Screening the current soil drainage class map of Flanders (Belgium) for its predictive quality

The predictive quality of the current drainage class map of Flanders was evaluated using data from two monitoring networks: one with good spatial coverage but poor temporal coverage and another with better temporal but poor spatial coverage. We combine both networks to obtain 1678 point predictions for mean highest water (MHW) and mean lowest water (MLW) tables by applying time series modelling and total least squares regression. The resulting MHW and MLW point data set was used to evaluate the currency of the existing map and to identify regional differences. The quality of the current map is moderate, and large differences occur between regions. Especially the Campine region shows large and systematic differences, whereas the southeastern hills and chalk–loam region is relatively accurate. If more weight is given to errors in the wetter drainage classes, about 50% of the area of Flanders would benefit from remapping. Copyright © 2011 John Wiley & Sons, Ltd.     

Snow cover and snowmelt of an extensive High Arctic wetland: spatial and temporal seasonal patterns

Abstract

This study examined the end-of-winter snow storage, its distribution and the spatial and temporal melt patterns of a large, low gradient wetland at Polar Bear Pass, Bathurst Island, Nunavut, Canada. The project utilized a combination of field observations and a physically-based snowmelt model. Topography and wind were the major controls on snow distribution in the region, and snow was routinely scoured from the hilltop regions and deposited into hillslopes and valleys. Timing and duration of snowmelt at Polar Bear Pass were similar in 2008 and 2009. The snowmelt was initiated by an increase in air temperature and net radiation receipt. Inter-annual variability in spatial snowmelt patterns was evident at Polar Bear Pass and was attributed to a non-uniform snow cover distribution and local microclimate conditions. In situ field studies and modelling remain important in High Arctic regions for assessing wetland water budgets and runoff, in addition to model parameterization and validation of satellite imagery.

Editor Z.W. Kundzewicz

Citation Assini, J. and Young, K.L., 2012. Snow cover and snowmelt of an extensive High Arctic wetland: spatial and temporal seasonal patterns. Hydrological Sciences Journal, 57 (4), 738–755.     

Potential Influence of a Developing La Niña on the Sea-Ice Reduction in the Barents–Kara Seas

Abstract

The potential influence of a developing La Niña on Arctic sea-ice annual variability is investigated using both observational data and an atmospheric general circulation model. It is found that during the developing phase of an eastern Pacific (EP) La Niña event in June, July, and August (JJA) and September, October, and November (SON), the sea-ice concentration (SIC) over the Barents–Kara Seas declines more than 15%. The local atmospheric circulation pattern associated with the EP La Niña is characterized as a weak decrease in geopotential height over the Barents–Kara Seas, combined with an anticyclone in the North Atlantic. The corresponding southerly winds push warm waters northward into the key sea-ice reduction region and directly accelerate sea-ice melt. Meanwhile, the abundant moisture contained in the lower troposphere is transported into the Arctic region by winds resulting from the local barotropic structure. The humid atmosphere contributes to both net shortwave and longwave radiation and thus indirectly accelerates the decline in sea ice. Simulations by the European Centre Hamburg Model, version 5.4, are forced by observed sea surface temperature anomalies associated with EP La Niña events. The results of the simulations capture the North Atlantic anticyclone and reproduce the moisture transport, which supports the premise that an EP La Niña plays a crucial role in sea-ice reduction over the Barents–Kara sector from the perspective of atmospheric circulation and net surface heat flux.     

Mosaic desert pavement influences water infiltration and vegetation distribution on fluvial fan surfaces

Desert pavements (DPs) are critical for maintaining ecological stability and promoting near-surface hydrological cycling in arid regions. However, few studies have focused on eco-hydrological processes of DPs in the ecological systems of fluvial fans. Although DP surfaces appear to be barren and flat, we found that the surfaces are characterized by surface mosaic patterns of desert pavement (mosaic DP) and bare ground (mosaic BG). We investigated the effects of mosaic DP on water infiltration and vegetation distribution at six sites in fluvial fans (one on a hillside and five within the sectors of fans) along a southwest belt transect in northern Linze County, in the central Hexi Corridor (China). We found significant differences in mosaic DP between the hillside and sector sites in terms of pavement thickness and vesicular horizon thickness (Av thickness), particle composition, and bulk density, although significant differences were absent for mass soil water content, gravel coverage, and surface gravel size. The mosaic DP inhibited water infiltration by the pavement layer, where the sorptivity (S), initial infiltration rate (i_int), steady-state infiltration rate (i_sat) and infiltration time (T) averaged 1.19 cm/min^-0.5, 0.64 cm/min, 0.13 cm/min and 12.76 min, respectively. Where the pavement layer was scalped, the S, i_int, and i_sat increased by 0.27 cm/min^-0.5, 0.52 cm/min, and 0.40 cm/min, respectively, and the T reduced by 7.42 min. Water infiltration was mainly controlled by the pavement layer thickness (+), Av thickness (−), surface gravel coverage (−), fine earth (+) and fine gravel (−) in the pavement layer. The DP surfaces only had a sparse covering of shrubs, but an abundance of herbs. Few shrubs were present on the mosaic DP, but a greater number of shrubs and herbs grew on the mosaic BG. It can be concluded that DPs can maintain vegetation stability for different surface mosaic patterns. This study deepens our understanding of the eco-hydrological cycle of DP landscapes in arid regions.     

A comparison of fibre‐optic distributed temperature sensing to traditional methods of evaluating groundwater inflow to streams

There are several methods for determining the spatial distribution and magnitude of groundwater inputs to streams. We compared the results of conventional methods [dye dilution gauging, acoustic Doppler velocimeter (ADV) differential gauging, and geochemical end‐member mixing] to distributed temperature sensing (DTS) using a fibre‐optic cable installed along 900 m of Ninemile Creek in Syracuse, New York, USA, during low‐flow conditions (discharge of 1·4 m³ s^?1). With the exception of differential gauging, all methods identified a focused, contaminated groundwater inflow and produced similar groundwater discharge estimates for that point, with a mean of 66·8 l s^?1 between all methods although the precision of these estimates varied. ADV discharge measurement accuracy was reduced by non‐ideal conditions and failed to identify, much less quantify, the modest groundwater input, which was only 5% of total stream flow. These results indicate ambient tracers, such as heat and geochemical mixing, can yield spatially and quantitatively refined estimates of relatively modest groundwater inflow even in large rivers. DTS heat tracing, in particular, provided the finest spatial characterization of groundwater inflow, and may be more universally applicable than geochemical methods, for which a distinct and consistent groundwater end member may be more difficult to identify. Copyright © 2011 John Wiley & Sons, Ltd.     

Spatial–temporal variability and hydrologic connectivity of runoff generation areas in a North Alabama pasture—implications for phosphorus transport

This study delineated spatially and temporally variable runoff generation areas in the Sand Mountain region pasture of North Alabama under natural rainfall conditions, and demonstrated that hydrologic connectivity is important for generating hillslope response when infiltration‐excess (IE) runoff mechanism dominates. Data from six rainfall events (13·7–32·3 mm) on an intensively instrumented pasture hillslope (0·12 ha) were analysed. Analysis of data from surface runoff sensors, tipping bucket rain gauge and HS‐flume demonstrated spatial and temporal variability in runoff generation areas. Results showed that the maximum runoff generation area, which contributed to runoff at the outlet of the hillslope, varied between 67 and 100%. Furthermore, because IE was the main runoff generation mechanism on the hillslope, the data showed that as the rainfall intensity changed during a rainfall event, the runoff generation areas expanded or contracted. During rainfall events with high‐intensity short‐ to medium‐duration, 4–8% of total rainfall was converted to runoff at the outlet. Rainfall events with medium‐ to low‐intensity, medium‐duration were found less likely to generate runoff at the outlet. In situ soil hydraulic conductivity (k) was measured across the hillslope, which confirmed its effect on hydrologic connectivity of runoff generation areas. Combined surface runoff sensor and k‐interpolated data clearly showed that during a rainfall event, lower k areas generate runoff first, and then, depending on rainfall intensity, runoff at the outlet is generated by hydrologically connected areas. It was concluded that in IE‐runoff‐dominated areas, rainfall intensity and k can explain hydrologic response. The study demonstrated that only connected areas of low k values generate surface runoff during high‐intensity rainfall events. Identification of these areas would serve as an important foundation for controlling nonpoint source pollutant transport, especially phosphorus. The best management practices can be developed and implemented to reduce transport of phosphorus from these hydrologically connected areas. Copyright © 2009 John Wiley & Sons, Ltd.     

SWAT‐simulated hydrological impact of land‐use change in the Zanjanrood basin,Northwest Iran

Understanding the impacts of land‐use changes on hydrology at the watershed scale can facilitate development of sustainable water resource strategies. This paper investigates the hydrological effects of land‐use change in Zanjanrood basin, Iran. The water balance was simulated using the Soil and Water Assessment Tool (AVSWAT2000). Model calibration and uncertainty analysis were performed with sequential uncertainty fitting (SUFI‐2). Simulation results from January 1998 to December 2002 were used for parameter calibration, and then the model was validated for the period of January 2003 to December 2004. The predicted monthly streamflow matched the observed values: during calibration the correlation coefficient was 0·86 and the Nash–Sutcliffe coefficient 0·79, compared with 0·80 and 0·79, respectively, during validation. The model was used to simulate the main components of the hydrological cycle, in order to study the effects of land‐use changes in 1967, 1994 and 2007. The study reveals that during 1967 a 34·5% decrease of grassland with concurrent increases of shrubland (13·9%), rain‐fed agriculture (12·1%), bare ground (5·5%) irrigated agriculture (2·2%), and urban area (0·7%) led to a 33% increase in the amount of surface runoff and a 22% decrease in the groundwater recharge. Furthermore, the area of sub‐basins that was influenced by high runoff (14–28 mm) increased. The results indicate that the hydrological response to overgrazing and the replacing of rangelands (grassland and shrubland) with rain‐fed agriculture and bare ground (badlands) is nonlinear and exhibits a threshold effect. The runoff rises dramatically when more than 60% of the rangeland is removed. For groundwater this threshold lies at an 80% decrease in rangeland. Copyright © 2009 John Wiley & Sons, Ltd.     

Groundwater–surface water interactions in a lowland watershed: source contribution to stream flow

The lower coastal plain of the Southeast USA is undergoing rapid urbanisation as a result of population growth. Land use change has been shown to affect watershed hydrology by altering stream flow and, ultimately, impairing water quality and ecologic health. However, because few long‐term studies have focused on groundwater–surface water interactions in lowland watersheds, it is difficult to establish what the effect of development might be in the coastal plain region. The objective of this study was to use an innovative improvement to end‐member mixing analysis (EMMA) to identify time sequences of hydrologic processes affecting storm flow. Hydrologic and major ion chemical data from groundwater, soil water, precipitation and stream sites were collected over a 2‐year period at a watershed located in USDA Forest Service's Santee Experimental Forest near Charleston, South Carolina, USA. Stream flow was ephemeral and highly dependent on evapotranspiration rates and rainfall amount and intensity. Hydrograph separation for a series of storm events using EMMA allowed us to identify precipitation, riparian groundwater and streambed groundwater as main sources to stream flow, although source contribution varied as a function of antecedent soil moisture condition. Precipitation, as runoff, dominated stream flow during all storm events while riparian and streambed groundwater contributions varied and were mainly dependent on antecedent soil moisture condition. Sensitivity analyses examined the influence of 10% and 50% increases in analyte concentration on EMMA calculations and found that contribution estimates were very sensitive to changes in chemistry. This study has implications on the type of methodology used in traditional forms of EMMA research, particularly in the recognition and use of median end‐member water chemistry in hydrograph separation techniques. Potential effects of urban development on important hydrologic processes (groundwater recharge, interflow, runoff, etc.) that influence stream flow in these lowland watersheds were qualitatively examined. Copyright © 2011 John Wiley & Sons, Ltd.     

Explicit integration of bounding surface model for the analysis of earthquake soil liquefaction

This paper presents a new plasticity model developed for the simulation of monotonic and cyclic loading of non‐cohesive soils and its implementation to the commercial finite‐difference code FLAC, using its User‐Defined‐Model (UDM) capability. The new model incorporates the framework of Critical State Soil Mechanics, while it relies upon bounding surface plasticity with a vanished elastic region to simulate the non‐linear soil response. Stress integration of constitutive relations is performed using a recently proposed explicit scheme with automatic error control and substepping, which so far has been employed in the literature only for constitutive models aiming at monotonic loading. The overall accuracy of this scheme is evaluated at element level by simulating cyclic loading along complex stress paths and by using iso‐error maps for paths involving change of the Lode angle. The performance of the new constitutive model and its stress integration scheme in complex boundary value problems involving earthquake‐induced liquefaction is evaluated, in terms of accuracy and computational cost, via a number of parametric analyses inspired by the successful simulation of the VELACS centrifuge Model Test No. 2 studying the lateral spreading response of a liquefied sand layer. Copyright © 2009 John Wiley & Sons, Ltd.