River evaporation,condensation and heat fluxes within a first‐order tributary of Catamaran Brook (New Brunswick,Canada)

Stream temperature plays an important role in many biotic and abiotic processes, as it influences many physical, chemical and biological properties in rivers. As such, a good understanding of the thermal regime of rivers is essential for effective fisheries management and the protection aquatic habitats. Moreover, a thorough understanding of underlying physical processes and river heat fluxes is essential in the development of better and more adaptive water temperature models. Very few studies have measured river evaporation and condensation and subsequently calculated corresponding heat fluxes in small tributary streams, mainly because microclimate data (data collected within the stream environment) are essential and rarely available. As such, the present study will address these issues by measuring river evaporation and condensation in tributary 1 (Trib 1, a small tributary within Catamaran Brook) using floating minipans. The latent heat flux and other important fluxes were calculated. Results showed that evaporation was low within the small Trib 1 of Catamaran Brook, less than 0.07 mm day^?1. Results showed that condensation played an important role in the latent heat flux. In fact, condensation was present during 34 of 92 days (37%) during the summer, which occurred when air temperature was greater than water temperature by 4–6 °C. Heat fluxes within this small stream showed that solar radiation dominated the heat gains and long‐wave radiation dominated the heat losses. © 2015 Her Majesty the Queen in Right of Canada. Hydrological Processes. © 2015 John Wiley & Sons, Ltd.     

Study of stream temperature dynamics and corresponding heat fluxes within Miramichi River catchments (New Brunswick,Canada)

Water temperature is a key physical habitat determinant in lotic ecosystems as it influences many physical, chemical, and biological properties of rivers. Hence, a good understanding of the thermal regime of rivers and river heat fluxes is essential for effective management of water and fisheries resources. This study dealt with the modelling of river water temperature using a deterministic model. This model calculated the different heat fluxes at the water surface and from the streambed using different hydrometeorological conditions. The water temperature model was applied on two watercourses of different sizes and thermal characteristics, but within a similar meteorological region, namely, the Little Southwest Miramichi River and Catamaran Brook (New Brunswick, Canada). The model was also applied using microclimate data, i.e. meteorological conditions within the river environment (1–2 m above the water surface), for a better estimation of river heat fluxes. Water temperatures at different depths within the riverbed were also used to estimate the streambed heat fluxes. Results showed that microclimate data were essential to get accurate estimates of the surface heat fluxes. Results also showed that for larger river systems, the surface heat fluxes were generally the dominant component of the heat budget with a correspondingly smaller contribution from the streambed. As watercourses became smaller and groundwater contribution more significant, the streambed contribution became important. For instance, approximately 80% of the heat fluxes occurred at the surface for Catamaran Brook (20% from the streambed) whereas the Little Southwest Miramichi River showed values closer to 90% (10% from the streambed). As was reported in previous studies, the solar radiation input dominated the contribution to the heat gain at 63% for Catamaran Brook and 89% for Little Southwest Miramichi River. Copyright © 2011 John Wiley & Sons, Ltd.     

Sensitivity analysis of a deterministic water temperature model to forest canopy and soil temperature in Catamaran Brook (New Brunswick,Canada)

A coupled deterministic hydrological and water temperature model, CEQUEAU, was modified to include soil temperature and crown closure in its calculation of local advective terms in the heat budget. The modified model was than tested to verify its sensitivity to these modifications. An analysis of the heat budget of a small forested catchment in eastern Canada revealed that the advective term related to interflow plays a significant role in the daily water heat budget, providing on average 28% of the local advective budget (which also includes advective heat terms from surface runoff and groundwater) and nearly 14% of the total heat budget (which includes all radiative terms at the water surface, convection and evaporation, as well as the local advective terms). Relative sensitivity indices (RSIs) were used to verify the impact of the newly introduced parameters and variables. Among them, parameters related to the forest cover (crown closure and leaf area index) have a maximum RSI of ?0·6; i.e. a 100% increase in value produces a 60% decrease in the local advective term. Parameters with the greatest influence are the volume of water contributing to interflow and the amplitude of the net radiative flux at the soil surface, which, if doubled, would double the contribution of the local interflow advective term to the heat budget. Copyright © 2003 John Wiley & Sons, Ltd.     

Predicting river water temperatures using the equilibrium temperature concept with application on Miramichi River catchments (New Brunswick,Canada)

Water temperature influences most of the physical, chemical and biological properties of rivers. It plays an important role in the distribution of fish and the growth rates of many aquatic organisms. Therefore, a better understanding of the thermal regime of rivers is essential for the management of important fisheries resources. This study deals with the modelling of river water temperature using a new and simplified model based on the equilibrium temperature concept. The equilibrium temperature concept is an approach where the net heat flux at the water surface can be expressed by a simple equation with fewer meteorological parameters than required with traditional models. This new water temperature model was applied on two watercourses of different size and thermal characteristics, but within a similar meteorological region, i.e., the Little Southwest Miramichi River and Catamaran Brook (New Brunswick, Canada). A study of the long‐term thermal characteristics of these two rivers revealed that the greatest differences in water temperatures occurred during mid‐summer peak temperatures. Data from 1992 to 1994 were used for the model calibration, while data from 1995 to 1999 were used for the model validation. Results showed a slightly better agreement between observed and predicted water temperatures for Catamaran Brook during the calibration period, with a root‐mean‐square error (RMSE) of 1·10 °C (Nash coefficient, NTD = 0·95) compared to 1·45 °C for the Little Southwest Miramichi River (NTD = 0·94). During the validation period, RMSEs were calculated at 1·31 °C for Catamaran Brook and 1·55 °C for the Little Southwest Miramichi River. Poorer model performances were generally observed early in the season (e.g., spring) for both rivers due to the influence of snowmelt conditions, while late summer to autumn modelling performances showed better results. Copyright © 2005 John Wiley & Sons, Ltd.     

Thermal regime of a headwater stream within a clear‐cut,coastal British Columbia,Canada

This study examined the thermal regime of a headwater stream within a clear‐cut. The stream had a complex morphology dominated by step–pool features, many formed by sediment accumulation upstream of woody debris. Maximum daily temperatures increased up to 5 °C after logging, and were positively associated with maximum daily air temperature and negatively with discharge. Maximum daily temperatures generally increased with downstream distance through the cut block, but decreased with distance in two segments over distances of tens of metres, where the topography indicated relatively concentrated lateral inflow. Localized cool areas within a step–pool unit were associated with zones of concentrated upwelling. Bed temperatures tended to be higher and have greater ranges in areas of downwelling flow into the bed. Heat budget estimates were made using meteorological measurements over the water surface and a model of net radiation using canopy characteristics derived from fisheye photography. Heat exchange driven by hyporheic flow through the channel step was a cooling effect during daytime, with a magnitude up to approximately 25% that of net radiation during the period of maximum daytime warming. Heat budget calculations in these headwater streams are complicated by the heterogeneity of incident solar radiation and channel geometry, as well as uncertainty in estimating heat and water exchanges between the stream and the subsurface via hyporheic exchange and heat conduction. Copyright © 2005 John Wiley & Sons, Ltd.     

Intra‐annual variability in the non‐advective heat energy budget of Devon streams and rivers

The nature of intra‐annual variability in the non‐advective heat fluxes affecting streams and rivers in Devon, UK was investigated through detailed monitoring of study reaches in an upland moorland catchment, below a regulating reservoir, and flowing through deciduous woodland and coniferous forest during the period May 1995 to April 1996. A clear pattern of seasonal variation was evident, whereby net radiation provided a heat source during the summer but a heat sink in the winter, as incoming short‐wave radiation declined and outgoing long‐wave radiation increased. Sensible transfer added heat to the study reaches in the summer but removed it during the winter, and bed conduction acted as a heat sink in the summer period but as a heat source in the winter months. Friction and evaporation added and removed heat, respectively, from the study reaches throughout the year, but the magnitude of these fluxes reflected seasonal variations in discharge and in wind speed. Water temperature generally followed the net non‐advective heat energy budget, which was positive in summer but negative in winter. Although a general pattern of seasonal variability in the non‐advective heat energy budget was evident, detailed differences in the nature and extent of intra‐annual variability were apparent between the study reaches and particularly between forested and non‐forested sites. Copyright © 2004 John Wiley & Sons, Ltd.     

Long‐term monitoring of a mercury contaminated estuary (Ria de Aveiro,Portugal): the effect of weather events and management in mercury transport

The main aim of this research was to assess the mercury transport from an estuarine basin with a background of anthropogenic contamination during a spring tidal cycle (year 2009) and compare it with two previous tidal cycles (years 1994 and 1999), as part of a long‐term monitoring program. Results showed that effective mercury transport occurs both in the dissolved and particulate fractions (0.18 and 0.20 kg per tidal cycle, respectively), and despite an overall decrease in environmental contamination, results more than double previous findings on particulate transport in the system. These findings result essentially from changes in the tidal prism (net export of 2 million m³ of water), given that both dissolved and particulate concentrations did not increase over time. Hydrodynamic simulations were performed to evaluate the effect of physical disturbance (dredging) and weather events (increased freshwater flow) in these processes, and results suggest the increased freshwater flow into the system as the main forcing function for the mercury transport increment. These results highlight the importance of long‐term monitoring programs, since despite an overall improvement in local contamination levels, the enhancement of transport processes through hydrological changes increases environmental pressure away from the contamination source. Copyright © 2012 John Wiley & Sons, Ltd.     

Rainfall,run‐off,and sediment transport dynamics in a humid mountain badland area: Long‐term results from a small catchment

In this study, we investigated rainfall, run‐off, and sediment transport dynamics (414 run‐off events and 231 events with sediment information) of a humid mountain badland area—the Araguás catchment (Central Pyrenees, Spain)—from October 2005 to September 2016. Use of this long‐term database allows characterization of the hydrological response, which consist of low‐magnitude/high‐frequency events and high‐magnitude/low‐frequency events, and identification of seasonal dynamics and rainfall‐run‐off thresholds. Our results indicate that the Araguás catchment, similarly to other humid badlands, had high hydrological responsiveness (mean annual run‐off coefficient: 0.52), a non‐linear relationship of rainfall with run‐off (common in Mediterranean environments), and seasonal hydrological and sedimentological dynamics. We created and validated a multivariate regression model to characterize the hydrological variables (stormflow and peak discharge) and sedimentological variables (mean and maximum suspended sediment concentrations and total suspended sediment load). In summer and at the beginning of autumn, the response was mainly related to rainfall intensity, suggesting a predomination of Hortonian flows. In contrast, in spring and winter, the responses were mainly related to the antecedent conditions (previous rainfall and baseflow), suggesting the occurrence of saturated excess flow processes, and the contribution of neighbouring vegetated areas. The multivariate analysis also showed that total sediment load is better predicted by a multivariate regression model that integrates pre‐event, rainfall, and run‐off variables. In general, our models provided more accurate predictions of small‐magnitude/high‐frequency events than high‐magnitude/low‐frequency events. This study highlights the high inter‐ and intra‐annual variability response in humid badland areas and that long‐term records are needed to reduce the uncertainty of hydrological and sedimentological responses in Mediterranean badland areas.     

Flow behaviour,suspended sediment transport and transmission losses in a small (sub‐bank‐full) flow event in an Australian desert stream

The behaviour of a discrete sub‐bank‐full flow event in a small desert stream in western NSW, Australia, is analysed from direct observation and sediment sampling during the flow event and from later channel surveys. The flow event, the result of an isolated afternoon thunderstorm, had a peak discharge of 9 m³/s at an upstream station. Transmission loss totally consumed the flow over the following 7·6 km. Suspended sediment concentration was highest at the flow front (not the discharge peak) and declined linearly with the log of time since passage of the flow front, regardless of discharge variation. The transmission loss responsible for the waning and eventual cessation of flow occurred at a mean rate of 13.2% per km. This is quite rapid, and is more than twice the corresponding figure for bank‐full flows estimated by Dunkerley (1992) on the same stream system. It is proposed that transmission losses in ephemeral streams of the kind studied may be minimized in flows near bank‐full stage, and be higher in both sub‐bank‐full and overbank flows. Factors contributing to enhanced flow loss in the sub‐bank‐full flow studied included abstractions of flow to pools, scour holes and other low points along the channel, and overflow abstractions into channel filaments that did not rejoin the main flow. On the other hand, losses were curtailed by the shallow depth of banks wetted and by extensive mud drapes that were set down over sand bars and other porous channel materials during the flow. Thus, in contrast with the relatively regular pattern of transmission loss inferred from large floods, losses from low flows exhibit marked spatial variability and depend to a considerable extent on streamwise variations in channel geometry, in addition to the depth and porosity of channel perimeter sediments. Copyright © 1999 John Wiley & Sons, Ltd.     

Inter‐annual variability in the effects of riparian woodland on micro‐climate,energy exchanges and water temperature of an upland Scottish stream

The influence of riparian woodland on stream temperature, micro‐climate and energy exchange was investigated over seven calendar years. Continuous data were collected from two reaches of the Girnock Burn (a tributary of the Aberdeenshire Dee, Scotland) with contrasting land use characteristics: (1) semi‐natural riparian forest and (2) open moorland. In the moorland reach, wind speed and energy fluxes (especially net radiation, latent heat and sensible heat) varied considerably between years because of variable riparian micro‐climate coupled strongly to prevailing meteorological conditions. In the forested reach, riparian vegetation sheltered the stream from meteorological conditions that produced a moderated micro‐climate and thus energy exchange conditions, which were relatively stable between years. Net energy gains (losses) in spring and summer (autumn and winter) were typically greater in the moorland than the forest. However, when particularly high latent heat loss or low net radiation gain occurred in the moorland, net energy gain (loss) was less than that in the forest during the spring and summer (autumn and winter) months. Spring and summer water temperature was typically cooler in the forest and characterised by less inter‐annual variability due to reduced, more inter‐annually stable energy gain in the forested reach. The effect of riparian vegetation on autumn and winter water temperature dynamics was less clear because of the confounding effects of reach‐scale inflows of thermally stable groundwater in the moorland reach, which strongly influenced the local heat budget. These findings provide new insights as to the hydrometeorological conditions under which semi‐natural riparian forest may be effective in mitigating river thermal variability, notably peaks, under present and future climates. © 2014 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.     

The effect of terrace geology on ground‐water movement and on the interaction of ground water and surface water on a mountainside near Mirror Lake,New Hampshire,USA

The west watershed of Mirror Lake in the White Mountains of New Hampshire contains several terraces that are at different altitudes and have different geologic compositions. The lowest terrace (FSE) has 5 m of sand overlying 9 m of till. The two next successively higher terraces (FS2 and FS1) consist entirely of sand and have maximum thicknesses of about 7 m. A fourth, and highest, terrace (FS3) lies in the north‐west watershed directly adjacent to the west watershed. This highest terrace has 2 m of sand overlying 8 m of till. All terraces overlie fractured crystalline bedrock. Numerical models of hypothetical settings simulating ground‐water flow in a mountainside indicated that the presence of a terrace can cause local ground‐water flow cells to develop, and that the flow patterns differ based on the geologic composition of the terrace. For example, more ground water moves from the bedrock to the glacial deposits beneath terraces consisting completely of sand than beneath terraces that have sand underlain by till. Field data from Mirror Lake watersheds corroborate the numerical experiments. The geology of the terraces also affects how the stream draining the west watershed interacts with ground water. The stream turns part way down the mountainside and passes between the two sand terraces, essentially transecting the movement of ground water down the valley side. Transects of water‐table wells were installed across the stream's riparian zone above, between, and below the sand terraces. Head data from these wells indicated that the stream gains ground water on both sides above and below the sand terraces. However, where it flows between the sand terraces the stream gains ground water on its uphill side and loses water on its downhill side. Biogeochemical processes in the riparian zone of the flow‐through reach have resulted in anoxic ground water beneath the lower sand terrace. Results of this study indicate that it is useful to understand patterns of ground‐water flow in order to fully understand the flow and chemical characteristics of both ground water and surface water in mountainous terrain. Copyright © 2007 John Wiley & Sons, Ltd.     

Combining isotopic tracers (222Rn and δ13C) for improved modelling of groundwater discharge to small rivers

In regions where aquifers sustain rivers, the location and quantification of groundwater discharge to surface water are important to prevent pollution hazards, to quantify and predict low flows and to manage water supplies. ²²²Rn is commonly used to determine groundwater discharge to rivers. However, using this isotopic tracer is challenging because of the high diffusion capacity of ²²²Rn in open water. This study illustrates how a combination of isotopic tracers can contribute to an enhanced understanding of groundwater discharge patterns in small rivers. The aim of this paper is to combine ²²²Rn and δ¹³C_DIC to better constrain the physical parameters related to the degassing process of these tracers in rivers. The Hallue River (northern France) was targeted for this study because it is sustained almost exclusively by a fractured chalk aquifer. The isotopes ²²²Rn, δ¹³C_DIC, δ²H and δ¹⁸O were analysed along with other natural geochemical tracers. A mass balance model was used to simulate ²²²Rn and δ¹³C_DIC. The results of δ²H and δ¹⁸O analyses prove that evaporation did not occur in the river. The calibration of a numerical model to reproduce ²²²Rn and δ¹³C_DIC provides a best‐fit diffusive layer thickness of 3.21 × 10^?5 m. This approach is particularly useful for small rivers flowing over carbonate aquifers with high groundwater DIC where the evolution of river DIC reflects the competing processes of groundwater inflow and CO₂ degassing. This approach provides a means to evaluate groundwater discharge in small ungauged rivers. Copyright © 2014 John Wiley & Sons, Ltd.     

Using high resolution tracer data to constrain water storage,flux and age estimates in a spatially distributed rainfall‐runoff model

Models simulating stream flow and conservative tracers can provide a representation of flow paths, storage distributions and mixing processes that is advantageous for many predictive purposes. Compared with models that only simulate stream flow, tracer data can be used to investigate the internal consistency of model behaviour and to gain insight into model performance. Here, we examine the strengths and weaknesses of a data‐driven, spatially distributed tracer‐aided rainfall‐runoff model. The model structure allowed us to assess the influence of landscape characteristics on the routing and mixing of water and tracers. The model was applied to a site in the Scottish Highlands with a unique tracer data set; ~4 years of daily isotope ratios in stream water and precipitation were available, as well as 2 years of weekly soil and ground water isotopes. The model structure was based on an empirically based, lumped tracer‐aided model previously developed for the catchment. The best model runs were selected from Monte Carlo simulations based on dual calibration criteria using objective functions for both stream isotopes and discharge at the outlet. Model performance for these criteria was reasonable (Nash–Sutcliffe efficiencies for discharge and isotope ratios were ~0.4–0.6). The model could generally reproduce the variable isotope signals in the soils of the steeper hill slopes where storage was low, and damped isotope responses in valley bottom cells with high storage. The model also allowed us to estimate the age distributions of internal stores, water fluxes and stream flow. Average stream water age was ~1.6 years, integrating older groundwater in the valley bottom and dynamic younger soil waters. By tracking water ages and simulating isotopes, the model captured the changes in connectivity driven by distributed storage dynamics. This has substantially improved the representation of spatio‐temporal process dynamics and gives a more robust framework for projecting environmental change impacts. Copyright © 2016 The Authors Hydrological Processes Published by John Wiley & Sons Ltd.     

Field investigation and modelling of coupled stream discharge and shallow water‐table dynamics in a small Mediterranean catchment (Sardinia)

In the semi‐arid Mediterranean environment, the rainfall–runoff relationships are complex because of the markedly irregular patterns in rainfall, the seasonal mismatch between evaporation and rainfall, and the spatial heterogeneity in landscape properties. Watersheds often display considerable non‐linear threshold behavior, which still make runoff generation an open research question. Our objectives in this context were: to identify the primary processes of runoff generation in a small natural catchment; to test whether a physically based model, which takes into consideration only the primary processes, is able to predict spatially distributed water‐table and stream discharge dynamics; and to use the hydrological model to increase our understanding of runoff generation mechanisms. The observed seasonal dynamics of soil moisture, water‐table depth, and stream discharge indicated that Hortonian overland‐flow was negligible and the main mechanism of runoff generation was saturated subsurface‐flow. This gives rise to base‐flow, controls the formation of the saturated areas, and contributes to storm‐flow together with saturation overland‐flow. The distributed model, with a 1D scheme for the kinematic surface‐flow, a 2D sub‐horizontal scheme for the saturated subsurface‐flow, and ignoring the unsaturated flow, performed efficiently in years when runoff volume was high and medium, although there was a smoothing effect on the observed water‐table. In dry years, small errors greatly reduced the efficiency of the model. The hydrological model has allowed to relate the runoff generation mechanisms with the land‐use. The forested hillslopes, where the calibrated soil conductivity was high, were never saturated, except at the foot of the slopes, where exfiltration of saturated subsurface‐flow contributed to storm‐flow. Saturation overland‐flow was only found near the streams, except when there were storm‐flow peaks, when it also occurred on hillslopes used for pasture, where soil conductivity was low. The bedrock–soil percolation, simulated by a threshold mechanism, further increased the non‐linearity of the rainfall–runoff processes. Copyright © 2013 John Wiley & Sons, Ltd.     

Temporal trends of bulk precipitation and stream water chemistry (1977–1997) in a small forested area,Krusné hory,northern Bohemia,Czech Republic

The Krusné hory (Erzgebirge or Ore Mountains) has been heavily affected by high atmospheric pollutant deposition caused by fossil fuel combustion in an adjacent Tertiary coal basin. Long‐term routine sampling of bulk precipitation (1977–1996) and stream water (1977–1998) in a forested area on the south‐eastern slope of the mountains were used to evaluate trends and patterns in solute concentration and flux with respect to controlling processes. From 1977 to 1996, the annual volume‐weighted Ca²⁺ and SOconcentrations decreased in bulk precipitation. However, after 1989, when a pronounced and continuous decrease occurred in coal production, annual volume‐weighted concentrations decreased for most solutes, except H⁺. The concentration decreases were marked, with 1996 levels at or below 50% of those in 1989. The lack of a trend in H⁺ is attributed to similar decreases in both acid anions and neutralizing base cations. Stream water concentrations of most solutes, i.e. H⁺, Ca²⁺, Mg²⁺, SONOwere highest at the onset of sampling in 1977, decreased markedly from 1977 to 1983 and decreased more gradually from 1983 to 1998. The spruce forest die‐back and removal reduced dry deposition of these solutes by reducing the filtering action, which was provided by the forest canopy. A notable decrease in stream water Ca²⁺ concentrations occurred after 1995 and may be due to the depletion of Ca²⁺, which was provided by catchment liming in 1986, 1988 and 1989. Solute flux trends in bulk atmospheric deposition and stream water generally were not significant and the lack of trend is attributed to the large interannual variability in precipitation quantity and runoff, respectively. All solutes except Na⁺ varied seasonally. The average seasonal concentrations varied between the solutes, but for most solutes were highest in winter and spring and lowest in summer, correlating with the seasonal trend in runoff. For Ca²⁺, Mg²⁺ and SOthe concentration minimum occurs in September and the maximum occurs in February or March, correlating with the seasonal baseflow. These solutes are primarily controlled by the contribution of soil water and groundwater to stream flow. During snowmelt, the meltwater generally causes concentrations to decrease as soil water and groundwater are diluted. For NO₃ , average minimum concentrations occur in August at the end of the growing season concurrent with the lowest stream flow, and the maximum occurs in February and March with high stream flow during snowmelt. Seasonal stream water NOconcentration variations are large compared with the long‐term decrease. Copyright © 1999 John Wiley & Sons, Ltd.     

The use of small‐format and low‐altitude aerial photos for the realization of high‐resolution DEMs in mountainous areas: application to the Super‐Sauze earthflow (Alpes‐de‐Haute‐Provence,France)

Geomorphologists have to make choices and compromises, as acquisition techniques of geometrical information are numerous, depending on the specific complexity of the targeted three‐dimensional objects and the requirements of the end user. This article presents the methodology and the results over a well known and documented site. This ready‐to‐use, low‐altitude, aerial photo methodology reveals itself to be a satisfying compromise between cost, accuracy and difficulty of implementation. The selected equipment package is light enough to enable a quick reaction to unexpected events and the tools and methods are competitive with field acquisition techniques. An evaluation has demonstrated a sub‐metric accuracy for the final result. Copyright © 2002 John Wiley & Sons, Ltd.     

Evaluating the use of a gridded climate surface for modelling groundwater recharge in a semi‐arid region (Okanagan Basin,Canada)

Spatially distributed groundwater recharge was simulated for a segment of a semi‐arid valley using three different treatments of meteorological input data and potential evapotranspiration (PET). For the same area, timeframe, land cover characteristics and soil properties, groundwater recharge was estimate using (i) single‐station climate data with monthly PET calculated by the Thornthwaite method; (ii) single‐station climate data with daily PET calculated by the Penman–Monteith method; and (iii) daily gridded climate data with spatially distributed PET calculated using the Penman–Monteith method. For each treatment, the magnitude and distribution of actual evapotranspiration (AET) for summer months compared well with those estimated for a 5‐year crop study, suggesting that the near‐surface hydrological processes were replicated and that subsequent groundwater recharge rates are realistic. However, for winter months, calculated AET was near zero when using the Thornthwaite PET method. Mean annual groundwater recharge varied from ～3·2 to 10·0 mm when PET was calculated by the Thornthwaite method, and from ～1·8 to 7·5 mm when PET was calculated by the Penman–Monteith method. Comparisons of bivariate plots of seasonal recharge rates estimated from single‐station versus gridded surface climate reveal that there is greater variability between the different methods for spring months, which is the season of greatest recharge. Furthermore, these seasonal differences are shown to provide different results when compared to the depth to water table, which could lead to different results of evaporative extinction depth. These findings illustrate potential consequences of using different approaches for representing spatial meteorological input data, which could provide conflicting predictions when modelling the influence of climate change on groundwater recharge. Copyright © 2010 John Wiley & Sons, Ltd.     

Schmidt‐hammer exposure‐age dating (SHD) of snow‐avalanche impact ramparts in southern Norway: approaches,results and implications for landform age,dynamics and development

Schmidt‐hammer exposure‐age dating (SHD) was applied to the problem of dating the diachronous surfaces of five distal river‐bank boulder ramparts deposited by snow avalanches plunging into the Jostedøla and Sprongdøla rivers in the Jostedalsbreen region of southern Norway. Approaches to local high‐precision linear age calibration, which controlled in different ways for boulder roundness, were developed. The mean age (SHD_mean) and the maximum age (SHD_max) of surface boulders were estimated for whole ramparts, crests and distal fringes. Interpretation was further assisted by reference to R‐value distributions. SHD_mean ages (with 95% confidence intervals) ranged from 520 ± 270 years to 5375 ± 965 years, whereas SHD_max ages (expected to be exceeded by <5% of surface boulders) ranged from 675 to 9065 years. SHD ages from the Jostedøla ramparts tended to be older than those associated with the Sprongdøla, rampart crests were younger than the respective distal fringes, and use of relatively rounded boulders yielded more consistent SHD ages than angular boulders. The SHD_mean ages indicate differences in recent levels of snow‐avalanche activity between ramparts and provide insights into rampart dynamics as boulders are deposited on rampart crests and, in smaller numbers, on the distal fringes. SHD_max ages provide minimum age estimates of rampart age (i.e. the time elapsed since the ramparts began to form) and suggest that at least some of the ramparts have been developing since the early Holocene. Copyright © 2015 John Wiley & Sons, Ltd.     

A comparison of groundwater recharge estimation methods in a semi‐arid,coastal avocado and citrus orchard (Ventura County,California)

We assess the relative merits of application of the most commonly used field methods (soil‐water balance (SWB), chloride mass balance (CMB) and soil moisture monitoring (NP)) to determine recharge rates in micro‐irrigated and non‐irrigated areas of a semi‐arid coastal orchard located in a relatively complex geological environment. Application of the CMB method to estimate recharge rates was difficult owing to the unusually high, variable soil‐water chloride concentrations. In addition, contrary to that expected, the chloride concentration distribution at depths below the root zone in the non‐irrigated soil profiles was greater than that in the irrigated profiles. The CMB method severely underestimated recharge rates in the non‐irrigated areas when compared with the other methods, although the CMB method estimated recharge rates for the irrigated areas, that were similar to those from the other methods, ranging from 42 to 141 mm/year. The SWB method, constructed for a 15‐year period, provided insight into the recharge process being driven by winter rains rather than summer irrigation and indicated an average rate of 75 mm/year and 164 mm/year for the 1984 – 98 and 1996 – 98 periods, respectively. Assuming similar soil‐water holding capacity, these recharge rates applied to both irrigated and non‐irrigated areas. Use of the long period of record was important because it encompassed both drought and heavy rainfall years. Successful application of the SWB method, however, required considerable additional field measurements of orchard ET_c, soil‐water holding capacity and estimation of rainfall interception – runoff losses. Continuous soil moisture monitoring (NP) was necessary to identify both daily and seasonal seepage processes to corroborate the other recharge estimates. Measured recharge rates during the 1996 – 1998 period in both the orchards and non‐irrigated site averaged 180 mm/year. The pattern of soil profile drying during the summer irrigation season, followed by progressive wetting during the winter rainy season was observed in both irrigated and non‐irrigated soil profiles, confirming that groundwater recharge was rainfall driven and that micro‐irrigation did not ‘predispose’ the soil profile to excess rainfall recharge. The ability to make this recharge assessment, however, depended on making multiple field measurements associated with all three methods, suggesting that any one should not be used alone. Copyright © 2000 John Wiley & Sons, Ltd.     

Impact of an inter‐basin water transfer and reservoir operation on a karst open streamflow hydrological regime: an example from the Dinaric karst (Croatia)

This paper describes the hydrological changes caused by inter‐basin water transfer and the reservoir development on the hydrological regimes of two rivers. The Sabljaki Reservoir in the Zagorska Mre?nica River and the Bukovik Reservoir in the upper Dobra River began operation in 1959. Both are part of the hydroelectric power plant (HEPP) Gojak, whose installed capacity is 50 m³/s. Their water volumes at the spillway altitudes of 320·10 and 320·15 m a. s. l. are 3·3 × 10⁶ and 0·24 × 10⁶ m³ respectively. Both the Dobra and Mre?nica Rivers are losing, sinking and underground karst rivers. A 9376‐m‐long tunnel provides water from the Sabljaki Reservoir to the HEPP Gojak, which was constructed in the Lower Dobra River. The Sabljaki Reservoir is located in the Pla?ki karst polje, while the Bukovik Reservoir is located in the neighbouring Ogulin karst polje. The consequences of the inter‐basin water transfer are strong and have caused abrupt changes in the hydrological regimes of the downstream sections of both rivers. At the same time, the construction and development of both the reservoirs have also caused hydrological changes to the upstream section of the Upper Dobra River. Copyright © 2010 John Wiley & Sons, Ltd.