# Computers Geosciences Modeling for Environmental Change

From CSDMS

# COMPUTERS & GEOSCIENCES Modeling for Environmental Change

CSDMS annual meeting 2010 **Modeling for Environmental Change** took place October 14-17, 2010 in San Antonio, Texas. One of the outcomes was a special issue of Computers & Geosciences, volume 53, ISSN 0098-3004, that will be published April, 2013. Below is an overview of the papers with their abstracts.**We would like to thank all authors as well as the reviewers for their effort!**

**Content**

**Modeling for environmental change***Albert J. Kettner and James P.M. Syvitski*No abstract is available for this article.

Albert J. Kettner and James P.M. Syvitski, 2013. Modeling for environmental change,*Computers & Geosciences*, V.**53**, 1-2. DOI: 10.1016/j.cageo.2012.07.028**A component-based approach to integrated modeling in the geosciences: The design of CSDMS***Scott D. Peckham, Eric W.H. Hutton and Boyana Norris*Development of scientific modeling software increasingly requires the coupling of multiple, independently developed models. Component-based software engineering enables the integration of plug-and-play components, but significant additional challenges must be addressed in any specific domain in order to produce a usable development and simulation environment that also encourages contributions and adoption by entire communities. In this paper we describe the challenges in creating a coupling environment for Earth-surface process modeling and the innovative approach that we have developed to address them within the Community Surface Dynamics Modeling System.

Scott D. Peckham, Eric W.H. Hutton and Boyana Norris, 2013. A component-based approach to integrated modeling in the geosciences: The design of CSDMS,*Computers & Geosciences*, V.**53**, 3-12. DOI: 10.1016/j.cageo.2012.04.002**A feature model of coupling technologies for Earth System Models***Rocky Dunlap, Spencer Rugaber and Leo Mark*Couplers that link together two or more numerical simulations are well-known abstractions in the Earth System Modeling (ESM) community. In the past decade, reusable software assets have emerged to facilitate scientists in implementing couplers. While there is a large amount of overlap in the features supported by software coupling technologies, their implementations differ significantly in terms of both functional and non-functional properties. Using a domain analysis method called feature analysis, we explore the spectrum of features supported by coupling technologies used to build today's production ESMs.

Rocky Dunlap, Spencer Rugaber and Leo Mark, 2013. A feature model of coupling technologies for Earth System Models,*Computers & Geosciences*, V.**53**, 13-20. DOI: 10.1016/j.cageo.2011.10.002**Progress in coupling models of coastline and fluvial dynamics***Andrew D. Ashton, Eric W.H. Hutton, Albert J. Kettner, Fei Xing, Jisamma Kallumadikal, Jaap Nienhuis and Liviu Giosan*The morphology and depositional history of wave-influenced deltas reflects the interplay between the fluvial and coastal domains. Here we present initial results of the coupling of stand-alone coastal and terrestrial models within the Community Surface Dynamics Modeling System (CSDMS) Component Modeling Tool (CMT), applied to study the evolution of wave-influenced deltas. The coastal domain is modeled using the Coastline Evolution Model (CEM), which simulates plan-view shoreline evolution due to wave-driven alongshore sediment transport, with fluvial influence incorporated by adding sediment along the coastline. The first application involves one-way coupling of the climate-driven hydrological transport model HydroTrend with CEM to investigate how fluctuations in sediment input rates due to climate change may affect the plan-view delta morphology and evolution. Simulations reveal that sediment discharge variability can have a significant effect on delta morphology if fluvial delivery of sediment temporarily exceeds the capacity for alongshore sediment transport to remove sediment from regions proximal to the river mouth. The second application involves two-way coupling of CEM with a river with multiple active distributary channels. In this case, changes to the coastline affect the apportionment of discharge flowing out of coeval distributaries through a two-way feedback. Model simulations where distributary length affects sediment discharge demonstrate how the dynamics of one distributary can control the sediment discharge of another. Wave-influenced deltas exhibiting strong channel feedbacks may prograde delta lobes faster than those without feedback. These preliminary model experiments demonstrate the capability of CMT to bidirectionally couple models that represent different process domains and were developed and designed independently (i.e. without the intentions of such coupling), offering the potential for further numerical studies of interactions taking place at the intersection of different process realms.

Andrew D. Ashton, Eric W.H. Hutton, Albert J. Kettner, Fei Xing, Jisamma Kallumadikal, Jaap Nienhuis and Liviu Giosan, 2013. Progress in coupling models of coastline and fluvial dynamics,*Computers & Geosciences*, V.**53**, 21-29. DOI: 10.1016/j.cageo.2012.04.004**Progress in coupling models of human and coastal landscape change***A. Brad Murray, Sathya Gopalakrishnan, Dylan E. McNamara and Martin D. Smith*Humans are increasingly altering the Earth's surface, and affecting processes that shape and reshape landscapes. In many cases, humans are reacting to landscape-change processes that represent natural hazards. Thus, the landscape is reacting to humans who are reacting to the landscape. When the timescales for landscape change are comparable to those of human dynamics, human and ‘natural’ components of developed environments are dynamically coupled—necessitating coupling models of human and physical/biological processes to study either environmental change or human responses. Here we focus on a case study coupling models of coastal economics and physical coastline change. In this modeling, coastline change results from patterns of wave-driven sediment transport and sea-level rise, and shoreline stabilization decisions are based on the benefits of wide beaches (capitalized into property values) balanced against the costs of stabilization. This interdisciplinary modeling highlights points that may apply to other coupled human/natural systems. First, climate change, by accelerating the rates of landscape change, tends to strengthen the coupling with human dynamics. In our case study, both increasing sea-level-rise rates and changing storm patterns tend to increase shoreline change rates, which can induce more vigorous shoreline stabilization efforts. However, property values can fall dramatically as erosion rates and stabilization costs rise, which can also lead to the abandonment of expensive stabilization methods as shoreline change rates increase. Second, socio-economic change can also strengthen the human/landscape coupling. Changing costs of shoreline stabilization can alter stabilization decisions, which in turn alters patterns of coastline change. The coupled modeling illuminates the long-range effects of localized shoreline stabilization efforts; communities arrayed along a coastline are unwittingly affecting each other's erosion rates, and therefore each other's economies. Our coupled modeling experiments show that spatial distributions of property values and erosion rates can jointly affect economic outcomes, resource allocation between communities, and patterns of shoreline change. These findings raise questions about coastal management strategies, and efficient and equitable allocation of scarce resources among coastal communities.

A. Brad Murray, Sathya Gopalakrishnan, Dylan E. McNamara and Martin D. Smith, 2013. Progress in coupling models of human and coastal landscape change,*Computers & Geosciences*, V.**53**, 30-38. DOI: 10.1016/j.cageo.2011.10.010**A geometric model for the dynamics of a fluvially dominated deltaic system under base-level change***Jorge Lorenzo-Trueba, Vaughan R. Voller and Chris Paola*We present a geometric model to study the role of base-level change in the dynamics of the alluvial-bedrock transition and shoreline positions in a fluvially dominated deltaic system. The domain of the problem is a sediment wedge in the long-profile cross-section. On assuming that the fluvial surface has a quadratic form, its evolution is determined by imposing an overall volume balance, and conditions for the elevations and slopes at the domain boundaries. This results in a coupled system, involving one ordinary differential equation and one non-linear equation. These equations are solved through an explicit Euler time stepping algorithm to predict the movement of the shoreline and alluvial-bedrock transition boundaries under a wide range of base-level change conditions. The mathematics of the approach are verified by comparing predictions from the geometric model with a closed form solution of a downslope gravity-driven transport model under the specific case of a square-root of time base-level change. Testing with more general base-level change scenarios reveals that this simple geometric mass balance is able to predict system dynamics that are fully consistent with both physical and numerical experiments. Moreover, model predictions under a base-level cycle (fall-rise) suggest a behavior where river incision occurs during the base-level rise stage, a predicted dynamic that has not been previously reported.

Jorge Lorenzo-Trueba, Vaughan R. Voller and Chris Paola, 2013. A geometric model for the dynamics of a fluvially dominated deltaic system under base-level change,*Computers & Geosciences*, V.**53**, 39-47. DOI: 10.1016/j.cageo.2012.02.010**Simulating post-LGM riverine fluxes to the coastal zone: The Waipaoa River System, New Zealand***Phaedra Upton, Albert J. Kettner, Basil Gomez, Alan R. Orpin, Nicola Litchfield and Michael J. Page*HydroTrend, a climate-driven hydrologic transport model, is used to simulate the suspended sediment discharge of the Waipaoa River System (WRS) over the last 5.5 kyr. We constrain the precipitation input with a paleo-rainfall index derived from the high-resolution Lake Tutira storm sediment record. The simulation is extended to 22 ka using a lower resolution version of the model, constrained by terrestrial and marine paleoenvironment indicators and a simulated model of northeast New Zealand's climate at the Last Glacial Maximum (LGM). Comparison of the 5.5 kyr simulation with the shelf sediment core MD97-2122 suggests that the sediment flux variations observed on the shelf primarily reflect changes in rainfall associated with wetter and drier periods of centuries to millennia duration. Storage of sediment on the Waipaoa River floodplain (Poverty Bay Flats) moderates the signal by reducing the sediment flux reaching the coast. During the LGM conditions were more erosive than the Holocene with tussock and grass dominated vegetation. For erodibility four times the Holocene's and half today's, the LGM Waipaoa River System would have generated approximately half the current sediment yield and about 3 times the amount generated when the catchment was fully forested.

Phaedra Upton, Albert J. Kettner, Basil Gomez, Alan R. Orpin, Nicola Litchfield and Michael J. Page, 2013. Simulating post-LGM riverine fluxes to the coastal zone: The Waipaoa River System, New Zealand,*Computers & Geosciences*, V.**53**, 48-57. DOI: 10.1016/j.cageo.2012.02.001**Isostatic flexure of a finite slope due to sea-level rise and fall***Eric W.H. Hutton, James P.M. Syvitski and Anthony B. Watts*Sea level has risen on order of 100 m since the last glacial maximum (LGM), increasing the load on continental shelves and inducing lithospheric flexure. An analytic solution for the deflection of a linear slope due to sea level fluctuations is derived, based on a one-dimensional elastic plate model. This analytic solution provides deflection estimates of global continental shelves, due only to increases in water loading, effective elastic thickness (which is a proxy for the strength of the lithosphere with 2°×2° resolution) and the local shape of LGM continental margins (one-arc minute resolution). Changes in eustatic sea level are thus disengaged from changes in relative sea level. Variations in water loading can alter the slopes of continental shelves on the order of 30%, but importantly the magnitude is regionally variable. Hydro-isostasy adds to the magnitude of a sea-level rise, long after the eustatic component of the sea-level rise has ended. A sea-level rise will produce a steepening of a continental shelf, while a sea-level drop causes a decrease in shelf gradient and an increase in the total shoreline regression. Quantifying this effect is essential to reconstructing stream gradients, estimating sediment delivered by rivers, for estimating accommodation space through a sea-level cycle, and to support the use of paleo-shoreline to estimate eustatic sea-level fluctuations.

Eric W.H. Hutton, James P.M. Syvitski and Anthony B. Watts, 2013. Isostatic flexure of a finite slope due to sea-level rise and fall,*Computers & Geosciences*, V.**53**, 58-68. DOI: 10.1016/j.cageo.2012.03.020**Modeling the subsurface thermal impact of Arctic thaw lakes in a warming climate***Nora Matell, Robert S. Anderson, Irina Overeem, Cameron Wobus, Frank E. Urban and Gary D. Clow*Warming air temperatures in the Arctic are modifying the rates of thermokarst processes along Alaska's Arctic Coastal Plain. The Arctic Coastal Plain is dominated by thaw lakes. These kilometer-scale lakes are the most visible surface features in the region, and they provide important habitats for migratory birds. The lakes are formed by thermokarst processes, and are therefore susceptible to change as warming continues. We present a 1D numerical model of permafrost and subsidence processes in order to investigate the subsurface thermal impact of thaw lakes of various depths, and to evaluate how this impact might change in a warming climate. Currently, most thaw lakes in the region are shallow (<∼2 m deep), freeze to their base each winter, and are not underlain by permanently unfrozen ground (taliks). Field observations indicate that these shallow lakes have not greatly altered the thermal structure of the subsurface. Our model suggests that under a warming scenario, the number of lakes that do not freeze to their base during the winter, and are therefore underlain by taliks, will increase. Such changes could substantially alter the hydrology of the Arctic Coastal Plain.

Nora Matell, Robert S. Anderson, Irina Overeem, Cameron Wobus, Frank E. Urban and Gary D. Clow, 2013. Modeling the subsurface thermal impact of Arctic thaw lakes in a warming climate,*Computers & Geosciences*, V.**53**, 69-79. DOI: 10.1016/j.cageo.2011.08.028**WBMsed, a distributed global-scale riverine sediment flux model: Model description and validation***Sagy Cohen, Albert J. Kettner, James P.M. Syvitski and Balázs M. Fekete*Quantifying continental sediment flux is a fundamental goal of earth-system science. Ongoing measurements of riverine-suspended sediment fluxes to the oceans are limited (<10% of rivers) and intrabasin measurements are even scarcer. Numerical models provide a useful bridge to this measurement gap and offer insight to past and future trends in response to human and environmental changes. BQART is a global empirical model that calculates long-term suspended sediment loads. The Psi statistical model accounts for intra- and interannual variability in these BQART sediment flux predictions. Here BQART and Psi are compiled as a new module of the WBMplus global daily water balance/transport model, a central component in the FrAMES hydrological–biogeochemical modeling scheme. The resulting model (WBMsed) simulates spatially and temporally explicit (pixel scale and daily) sediment fluxes over continental Earth. We test WBMsed predictions with (1) observed sediment loads at 95 river mouths and to the original BQART predictions for these rivers, and (2) 11 years of daily sediment flux observations of 11 USGS stations. The results show that WBMsed captures the multiyear average, interannual and intraannual trends but considerably over- and underpredict daily fluxes for extreme discharge periods. These over- and underpredictions are mainly driven by respective mispredictions of water discharge fluxes. Future improvements to WBMsed to address these limitations are provided.

Sagy Cohen, Albert J. Kettner, James P.M. Syvitski and Balázs M. Fekete, 2013. WBMsed, a distributed global-scale riverine sediment flux model: Model description and validation,*Computers & Geosciences*, V.**53**, 80-93. DOI: 10.1016/j.cageo.2011.08.011**Software for evaluating sediment-induced stratification in open-channel flows***Tzu-hao Yeh and Gary Parker*Open channel flow containing sediment suspension subjects itself to a density gradient in the vertical direction, i.e. density self-stratification, due to the tendency for suspended sediment to settle. Velocity and concentration profiles under the effect of density stratification may differ significantly from the conventional logarithmic and Rousean distributions associated with open channel flow. It is hence important to include this effect into flow computations in order to accurately predict flow characteristics such as the resistance coefficient, near-bed sediment concentration, flow and sediment discharge. In this study we introduce a software, StratSedOC, for such purpose. The application contains a user-friendly interface which allows users to evaluate and visualize the differences in the velocity, concentration and eddy viscosity profiles when stratification effects are taken into account. In addition to the standard logarithmic/Rousean formulation, the model uses three turbulence closures, i.e. an algebraic model (Smith–McLean) and two differential models (k-ε and Mellor–Yamada). The software application can also be used to study the effect of sediment mixtures on flow stratification under different boundary conditions for near-bed sediment concentration. Comparison among the model and experimental results suggests that the Mellor–Yamada model predicts a damping effect on the eddy viscosity which is similar to the Smith–McLean model, while the k-ε model consistently predicts weaker stratification effects. Based on this result, a modified boundary condition for the k-ε model is then proposed.

Tzu-hao Yeh and Gary Parker, 2013. Software for evaluating sediment-induced stratification in open-channel flows,*Computers & Geosciences*, V.**53**, 94-104. DOI: 10.1016/j.cageo.2011.12.004**Morphodynamic modeling using the Telemac finite-element system***Catherine Villaret, Jean-Michel Hervouet, Rebekka Kopmann, Uwe Merkel and Alan G. Davies*The open-source finite-element system Telemac has been applied to simulate various complex hydrodynamic and morphodynamic situations including waterways, curved channels, recirculating flows and wave-induced littoral transport. In the applications presented here, the sediment transport model is mainly restricted to the transport of non-cohesive sediments, which relies on classical semi-empirical concepts including sand grading effects, parameterization of secondary currents and wave effects. In comparison with other comprehensive modeling systems (Delft-3D, Mike-21, etc.), the main originality lies in the efficiency and flexibility of the finite elements. Thanks to the optimization of numerical schemes, parallelism, as well as tremendous progress in the performance of computers, bed evolution can be calculated on basin scale (10–100 km) and for the medium term (years to decades), without the use of hydrodynamic filtering methods. As a novelty in release 6.0, we present a method of feedback for the bed roughness, which reduces uncertainty in the prediction of both transport rates and flow velocities.

Catherine Villaret, Jean-Michel Hervouet, Rebekka Kopmann, Uwe Merkel and Alan G. Davies, 2013. Morphodynamic modeling using the Telemac finite-element system,*Computers & Geosciences*, V.**53**, 105-113. DOI: 10.1016/j.cageo.2011.10.004**A numerical model to develop long-term sediment budgets using isotopic sediment fingerprints***Enrica Viparelli, J. Wesley Lauer, Patrick Belmont and Gary Parker*Developing accurate long-term, basin-scale sediment budgets using isotopic sediment fingerprints requires a sediment routing model that not only accounts for a range of sediment source terms (e.g. tributaries, surface erosion and erosion of bluffs and terraces) but also considers the variation in time of volume and tracer concentration for the sediment stored in the floodplain. This is accomplished here using a tracer routing model that accounts for production and decay of radioisotopes in the floodplain. The numerical model focuses on the average (i.e. across many hydrographs or years) budget of sediment and tracers at reach scale. To account for storage and remobilization of bulk sediment and/or tracer material, the model represents the floodplain as a system that can gain or lose mass depending on overbank deposition and net bank erosion rates. Isotopic tracers within the floodplain reservoir can be produced as a function of cosmic ray bombardment or atmospheric fallout, and can decay according to a first-order rate equation. Governing equations are derived using a simplified geometry that treats rivers at reach scale: channel sinuosity and migration rates are user-specified parameters, exchange of sediment and tracers between the river and floodplain is modeled at each cross section, and governing equations are derived in a 1D, width-averaged formulation. When the system reaches mobile equilibrium, the sediment deposited on the floodplain through overbank deposition is balanced by the sediment eroded from the floodplain through channel migration and by sediment contributed from external sources. The model is applied to a generic river system and is shown to converge over time to an equilibrium condition that is consistent with an independent analytical solution.

Enrica Viparelli, J. Wesley Lauer, Patrick Belmont and Gary Parker, 2013. A numerical model to develop long-term sediment budgets using isotopic sediment fingerprints,*Computers & Geosciences*, V.**53**, 114-122. DOI: 10.1016/j.cageo.2011.10.003**Taking it to the streets: The case for modeling in the geosciences undergraduate curriculum***Karen Campbell, Irina Overeem and Maureen Berlin*The United States faces a crisis in education: a dire shortage of students sufficiently prepared in the STEM (Science, Technology, Engineering and Mathematics) disciplines to competitively enter the workforce (National Education Technology Plan, 2010). At the same time, there is increasing demand for well-trained geoscientists in a variety of careers related to the environment and natural resources. Many efforts, including the recently released Earth Science and Climate Literacy Principles, seek to promote better Earth science education, as well as to strengthen the Earth science literacy of the entire US population. Yet even those undergraduate students who choose to major in geology or related geoscience disciplines rarely acquire sufficient quantitative skills to be truly competitive graduate students or professionals. Experience with modeling, during their undergraduate careers, could greatly increase the quantitative literacy of geoscience majors and help them appreciate the real world applicability of mathematics and computational methods in their future careers in the geosciences.

Karen Campbell, Irina Overeem and Maureen Berlin, 2013. Taking it to the streets: The case for modeling in the geosciences undergraduate curriculum,*Computers & Geosciences*, V.**53**, 123-128. DOI: 10.1016/j.cageo.2011.09.006**CarboCAT: A cellular automata model of heterogeneous carbonate strata***Peter M. Burgess*CarboCAT is a new numerical model of carbonate deposystems that uses a cellular automata to calculate lithofacies spatial distributions and hence to calculate the accumulation of heterogeneous carbonate strata in three dimensions. CarboCAT includes various geological processes, including tectonic subsidence, eustatic sea-level oscillations, water depth-dependent carbonate production rates in multiple carbonate factories, lateral migration of carbonate lithofacies bodies, and a simple representation of sediment transport. Results from the model show stratigraphically interesting phenomena such as heterogeneous strata with complex stacking patterns, laterally discontinuous subaerial exposure surfaces, nonexponential lithofacies thickness distributions, and sensitive dependence on initial conditions whereby small changes in the model initial conditions have a large effect on the final model outcome. More work is required to fully assess CarboCAT, but these initial results suggest that a cellular automata approach to modeling carbonate strata is likely to be a useful tool for investigating the nature and origins of heterogeneity in carbonate strata.

Peter M. Burgess, 2013. CarboCAT: A cellular automata model of heterogeneous carbonate strata,*Computers & Geosciences*, V.**53**, 129-140. DOI: 10.1016/j.cageo.2011.08.026**Polydisperse turbidity currents propagating over complex topography: Comparison of experimental and depth-resolved simulation results***Mohamad M. Nasr-Azadani, Brandon Hall and Eckart Meiburg*A computational investigation is presented of mono-, bi-, and polydisperse lock-exchange turbidity currents interacting with complex bottom topography. Simulation results obtained with the software TURBINS are compared with laboratory experiments of other authors. Several features of the flow, such as deposit profiles, front location, suspended mass, and runout length, are discussed. For a monodisperse lock-exchange current propagating over a flat surface, we investigate the influence of the boundary conditions at the streamwise and top boundaries, and we generally find good agreement with corresponding laboratory experiments. However, we note some differences with a second set of experimental data for polydisperse turbidity currents over flat surfaces. A comparison with experimental data for bidisperse currents with varying mass fractions of coarse and fine particles yields good agreement for all cases except those where the current consists almost exclusively of fine particles. For polydisperse currents over a two-dimensional bottom topography, significant discrepancies are observed. Possible reasons are discussed, including erosion and bed load transport. Finally, we investigate the influence of a three-dimensional Gaussian bump on the deposit pattern of a bidisperse current.

Mohamad M. Nasr-Azadani, Brandon Hall and Eckart Meiburg, 2013. Polydisperse turbidity currents propagating over complex topography: Comparison of experimental and depth-resolved simulation results,*Computers & Geosciences*, V.**53**, 141-153. DOI: 10.1016/j.cageo.2011.08.030**Driving plug-and-play models with data from web services: A demonstration of interoperability between CSDMS and CUAHSI-HIS***Scott D. Peckham and Jonathan L. Goodall*There has recently been an increased focus within the earth science community on integration of data and modeling resources. Two examples of projects in this area are the Community Surface Dynamics Modeling System (CSDMS) and the Hydrologic Information System (HIS) project of the Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI). The primary focus of CSDMS is on modeling, specifically on approaches and tools that allow scientists to construct a simulation model as a configuration of linked, interchangeable model components. The primary focus of the HIS is on data, specifically on approaches and tools that allow scientists to easily access and integrate data from different data providers. The synergies between these two projects are obvious as both data and models are needed to support scientific analysis and natural resource management. For this reason, we have explored a means for providing interoperability between the CSDMS and the HIS. In the approach presented here, the HIS web services are used within the CSDMS modeling framework to search and download hydrologic data that can then be easily fed into CSDMS model components. The result of the work is a CSDMS component able to query, download, and provide plug-and-play access to HIS data directly within the CSDMS modeling framework. This approach therefore provides a means for leveraging large sets of scientific data within a sophisticated modeling framework.

Scott D. Peckham and Jonathan L. Goodall, 2013. Driving plug-and-play models with data from web services: A demonstration of interoperability between CSDMS and CUAHSI-HIS,*Computers & Geosciences*, V.**53**, 154-161. DOI: 10.1016/j.cageo.2012.04.019