Groundwater Elevation Research Articles

Comparison of Seepage Simulation in a Saline Environment below an Estuary Using MODFLOW and SEAWAT

This paper compares the results produced by MODFLOW, a constant-density model, to results produced by SEAWAT, a variable-density model, to investigate the feasibility of using MODFLOW in a saline environment below an estuary known as the Indian River Lagoon. The comparison was conducted over sixteen numerical simulation cases at different conditions of estuarine salinity CL, hydraulic conductivity anisotropy ratio Kr, and water table elevations on the freshwater boundaries in a two-dimensional vertical domain. The use of MODFLOW at the study site under the calibrated Kr distribution ranging from 1000-20,000 was found to accurately match the field-measured and SEAWATsimulated results with a remarkable increase in accuracy at higher groundwater elevations. The study determined a critical value of Kr of 1000 above which, MODFLOW simulations of the variable-density problem produced results that agreed well with those produced by SEAWAT. However, MODFLOW starts to produce significant errors with Kr below the critical value and hence, it should not be used for simulating variable-density environments when Kr<1000. The amount of submarine groundwater discharge (SGD) predicted by either model, and also MODFLOW accuracy in predicting the SGD are directly proportional to the head difference between the groundwater divide elevation and the lagoon water surface, but to a lower extent, are inversely proportional to CL.

Long-term Changes in Annual Precipitation and Monsoon Seasonal Characteristics in Myanmar

This paper compares the results produced by MODFLOW, a constant-density model, to results produced by SEAWAT, a variable-density model, to investigate the feasibility of using MODFLOW in a saline environment below an estuary known as the Indian River Lagoon. The comparison was conducted over sixteen numerical simulation cases at different conditions of estuarine salinity CL, hydraulic conductivity anisotropy ratio Kr, and water table elevations on the freshwater boundaries in a two-dimensional vertical domain. The use of MODFLOW at the study site under the calibrated Kr distribution ranging from 1000-20,000 was found to accurately match the field-measured and SEAWATsimulated results with a remarkable increase in accuracy at higher groundwater elevations. The study determined a critical value of Kr of 1000 above which, MODFLOW simulations of the variable-density problem produced results that agreed well with those produced by SEAWAT. However, MODFLOW starts to produce significant errors with Kr below the critical value and hence, it should not be used for simulating variable-density environments when Kr<1000. The amount of submarine groundwater discharge (SGD) predicted by either model, and also MODFLOW accuracy in predicting the SGD are directly proportional to the head difference between the groundwater divide elevation and the lagoon water surface, but to a lower extent, are inversely proportional to CL.

Groundwater resource vulnerability and spatial variability of nitrate contamination: Insights from high density tubewell monitoring in a hard rock aquifer.

Agriculture has been increasingly relying on groundwater irrigation for the last decades, leading to severe groundwater depletion and/or nitrate contamination. Understanding the links between nitrate concentration and groundwater resource is a prerequisite for assessing the sustainability of irrigated systems. The Berambadi catchment (ORE-BVET/Kabini Critical Zone Observatory) in Southern India is a typical example of intensive irrigated agriculture and then an ideal site to study the relative influences of land use, management practices and aquifer properties on NO3 spatial distribution in groundwater. The monitoring of >200 tube wells revealed nitrate concentrations from 1 to 360mg/L. Three configurations of groundwater level and elevation gradient were identified: i) NO3 hot spots associated to deep groundwater levels (30-60m) and low groundwater elevation gradient suggest small groundwater reserve with absence of lateral flow, then degradation of groundwater quality due to recycling through pumping and return flow; ii) high groundwater elevation gradient, moderate NO3 concentrations suggest that significant lateral flow prevented NO3 enrichment; iii) low NO3 concentrations, low groundwater elevation gradient and shallow groundwater indicate a large reserve. We propose that mapping groundwater level and gradient could be used to delineate zones vulnerable to agriculture intensification in catchments where groundwater from low-yielding aquifers is the only source of irrigation. Then, wells located in low groundwater elevation gradient zones are likely to be suitable for assessing the impacts of local agricultural systems, while wells located in zones with high elevation gradient would reflect the average groundwater quality of the catchment, and hence should be used for regional mapping of groundwater quality. Irrigation with NO3 concentrated groundwater induces a "hidden" input of nitrogen to the crop which can reach 200kgN/ha/yr in hotspot areas, enhancing groundwater contamination. Such fluxes, once taken into account in fertilizer management, would allow optimizing fertilizer consumption and mitigate high nitrate concentrations in groundwater.

Hydro-geomorphic response of Everglades to changing climate and anthropogenic activities

The Everglades has been experiencing major changes, both natural and anthropogenic, such that the landscape is deviating away from its natural equilibrium. The land within the Everglades has undergone severe modifications that may have detrimental effects on wildlife and natural features, such as rivers and landscape connectivity. Here in this study, we focus on understanding and quantifying hydrologic and geomorphic signatures of climatic and anthropogenic changes on the Everglades landscape. For this, in particular, we use available data on natural hydrological processes, such as rainfall, groundwater elevation, streamflow as well as surface elevations and satellite images for three different regions. These regions are categorized as forested, urban (nearby Everglades regions) and transition (in between forested and urban regions). Our results show distinct differences in the statistics of observed hydrologic variables for the three different regions. For example, the probability distribution functions (PDFs) of groundwater elevation for the case of urban region show a shift in mean as well as lower asymmetry as compared to forested regions. In addition, a significant difference in the slopes between smaller and larger scales of the power spectral densities (PSDs) is observed when transitioning from forested to urban. For the case of the streamflow PDFs and PSDs, we observe the opposite trends. Finally, computing the interarrival times of extreme (>95th percentile) events that suggest power-law behavior, the changes in power-law exponents of the hydrologic processes further highlights how these processes differ spatially and how the landscape has to respond to these changes. Quantifying these observed changes will help us develop a better understanding of the Everglades and other wetlands ecosystems for management to future changes and restoration.

Flow modelling of strategically vital freshwater aquifers in Kuwait

An oil flow from the oil wells damaged during the 1991 Gulf War and the sea water used for extinguishing the resulting oil fire have contaminated the freshwater aquifers of Raudhatain and Umm Al-Aish water fields in north Kuwait. The numerical flow modelling of the aquifers was undertaken to create a calibrated and validated model that could be used in the future to explore a viable remediation strategy for the aquifers. The Environmental Visualization Software (EVS-pro) 3-D data presentation program was used to construct a conceptual model as a preliminary step. A 3-D numerical model was developed using the MODFLOW-SURFACT code that overcame the limitations of the classical MODFLOW. This model was able to combine both freshwater lenses in one model domain simulating the vadose zone together with the saturated zone. The model domain covered an area of 580 km2 encompassing the Al-Raudhatain and Umm Al-Aish basins. A steady-state model was developed first to study regional flow patterns in the aquifer. A transient model was developed subsequently to assess seasonal recharge on groundwater and investigate their effects on flow patterns. Analysis of the calibrated steady-state model output indicated that the model simulated the groundwater elevation and flow direction across the model domain to an acceptable level. The calibrated transient flow model is of significant importance to assess the vertical and lateral plume migration in the area and helps to come up with a plausible remediation strategy.

Model Establishment for Ponding in Coal Mining Subsidence Areas and its Prediction: Case Study of Northern Jining, China

Mining in areas with a high phreatic water surface leads to groundwater exposure and the accumulation of the water in the subsidence basin. The calculation of the volume of water is of high importance. This paper analyzes the seasonal or perennial ponding caused by mining in areas with high phreatic water surfaces. With the help of digital elevation model, the estimated groundwater elevation, and the basis of a mining subsidence prediction model, a model of ponding in subsidence areas has been established. Using this model, the amount of mining subsidence ponding in northern Jining has been calculated. Furthermore, the evolution of ponding has been forecasted. Our experimental results indicate that the average depth of the ponding area is projected to be about 3 m after mine closure. The volume of the new perennial ponding is 0.2–2 million m3 per year and it is negligible to the river confluence in Jining. This model helps in the calculation of the amount of water in the subsidence area and the evaluation of the impact of mining subsidence area on the catchment, which would provide a certain basis for the reclamation and protection of water resources in the locality.

Evaluating Flow Diversion Impacts to Groundwater‐Dependent Riparian Vegetation with Flow Alteration and Groundwater Model Analysis

AbstractAn approach for assessing the potential ecologic response of groundwater‐dependent riparian vegetation to flow alteration is developed, focusing on change to groundwater. Groundwater requirements for riparian vegetation are reviewed in conjunction with flow alteration statistics. Where flow alteration coincides with groundwater‐related vegetation sensitivities, scenarios are developed for groundwater simulation. Groundwater depths and recession rates in the riparian zone are simulated for baseline and altered stream hydrographs, with changes to river stage and width represented with a transient, flow‐dependent boundary condition. Potential flow diversion from the Upper Gila River in New Mexico is examined. Statistical flow alteration analysis, applying prospective diversions to a 76‐year record of daily flow, shows that flows in the winter‐spring months and within the high‐pulse to small flood range are subject to greatest potential change. Groundwater simulation scenarios are developed for these flow conditions in representative dry, near‐average, and wet years. Differences in groundwater elevations, generally less than 0.25 m during the flow alteration period, dissipate rapidly following cessation of diversion. Relating groundwater depth, recession rates and range of fluctuations to riparian vegetation needs, we find adverse ecological response is not expected from groundwater impacts for the flow alteration examined.

Uncertainty and sensitivity in a bank stability model: implications for estimating phosphorus loading

AbstractEutrophication of aquatic ecosystems is one of the most pressing water quality concerns in the United States and around the world. Bank erosion has been largely overlooked as a source of nutrient loading, despite field studies demonstrating that this source can account for the majority of the total phosphorus load in a watershed. Substantial effort has been made to develop mechanistic models to predict bank erosion and instability in stream systems; however, these models do not account for inherent natural variability in input values. To quantify the impacts of this omission, uncertainty and sensitivity analyses were performed on the Bank Stability and Toe Erosion Model (BSTEM), a mechanistic model developed by the US Department of Agriculture – Agricultural Research Service (USDA‐ARS) that simulates both mass wasting and fluvial erosion of streambanks. Generally, bank height, soil cohesion, and plant species were found to be most influential in determining stability of clay (cohesive) banks. In addition to these three inputs, groundwater elevation, stream stage, and bank angle were also identified as important in sand (non‐cohesive) banks. Slope and bank height are the dominant variables in fluvial erosion modeling, while erodibility and critical shear stress had low sensitivity indices; however, these indices do not reflect the importance of critical shear stress in determining the timing of erosion events. These results identify important variables that should be the focus of data collection efforts while also indicating which less influential variables may be set to assumed values. In addition, a probabilistic Monte‐Carlo modeling approach was applied to data from a watershed‐scale sediment and phosphorus loading study on the Missisquoi River, Vermont to quantify uncertainty associated with these published results. While our estimates aligned well with previous deterministic modeling results, the uncertainty associated with these predictions suggests that they should be considered order of magnitude estimates only. Copyright © 2016 John Wiley &amp; Sons, Ltd.

A comparison of watershed storage trends over the eastern and upper Midwestern regions of the United States, 2003–2015

AbstractBasin‐scale groundwater storage trends calculated from long‐term streamflow records provide insight into the evolution of watershed behaviors. Our study presents the first spatially relevant validation of recession‐based trend approaches by comparing three independent storage trend estimates using GRACE‐derived groundwater storage, in situ groundwater elevation observations, and recession‐based approaches for the time period of 2003–2015. Results documented consistent agreement between spatially interpolated groundwater observation trends and recession‐based storage trends, while GRACE‐derived groundwater trends were found to exhibit variable, poor comparisons. A decreasing trend in watershed storage was identified in the southeastern U.S. while increasing trends were identified in the northeast and upper Midwest estimated from recession‐based approaches. Our recession‐based approach conducted using nested watershed streamflow records identified variable watershed storage trends at scales directly applicable for comparative hydrology studies and for assisting in watershed‐based water resources management decisions.

Model of Ground Water Elevation around Mud Reservoir in Coastal Area of Porong Sidoarjo

The previous research got several difference curves of the water level in the large scale from the coastal line perpendicular around 20 km to the land direction over the reservoir area . These curves were caused by both variation of precipitation and sea water level fluctuation of tide. The purpose of this research is to estimate the physical characteristics of water level of ground water around the mud reservoir. The numerical modeling of D-F theory is has be implemented. The idea is to take the solution of discharge equation for well from the ground water level. The model includes the shape of the infiltration mud-volcano from the reservoir to the natural water level of ground water. The field records will be used to make confirmation and validation. The result of this research is to support the result of the previous research, the level of water table around mud reservoir about 2 km perpendicular to the coastline direction (East direction) is full-filled by mud-volcano. On the other hand, for the opposite direction i.e.West direction from mud reservoir about 1.5 km is also full-filled by mud-volcano. The error between numerical model and field records is around 1%.

Food, water, and fault lines: Remote sensing opportunities for earthquake-response management of agricultural water

Earthquakes often cause destructive and unpredictable changes that can affect local hydrology (e.g. groundwater elevation or reduction) and thus disrupt land uses and human activities. Prolific agricultural regions overlie seismically active areas, emphasizing the importance to improve our understanding and monitoring of hydrologic and agricultural systems following a seismic event. A thorough data collection is necessary for adequate post-earthquake crop management response; however, the large spatial extent of earthquake's impact makes challenging the collection of robust data sets for identifying locations and magnitude of these impacts. Observing hydrologic responses to earthquakes is not a novel concept, yet there is a lack of methods and tools for assessing earthquake's impacts upon the regional hydrology and agricultural systems. The objective of this paper is to describe how remote sensing imagery, methods and tools allow detecting crop responses and damage incurred after earthquakes because a change in the regional hydrology. Many remote sensing datasets are long archived with extensive coverage and with well-documented methods to assess plant-water relations. We thus connect remote sensing of plant water relations to its utility in agriculture using a post-earthquake agrohydrologic remote sensing (PEARS) framework; specifically in agro-hydrologic relationships associated with recent earthquake events that will lead to improved water management.

Estimating groundwater dynamics at a Colorado River floodplain site using historical hydrological data and climate information

AbstractLong‐term prediction of groundwater dynamics is important for assessing water resources and their impacts on biogeochemical cycling. However, estimating future groundwater dynamics is challenging due to the wide range of spatiotemporal scales in hydrological processes and uncertainty in future climate conditions. In this study, we develop a Bayesian model to combine small‐scale historical hydrological data with large‐scale climate information to estimate groundwater dynamics at a floodplain site in Rifle, Colorado. Although we have only a few years of groundwater elevation measurements, we have 47 years of streamflow data from a gaging station approximately 43 km upstream and long‐term climate prediction on the Upper Colorado River Basin. To estimate future daily groundwater dynamics, we first develop a time series model to downscale the monthly streamflow derived from climate information to daily streamflow, and then transform the daily streamflow to groundwater dynamics at the downstream floodplain site. We use Monte Carlo methods to estimate future groundwater dynamics at the site through sampling from the joint posterior probability distribution. The results suggest that although future groundwater levels are expected to be similar to the current levels, the timing of the high groundwater levels is predicted to occur about 1 month earlier. The developed framework is extendable to other sites to estimate future groundwater dynamics given disparate data sets and climate projections. Additionally, the obtained estimates are being used as input to a site‐specific watershed reactive transport models to predict how climate‐induced changes will influence future biogeochemical cycling relevant to a variety of ecosystem services.

Characterization of Seismic Levee Fragility Using Field Performance Data

We characterize the seismic fragility of levees along the Shinano River system in Japan using field performance data from two M 6.6 shallow crustal earthquakes. Levee damage is quantified based on crack depth, crack width, and crest subsidence for 3,318 levee segments each 50 m long. Variables considered for possible correlation to damage include peak ground velocity ( PGV), geomorphology, groundwater elevation, and levee geometry. Seismic levee fragility is expressed as the probability of exceeding a damage level conditioned on PGV alone and PGV in combination with other predictive variables. The probability of damage (at any level) monotonically increases from effectively zero for PGV &lt; 14 cm/s to approximately 0.5 for PGV ≈ 80 cm/s. Of the additional parameters considered, groundwater elevation relative to the levee base most significantly affects fragility functions, increasing and decreasing failure probabilities (relative to the PGV-only function) for shallow and deep groundwater conditions, respectively.

MAPPING REGIONAL DROUGHT VULNERABILITY: A CASE STUDY

Abstract. Drought is among the natural disaster that causes damages and affects many people’s life in many part of the world including in Iran. Recently, some factors such as climate variability and the impact of climate change have influenced drought frequency and intensity in many parts of the world. Drought can be divided into four categories of meteorological, hydrological, agricultural and social-economic. In meteorological the important feature is lack of rainfall. In hydrological drought river flows and dam storage are considered. Lack of soil moisture is the key factor in agricultural droughts while in social-economic type of drought the relation between supply and demand and social-economic damages due to water deficiency is studied. While the first three types relates to the lack of some hydrological characteristics, social-economic type of drought is actually the consequence of other types expressed in monetary values. Many indices are used in assessing drought; each has its own advantages and disadvantages and can be used for specific types of drought. Therefore knowing the types of drought can provide a better understanding of shortages and their characteristics. Drought vulnerability is a concept which shows the likelihood of damages from hazard in a particular place by focusing on the system status prior to the disaster. Drought vulnerability has been viewed as a potential for losses in the region due to water deficiency at the time of drought. In this study the application of vulnerability concept in drought management in East Azarbaijan province in Iran is investigated by providing vulnerability maps which demonstrates spatial characteristics of drought vulnerability. In the first step, certain governing parameters in drought analysis such as precipitation, temperature, land use, topography, solar radiation and ground water elevation have been investigated in the region. They are described in details and calculated in suitable time series. Vulnerabilities are ranked in 5 intervals and for each parameter vulnerability maps are prepared in GIS environment. Selection of theses parameters are based on factors such as regional features and availability of data. Considering the fact that the aforementioned parameters have different level of importance in vulnerability maps, different weights are assigned to the parameters considering how critical each parameter is in the overall drought analysis. Expert's opinion is selected in assigning weights. A multi-criteria decision making (MCDM) framework is used to check the consistency of the provided information. Then the weighted maps are overlaid to find the overall vulnerability map. The map shows very low, low, medium, intense and very intense regional vulnerabilities. According to the results, the west part of East Azarbaijan province is the most vulnerable region to drought which is expected due to the vicinity of this part to Urumia Lake that has been lost most of its water during the last decades. The least vulnerable part seems to be the Eastern part of the province with longer lasting resources. Taking into consideration that Caspian Sea is near this part with high precipitation record, the outcome of this study is in line with the general expectations. The result of this study can be used for preparedness planning and for allocating resources for facing droughts in this region.

Impacts of beaver dams on hydrologic and temperature regimes in a mountain stream

Abstract. Beaver dams affect hydrologic processes, channel complexity, and stream temperature in part by inundating riparian areas, influencing groundwater–surface water interactions, and changing fluvial processes within stream systems. We explored the impacts of beaver dams on hydrologic and temperature regimes at different spatial and temporal scales within a mountain stream in northern Utah over a 3-year period spanning pre- and post-beaver colonization. Using continuous stream discharge, stream temperature, synoptic tracer experiments, and groundwater elevation measurements, we documented pre-beaver conditions in the first year of the study. In the second year, we captured the initial effects of three beaver dams, while the third year included the effects of ten dams. After beaver colonization, reach-scale (~ 750 m in length) discharge observations showed a shift from slightly losing to gaining. However, at the smaller sub-reach scale (ranging from 56 to 185 m in length), the discharge gains and losses increased in variability due to more complex flow pathways with beaver dams forcing overland flow, increasing surface and subsurface storage, and increasing groundwater elevations. At the reach scale, temperatures were found to increase by 0.38 °C (3.8 %), which in part is explained by a 230 % increase in mean reach residence time. At the smallest, beaver dam scale (including upstream ponded area, beaver dam structure, and immediate downstream section), there were notable increases in the thermal heterogeneity where warmer and cooler niches were created. Through the quantification of hydrologic and thermal changes at different spatial and temporal scales, we document increased variability during post-beaver colonization and highlight the need to understand the impacts of beaver dams on stream ecosystems and their potential role in stream restoration.

Hydrological resilience of a Canadian Rockies headwaters basin subject to changing climate, extreme weather, and forest management

AbstractMarmot Creek Research Basin in the Canadian Rockies has been the site of intensive streamflow, groundwater, snow accumulation, precipitation, and air temperature observations at multiple elevations. The basin was instrumented in 1962, subjected to forestry experiments in the mid‐1970s, and experienced extreme flooding in 2013. Climate change, forest cover change, and recent extreme weather make the basin an ideal laboratory for studying hydrological resilience. Observations show increases in low elevation air temperature, multiple day and spring precipitation, interannual variability of precipitation, and high elevation groundwater levels. Observations also show decreases in peak seasonal snow accumulation and low elevation groundwater levels. Despite these substantial hydrometeorological and groundwater changes, streamflow volume, timing of peak, and magnitude of the peak are not changing. Streamflow volumes are also insensitive to forest cover changes and teleconnections. The June 2013 flood was unprecedented in the period of record, and the basin significantly moderated the hydrological response to the extreme precipitation; the 2013 storm precipitation depth was 65% greater than the next highest storm total over 51 years; however, the 2013 peak streamflow was only 32% greater than the next highest peak flow recorded. The hydrology of Marmot Creek Research Basin displays remarkable resilience to changing climate, extreme weather, and forest cover change. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Sustainable Groundwater Management in the Arid Southwestern US: Coachella Valley, California

Sustainable groundwater management requires approaches to assess the influence of climate and management actions on the evolution of groundwater systems. Traditional approaches that apply continuity to assess groundwater sustainability fail to capture the spatial variability of aquifer responses. To address this gap, our study evaluates groundwater elevation data from the Coachella Valley, California, within a groundwater sustainability framework given the adoption of integrative management strategies in the valley. Our study details an innovative approach employing traditional statistical methods to improve understanding of aquifer responses. In this analysis, we evaluate trends at individual groundwater observation wells and regional groundwater behaviors using field significance. Regional elevation trends identified no significant trends during periods of intense groundwater replenishment, active since 1973, despite spatial variability in individual well trends. Our results illustrate the spatially limited effects of groundwater replenishment occur against a setting of long-term groundwater depletion, raising concerns over the definition of sustainable groundwater management in aquifer systems employing integrative management strategies.

Tamarix transpiration along a semiarid river has negligible impact on water resources

AbstractThe proliferation of saltcedar (Tamarix spp.) along regulated rivers in the western United States has transformed riparian plant communities. It is commonly assumed that transpiration by these alien plants has led to large losses of water that would otherwise contribute to streamflow. Control of saltcedar, therefore, has been considered a viable strategy for conserving water and increasing streamflow in these regions. In an effort to better understand the linkage between transpiration by saltcedar and streamflow, we monitored transpiration, stream stage, and groundwater elevations within a saltcedar stand along the Pecos River during June 2004. Transpiration, as determined by sap flow measurements, exhibited a strong diel pattern; stream stage did not. Diel fluctuations in groundwater levels were observed, but only in one well, which was located in the center of the saltcedar stand. In that well, the correlation between maximal transpiration and minimal groundwater elevation was weak (R2 = 0.16). No effects of transpiration were detected in other wells within the saltcedar stand, nor in the stream stage. The primary reason, we believe, is that the saltcedar stand along this reach of the Pecos River has relatively low sapwood area and a limited spatial extent resulting in very low transpiration compared with the stream discharge. Our results are important because they provide a mechanistic explanation for the lack of increase in streamflow following large‐scale control of invasive trees along semiarid rivers.

Dynamic river–groundwater exchange in the presence of a saline, semi‐confined aquifer

AbstractUnderstanding groundwater–surface water exchange in river banks is crucial for effective water management and a range of scientific disciplines. While there has been much research on bank storage, many studies assume idealized aquifer systems. This paper presents a field‐based study of the Tambo Catchment (southeast Australia) where the Tambo River interacts with both an unconfined aquifer containing relatively young and fresh groundwater (&lt;500 μS/cm and &lt;100 years old) and a semi‐confined artesian aquifer containing old and saline groundwater (electrical conductivity &gt; 2500 μS/cm and &gt;10 000 years old). Continuous groundwater elevation and electrical conductivity monitoring within the different aquifers and the river suggest that the degree of mixing between the two aquifers and the river varies significantly in response to changing hydrological conditions. Numerical modelling using MODFLOW and the solute transport package MT3DMS indicates that saline water in the river bank moves away from the river during flooding as hydraulic gradients reverse. This water then returns during flood recession as baseflow hydraulic gradients are re‐established. Modelling also indicates that the concentration of a simulated conservative groundwater solute can increase for up to ~34 days at distances of 20 and 40 m from the river in response to flood events approximately 10 m in height. For the same flood event, simulated solute concentrations within 10 m of the river increase for only ~15 days as the infiltrating low‐salinity river water drives groundwater dilution. Average groundwater fluxes to the river stretch estimated using Darcy's law were 7 m3/m/day compared with 26 and 3 m3/m/day for the same periods via mass balance using Radon (222Rn) and chloride (Cl), respectively. The study shows that by coupling numerical modelling with continuous groundwater–surface water monitoring, the transient nature of bank storage can be evaluated, leading to a better understanding of the hydrological system and better interpretation of hydrochemical data. Copyright © 2015 John Wiley &amp; Sons, Ltd.

A Habitat Suitability Index (HSI) for the Western Prairie Fringed Orchid (Platanthera praeclara) on the Sheyenne National Grassland, North Dakota, USA

The Western Prairie Fringed Orchid (Platanthera praeclara) is a threatened species found on the Sheyenne National Grassland (SNG) in southeast North Dakota, USA. The SNG is subject to management for multiple uses including biodiversity conservation, livestock grazing and recreation. Therefore, there is a need for the development of indicators of suitable orchid habitat. The orchids are continuously monitored, but understanding of the relationship between landscape properties and orchid locations is limited. In this study data that characterize topography, moisture, and groundwater were used to construct indicators of landscape suitability and an overall Habitat Suitability Index (HSI) for the orchid. A LiDAR-derived DEM and groundwater well observations were used to develop landscape indicators. The Topographic Wetness Index (TWI: a measure of moisture on the landscape), the Topographic Position Index (TPI: a measure of position on the landscape), and the distance to groundwater (DTG: a measure of the distance from the land surface to the groundwater surface) provided the best set of indicators of orchid habitat. Point-based field observations of orchid occurrence were used to develop Orchid Suitability Metrics (OSMs) that identified the range of indicator values most strongly associated with orchids. These OSMs were used to define year by year suitability zones for each indicator that were combined to create the HSI. Comparison of orchid locations with groundwater elevations showed that orchids occurred on average 0.98±0.39 (2σ)m above the water table. TWI and TPI demonstrated that orchids occur near flow paths and areas of lower elevation than their surroundings. HSI values of 0.67 and above were associated with 89.8% of all orchid observations used in the analysis. The landscape indicators, OSM concept and HSI could be generally applied to monitoring and conservation management of orchid habitat and the concept may be applicable to other valued species with similar niche properties.