Analysis of groundwater exchange for a large plains river in Colorado (USA)

Complete daily water budget information was assembled for a 105 km segment of the South Platte River in the plains region below Denver, CO, for the period 1983–1993. The data were used in testing the possibility that dependence of alluvial exchange mechanisms on stage height, as shown by models of alluvial exchange, allows alluvial exchange to be predicted continuously over a given reach through use of statistical information on river discharge. The study segment was divided into an upper and a lower reach; daily alluvial exchanges for each reach were estimated by the method of residuals. The two reaches show small (15%) but statistically significant annual differences in rates of exchange. For each reach, there is a seasonal pattern (2·5‐fold oscillation) in alluvial discharge to the channel, reflecting seasonality in recharge of the alluvium by irrigation. At discharges up to 40 m³/s (82nd percentile), alluvial discharge to the channel occurs at a rate independent of river discharge. Above 40 m³/s, net alluvial discharge into the channel is progressively reduced; at 60 m³/s (92nd percentile) there is no net alluvial exchange. At still higher river discharges, water is lost to the alluvium through bank storage at a rate that is linearly related to the logarithm of discharge. Annually, alluvial discharge accounts for 15–18% of water entering the study segment, and alluvial recharge through bank storage accounts for 2–4% of water leaving the segment. Alluvial recharge through bank storage at the highest discharges can, however, exceed low‐flow alluvial discharge rates by five‐fold over short intervals. Even though daily alluvial exchanges vary widely, they can be estimated at r² values above 80% on the basis of reach, season, and river discharge. Copyright © 2001 John Wiley & Sons, Ltd.     

Spectral responses of water level in tidal river and groundwater

The water level of five river stages and seven groundwater wells in the Taipei Basin were analysed by spectral analysis in the frequency domain. The diurnal, semi‐diurnal and quarter‐diurnal tidal components of the Tanshui River appear to relate closely to astronomical tides as K₁, M₂ and M₄, respectively. It is also found that the diurnal component reveals a reversed phase angle in the middle section of the Tanshui River; the phase of the quarter‐diurnal component is also found to be reversed at stations upstream in the Tanshui River and Hsintien Stream. It is believed that these phenomena could be caused by local variation in the river channel topography. The autospectrum and cross‐spectrum between groundwater elevation and nearby river stage were observed to correlate highly with the frequency of the astronomical tides K₁, M₂ and M₄. From the study of the phase shift and time lag of water level fluctuations at river stages and groundwater wells, it was found that the tidal effects of diurnal, semi‐diurnal, and quarter‐diurnal components were significantly different. The relationships between phase and the fluctuated range of atmospheric pressure and water level imply that change in atmospheric pressure does not affect water level fluctuation in the river stage and groundwater well. Copyright © 1999 John Wiley & Sons, Ltd.     

Analysis and integrated modelling of groundwater infiltration to sewer networks

Infiltration of groundwater to sewer systems is a problem for the capacity of the system as well as for treatment processes at waste water treatment plants. This paper quantifies the infiltration of groundwater to a sewer system in Frederikshavn Municipality, Denmark, by measurements of sewer flow and novel model set‐up, which simulates the interaction between groundwater and sewer flow. The study area has a separate waste water sewer system, but the discharged volumes from the system are approximately twice the volumes from a tight system without infiltration. The model set‐up makes use of two commercial models: mike she for simulation of groundwater transport and mike urban (mouse ) [DHI, Hørsholm, Denmark] for simulation of sewer flow. By simulating the groundwater level and calibrating infiltration coefficients against sewer flow measurements, it has been possible to estimate the average infiltration to the sewer system with satisfying results. The infiltration processes are indeed complicated and to a large degree heterogeneous throughout the sewer system. The paper shows contribution from both saturated and unsaturated groundwater zones, which makes the modelling process complex. Copyright © 2016 John Wiley & Sons, Ltd.     

Conceptual and numerical models for groundwater flow in an arid inland river basin

The Heihe River Basin (HRB) is an inland watershed in northwest China with a total area of approximately 130,000 km², stretching from the Qilian Mountains in the south to the oases and agricultural fields in the middle and further to the Gobi desert in the north bordering Mongolia. As part of a major ecohydrological research initiative to provide a stronger scientific underpinning for sustainable water management in arid ecosystems, a regional‐scale integrated ecological and hydrological model is being developed, incorporating the knowledge based on the results of environmental isotope tracer analysis and the multiscale observation datasets. The first step in the model development effort is to construct and calibrate a groundwater flow model for the middle and lower HRB where the oases and vegetation along the Heihe river corridor are highly dependent on groundwater. In this study, the software tool ‘Arc Hydro Groundwater’ is used to build and visualize a hydrogeological data model for the HRB that links all relevant spatiotemporal hydrogeological data in a unified geodatabase within the ArcGIS environment. From the conceptual model, a regional‐scale groundwater flow model has been developed using MODFLOW‐2005. Critical considerations in developing the flow model include the representation of mountainous terrains and fluvial valleys by individual model layers, treatment of aquifer heterogeneities across multiple scales and selection of proper observation data and boundary conditions for model calibration. This paper discusses these issues in the context of the Heihe River Basin, but the results and insights from this study will have important implications for other large, regional groundwater modelling studies, especially in arid and semiarid inland river basins. Copyright © 2014 John Wiley & Sons, Ltd.     

Meander hydrodynamics initiated by river restoration deflectors

River restoration projects have installed j‐hook deflectors along the outer bank of meander bends to reduce hydraulic erosion, and in this study we use a computational fluid dynamics (CFD) model to document how these deflectors initiate changes in meander hydrodynamics. We validated the CFD with streamwise and cross‐channel bankfull velocities from a 193° meander bend flume (inlet at 0°) with a fixed point bar and pool equilibrium bed but no j‐hooks, and then used the CFD to simulate changes to flow initiated by bank‐attached boulder j‐hooks (1^st attached at 70°, then a 2^nd at 160°). At bankfull and half bankfull flow the j‐hooks flattened transverse water surface slopes, formed backwater pools upstream of the boulders, and steepened longitudinal water slopes across the boulders and in the conveyance region off the mid‐channel boulder tip. Streamwise velocity and mass transport jets upstream of the j‐hooks were stilled, mid‐channel jets were initiated in the conveyance region, eddies with a cross‐channel axis formed below boulders, and eddies with a vertical axis were shed into wake zones downstream of the point bar and outer bank boulders. At half bankfull depth conveyance region flow cut toward the outer bank downstream of the j‐hook boulders and the secondary circulation cells were reshaped. At bankfull depth the j‐hook at 160° was needed to redirect bank‐impinging flow sent by the upstream j‐hook. The hooked boulder tip of both j‐hooks funneled surface flow into mid‐channel plunging jets, which reversed the secondary circulation cells and initiated 1 to 3 counter rotating cells through the entire meander. The main outer bank collision zone centered at 50° without the j‐hook was moved by the j‐hook to within and just beyond the 70° j‐hook boulder region, which displaced other mass transport zones downstream. J‐hooks re‐organized water surface slopes, streamwise and cross‐channel velocities, and mass transport patterns, to move shear stress from the outer bank and into the conveyance and mid‐channel zones at bankfull flow. At half bankfull flows a patch of high shear re‐attached to the outer bank below the downstream j‐hook. J‐hook geometry and placement within natural meanders can be analyzed with CFD models to help restoration teams reach design goals and understand hydraulic impacts. Copyright © 2011 John Wiley & Sons, Ltd.     

A coupled model for simulating surface water and groundwater interactions in coastal wetlands

Coastal wetlands are characterized by strong, dynamic interactions between surface water and groundwater. This paper presents a coupled model that simulates interacting surface water and groundwater flow and solute transport processes in these wetlands. The coupled model is based on two existing (sub) models for surface water and groundwater, respectively: ELCIRC (a three‐dimensional (3‐D) finite‐volume/finite‐difference model for simulating shallow water flow and solute transport in rivers, estuaries and coastal seas) and SUTRA (a 3‐D finite‐element/finite‐difference model for simulating variably saturated, variable‐density fluid flow and solute transport in porous media). Both submodels, using compatible unstructured meshes, are coupled spatially at the common interface between the surface water and groundwater bodies. The surface water level and solute concentrations computed by the ELCIRC model are used to determine the boundary conditions of the SUTRA‐based groundwater model at the interface. In turn, the groundwater model provides water and solute fluxes as inputs for the continuity equations of surface water flow and solute transport to account for the mass exchange across the interface. Additionally, flux from the seepage face was routed instantaneously to the nearest surface water cell according to the local sediment surface slope. With an external coupling approach, these two submodels run in parallel using time steps of different sizes. The time step (Δt_g) for the groundwater model is set to be larger than that (Δt_s) used by the surface water model for computational efficiency: Δt_g = M × Δt_s where M is an integer greater than 1. Data exchange takes place between the two submodels through a common database at synchronized times (e.g. end of each Δt_g). The coupled model was validated against two previously reported experiments on surface water and groundwater interactions in coastal lagoons. The results suggest that the model represents well the interacting surface water and groundwater flow and solute transport processes in the lagoons. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of intensive aquifers exploitation on groundwater salinity in coastal wetlands

The coastal plain of the Río de la Plata constitutes a large wetland which develops on the right margin of the river estuary. Anthropic activities such as intensive exploitation of groundwater carried out in the vicinity of the wetland can modify the natural hydrological regime. The aim of this work is to asses the effects of intensive aquifer exploitation in coastal wetlands using hydrogeological models. Such models allow to evaluate changes in the environmental conditions of wetland at regional level. The hydrogeological model exposed in this work shows how the intensive groundwater exploitation affects the wetland area, generating important variations both in the groundwater flows and in the salinity of the groundwater. Identification of these modifications to the environment is important to generate guidelines leading to minimize these affectations.     

Riverine groundwater discharge estimation in a dynamic river corridor using 222Rn

Groundwater discharge flux into rivers (riverine groundwater discharge or RGD) is essential information for the conservation and management of aquatic ecosystems and resources. One way to estimate area-integrated groundwater discharge into surface water bodies is to measure the concentration of a groundwater tracer within the water body. We assessed groundwater discharge using ²²²Rn, a tracer common in many surface water studies, through field measurements, surface water ²²²Rn mass balance model, and groundwater flow simulation, for the seldom studied but ubiquitous setting of a flooding river corridor. The investigation was conducted at the dam-regulated Lower Colorado River (LCR) in Austin, Texas, USA. We found that ²²²Rn in both the river water and groundwater in the river bank changed synchronously over a 12-hour flood cycle. A ²²²Rn mass balance model allowed for estimation of groundwater discharge into a 500-m long reach of the LCR over the flood. The groundwater discharge ranged between negative values (indicating recharge) to 1570 m³/h; groundwater discharge from groundwater flow simulations corroborated these estimates. However, for the dynamic groundwater discharge estimated by the ²²²Rn box model, assuming whether the groundwater ²²²Rn endmember was constant or dynamic led to notably different results. The resultant groundwater discharge estimates are also highly sensitive to river ²²²Rn values. We thus recommend that when using this approach to accurately characterize dynamic groundwater discharge, the ²²²Rn in near-stream groundwater should be monitored at the same frequency as river ²²²Rn. If this is not possible, the ²²²Rn method can still provide reasonable but approximate groundwater discharge given background information on surface water-groundwater exchange time scales.     

The influence of groundwater representation on hydrological simulation and its assessment using satellite‐based water storage variation

The interaction between surface water and groundwater is an important aspect of hydrological processes. Despite its importance, groundwater is not well represented in many land surface models. In this study, a groundwater module with consideration of surface water and groundwater dynamic interactions is incorporated into the distributed biosphere hydrological (DBH) model in the upstream of the Yellow River basin, China. Two numerical experiments are conducted using the DBH model: one with groundwater module active, namely, DBH_GW and the other without, namely, DBH_NGW. Simulations by two experiments are compared with observed river discharge and terrestrial water storage (TWS) variation from the Gravity Recovery and Climate Experiment (GRACE). The results show that river discharge during the low flow season that is underestimated in the DBH_NGW has been improved by incorporating the groundwater scheme. As for the TWS, simulation in DBH_GW shows better agreement with GRACE data in terms of interannual and intraseasonal variations and annual changing trend. Furthermore, compared with DBH_GW, TWS simulated in DBH_NGW shows smaller decreases during autumn and smaller increases in spring. These results suggest that consideration of groundwater dynamics enables a more reasonable representation of TWS change by increasing TWS amplitudes and signals and as a consequence, improves river discharge simulation in the low flow seasons when groundwater is a major component in runoff. Additionally, incorporation of groundwater module also leads to wetter soil moisture and higher evapotranspiration, especially in the wet seasons.     

Multiple‐indicator study of groundwater flow and chemistry and the impacts of river and paddy water on groundwater in the alluvial fan of the Tedori River,Japan

To investigate the source, flow paths, and chemistry of rich resources of high‐quality, shallow groundwater in the alluvial fan between the Tedori and Sai rivers in central Japan, we analysed stable isotope ratios of H, O, and Sr and concentrations of major dissolved ions and trace elements in groundwater, river water, and paddy water. The ⁸⁷Sr/⁸⁶Sr ratios of the groundwater are related to near‐surface geology: groundwater in sediment from the Tedori River has high ⁸⁷Sr/⁸⁶Sr ratios (>0.711), whereas that from the Sai River in the north of the fan has low ⁸⁷Sr/⁸⁶Sr ratios (<0.711). δ²H and δ¹⁸O values and ⁸⁷Sr/⁸⁶Sr ratios indicate that groundwater in the central and southern fans is recharged by the Tedori River, whereas recharge in the north is from the Sai River. Mg²⁺, Ca²⁺, Sr²⁺, HCO₃^?, and SO₄^2? concentrations and δ²H and δ¹⁸O values in the groundwater are high in the central fan and, except for the northern area, tend to increase with distance from the Tedori River. There are linear relationships between ⁸⁷Sr/⁸⁶Sr ratio and the reciprocal concentrations of Sr²⁺, Mg²⁺, and Ca²⁺. These geochemical characteristics suggest that as groundwater recharged from the Tedori River flows towards the central fan, it mixes with waters derived from precipitation and paddy water that have become enriched in these components during downward infiltration. These results are consistent with our hydrological analysis and numerical simulation of groundwater flow, thus verifying the validity of the model we used in our simulation of groundwater flow. Copyright © 2016 John Wiley & Sons, Ltd.     

Modelling the effects of spatial and temporal resolution of rainfall and basin model on extreme river discharge

Abstract

Important characteristics of an appropriate river basin model, intended to study the effect of climate change on basin response, are the spatial and temporal resolution of the model and the rainfall input. The effects of input and model resolution on extreme discharge of a large river basin are assessed to give some indication on appropriate resolutions. A simple stochastic rainfall model and a river basin model with uniform parameters and multiple rainfall input have been developed and applied to the River Meuse basin in northwestern Europe. The results show that the effect of model resolution on extreme river discharge is much greater than that of input resolution. The highest model resolution seems to be quite accurate in determining extreme discharge. Although the results should be interpreted with caution, they may give some indication of appropriate input and model resolutions for the determination of extreme discharge of a large river basin.     

Analysis of incorporating groundwater exchanges in hydrological models

In many catchments, the geographical demarcation does not coincide with the limits of the aquifers, so groundwater may be exchanged beyond their topographic boundaries. By studying groundwater exchanges, the natural resources of a catchment can be better assessed, and the divergences between hydrological models and measurements can be explained. The aim of this work is to reveal the importance of including groundwater exchanges in the hydrological modelling of some catchments, using a water balance model. For this purpose, a simple example is conducted. The so‐called parent model scheme is modified to only allow groundwater exchanges, and it is applied to the headwater of the Segura River Basin District, located in the southeast of Spain. This area is selected because groundwater plays an important role in surface hydrology. The results reveal that groundwater exchanges cannot be neglected in some catchments when assessing water resources because their integration in the hydrological model corrects errors in the water balance. Moreover, this paper proves that water balance models are a useful tool for estimating groundwater exchanges between catchments, which can be contrasted with more complex distributed models or isotopic tracers if there is enough information available. Copyright © 2015 John Wiley & Sons, Ltd.     

Simulated groundwater interaction with rivers and springs in the Heihe river basin

Surface water and groundwater in the Heihe river basin of China are interconnected and the pattern of water resources exploitation has a direct effect on the interaction of groundwater and surface water, especially on a downstream oasis. A three‐dimensional groundwater flow simulation model with eight model layers was established to simulate the regional groundwater flow in the multilayered aquifer system and the interaction among the rivers, springs, and groundwater. The model was calibrated not only with historical water levels but also with the investigated baseflow and spring flux. The simulation results of the numerical model match reasonably well with the observed groundwater levels, baseflow to rivers, and spring flux. The numerical simulation also demonstrates that the hydraulic connection between the river and the aquifers has transferred from the coupling to decoupling at some reaches. It is suggested that there is a vital need to reduce groundwater withdrawal and to rationalize the use of both groundwater and surface water in order to maintain sustainable development in the study area. Copyright © 2007 John Wiley & Sons, Ltd.     

A numerical model for estimating groundwater flux from subsurface temperature profiles

A simple numerical model is presented for estimating vertical groundwater flux from transient subsurface temperature profiles obtained from field measurements. The model developed utilizes the MacCormack scheme, which is based on the Finite Difference Method (FDM), for solving the governing partial differential equation of convection–diffusion heat transport with appropriate initial and boundary conditions within the subsurface. In order to validate the model, numerical solutions obtained for the study area located in the Nagoka plain, Japan are compared with the published measured data and results obtained by others. Results obtained show good agreement and fit the observed data with a correlation coefficient, R², of 0·88. The estimated groundwater flux is 1·85 × 10⁻⁷ m s⁻¹. Sensitivity analyses were also carried out to investigate the effect of variations in groundwater fluxes, thermal properties and the annual thermal variability due to climatic changes on the transient subsurface temperature profiles and to have a better understanding of the subsurface thermal dynamics. A substantial effect of annual climatic variability is observed on the temporal distributions of temperature depth profiles, and a better estimate of thermal parameters is required to estimate vertical groundwater flux. The largest change in subsurface temperature depth profiles due to groundwater flux over a year is within ± 4 °C. The influence of groundwater flux on subsurface temperature distributions in space and time may be more pronounced in areas where the top of the saturated layer fluctuates considerably. Variation in thermal diffusivity results in temperature change up to ± 1·5% and may cause change in groundwater flux estimate by ± 18%. The model presented has merits over analytical solutions (type curve matching techniques) in terms of suitability and applicability to real field problems, and can be a good asset to hydrological models as quantifying groundwater recharge or deducing it from other quantities, such as rainfall, evapotranspiration and runoff, is often complicated. Copyright © 2007 John Wiley & Sons, Ltd.     

A test of TOPMODEL'a ability to predict spatially distributed groundwater levels

TOPMODEL was calibrated to a small catchment using precipitation and runoff data. Acceptable fits of simulated and observed runoff were obtained during both the calibration and validation periods. Predictions of groundwater levels using this calibration did not agree well with observations at the 37 points within the catchment where groundwater levels were measured, including three locations with continuous recordings. Groundwater level observations at one single point in time, however, sufficed to calibrate new topographic–soil indices that improved the prediction of the local groundwater levels at the observed tubes. This suggests that spatially distributed calibration data are necessary to exploit reliably TOPMODEL's ability to predict spatially distributed hydrology. The mean or recalibrated transmissivity values at these 37 points differed from the catchment mean as determined by the precipitation–runoff calibration. Thus, while groundwater information can help in predicting groundwater levels at specific locations, increasing the number of local groundwater level measurements is not sufficient to improve the spatially distributed representation of subsurface flow by TOPMODEL for the catchment as a whole, as long as the groundwater information is not integrated in the precipitation–runoff calibration. © 1997 John Wiley & Sons, Ltd.     

Interactions between dam‐regulated river flow and riparian groundwater: a case study from the Yellow River,China

The Xiaolangdi Dam, completed in 2000, is second in scale in China to the Three Gorges Project. It has generated remarkable economic and social benefits but with profound impacts to the riverine and regional environments. This paper reports field monitoring of riparian groundwater in the Kouma section of the Yellow River to illustrate the interactions between dam‐regulated river flow and riparian groundwater. The results show that the hydrological condition in riparian zones downstream from the dam has changed from a typical wet–dry cycle to a condition of semi‐permanent dryness, resulting in degradation of the typical attributes and functions of the wetland ecosystem. Hydrological processes in the riparian zone have changed from a complex multiple flooding regime to a simple regime of dominant groundwater drainage towards the river, which only reverses temporarily during the water and sediment regulation period of the dam. Data on groundwater level and groundwater quality show that there are two key points, at ca 200 and 400 m from the river bank, which distinguish zones with different sensitivity to changes of river flow and indicate different interactions between river water and groundwater. The shallow groundwater quality also is negatively affected by the intensive agricultural development that has occurred since the dam was completed. Ecological restoration needs to be carried out to construct a protective natural riparian zone within ca 200 m from the river, this being an ecotone, which is key to the protection of both riparian groundwater and the river. The riparian zone from 200 to 400 m also should be treated as a transitional zone. In addition, ecologically sensitive agriculture and ecotourism organized by local communities would be beneficial in the area beyond 400 m. Copyright © 2011 John Wiley & Sons, Ltd.     

鄱阳湖拟建水利枢纽工程对洪泛区地下水动力的影响及其生态意义

洪泛湿地是位于水生系统和陆生系统之间的过渡带,在河流和陆地之间的水文生态方面起着纽带作用,受气候变化和人类活动的叠加影响,其水文过程改变很大程度上影响了湿地生态系统循环、结构和功能的稳定。本文以鄱阳湖洪泛区湿地为研究区,应用湖泊水动力和洪泛区地下水数值模型,评估鄱阳湖拟建水利枢纽工程对洪泛区地下水系统的影响。模拟结果表明,拟建水利枢纽工程将会遵循调度方案使得湖泊水位明显提高,但同时导致洪泛区地下水位的整体抬升,且东部主湖区附近的地下水位受到的影响（约1～3 m）要明显强于洪泛区其它区域（约小于1 m）。地下水位的变化同时导致不同典型时期洪泛区地下水流速的减小及地下水流向的改变,表现为枢纽建设后地下水流向的逆转和流速基本小于0.1 m/d。鄱阳湖涨水-丰水期总体为湖水补给洪泛区地下水模式,枯水-退水期主要为地下水补给湖水模式,但水利枢纽可能导致洪泛区地下水系统水均衡状态发生转变,影响了地下水系统的补给和排泄状态,最终形成了长期稳定的湖泊补给地下水的作用模式。从地下水-生态系统响应变化的角度分析,拟建水利枢纽建设引起的地下水位上升,可能会给湿地生物地球化学元素的迁移转化、植被群落的演变与退...     

太湖流域平原水网区浅层地下水动态特征及影响因素

鉴于浅层地下水在维持区域生态功能方面的重要作用,基于2005-2015年太湖平原水网地区苏州市的14个浅层地下水监测井水位及2005-2014年降水、河道水位和蒸发等日尺度数据,开展浅层地下水埋深动态特征及影响因素研究.结果显示:苏州市浅层地下水总体呈由北往南、自西向东的流场方向,主要受地形因素的影响;年际及丰水期埋深有所减小,枯水期反之,各区域变化过程不一致;枯水期浅层地下水动态特征受不同量级降水总量和次数的显著影响,且与地表水过程关系密切,汛期反之.此外均受到引排水和下垫面变化等因素的影响;浅层地下水埋深对降水具有滞后性,多滞后1~2 d;通过对地形地貌条件、土地利用类型、河湖密度以及浅层地下水埋深状况等因素的综合分析,浅层地下水动态特征可表达为耕地区、水网密布区、高度城镇化区及低山林区4种特征类型.     

Multi-objective optimization for sustainable groundwater resource management in a semiarid catchment

Abstract

Groundwater is an important water resource and its management is vital for integrated water resources development in semiarid catchments. The River Shiyang catchment in the semiarid area of northwestern China was studied to determine a sustainable multi-objective management plan of water resources. A multi-objective optimization model was developed which incorporated water supplies, groundwater quality, ecology, environment and economics on spatial and temporal scales under various detailed constraints. A calibrated groundwater flow model was supplemented by grey simulation of groundwater quality, thus providing two lines of evidence to use in the multi-objective water management. The response matrix method was used to link the groundwater simulation models and the optimization model. Multi-phase linear programming was used to minimize and compromise the objectives for the multi-period, conjunctive water use optimization model. Based on current water demands, this water use optimization management plan was able to meet ecological, environmental and economic objectives, but did not find a final solution to reduce the overall water deficit within the catchment.     

Spatial variation of flow characteristics in a subarctic meandering river in ice-covered and open-channel conditions: A 2D hydrodynamic modelling approach

To be able to understand year-round river channel evolution both at present and in the future, the spatial variation of the flow characteristics and their sediment transport capabilities under ice cover need to be detected. As the measurements done through cross-sectional drill holes cover only a small portion of the river channel area, the numerical simulations give insight into the wider spatial horizontal variation of the flow characteristics. Therefore, we simulate the ice-covered flow with a hydrodynamic two-dimensional (2D) model in a meandering subarctic river (Pulmanki River, Finland) in mid-winter conditions and compare them to the pre-winter open-channel low flow situation. Based on the simulations, which are calibrated with reference measurements, we aim to detect (1) how ice-covered mid-winter flow characteristics vary spatially and (2) the erosion and sedimentation potential of the ice-covered flow compared to open-channel conditions. The 2D hydrodynamic model replicated the observed flow characteristics in both open-channel and ice-covered conditions. During both seasons, the greatest erosional forces locate in the shallow sections. The narrow, freely flowing channel area found in mid-winter cause the main differences in the spatial flow variation between seasons. Despite the causes of the horizontal recirculating flow structures being similar in both seasons, the structures formed in different locations depended on whether the river was open or ice covered. The critical thresholds for particle entrainment are exceeded more often in open-channel conditions than during ice-covered flow. The results indicate spatially extensive sediment transport in open-channel conditions, but that the spatial variability and differences in depositional and erosional locations increase in ice-covered conditions. Asymmetrical bends and straight reaches erode throughout the year, whereas symmetrical, smaller bends mainly erode in open-channel conditions and are prone to deposition in winter. The long ice-covered season can greatly affect the annual morphology of the submerged channel. © 2019 John Wiley & Sons, Ltd.