Basin-wide Model Research Articles

Impact of tropical and extra tropical climate variability on Indian Ocean surface waves

Understanding the impact of various climate features on wave climate is important for effective coastal climate adaptation and mitigation strategy planning. In the present study, the effect of tropical and extra-tropical climate modes such as Indian Ocean Dipole (IOD), El Nino Southern Oscillation (ENSO) and Southern Annular Mode (SAM) on wind-wave climate of the Indian Ocean (IO) is studied using multiple linear regression of individual climate indices on relevant wind-wave parameters. There are two regions of importance for swell generation in the Indian Ocean - a region between 40° and 60° S in the Southern Ocean (SO) and another region in the Eastern Tropical Indian Ocean (ETIO; 10°–30° S, 60°–100 °E). SAM, the strongest inter-annual mode of the SO, generates swells in the 40°–60°S band throughout the year that eventually propagates to the entire North IO. Both the positive and negative phases of SAM generate swells from SO, but it’s genesis region vary meridionally depending on the phase of SAM. The positive phase of ENSO (LaNina) generally reduce the westerly wind anomalies in the SO caused by a positive phase of SAM and hence reduce the swell generation from SO, but causes stronger south-easterlies in the ETIO, generating more swells from there. IOD that peaks in September–October–November period has its effect on swell generation limited to eastern equatorial IO. Our analysis suggests that interannual climate features are important in modulating wind-wave climate of IO and a basin-wide model set-up with an accurate representation of various interannual climate features is a prerequisite for accurate wave forecast.

Improving the Real-time Marine Forecasting of the Northern South China Sea by Assimilation of Glider-observed T/S Profiles

Prediction of marine conditions is notoriously challenging in the northern South China Sea (NSCS) due to inadequate observations in the region. The underwater gliders that were developed during the past decade may provide observing platforms that could produce required observations. During a field experiment, temperature/salinity (T/S) profiles from a set of underwater gliders were assimilated into a real-time marine forecasting system, along with the assimilation of climatological monthly mean Argo data to constrain the basin-wide model biases. The results show that, in addition to the reduction of the basin-wide model biases by the assimilation of the climatological monthly mean Argo data, the assimilation of glider-observed T/S profiles is efficient to reduce the local biases of the NSCS marine forecasting by as much as 28–31% (19–36%) in 24 h to 120 h forecasts for temperature (salinity) from sea surface to a depth of 1000 m. Our results imply that the real-time marine forecasting for the NSCS can largely benefit from a sustainable glider observing network of the NSCS in the future.

Global soundscapes: Parabolic equation modeling and the CTBTO observing system

The open ocean is not a quiet place, particularly in the Northern Hemisphere. The soundscape of a local environment is defined as detailed understanding of the noise sources observed in time, frequency and space. In this paper we present a set of models and observations of the open ocean sound field utilizing the long-term observations from the Comprehensive Test Ban Treaty Organization (CTBTO) of the United Nations. This system of axial hydrophones spanning the globe in remote locations provides a treasure chest of data for looking at low frequency sound. For frequencies below 125 Hz, half the CTBTO sample rate, the sound field is dominated by local and distant ships, local wind, marine mammals, seismic surveying and seismic events. A basin wide model, with the Parabolic Equation model for propagation, will be presented using Satellite AIS data, surface wind fields and some estimates of fin whale distributions and seismic surveys. The science questions to be addressed are: Can we observe the wind noise or is shipping to dominant? What mechanisms explain wind noise below 50 Hz? Can we use data to move towards a better model for surface shipping source levels? Can we evaluate Fin Whale distributions from regular recordings?

An invader in salmonid rearing habitat: current and future distributions of smallmouth bass (Micropterus dolomieu) in the Columbia River Basin

Invasive species and climate change are leading threats to freshwater ecosystems. In the Columbia River Basin (CRB), nonnative fishes are a critical consideration in salmon recovery, yet managers lament a lack of distribution information. Combining a species distribution model (SDM) with environmental DNA (eDNA), we locate range boundary regions of nonnative smallmouth bass (Micropterus dolomieu) and evaluate its overlap with native salmonids. A combination of thermal, hydrological, and geomorphic variables predict that smallmouth bass is distributed across ∼18 000 river kilometres and overlaps with 3%–62% of rearing habitat of salmonids (species-dependent) in the CRB. Under a moderate climate change scenario, smallmouth bass is predicted to expand its range by two-thirds (totaling ∼30 000 river kilometres) by 2080. Basin-wide models were sufficiently accurate to identify upstream invasion extents to within 15 km of the eDNA-based boundary, and including eDNA data improved model performance at critical range boundary regions without sacrificing broadscale model performance. Our study highlights how eDNA approaches can supplement large geospatial data sets to result in more accurate SDM predictions, guiding nonnative species management.

Extending the forecast model: Predicting Western Lake Erie harmful algal blooms at multiple spatial scales

Lake Erie is a classic case of development, recovery from, and return to eutrophication, hypoxia, and harmful algal blooms. Forecast models are used annually to predict bloom intensity for the whole Western Lake Erie Basin, but do not necessarily reflect nearshore conditions or regional variations, which are important for local stakeholders. In this study we: 1) developed relationships between observed whole basin and nearshore bloom sizes, and 2) updated and extended a Bayesian seasonal bloom forecast model to provide new regional predictions. The western basin was subdivided into 5 km near-shore regions, and bloom start date, size, and intensity were quantified with MODIS-derived images of chlorophyll concentrations for July–October 2002–2016 for each subdivision and for the entire basin. While bloom severity within each subdivision is temporally and spatially unique, it increased over the study period in each subdivision. The models for the 5 km subdivisions explained between 83 and 95% of variability between regional sizes and whole bloom size for US subdivisions and 51% for the Canadian subdivision. By linking predictive basin-wide models to regional regression estimates, we are now able to better predict potential bloom impacts at scales and in specific areas that are vital to the economic well-being of the region and allow for better management responses.

A Framework for Assessing Instream Supporting Ecosystem Services Based on Hydroecological Modelling

River systems provide diverse ecosystem services (ES), such as flood regulation (regulating), fresh water (provisioning), nutrient cycling (supporting), and recreation (cultural), among others. The construction of infrastructure (e.g., for hydropower, irrigation) enhances the delivery of tangible ES for example food or energy (generally provisioning) to meet human needs. However, the resulting change to river flows threatens both the ecological health of a river and its ability to provide intangible but vital ES, for example those which support the delivery of other services. Understanding these supporting ES processes in river systems is essential to fully recognise the impact of water resources development on ES delivery. Whilst approaches for assessing instream supporting ES are under development, to date few provide quantitative methods for assessing delivery. Thus, this paper sets out a framework for the assessment of instream supporting ES using hydroecological modelling. It links supporting ES delivery to fluvial hydrological indicators through the use of ecologically relevant hydrological indices and macroinvertebrate flow preferences. The proposed framework is demonstrated on the Beas River basin (Western Himalayas, India), and is flexible enough to be transferred to a basin-wide model, thereby allowing ES relationships to be accounted for in basin-wide water resources planning.

Modelling sediment fluxes in the Danube River Basin with SWAT

Sediment management is of prior concern in the Danube Basin for provision of economic and environmental services. This study aimed at assessing current (1995–2009) sediment fluxes of the Danube Basin with SWAT model and identifying sediment budget knowledge gaps. After hydrologic calibration, hillslope gross erosion and sediment yields were broadly calibrated using ancillary data (measurements in plots and small catchments, and national and European erosion maps). Mean annual sediment concentrations (SSC) from 269 gauging stations (2968 station-year entries; median 19mg/L, interquartile range IQR 10–36mg/L) were used for calibrating in-stream sediments. SSC residuals (simulations-observations) median was 2mg/L (IQR −14; +22mg/L). In the validation dataset (172 gauging stations; 1457 data-entries, median 17mg/L, IQR 10–28), median residual was 9mg/L (IQR −9; +39mg/L). Percent bias in an independent dataset of annual sediment yields (SSY; 689 data-entries in 95 stations; median 52t/km2/y, IQR 20–151t/km2/y) was −21.5%. Overall, basin-wide model performance was considered satisfactory. Sediment fluxes appeared overestimated in some regions (Sava and Velika Morava), and underestimated in others (Siret-Prut and Romanian Danube), but unbiased elsewhere. According to the model, most sediments were generated by hillslope erosion. Streambank degradation contributed about 5% of sediments, and appeared important in high stream power Alpine reaches. Sediment trapping in reservoirs and floodplain deposition was probably underestimated and counterbalanced by high stream deposition. Factor analysis showed that model underestimations were correlated to Alpine and karst areas, whereas underestimations occurred in high seismicity areas of the Lower Danube. Contemporary sediment fluxes were about one third of values reported for the 1980s for several tributaries of the Middle and Lower Danube. Knowledge gaps affecting the sediment budget were identified in the contributions of some erosion processes (glacier erosion, gully erosion and mass movements), and in-stream sediment dynamics.

Developing an Effective Model for Predicting Spatially and Temporally Continuous Stream Temperatures from Remotely Sensed Land Surface Temperatures

Although water temperature is important to stream biota, it is difficult to collect in a spatially and temporally continuous fashion. We used remotely-sensed Land Surface Temperature (LST) data to estimate mean daily stream temperature for every confluence-to-confluence reach in the John Day River, OR, USA for a ten year period. Models were built at three spatial scales: site-specific, subwatershed, and basin-wide. Model quality was assessed using jackknife and cross-validation. Model metrics for linear regressions of the predicted vs. observed data across all sites and years: site-specific r2 = 0.95, Root Mean Squared Error (RMSE) = 1.25 °C; subwatershed r2 = 0.88, RMSE = 2.02 °C; and basin-wide r2 = 0.87, RMSE = 2.12 °C. Similar analyses were conducted using 2012 eight-day composite LST and eight-day mean stream temperature in five watersheds in the interior Columbia River basin. Mean model metrics across all basins: r2 = 0.91, RMSE = 1.29 °C. Sensitivity analyses indicated accurate basin-wide models can be parameterized using data from as few as four temperature logger sites. This approach generates robust estimates of stream temperature through time for broad spatial regions for which there is only spatially and temporally patchy observational data, and may be useful for managers and researchers interested in stream biota.

Comparative evaluation of numerical model and artificial neural network for simulating groundwater flow in Kathajodi–Surua Inter-basin of Odisha, India

• Development of groundwater simulation model is first of its kind in the study area. • ANN model developed for groundwater level forecasting in the study area. • ANN model provided better prediction of groundwater levels for shorter horizons. In view of worldwide concern for the sustainability of groundwater resources, basin-wide modeling of groundwater flow is essential for the efficient planning and management of groundwater resources in a groundwater basin. The objective of the present study is to evaluate the performance of finite difference-based numerical model MODFLOW and the artificial neural network (ANN) model developed in this study in simulating groundwater levels in an alluvial aquifer system. Calibration of the MODFLOW was done by using weekly groundwater level data of 2 years and 4 months (February 2004 to May 2006) and validation of the model was done using 1 year of groundwater level data (June 2006 to May 2007). Calibration of the model was performed by a combination of trial-and-error method and automated calibration code PEST with a mean RMSE (root mean squared error) value of 0.62 m and a mean NSE (Nash–Sutcliffe efficiency) value of 0.915. Groundwater levels at 18 observation wells were simulated for the validation period. Moreover, artificial neural network models were developed to predict groundwater levels in 18 observation wells in the basin one time step (i.e., week) ahead. The inputs to the ANN model consisted of weekly rainfall, evaporation, river stage, water level in the drain, pumping rate of the tubewells and groundwater levels in these wells at the previous time step. The time periods used in the MODFLOW were also considered for the training and testing of the developed ANN models. Out of the 174 data sets, 122 data sets were used for training and 52 data sets were used for testing. The simulated groundwater levels by MODFLOW and ANN model were compared with the observed groundwater levels. It was found that the ANN model provided better prediction of groundwater levels in the study area than the numerical model for short time-horizon predictions.

Identifying the sustainable groundwater yield in a Chinese semi-humid basin

Summary The primary goal of this work was to identify the sustainable groundwater yield which is a key reference of reasonable groundwater development, but also a complex issue in current hydrogeologic science. One major limit to identify sustainable groundwater yield is the lack of a unified evaluation criterion because there are many factors involved in hydrological systems that are difficult to quantify. To address this problem, an integrated evaluation model was constructed for a series of purposes including the maximal efficiency of water use, the integral benefit of development and utilization, the optimized environmental water demand and the minimal anthropogenic influence on groundwater system. It consists of a benefit model, a water cycling simulation model and an optimization model. The basin-wide model for water cycling simulation was a basic component to simulate scenarios with different constraints, and the best water development strategy was thereafter identified using the integral benefit model of water resources development. The Yinma River basin in a Chinese semi-humid region was selected as the case study area. Results indicated the optimized groundwater yield could be sustained by intensive reservoir supply and maintain suitable ecological water demand simultaneously. The work proposed a potential groundwater utilization strategy for economically developing countries across the world.

Assessing the condition of the Missouri, Ohio, and Upper Mississippi rivers (USA) using diatom-based indicators

Diatom-based indicators were developed to assess environmental conditions in the Missouri, Ohio, and Upper Mississippi rivers. Disturbance gradients, comprising the first two principal components derived from a suite of stressor variables, included a trophic gradient (Trophic) and a gradient reflecting agriculture and other development activities (Ag/Dev). Diatom-based indicators were developed by creating models using weighted average calibration and regression-based transfer functions to relate planktonic and periphytic diatom species assemblages to each disturbance gradient. The most predictive disturbance models combined phytoplankton and periphyton assemblages into a single bioindicator model (observed versus inferred: Trophic \( r_{\text{boot}}^{2} = 0. 5 6 \); Ag/Dev \( r_{\text{boot}}^{2} = 0. 7 0 \)). The geographic applicability of bioindicators was assessed by limiting sample geographical range during model calibrations. Geographic scale was limited by creating bioindicators using samples from: (a) each river, and (b) combined Mississippi/Missouri samples excluding Ohio River sites which were chemically unique. Indicator performance decreased with geographically restrictive models, therefore river basin-wide models, developed across all three rivers, is recommended. The most effective diatom-based disturbance bioindicators for this great river ecosystem could be applied using phytoplankton, periphyton, or combined assemblages to infer both trophic and agriculture/development disturbances.

Groundwater occurrence and flow patterns in the Ishiagu mining area of southeastern Nigeria

The Ishiagu area is a water scarce region and has played host to mining activities for more than four decades. Mining-related activities have become a threat to potable water supply in the area. This paper is an attempt to show the extent of this threat and in particular, investigate the regional groundwater occurrence and flow pattern based on GPS, water well and geological data. This basinwide model can be used for further groundwater assessment, pollution control and contaminant management. Groundwater occurs between 2.4 and 9 m in the Lekwesi-Lokpaukwu area; 1.5–3.7 m in the Ndi-Ugbugbor-Ayaragu axis and 1.2–4.6 m in the Ishiagu area. Recharge areas include the Leru-Amaubiri-Lekwesi sandstone hills and the Ihetutu-Ugwuajirija mine field. While the ultimate sink of contamiants is the Ivo River system, other discharge axis is the Ishiagu-Ayaragu axis and the Ogwor Ndi-Ugbugbor zone. An unconfined and a confined (>10) circulation groundwater system was inferred, and flow model reveals that a large part of Ishiag-Ayaragu and Ndi-Ugbugbor part of the study area suffer polluted recharge from the Pb/Zn mining area. Groundwater was also subjected to hierarchical cluster analysis and the existence of 3–4 hydrological regimes, which revealed: Unpolluted recharge areas, areas affected by polluted recharge, a deep water and shallow water circulation and mine effluents.

Basin modelling and source rock evaluation in the Guyana Basin

The Guyana Basin contains a world-class source rock of Late Cretaceous age, but no hydrocarbon fields have yet been discovered offshore. In order to evaluate source rock maturity, we used basin modelling software to model a grid of interpreted 2D seismic sections and combined the 2D modelling results to build a basin-wide model. The burial depth, temperature, and transformation ratio of the Cretaceous source rocks were calculated from the end of the Cretaceous to the present, and mapped over the entire basin. The modelling results show that regional uplift during Late Cretaceous–middle Miocene time slowed the maturation of the Cretaceous source rock in the basin except in the south-eastern depocentre. In this depocentre, the oil window was reached during the Palaeogene, by which time few reservoir and seal rocks had been deposited. For the rest of the basin, uplift of the Waini arch and the middle Miocene regional uplift slowed maturation of the source rock. Possible reservoirs that could have received hydrocarbons from the south-eastern depocentre include Cretaceous-middle Miocene clastic rocks that pinch out against the southern flank of the Waini arch and stratigraphic traps along the shelf.

Physical controls on carbon dioxide transfer velocity and flux in low-gradient river systems and implications for regional carbon budgets

[1] Outgassing of carbon dioxide (CO2) from rivers and streams to the atmosphere is a major loss term in the coupled terrestrial-aquatic carbon cycle of major low-gradient river systems (the term “river system” encompasses the rivers and streams of all sizes that compose the drainage network in a river basin). However, the magnitude and controls on this important carbon flux are not well quantified. We measured carbon dioxide flux rates (FCO2), gas transfer velocity (k), and partial pressures (pCO2) in rivers and streams of the Amazon and Mekong river systems in South America and Southeast Asia, respectively. FCO2 and k values were significantly higher in small rivers and streams (channels 100 m wide). Small rivers and streams also had substantially higher variability in k values than large rivers. Observed FCO2 and k values suggest that previous estimates of basinwide CO2 evasion from tropical rivers and wetlands have been conservative and are likely to be revised upward substantially in the future. Data from the present study combined with data compiled from the literature collectively suggest that the physical control of gas exchange velocities and fluxes in low-gradient river systems makes a transition from the dominance of wind control at the largest spatial scales (in estuaries and river mainstems) toward increasing importance of water current velocity and depth at progressively smaller channel dimensions upstream. These results highlight the importance of incorporating scale-appropriate k values into basinwide models of whole ecosystem carbon balance.

The Impact of Nitrogen and Phosphorus Fertilizer Loading on River and Subsurface Water Quality in Yata River Basin: An Integrated, Basin-wide Modeling Approach

The Impact of Nitrogen and Phosphorus Fertilizer Loading on River and Subsurface Water Quality in Yata River Basin: An Integrated, Basin-wide Modeling Approach

Analysis on Equitable and Reasonable Allocation Models of Water Resources in the Lancang-Mekong River Basin

In this paper, according to the basic rule of the equitable and reasonable utilization of water resources in international rivers, the normal approaches of resolving the conflicts over water and the basic models of water allocation are introduced. The tendency and the problems of water utilization among the riparian states in Lancang-Mekong River are discussed. The extent of cooperation and the conditions of the management institution of the river basin are analyzed. In the present situation, it is considered that the basin-wide allocation model of water resources is the best one in Lancang-Mekong River.

High resolution simulations on the North Aegean Sea seasonal circulation

Abstract. The seasonal characteristics of the circulation in the North Aegean Sea are examined with the aid of a climatological type simulation (three-year run with perpetual year forcing) on a fine resolution grid (2.5 km by 2.5 km). The model is based on the Princeton Ocean Model with a parameterisation of plume dynamics that is employed for the input of waters with hydrographic properties that are different than the properties of basin waters, as the Black Sea Water (BSW) outflow through the Dardanelles Strait and riverine sources. The model is nested with a sequence of coarser regional and basin-wide models that provide for the long-term interaction between the study area and the Eastern Mediterranean at large. The results are employed to discuss the response of the North Aegean to the important circulation forcing mechanisms in the region, namely wind stress, heat and salt fluxes, buoyancy due to rivers and the BSW outflow (which is low in salinity and occasionally low in temperature) and the interaction with the Southern Aegean. The high resolution allows for the detailed representation of the complicated topography that presides in the region. This helps produce a rich eddy field and it allows for variability in the pathways of BSW that has implications in the basin hydrography and circulation.Key words. Oceanography: general (continental shelf processes; numerical modeling)

Scale-Related Aspects of Nested Finite Difference Ocean Models

We describe a fully nonlinear wind-forced nested ocean model. The model has been configured for both the Greenland–Iceland–Norwegian (GIN) Sea, an open ocean basin, and the Mediterranean Sea, a semienclosed basin. Prescribed nested boundary conditions are corrected with a mixed Orlanski/Flather-type radiation of the difference between the two numerical solutions. A second correction can then be made to restore conservation of desired properties across the grid interface. The nested experiments have produced multiyear simulations in good agreement with the basin-wide model. The differences between the basin-wide and the limited-area solutions are related, in part, to the different scales present in the respective numerical solutions. We attribute our ability to produce realistic year long limited-area nested simulations to a reduction of these scale-related modeling differences, including reducing the effects of aliasing between the two grids.

Tectonic modelling of the Middle Jurassic synrift stratigraphy in the Oseberg–Brage area, northern Viking Graben

A finite difference model, allowing for episodic movements along different faults, is used to examine the effect of tectonics on the stratigraphic signature in the Oseberg–Brage area in the northern Viking Graben. Constraints are provided by local exploration and production well data and 3‐D seismic coverage, and a regional depth‐converted seismic line.In the modelling, we focus on the influence of varying rates of fault movement on stratigraphic signatures such as upflank unconformities and changes in layer thickness. We couple the basinwide features of the northern Viking Graben with the fault‐block‐scale features of the Oseberg–Brage area by using parameter constraints derived by large‐scale modelling as input for the local‐scale model. In addition, subsidence patterns resulting from the basinwide model were used as background subsidence for the fault block model of the Oseberg–Brage area.The model results indicate that the alternating activation of different faults with varying extension rates can cause stratigraphic features such as unconformities, condensation and onlap/offlap patterns. Onlap occurs during periods of low extension rates. An increase in extension rate along a fault causes footwall uplift, resulting in condensation or upflank erosion yielding unconformities. This influence can also affect sub‐basins further away from the fault. Downdip layer thickening reflects the local tilting of fault blocks.The coupling of the local and regional scales turns out to be essential in explaining the stratigraphy of the Oseberg–Brage area: basinward and, notably, updip layer thickening as observed on some of the fault blocks can only be explained by activity of the boundary fault on the opposing, western margin of the northern Viking Graben.

Sedimentology and Diagenesis of the St. Peter Sandstone, Central Michigan Basin, United States (1)

The Middle Ordovician St. Peter Sandstone occurs at depths between 1600 and 3600 m in the central Michigan basin. Integration of conventional core and wireline log studies indicates that the formation consists of, from base to top, (1) up to 250 m of sandstone deposited in intertidal and supratidal sand flats with associated dolomitic lagoonal deposits, and shallow subtidal shoreface environments, (2) sandstones deposited in subtidal shoreface to upper offshore environments, and, (3) dolomitic and argillaceous sands deposited in a storm-dominated epeiric sea. Sandstone composition is closely related to depositional environment: quartz arenites occur in higher energy littoral facies, whereas feldspathic and carbonate-rich sands occur in predominantly lower energy shelfal f cies. Important modification of primary mineralogy and porosity occurred during diagenesis. A generalized, basinwide model for paragenesis includes (1) early calcite marine cement, (2) syndepositional dolomitization, (3) widespread precipitation of quartz and K-feldspar overgrowths, (4) pervasive replacement of early carbonate by burial dolomite, (5) local dissolution of unstable framework grains (e.g., K-feldspar) and carbonate cement, (6) growth of authigenic clay, and (7) pressure solution and additional precipitation of quartz overgrowths. Authigenic clays apparently formed along with or subsequent to economically significant secondary porosity. The different pathways of sandstone diagenesis observed in the St. Peter Sandstone are largely dependent on primary textures and composition inherited from the environment of deposition rather than other factors, such as depth of burial or position in the basin. The relationships among primary textures and composition, diagenesis, and reservoir sandstone properties is useful for prediction of reservoir quality in the St. Peter Sandstone in the Michigan subsurface. Weakly cemented sandstone reservoirs characteristic of high-energy shoreface and shallow offshore depositional environments have the best reservoir quality in the basin. Clay-cemented sandstone reservoirs deposited on offshore shelves have the poorest reservoir quality. Incompletely quartz-cemented sandstone reservoirs, comm n in intertidal/supratidal facies, have intermediate reservoir quality.