Topographic controls on shallow groundwater dynamics: implications of hydrologic connectivity between hillslopes and riparian zones in a till mantled catchment

Hydrologic connectivity is regarded as one of the key controls in determining catchment rainfall–run-off response and has been linked to the export of solutes from uplands to streams. We sought to identify the patterns of hydrologic connectivity within a small forested watershed by monitoring the shallow groundwater fluctuations of simple topographically defined landform sequences (footslope–backslope–shoulder). A spatially distributed instrument network was employed to continuously measure hydrometric responses of the shallow subsurface during seasonal wet-up from summer through winter in a small till mantled research catchment. We demonstrate that the spatial patterns of shallow water table extent and duration, and therefore hydrologic connectivity, had a strong seasonal signature. During the low antecedent soil moisture conditions typically associated with the growing season, water tables were patchy, discontinuous, and only the wettest near-stream footslope areas were consistently hydrologically connected with the stream network. During the dormant season, footslopes and backslopes maintained water tables that persisted between storm events and were almost continuously connected with the stream network. In the largest storm events, the typically driest landforms (shoulder slopes) established shallow transient water tables, suggesting that nearly the entire catchment was temporarily hydrologically connected with the stream network. In addition, we found significant differences (p < 0·05) in the magnitude and duration of groundwater responses to rainfall among landform groups both seasonally and during events. These results have implications for using a similarity approach in representing characteristic hydrologic responses of topographically defined watershed elements, determining hydrologic connectivity between watershed elements, as well as for understanding solute transport in catchments. Copyright © 2010 John Wiley & Sons, Ltd.

[1]  M. Hutchinson.  A new procedure for gridding elevation and stream line data with automatic removal of spurious pits , 1989 .

[2]  M. Tani,et al.  Effects of hillslope topography on hydrological responses in a weathered granite mountain, Japan: comparison of the runoff response between the valley-head and the side slope , 2008 .

[3]  R. Grayson,et al.  Toward capturing hydrologically significant connectivity in spatial patterns , 2001 .

[4]  Kelsey J. Sinclair,et al.  The use of stream flow routing for direct channel precipitation with isotopically-based hydrograph separations: the role of new water in stormflow generation , 2003 .

[5]  M. Sivapalan,et al.  Hydrological connectivity of upland-riparian zones in agricultural catchments: Implications for runoff generation and nitrate transport , 2006 .

[6]  John F. Dowd,et al.  A new interpretation of kinematic stormflow generation , 2002 .

[7]  Malcolm G. Anderson,et al.  The role of topography in controlling throughflow generation , 1978 .

[8]  C. Pringle.  What is hydrologic connectivity and why is it ecologically important? , 2003 .

[9]  G. Likens,et al.  Nutrient Loss Accelerated by Clear-Cutting of a Forest Ecosystem , 1968, Science.

[10]  P. Shand,et al.  Evidence for deep sub-surface flow routing in forested upland Wales: implications for contaminant transport and stream flow generation , 2004 .

[11]  Jeffrey J. McDonnell,et al.  Quantifying the relative contributions of riparian and hillslope zones to catchment runoff , 2003 .

[12]  Jan W. Hopmans,et al.  Frequency, electrical conductivity and temperature analysis of a low-cost capacitance soil moisture sensor , 2008 .

[13]  Michael N. Gooseff,et al.  Hydrologic connectivity between landscapes and streams: Transferring reach‐ and plot‐scale understanding to the catchment scale , 2009 .

[14]  Andrew W. Western,et al.  The Tarrawarra Data Set: Soil moisture patterns, soil characteristics, and hydrological flux measurements , 1998 .

[15]  K. McGuire,et al.  Threshold changes in storm runoff generation at a till‐mantled headwater catchment , 2010 .

[16]  James M. Buttle,et al.  Hydrologic coupling of slopes, riparian zones and streams: an example from the Canadian Shield , 2004 .

[17]  S. P. Anderson,et al.  Unsaturated zone processes and the hydrologic response of a steep, unchanneled catchment , 1998 .

[18]  Randall J. Charbeneau,et al.  Kinematic Models for Soil Moisture and Solute Transport , 1984 .

[19]  R. Hawkins,et al.  FLOW PATH OF RAIN FROM THE SOIL SURFACE TO THE WATER TABLE , 1965 .

[20]  Keith Beven,et al.  A dynamic TOPMODEL , 2001 .

[21]  R. D. Black,et al.  An Experimental Investigation of Runoff Production in Permeable Soils , 1970 .

[22]  P. Vidon,et al.  Landscape controls on the hydrology of stream riparian zones , 2004 .

[23]  L. Band,et al.  Export of nitrogen from catchments within a temperate forest: Evidence for a unifying mechanism regulated by variable source area dynamics , 1998 .

[24]  Jeffrey J. McDonnell,et al.  Where does water go when it rains? Moving beyond the variable source area concept of rainfall‐runoff response , 2003 .

[25]  R. Moore,et al.  RELATIONS BETWEEN TOPOGRAPHY AND WATER TABLE DEPTH IN A SHALLOW FOREST SOIL , 1996 .

[26]  M. Sivapalan,et al.  A similarity framework to assess controls on shallow subsurface flow dynamics in hillslopes , 2009 .

[27]  Jochen Schmidt,et al.  Fuzzy land element classification from DTMs based on geometry and terrain position , 2004 .

[28]  G. Likens,et al.  Linkages between Terrestrial and Aquatic Ecosystems , 1974 .

[29]  Mary C. Freeman,et al.  Hydrologic Connectivity and the Contribution of Stream Headwaters to Ecological Integrity at Regional Scales 1 , 2007 .

[30]  Roger E. Smith.  Approximate Soil Water Movement by Kinematic Characteristics1 , 1983 .

[31]  James P. McNamara,et al.  An approach to understanding hydrologic connectivity on the hillslope and the implications for nutrient transport , 2003 .

[32]  P. Shand,et al.  Near-stream soil water–groundwater coupling in the headwaters of the Afon Hafren, Wales: Implications for surface water quality , 2006 .

[33]  Kevin Bishop,et al.  Groundwater dynamics along a hillslope: A test of the steady state hypothesis , 2003 .

[34]  K. Beven,et al.  A physically based, variable contributing area model of basin hydrology , 1979 .

[35]  Keith Beven,et al.  Kinematic wave approximation to the initiation of subsurface storm flow in a sloping forest soil , 1986 .

[36]  Günter Blöschl,et al.  Preferred states in spatial soil moisture patterns: Local and nonlocal controls , 1997 .

[37]  G. Likens,et al.  Element Fluxes and Landscape Position in a Northern Hardwood Forest Watershed Ecosystem , 2000, Ecosystems.

[38]  C. Eagar,et al.  Hydrometeorological database for Hubbard Brook Experimental Forest: 1955-2000 , 2003 .

[39]  B. Ambroise,et al.  Variable ‘active’ versus ‘contributing’ areas or periods: a necessary distinction , 2004 .

[40]  Louise J. Bracken,et al.  The concept of hydrological connectivity and its contribution to understanding runoff‐dominated geomorphic systems , 2007 .

[41]  M. Fujita,et al.  Flow paths, rainfall properties, and antecedent soil moisture controlling lags to peak discharge in a granitic unchanneled catchment , 2005 .

[42]  A similarity approach to predict landscape saturation in catchments , 2002 .

[43]  Günter Blöschl,et al.  Observed spatial organization of soil moisture and its relation to terrain indices , 1999 .

[44]  Nigel T. Roulet,et al.  Investigating hydrologic connectivity and its association with threshold change in runoff response in a temperate forested watershed , 2007 .

[45]  Keith Beven,et al.  The role of bedrock topography on subsurface storm flow , 2002 .

[46]  Tim Burt,et al.  Topographic controls of soil moisture distributions , 1985 .

[47]  J. Seibert,et al.  A new triangular multiple flow direction algorithm for computing upslope areas from gridded digital elevation models , 2007 .

[48]  Jeffrey J. McDonnell,et al.  Threshold relations in subsurface stormflow: 2. The fill and spill hypothesis , 2006 .

[49]  G. Pinay,et al.  Linking hydrology and biogeochemistry in complex landscapes , 2004 .

[50]  J. C. Thompson,et al.  Are Water Table Variations in a Shallow Forest Soil Consistent with the TOPMODEL Concept , 1996 .