Godrej, A.

Hester, E.

Little, J.

I-Revues

NOVATECH 2016 
1 
Sustainable management of urban watersheds: a 
system-of-systems approach 
La gestion durable des bassins versants : une approche 
'systèmes de systèmes' 
 
John C. Little, Erich T. Hester, and Adil Godrej 
 
Environmental and Water Resources Engineering Program, Department of Civil 
and Environmental Engineering, Virginia Tech, Blacksburg, Virginia, USA 
(jcl@vt.edu) 
 
RÉSUMÉ 
On reconnaît de plus en plus clairement la nécessité d’une approche systématisée dans l’évaluation 
de la durabilité. Cette prise de conscience est due au fait que l’on doit pouvoir intégrer ou associer un 
large éventail de systèmes, y compris, par exemple, l’eau, l’énergie, l’air, la terre, le climat, 
l’agriculture, la pêche, la sylviculture, l’exploitation minière et l’extraction des ressources, les 
transports, les milieux urbains, la santé des personnes, les écosystèmes naturels, mais aussi d'autres 
systèmes économiques et sociaux. Nous illustrons le développement du cadre commun proposé en 
utilisant le modèle du bassin versant d'Occoquan qui est le premier d’une série de modules, et en 
mettant en valeur certains aspects environnementaux de la durabilité. Nous nous concentrons sur les 
orientations et les indicateurs qui se rapportent à la quantité ou la qualité de l'eau, et sur leurs effets 
sur les systèmes humains et les écosystèmes. Les caractéristiques essentielles du modèle de bassin 
versant sont mesurées au niveau de systèmes où un ensemble d'orientations et d’indicateurs à une 
échelle adéquate sont employés pour évaluer et améliorer la durabilité environnementale. Le 
développement d'une approche uniforme permettant d’évaluer et d’améliorer la durabilité est un défi 
de taille, qui peut prendre des décennies, mais l’objectif même de parvenir à la durabilité se jouera 
peut-être dans des délais similaires, et l’on pourrait gagner énormément en travaillant à la mise en 
place d’un cadre interdisciplinaire commun. 
ABSTRACT 
There is growing recognition of the need for a systems approach when evaluating sustainability.  This 
arises because of the need to integrate or couple a wide range of systems, including, for example, 
water, energy, air, land, climate, agriculture, fishing, forestry, mining and resource extraction, 
transportation, urban environment, human health, natural ecosystems, as well as other economic and 
social systems.  We illustrate the development of the proposed common framework using the 
Occoquan watershed model as the first in a series of modules, and emphasizing environmental 
aspects of sustainability.  We concentrate on orientors and indicators that relate to water quantity or 
quality, and their effects on human systems and ecosystems.  The essential features of the process 
level watershed model are up-scaled to the systems level where an appropriately scaled set of 
orientors and indicators are used to assess and enhance environmental sustainability.  The 
development of a unifying approach for assessing and enhancing sustainability is a daunting 
challenge that may take decades, but the goal of achieving sustainability will itself play out over similar 
timescales, and much could be gained by working toward a common interdisciplinary framework. 
KEYWORDS 
Catchment, Model, Sustainability, Systems, Watershed 
SESSION 
2 
1 INTRODUCTION AND OBJECTIVES 
While sustainability is an essential concept to ensure the future of humanity and the integrity of the 
resources and ecosystems on which we depend, identifying a comprehensive yet realistic way to 
assess and enhance sustainability may be one of the most difficult challenges of our time.  In recent 
decades, there have been numerous reviews focusing on sustainability and sustainable development, 
including those that analyze the development of sustainability science and those that evaluate the 
various frameworks, indicators, tools, approaches, methods and schemes (which we collectively refer 
to as approaches) used to assess sustainability.  In a recent conceptual review [1] we evaluated these 
approaches, including adaptive management, eco-efficiency analysis, ecological footprint, economic 
input-output life-cycle assessment, green accounting, green chemistry, green engineering, indicators, 
industrial metabolism, input-output models, integrated assessment, integrated indicators, material flow 
analysis, orientors, process life-cycle assessment, planetary boundaries, rating systems, resilience, 
scenarios, and whole-system design.  We also identified the collective limitations of the approaches, 
showing that there is not a consistent definition of sustainability, that the approaches are generally not 
comprehensive and are subject to unintended consequences, and that there is little to no connection 
between bottom-up and top-down approaches.  To overcome these challenges, we propose a unified, 
system-of-systems approach that is causal, modular, tiered and scalable. 
The development of a unifying approach for assessing and enhancing sustainability is a daunting 
challenge that may take decades, but the goal of achieving sustainability will itself play out over similar 
timescales, and much could be gained by working toward a common interdisciplinary framework [2].  
In this paper, we propose a common framework for assessing and enhancing sustainability using a 
system-of-systems approach.  We illustrate the framework using the Occoquan watershed model [3] 
as the first in a series of modules or systems, and emphasizing environmental aspects of 
sustainability. 
2 APPROACH 
There is growing recognition of the need for a systems approach when evaluating sustainability [4-6].  
This arises because of the need to integrate or couple a wide range of systems, for example water, 
energy, air, land, ocean, climate, agriculture, fishing, forestry, mining and resource extraction, 
transportation, urban environment, human health, natural ecosystems, as well as other economic and 
social systems.  Unfortunately, it is often the case that the complexity of the systems in which we are 
embedded overwhelms our ability to understand them [7].  Complex systems are constantly changing, 
tightly coupled, governed by feedbacks, nonlinear, history-dependent, self-organizing, adaptive and 
evolving, characterized by trade-offs, and counterintuitive [7].  As a result, many seemingly obvious 
solutions to problems fail or actually worsen the situation [7], causing unintended consequences.  
While mathematical models that are based on causal relationships may have substantial uncertainty, 
and may be subject to chaotic, nonlinear behavior, they represent our best hope when trying to 
understand complex systems.  The coupling of many systems in a modular fashion (see Figure 1) 
would be greatly facilitated if there was a common, systems-level computational language which is 
sufficiently generic to represent and couple a wide range of processes at the systems level.  System 
dynamics models [7] provide a good starting point as they are already being used extensively in 
evaluating the sustainability of natural, social and engineered systems [1], have no size restriction, and 
are essentially only limited by data availability and computational feasibility. 
Although the Brundtland definition of sustainability [8] is widely accepted, it lacks specificity.  In reality, 
the definition of sustainability is currently determined by the specific combination of assessment 
framework and/or indicators that are used, and these vary widely [1].  To allow sustainability to be 
assessed over a wide range of coupled systems, the definition of sustainability must be applied in a 
comprehensive fashion [9].  Bossel [10] proposed that the sustainability of autonomous, self-
organizing systems (which include both ecosystems and human systems) is completely determined by 
several basic orientors, including existence, effectiveness, security, adaptability, coexistence, and in 
the case of human systems, freedom of action, and psychological needs.  One advantage of this 
definition is that it treats human systems and natural systems in an equivalent fashion.  The basic 
orientors are abstract, but are translated into more pragmatic operational orientors.  Then, 
sustainability is assessed by comparing the operational orientors (which reflect the desired state of the 
system) to specific indicators or integrated indicators (which reflect the actual state of the system) and 
evaluating the extent of orientor satisfaction, with each orientor requiring a minimum level of 
satisfaction for the system to be considered sustainable. 
NOVATECH 2016 
3 
A system-of-systems approach that couples a wide range of environmental, economic and social 
systems is needed to assess and enhance sustainability.  Interestingly, a simplified systems approach 
is already being implemented by the climate change community, with integrated assessment models 
that include key features of human systems, such as demography, energy use, technology, the 
economy, agriculture, forestry and land use [11].  These models incorporate simplified representations 
of the climate system and are calibrated against more complex climate models.  The models are used 
to develop emissions scenarios, simulate feedbacks, estimate the potential economic impacts of 
climate change, evaluate the costs and benefits of mitigation, and evaluate uncertainties [11].  The 
development of these integrated assessment models involve two conceptual steps – the first being the 
creation of reduced-order models from more complex ones, also known as “up-scaling,” and the 
second being the coupling of the “up-scaled” components using a common computational language.  
The required characteristics of this common language are not completely clear, but are coming into 
focus.  For example, Kelly et al. [12] reviewed five approaches for modeling complex systems 
including system dynamics, Bayesian networks, coupled component models (which are assembled 
from a variety of different components), agent-based models and knowledge-based models (also 
known as expert systems) and mentioned the possibility of a hybrid approach [12].   
 
Figure 1. Tiered structure with process models up-scaled to the systems level, where they are coupled in a 
modular fashion and then used to assess and enhance sustainability. 
We believe that system dynamics should be included in the hybrid computational language.  As 
described by Kelly et al. [12] system dynamics models capture the causal relationships, feedback 
loops, delays, and decision rules that govern system behavior, and are conceptualized in terms of 
“stocks and flows.”  The stocks represent the system state variables while the flows are the processes 
that influence change in the levels of the stocks [13].  System dynamics is flexible and can explicitly 
represent time and space, capturing elements of dynamic complexity such as feedbacks, time delays, 
accumulations, and nonlinearities [14].  The visual nature of the influence diagrams helps system 
dynamics to be understood across disciplinary and organizational boundaries [7].  System dynamics 
can simulate complex processes [15] including social and economic phenomena, provided that 
appropriate equations and input data to quantify the relevant phenomena are available. 
The Occoquan watershed in northern Virginia is located in a temperate climate zone.  The watershed 
has an area of 1,530 km
2
 and a population of 478,000.  A well-calibrated watershed-stream-reservoir 
modeling system already exists.  The model uses seven applications of the Hydrological Simulation 
Procedure-Fortran (HSPF) software [16] for the overland, subsurface and stream components of the 
system; and two applications of CE-QUAL-W2 (W2) [17] for the two reservoirs.  For the Occoquan 
watershed model, seven HSPF models (simulating seven sub-basins) and two W2 models (simulating 
the two reservoirs) are linked to form the overall model.  Recent work has included a comparison of 
the PQUAL and AGCHEM modules of HSPF for agricultural Best Management Practice (BMP) 
assessment, of land segment size on predictive capabilities, and sensitivity analysis of the PQUAL and 
AGCHEM algorithms [18].  The model accounts for watershed runoff, shallow groundwater flow and 
interflow, stream processes related to parameters being simulated, full reservoir hydrodynamics and 
water quality with an emphasis on nutrients and algal growth.  Atmospheric deposition is implicitly 
included in runoff from various land-use types.   
A sophisticated wastewater reclamation facility that discharges to Occoquan waters has recently been 
modeled with iViewOps, and coupled with the Occoquan watershed model.  The safe yield from the 
Occoquan reservoir is almost doubled due to the discharge of reclaimed water from UOSA.  We are 
currently creating an iViewOps model for the water treatment plant that withdraws water from the 
SESSION 
4 
downstream end of the Occoquan reservoir.  Thus, the loop from abstraction of water, to water 
treatment and distribution for consumption, to collection and treatment of wastewater, to augmentation 
of the source water with the reclaimed wastewater, will be complete, and we will be able to model the 
entire system. 
We illustrate the development of the proposed common framework using the Occoquan watershed 
model as the first in a series of modules, and emphasizing environmental aspects of sustainability.  
We concentrate on orientors and indicators that relate to water quantity or quality, and their effects on 
human systems and ecosystems.  The essential features of the process level watershed model are 
up-scaled to the systems level where an appropriately scaled set of orientors and indicators will be 
used to assess and enhance environmental sustainability.  The project will assess baseline watershed 
sustainability, and then evaluate ways to enhance sustainability using a range of state-of-the-art 
watershed management scenarios. 
LIST OF REFERENCES 
1. Little, J.C., E.T. Hester, and C.C. Carey, Assessing and enhancing environmental sustainability – a 
conceptual review Environmental Science & Technology, Submitted, 2015. 
2. Little, J.C., E.T. Hester, and C.C. Carey, Assessing and enhancing environmental sustainability – toward 
a common interdisciplinary framework Environmental Science & Technology, Submitted, 2015. 
3. Xu, Z., A.N. Godrej, and T.J. Grizzard, The hydrological calibration and validation of a complexly-linked 
watershed–reservoir model for the Occoquan watershed, Virginia. Journal of Hydrology, 2007. 345(3–4): 
p. 167-183. 
4. Hadian, S. and K. Madani, A system of systems approach to energy sustainability assessment: Are all 
renewables really green? Ecological Indicators, 2015. 52(0): p. 194-206. 
5. Housh, M., et al., System of Systems Model for Analysis of Biofuel Development. Journal of 
Infrastructure Systems, 2014. 0(0): p. 04014050. 
6. Liu, J., et al., Systems integration for global sustainability. Science, 2015. 347(6225). 
7. Sterman, J.D., Sustaining sustainability: Creating a systems science in a fragmented academy and 
polarized world, in Sustainability Science: The Emerging Paradigm and the Urban Environment, M.P. 
Weinstein and R.E. Turner, Editors. 2012, Springer Science+Business Media. 
8. Brundtland, G.H., Report of the World Commission on Environment and Development: Our Common 
Future. 1987: United Nations. 
9. Hester, E.T. and J.C. Little, Measuring Environmental Sustainability of Water in Watersheds. 
Environmental Science & Technology, 2013. 47(15): p. 8083-8090. 
10. Bossel, H., Systems and Models: Complexity, Dynamics, Evolution, Sustainability. 2007, Norderstedt, 
Germany: BoD–Books on Demand. 
11. Moss, R.H., et al., The next generation of scenarios for climate change research and assessment. 
Nature, 2010. 463(7282): p. 747-756. 
12. Kelly, R.A., et al., Selecting among five common modelling approaches for integrated environmental 
assessment and management. Environmental Modelling & Software, 2013. 47(0): p. 159-181. 
13. Sterman, J.D., System Dynamics Modeling: Tools for Learning in a Complex World. California 
Management Review, 2001. 43(4): p. 8-25. 
14. Sterman, J.D., Business Dynamics: Systems Thinking and Modeling for A Complex World. Vol. 19. 2000, 
Boston, MA, USA: Irwin/McGraw-Hill. 
15. Sterman, J.D., et al., Management flight simulators to support climate negotiations. Environmental 
Modelling & Software, 2013. 44(0): p. 122-135. 
16. Bicknell, B.R., et al., Hydrological Simulation Program-FORTRAN, Version 12 User’s Manual. 2001, US 
Environmental Protection Agency, National Exposure Research Laboratory: Athens, Georgia. 
17. Cole, T.M. and S.A. Wells, CE-QUAL-W2: A Two-dimensional, laterally averaged, Hydrodynamic and 
Water Quality Model, Version 3.7. 2011, Department of Civil and Environmental Engineering, Portland 
State University: Portland, Oregon. 
18. Liu, Y., Effective Modeling of Nutrient Losses and Nutrient Management Practices in an Agricultural and 
Urbanizing Watershed, in Department of Civil and Environmental Engineering. 2011, Virginia Tech: 
Manassas, Virginia. p. 243. 
 


La gestion durable des bassins versants : une approche 'systèmes de systèmes'

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La gestion durable des bassins versants : une approche 'systèmes de systèmes'

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