, some storage needs to be filled before runoff occurs.Our heap of facts about runoff generation obtained by process observations have continued to grow, but there has been little construction of these facts into a body of knowledge. This seems to be a crucial next step in catchment hydrology, as it has been in other areas of science where observations gain significance when one uses reason to group them in meaningful ways (Beveridge, 1950). Indeed, "grouping" is a theme in the development of many fields; notably Darwin's (1859) observation that "science consists of grouping facts so that general laws or conclusions may be drawn from them" and Hughlings-Jackson's (1882) advice that we have multitudes of facts but "we require, as they accumulate, organizations of them into higher knowledge; we require generalizations and working hypotheses."

Assess hydrological responses to a warming climate at the Lysina Critical Zone Observatory in Central Europe

“…It is reasonable and practical to conceptualize subsurface flow dynamics as the two‐state integral‐balance between saturated and unsaturated storage (Duffy, 1996), though the subsurface flow can be much more complex due to heterogeneity of landscape, soil, and hydrogeological environments (McDonnell et al, 2021; Somers & McKenzie, 2020). The PIHM simulated saturated storage dynamics was validated by only streamflow but also water tables at three different locations, which increased our confidence in capturing the percentage of streamflow attributable to groundwater.…”

“…much more complex due to heterogeneity of landscape, soil, and hydrogeological environments(McDonnell et al, 2021;Somers & McKenzie, 2020). The PIHM simulated saturated storage dynamics was validated by only streamflow but also water tables at three different locations, which increased our confidence in capturing the per-centage of streamflow attributable to groundwater.…”

Antecedent Conditions Control Thresholds of Tile‐Runoff Generation and Nitrogen Export in Intensively Managed Landscapes

“…Although the landscape structure and associated runoff generation mechanisms of low‐gradient, tile‐drained IMLs differs from that of steep, bedrock hillslopes, the conceptual filling and spilling of landscape storages and resultant threshold runoff behavior are similar. Further, fill‐and‐spill was recently proposed as a framework to more broadly describe runoff generation processes by which landscape storages become progressively filled and connected (McDonnell et al., 2021). Another comparable bottom‐up mechanism explaining threshold runoff response in untiled, minimally managed hillslopes is “transmissivity feedback” (Bishop, 1991; Kendall et al., 1999).…”

Unique episodic groundwater recharge event in a South American sedimentary aquifer and its long‐term impact on baseflow

“…The use of a linear storage‐discharge relationship is a classic approach found and accepted in the literature (De Rooij, 2013; Ebrahim & Villholth, 2016; Fenicia et al, 2006). However, many studies have shown that basin temporal variations in the hydrological process such as evapotranspiration that may actively compete with subsurface drainage for the same water resource that supplies streamflow (Shaw & Riha, 2012; Tashie et al, 2019) and the water‐level elevation could be responsible for accelerating the exfiltration of pre‐event water into the river bed due to the fill and spill process (Mcdonnell et al, 2021; Wittenberg, 1999) or increase the stream network density (Godsey & Kirchner, 2014), could help to explain the exponential best fit for the storage increases. GRACE's mission ended in 2017 and it provided the 16 years of data used in this study; however, the continuity of the monitoring was guaranteed from the launched mission GRACE Follow‐On (GRACE‐FO) in 2018 (Frappart & Ramillien, 2018).…”