Effects of mid‐twenty‐first century climate and land cover change on the hydrology of the Puget Sound basin,Washington

The distributed hydrology–soil–vegetation model (DHSVM) was used to study the potential impacts of projected future land cover and climate change on the hydrology of the Puget Sound basin, Washington, in the mid‐twenty‐first century. A 60‐year climate model output, archived for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), was statistically downscaled and used as input to DHSVM. From the DHSVM output, we extracted multi‐decadal averages of seasonal streamflow, annual maximum flow, snow water equivalent (SWE), and evapotranspiration centred around 2030 and 2050. Future land cover was represented by a 2027 projection, which was extended to 2050, and DHSVM was run (with current climate) for these future land cover projections. In general, the climate change signal alone on sub‐basin streamflow was evidenced primarily through changes in the timing of winter and spring runoff, and slight increases in the annual runoff. Runoff changes in the uplands were attributable both to climate (increased winter precipitation, less snow) and land cover change (mostly reduced vegetation maturity). The most climatically sensitive parts of the uplands were in areas where the current winter precipitation is in the rain–snow transition zone. Changes in land cover were generally more important than climate change in the lowlands, where a substantial change to more urbanized land use and increased runoff was predicted. Both the annual total and seasonal distribution of freshwater flux to Puget Sound are more sensitive to climate change impacts than to land cover change, primarily because most of the runoff originates in the uplands. Both climate and land cover change slightly increase the annual freshwater flux to Puget Sound. Changes in the seasonal distribution of freshwater flux are mostly related to climate change, and consist of double‐digit increases in winter flows and decreases in summer and fall flows. Copyright © 2010 John Wiley & Sons, Ltd.     

Flows and sediment dynamics in the Ganga River under present and future climate scenarios

Identification of factors controlling sediment dynamics under natural flow regimes can establish a baseline for quantifying effects of present day hydrological alteration and future climate change on sediment delivery and associated flooding. The process-based INCA-Sediment model was used to simulate Ganga River sediment transport under baseline conditions and to quantify possible future changes using three contrasting climate scenarios. Construction of barrages and canals has significantly altered natural flow regimes, with profound consequences for sediment transport. Projected increases in future monsoonal precipitation will lead to higher peak flows, increasing flood frequency and greater water availability. Increased groundwater recharge during monsoon periods and greater rates of evaporation due to increased temperature complicate projections of water availability in non-monsoon periods. Rainfall and land surface interaction in high-relief areas drive uncertainties in Upper Ganga sediment loads. However, higher monsoonal peak flows will increase erosion and sediment delivery in western and lower reaches.     

Understanding land use and cover change impacts on run‐off and sediment load at flood events on the Loess Plateau,China

The Loess Plateau has been experiencing large‐scale land use and cover changes (LUCCs) over the past 50 years. It is well known about the significant decreasing trend of annual streamflow and sediment load in the catchments in this area. However, how surface run‐off and sediment load behaved in response to LUCC at flood events remained a research question. We investigated 371 flood events from 1963 to 2011 in a typical medium‐sized catchment within the Plateau in order to understand how LUCC affected the surface run‐off generation and sediment load and their behaviours based on the analysis of return periods. The results showed that the mean annual surface run‐off and sediment load from flood events accounted for 49.6% and 91.8% of their mean annual totals. The reduction of surface run‐off and associated sediment yield in floods explained about 85.0% and 89.2% of declines in the total annual streamflow and sediment load, respectively. The occurrences of flood events and peak sediment concentrations greater than 500 kg/m³ showed a significantly downward trend, yet the counterclockwise loop events still dominated the flood event processes in the catchment. The results suggest that LUCC over the past 50 years resulted in significant changes in the water balance components and associated soil erosion and sediment transportation in the catchment. This was achieved mainly by reducing surface run‐off and sediment yield during floods with return period of less than 5 years. Run‐off–sediment load behaviour during the extreme events with greater than 10‐year return periods has not changed. Outcomes from this study are useful in understanding the eco‐hydrological processes and assisting the sustainable catchment management and land use planning on the Loess Plateau, and the methodologies are general and applicable to similar areas worldwide.     

Insight into sediment transport processes on saline rangeland hillslopes using three‐dimensional soil microtopography changes

In arid and semi‐arid rangeland environments, an accurate understanding of runoff generation and sediment transport processes is key to developing effective management actions and addressing ecosystem response to changes. Yet, many primary processes (namely sheet and splash and concentrated flow erosion, as well as deposition) are still poorly understood due to a historic lack of measurement techniques capable of parsing total soil loss into these primary processes. Current knowledge gaps can be addressed by combining traditional erosion and runoff measurement techniques with image‐based three‐dimensional (3D) soil surface reconstructions. In this study, data (hydrology, erosion and high‐resolution surface microtopography changes) from rainfall simulation experiments on 24 plots in saline rangelands communities of the Upper Colorado River Basin were used to improve understanding on various sediment transport processes. A series of surface change metrics were developed to quantify and characterize various erosion and transport processes (e.g. plot‐wide versus concentrated flow detachment and deposition) and were related to hydrology and biotic and abiotic land surface characteristics. In general, erosivity controlled detachment and transport processes while factors modulating surface roughness such as vegetation controlled deposition. The extent of the channel network was a positive function of slope, discharge and vegetation. Vegetation may deflect runoff in many flow paths but promoted deposition. From a management perspective, this study suggests that effective runoff soil and salt load reduction strategies should aim to promote deposition of transported sediments rather than reducing detachment which might not be feasible in these resource‐limited environments. Copyright © 2016 John Wiley & Sons, Ltd.     

Reappraisal of sediment dynamics in the Lower Mekong River,Cambodia

The Mekong Basin in southeast Asia is facing rapid development, impacting its hydrology and sediment dynamics. Although the understanding of the sediment transport rates in the Mekong is gradually growing, the sediment dynamics in the lower Mekong floodplains (downstream from Kratie) are poorly understood. The aim of this study is to conduct an analysis to increase the understanding of the sediment dynamics at the Chaktomuk confluence of the Mekong River, and the Tonle Sap River in the Lower Mekong River in Cambodia. This study is based on the data from a detailed field survey over the three hydrological years (May 2008–April 2011) at the two sites (the Mekong mainstream and the Tonle Sap River) at the Chaktomuk confluence. We further compared the sediment fluxes at Chaktomuk to an upstream station (i.e. Mukdahan) with longer time series. Inflow sediment load towards the lake was lower than that of the outflow, with a ratio on average of 84%. Although annually only a small amount of sediment load from the Tonle Sap contributes to the delta (less than 15%), its share is substantial during the February–April period. The annual sediment load transport from the confluence to the delta in 2009 and 2010 accounted for 54 and 50 Mt, respectively. This was on average only 55% of the sediment fluxes measured at Mukdahan, a more upstream station. Furthermore when compared to sediment loads further downstream at the Cambodia–Vietnam border, we found that the suspended sediment flux continued to decline towards the South China Sea. Our findings thus indicate that the sediment load to the South China Sea is much lower than the previous estimate 150–160 Mt/yr. Copyright © 2014 John Wiley & Sons, Ltd.     

Numerical modeling of bedload and suspended load contributions to morphological evolution of the Seine Estuary (France)

This numerical modeling study (i) assesses the influence of the sediment erosion process on the sediment dynamics and subsequent morphological changes of a mixed-sediment environment, the macrotidal Seine estuary, when non-cohesive particles are dominant within bed mixtures (non-cohesive regime), and (ii) investigates respective contributions of bedload and suspended load in these dynamics. A three dimensional (3D) process-based morphodynamic model was set up and run under realistic forcings (including tide, waves, wind, and river discharge) during a 1-year period. Applying erosion homogeneously to bed sediment in the non-cohesive regime, i.e., average erosion parameters in the erosion law (especially the erodibility parameter, E₀), leads to higher resuspension of fine sediment due to the presence of coarser fractions within mixtures, compared to the case of an independent treatment of erosion for each sediment class. This results in more pronounced horizontal sediment flux (two-fold increase for sand, +30% for mud) and erosion/deposition patterns (up to a two-fold increase in erosion over shoals, generally associated with some coarsening of bed sediment). Compared to observed bathymetric changes, more relevant erosion/deposition patterns are derived from the model when independent resuspension fluxes are considered in the non-cohesive regime. These results suggest that this kind of approach may be more relevant when local grain-size distributions become heterogeneous and multimodal for non-cohesive particles. Bedload transport appears to be a non-dominant but significant contributor to the sediment dynamics of the Seine Estuary mouth. The residual bedload flux represents, on average, between 17 and 38% of the suspended sand flux, its contribution generally increasing when bed sediment becomes coarser (can become dominant at specific locations). The average orientation of residual fluxes and erosion/deposition patterns caused by bedload generally follow those resulting from suspended sediment dynamics. Sediment mass budgets cumulated over the simulated year reveal a relative contribution of bedload to total mass budgets around 25% over large erosion areas of shoals, which can even become higher in sedimentation zones. However, bedload-induced dynamics can locally differ from the dynamics related to suspended load, resulting in specific residual transport, erosion/deposition patterns, and changes in seabed nature.     

The responses of hydrological processes and sediment yield to land‐use and climate change in the Be River Catchment,Vietnam

In this study, we investigated the responses of hydrology and sediment yield with impacts of land‐use and climate change scenarios in the Be River Catchment, using the Soil and Water Assessment Tool (SWAT) hydrological model. The calibration and validation results indicated that the SWAT model is a powerful tool for simulating the impact of environmental change on hydrology and sediment yield in this catchment. The hydrologic and sediment yield responses to land‐use and climate changes were simulated based on the calibrated model. The results indicated that a 16.3% decrease in forest land is likely to increase streamflow (0.2 to 0.4%), sediment load (1.8 to 3.0%), and surface runoff (SURQ) (4.8 to 10.7%) and to decrease groundwater discharge (GW_Q) (3.5 to 7.9%). Climate change in the catchment leads to decreases in streamflow (0.7 to 6.9%) and GW_Q (3.0 to 8.4%), increase in evapotranspiration (0.5 to 2.9%), and changes in SURQ (?5.3 to 2.3%) and sediment load (?5.3 to 4.4%). The combined impacts of land‐use and climate changes decrease streamflow (2.0 to 3.9%) and GW_Q (12.3 to 14.0%), increase evapotranspiration (0.7 to 2.8%), SURQ (8.2 to 12.4%), and sediment load (2.0 to 7.9%). In general, the separate impacts of climate and land‐use changes on streamflow, sediment load, and water balance components are offset each other. However, SURQ and some component of subsurface flow are more sensitive to land‐use change than to climate change. Furthermore, the results emphasized water scarcity during the dry season and increased soil erosion during the wet season. Copyright © 2012 John Wiley & Sons, Ltd.     

Hydrologic‐response‐driven sediment transport at a regional scale,process‐based simulation

Assessing hydrologically driven erosion at regional scales from a process‐based perspective presents a significant challenge. Most regional‐scale erosion assessments are based upon a simple steady‐state hydrology foundation. For this study, the sediment transport version of the physics‐based Integrated Hydrology Model (InHM), excited by synthetically generated rainfall, was employed to assess long‐term hydrologically driven erosion for a regional‐scale island boundary‐value problem. The spatiotemporal dynamics of runoff generation, erosion, and deposition are illustrated through saturation, water depth, velocity, and sediment concentration results. The simulations demonstrate that process‐based assessment for concept development is both feasible and tractable at regional spatial and human time scales. Copyright © 2011 John Wiley & Sons, Ltd.     

Predictive modeling in sediment transportation across multiple spatial scales in the Jialing River Basin of China

This research models soil erosion and sediment transportation in the Jialing River Basin based on the Revised Universal Soil Loss Equation(RUSLE) with Geographic Information System(G1S) technology.Studies have shown that,the improved method based on the RUSLE model was effective in calculating and predicting the annual sediment transport rate in Jialing River Basin in consideration of the hydrological conditions causing the annual variability of soil loss and the changes in the underlying surface resulting from land management activities.Comparing the observed and simulated sediment loads in the period of 1989 and 1998,the simulation values showed a consistent trend with the observed values,and the relative errors were controlled at 20%or less.This shows that the model can be used to identify hotspot watersheds with different degree of sediment yield and help to make corresponding land use planning and soil and water conservation strategy,and thus help to reduce soil erosion in areas surrounding the Three Gorges Project and other reservoirs in other rivers.     

Temporal relations between meander deformation,water discharge and sediment fluxes in the floodplain of the Rio Beni (Bolivian Amazonia)

The Andean Cordillera and piedmont significantly influence river system and dynamics, being the source of many of the important rivers of the Amazon basin. The Beni River, whose upper sub‐catchments drain the Andean and sub‐Andean ranges, is a major tributary of the Madeira River. This study examines the river in the south‐western Amazonian lowlands of Bolivia, where it develops mobile meanders. Channel migration, meander‐bend morphology and ox‐bow lakes are analysed at different temporal and spatial scales. The first part of this study was undertaken with the aim to link the erosion–deposition processes in the active channel with hydrological events. The quantification of annual erosion and deposition areas shows high inter‐annual and spatial variability. In this study, we investigate the conditions of sediment exportation in the river in relation to three hydrological parameters (flood intensity, date of discharge peak and duration of the bank‐full stage level). The second part of this study, focusing on the abandoned meanders, analyses the cutoff processes and the post‐abandonment evolution during 1967–2001. This approach shows the influence of the active channel behaviour on the sediment diffusion and sequestration of the abandoned meanders and allows us to build a first model of the contemporary floodplain evolution. Copyright © 2006 John Wiley & Sons, Ltd.     

The job of the river

Earth scientists have traditionally conceptualized rivers and streams as geomorphic machines, whose role is to transfer sediment and to sculpt the landscape. Steady‐state relationships between sediment supply and transport capacity have traditionally been considered normative in fluvial systems. Rivers are hydrological entities, however, whose function is to redistribute excess moisture on land. The geomorphic work of the river – erosion, transport, deposition, etc. – is a byproduct of the hydrological job of the river. There is therefore no reason to expect any particular relationship between sediment supply and transport capacity to develop as a normative condition in fluvial systems. The apparent steady‐state equilibrium slope adjustments of rivers are a byproduct of four basic phenomena: (1) hydraulic selection, which favors channels and branching networks over other flux patterns; (2) water flows along the available path of least resistance; (3) energy dissipation; and (4) finite relaxation times. Recognizing converging trends of stream power or slope and sediment supply as common (but far from inevitable) side effects rather than self‐regulation has important implications for interpreting and predicting fluvial systems, and for river management and restoration. Such trends are variable, transient, contingent, and far from universal. Where they occur, they are an emergent byproduct of fundamental physical mechanisms, not a goal function or attractor state. Copyright © 2009 John Wiley & Sons, Ltd.     

Erosion, sediment transportation and accumulation in rivers

The present paper analyses the interrelation between erosion, sediment transportation and accumulation proposed by N. I. Makkaveyev （1908-1983） and its further development in modem studies of river channel processes in Russia. Spatio-temporal linkages between erosion and accumulation are defined considering channel processes at different scales - river longitudinal profile, channel morphological patterns, alluvial bedforms （bars, dunes） and individual sediment particles. Relations between river geomorphic activity, flow transportation capacity and sediment budgets are established （sediment input and output; channel bed erosion and sediment entrainment into flow - termination of sediment transport and its deposition）. Channel planforms, floodplain segments separated by the latter and alluvial channel bedforms are shown to be geomorphic expressions of sediment transport process at different spatial and temporal scales. This paper is dedicated to the 100th anniversary of N. I. Makkaveyev, Professor of the Moscow State University, author of the book ＂River channel and erosion in its basin＂ （1955）. That book is regarded in Russia as the pioneering work which initiated the complex hydrological and geographical studies of channel processes and laid a basis for the theory of unified fluvial erosion-accumulation process.     

Linking hydrology and sediment dynamics of large alluvial rivers to landscape diversity in the Ganga dispersal system,India

Discharge and sediment load data for several stations along the Ganga River and its major tributaries in the western Ganga plains (WGP) for a period of ~30 years have been analysed to understand the hydrological characteristics and sediment dynamics. In terms of hydrology, the rivers are less flood‐prone than believed, exceeding bankfull discharges less frequently than the expected 1.5 year return interval. This has been attributed to the rivers of this region occupying incised valleys formed in the Late Quaternary period. Rivers draining the WGP are supply‐limited systems compared to those draining the eastern Ganga plains (EGP) which have been characterized as transport‐limited systems. We suggest that such geomorphic diversity as a function of spatial variability in precipitation regime and hinterland geology has existed for at least the Late Quaternary period and they in turn influence the modern day hydrology of the river systems in a significant way. Copyright © 2016 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.     

Water flux and sediment transport within a forested landscape: the role of connectivity,subsurface flow,and slope length scale on transport mechanism

The connectivity and upscaling of overland runoff and sediment transport are important issues in hillslope hydrology to identify water flux and sediment transport within landscape. These processes are highly variable in time and space with regard to their interactions with vegetation and soil surface conditions. The generation of overland runoff and its spatial connectivity were examined along a slope to determine the variations in the transport mechanism of runoff and soil particles by rain splash and overland runoff. Field experiments were conducted by erosion plots on a steep hillslope at lengths of 5, 10, and 15 m. The overland runoff connectivity and flow transport distance decreased with the slope length, while spatial variability of infiltration increased significantly with the slope length. Observation of subsurface flow revealed that surface soil and litter layer could have important role in water transport. However, the surface soil water content and water flux transport along the slope was highly variable for different storm events; the variability was related to the complexity of the system, mainly by way of the initial wetness conditions and infiltration characteristics. Only net rain‐splashed soil was measurable, but examination of the water flux, overland runoff and sediment transport connectivity, characteristics of sheetwash, and the variability in spatial infiltration indicated an increase in the contribution of the rain splash transport mechanism along the slope. Copyright © 2013 John Wiley & Sons, Ltd.     

Spatiotemporal variations of suspended sediment transport in the upstream and midstream of the Yarlung Tsangpo River (the upper Brahmaputra), China

The Yarlung Tsangpo River, which flows from west to east across the southern part of the Tibetan Plateau, is the longest river on the plateau and an important center for human habitation in Tibet. Suspended sediment in the river can be used as an important proxy for evaluating regional soil erosion and ecological and environmental conditions. However, sediment transport in the river is rarely reported due to data scarcity. Results from this study based on a daily dataset of 3 years from four main stream gauging stations confirmed the existence of great spatiotemporal variability in suspended sediment transport in the Yarlung Tsangpo River, under interactions of monsoon climate and topographical variability. Temporally, sediment transport or deposition mainly occurred during the summer months from July to September, accounting for 79% to 93% of annual gross sediment load. This coincided with the rainy season from June to August that accounted for 51% to 80% of annual gross precipitation and the flood period from July to September that accounted for approximately 60% of annual gross discharge. The highest specific sediment yield of 177.6 t/km²/yr occurred in the upper midstream with the highest erosion intensity. The lower midstream was dominated by deposition, trapping approximately 40% of total sediment input from its upstream area. Sediment load transported to the midstream terminus was 10.43 Mt/yr with a basin average specific sediment yield of 54 t/km²/yr. Comparison with other plateau‐originated rivers like the upper Yellow River, the upper Yangtze River, the upper Indus River, and the Mekong River indicated that sediment contribution from the studied area was very low. The results provided fundamental information for future studies on soil and water conservation and for the river basin management. Copyright © 2017 John Wiley & Sons, Ltd.     

Evaluating the effect of land use changes on soil erosion and sediment yield using a grid‐based distributed modelling approach

Processes of soil erosion and sediment transport are strongly influenced by land use changes so the modelling of land use changes is important with respect to the simulation of soil degradation and its on‐site and off‐site consequences. The reliability of simulation results from erosion models is circumscribed by considerable spatial variation in many parameters. However, most of the currently widely used erosion models at the mesoscale are semidistributed, which leads to difficulties in incorporating a high degree of spatial information, especially land use information, so that the effects of land use changes on soil erosion have hitherto not been investigated in detail using these models. In this article, a grid‐based distributed erosion and sediment transport model is introduced, which simulates the spatial pattern of erosion and deposition rates and sediment transport processes in river channels. In this model, land use affects soil erosion through altering soil loss and influencing sediment delivery. Simulated soil erosion for events recorded in 1989 and 1996 in the Lushi basin in China was analyzed by comparing it with historical land use maps. The results indicated that even relatively minor land use changes had a significant effect on regional soil erosion rates and sediment transport to rivers. The average erosion rate increased from 1989 to 1996, after the transformation of forest to farmland. The results of the study suggest that the proposed soil erosion model can be applied in similar river basins. Copyright © 2011 John Wiley & Sons, Ltd.     

Temporal variation of suspended sediment load in the Pearl River due to human activities

Data on sediment flux at three hydrologic stations from the 1950s to 2006 are utilized to study the decadal,annual,and monthly variations in suspended sediment load delivered from the Pearl River to the ocean.Results show that variations in sediment flux from three main tributaries,including the West River,the North River and the East River,are spatially non-uniform.Since nearly 90%of the suspended sediment load comes from the West River,its variation has dominated the overall tendency of sediment flux in the entire Pearl River.Although a significant decreasing trend exists in the annual variation of the total sediment flux,the decadal change can be divided into an increasing phase and a decreasing phase,with the turning point between the two phases in the late 1980s.From the 1950s to the 1980s,the average annual river sediment flux increased by 30.43%.However,sediment flux has decreased significantly since the 1990s,with the average sediment flux being 38.60%less in the 2000s than that in the 1950s.The current sediment flux is also 52.93%less than its peak in the 1980s. The monthly variation pattern of the suspended sediment load transport to the sea is more interesting. For the West River,all months show a decreasing trend,and for most months the reduction values are significant.However,for the East River the sediment load shows a decrease trend in the dry season and an increase trend in the wet season.The method of regression analysis was used to study the influence of precipitation in the variation on the sediment flux.It was found that the climate change is not the main driving force behind the variation in suspended sediment load.Before the 1990s, intensive land use destroyed the vulnerable ecosystem of the upper Pearl River,and speeded up the process of rocky desertification.Consequently,aggravated soil erosion caused an increase in suspended sediment load.However,sediment retention within reservoirs had begun to play a dominant role after the massive construction of large dams after 1990,and resulted in a decrease in the suspended sediment load delivered to the ocean.     

Implications of climate change in the twenty‐first century for simulated magnitude and frequency of bed‐material transport in tributaries of the Saint‐Lawrence River

More frequent extreme flood events are likely to occur in many areas in the twenty‐first century due to climate change. The impacts of these changes on sediment transport are examined at the event scale using a 1D morphodynamic model (SEDROUT4‐M) for three tributaries of the Saint‐Lawrence River (Québec, Canada) using daily discharge series generated with a hydrological model (HSAMI) from three global climate models (GCMs). For all tributaries, larger flood events occur in all future scenarios, leading to increases in bed‐material transport rates, number of transport events and number of days in the year where sediment transport occurs. The effective and half‐load discharges increase under all GCM simulations. Differences in flood timing within the tributaries, with a shift of peak annual discharge from the spring towards the winter, compared to the hydrograph of the Saint‐Lawrence River, generate higher sediment transport rates because of increased water surface slope and stream power. Previous research had shown that channel erosion is expected under all GCMs' discharge scenarios. This study shows that, despite lower bed elevations, flood risk is likely to increase as a result of higher flood magnitude, even with falling base level in the Saint‐Lawrence River. Copyright © 2010 John Wiley & Sons, Ltd.     

How does afforestation affect the hydrology of a blanket peatland? A modelling study

Over the last century, afforestation in Ireland has increased from 1% of the land area to 10%, with most plantations on upland drained blanket peatlands. This land use change is considered to have altered the hydrological response and water balance of upland catchments with implications for water resources. Because of the difficulty of observing these long‐term changes in the field, the aim of this study was to utilize a hydrological model to simulate the rainfall runoff processes of an existing pristine blanket peatland and then to simulate the hydrology of the peatland if it were drained and afforested. The hydrological rainfall runoff model (GEOtop) was calibrated and validated for an existing small (76 ha) pristine blanket peatland in the southwest of Ireland for the 2‐year period, 2007–2008. The current hydrological response of the pristine blanket peatland catchment with regard to streamflow and water table (WT) levels was captured well in the simulations. Two land use change scenarios of afforestation were also examined, (A) a young 10‐year‐old and (B) a semi‐mature 15‐year‐old Sitka Spruce forest. Scenario A produced similar streamflow dynamics to the pristine peatland, whereas total annual streamflow from Scenario B was 20% lower. For Scenarios A and B, on an annual average basis, the WT was drawn down by 16 and 20 cm below that observed in the pristine peatland, respectively. The maximum WT draw down in Scenario B was 61 cm and occurred in the summer months, resulting in a significant decrease in summer streamflow. Occasionally in the winter (following rainfall), the WT for Scenario B was just 2 cm lower than the pristine peatland, which when coupled with the drainage networks associated with afforestation led to higher peak streamflows. Copyright © 2012 John Wiley & Sons, Ltd.