EFFECTS OF THE TOPOGRAPHIC INDEX DISTRIBUTION ON PREDICTED RUNOFF USING GRASS1

ABSTRACT: The effects of digital elevation model resolutions and contour lengths on the distribution of the topographic index, a fundamental parameter for the hydrologic model, TOPMODEL, and their influence on the predicted peak flows are investigated in this paper. A small agricultural catchment (3.38 km²) is used to determine the catchment response modeled by TOPMODEL for three rainfall events.     

Temporal variability of surface runoff due to cropping systems in cultivated catchment areas: Use of the DIAR model for the assessment of environmental public policies in the Pays de Caux (France)

This article proposes the use of a new model, DIAR (Diagnostic Agronomique du Ruissellement, or Agronomic Assessment of Runoff), for the prediction of the timing of the risk of runoff. DIAR is dedicated to loamy soils which are very sensitive to surface crusting, leading to runoff, soil erosion and muddy flows. The approach is proposed for the north-western European loess belt regions where muddy flows severely impact human activities. The likelihood of runoff is assessed from the sequence of soil surface states generated by cultivation practices. DIAR is based on the calculation of curve number values, for each stage of the soil-surface-state sequence, for calculating runoff for each of these stages. In this study, DIAR is applied to a catchment of 912 ha, cultivated by 26 farmers in the Pays de Caux (Normandy, France) where infrastructures located at the outlet have been damaged several times by muddy flows. Local public authorities involved in reducing muddy flows are eager to limit the agricultural upstream runoff by extending the planting of mustard as a winter cover crop. We tested the efficiency of such a policy on the reduction of the mean runoff. We also tested the year-to-year variability of this efficiency using the acreages of four successive years (1999–2000 to 2002–2003). Finally, the cost-efficiency of the policy was also considered. Though we used the same weather scenario, the initial situation (without much mustard cover) showed a wide year-to-year variation in the total runoff. This variation can be associated with the structure of the farms that cultivate the catchment (Utilised Agricultural Area (UAA) of each farm and percentage of this UAA inside the catchment). Our results showed that the widespread planting of winter cover crops could reduce the runoff by 10–20% compared with the initial situation (depending on the year), and also reduce the year-to-year variability of runoff. For each of the 4 tested years, the cost of the infiltrated m³, due to each ha of mustard cover, decreases with the increase in mustard cover. It indicates that the present siting of the mustard cover is not as efficient as it could be. We should ask why farmers do not sow it elsewhere.     

Application of a Three-Dimensional Water Quality Model as a Decision Support Tool for the Management of Land-Use Changes in the Catchment of an Oligotrophic Lake

While expansion of agricultural land area and intensification of agricultural practices through irrigation and fertilizer use can bring many benefits to communities, intensifying land use also causes more contaminants, such as nutrients and pesticides, to enter rivers, lakes, and groundwater. For lakes such as Benmore in the Waitaki catchment, South Island, New Zealand, an area which is currently undergoing agricultural intensification, this could potentially lead to marked degradation of water clarity as well as effects on ecological, recreational, commercial, and tourism values. We undertook a modeling study to demonstrate science-based options for consideration of agricultural intensification in the catchment of Lake Benmore. Based on model simulations of a range of potential future nutrient loadings, it is clear that different areas within Lake Benmore may respond differently to increased nutrient loadings. A western arm (Ahuriri) could be most severely affected by land-use changes and associated increases in nutrient loadings. Lake-wide annual averages of an eutrophication indicator, the trophic level index (TLI) were derived from simulated chlorophyll a, total nitrogen, and total phosphorus concentrations. Results suggest that the lake will shift from oligotrophic (TLI = 2–3) to eutrophic (TLI = 4–5) as external loadings are increased eightfold over current baseline loads, corresponding to the potential land-use intensification in the catchment. This study provides a basis for use of model results in a decision-making process by outlining the environmental consequences of a series of land-use management options, and quantifying nutrient load limits needed to achieve defined trophic state objectives.     

Land Use Change and Land Degradation in Southeastern Mediterranean Spain

The magnitude of the environmental and social consequences of soil erosion and land degradation in semiarid areas of the Mediterranean region has long been recognized and studied. This paper investigates the interrelationship between land use/cover (LULC) changes and land degradation using remotely sensed and ancillary data for southeastern Spain. The area of study, the Xaló River catchment situated in the north of the Alicante Province, has been subjected to a number of LULC changes during the second half of the 20th century such as agricultural abandonment, forest fires, and tourist development. Aerial photographs dating back to 1956 were used for the delineation of historic LULC types; Landsat ETM+ data were used for the analysis and mapping of current conditions. Two important indicators of land degradation, namely, susceptibility to surface runoff and soil erosion, were estimated for the two dates using easily parametrizable models. The comparison of 1956 to 2000 conditions shows an overall “recuperating” trend over the catchment and increased susceptibility to soil erosion only in 3% of the catchment area. The results also identify potential degradation hot-spots where mitigation measures should be taken to prevent further degradation. The readily implemented methodology, based on modest data requirements demonstrated by this study, is a useful tool for catchment to regional scale land use change and land degradation studies and strategic planning for environmental management.     

A Comprehensive Land-Use/Hydrological Modeling System for Scenario Simulations in the Elbow River Watershed, Alberta, Canada

The Elbow River watershed in Alberta covers an area of 1,238 km² and represents an important source of water for irrigation and municipal use. In addition to being located within the driest area of southern Canada, it is also subjected to considerable pressure for land development due to the rapid population growth in the City of Calgary. In this study, a comprehensive modeling system was developed to investigate the impact of past and future land-use changes on hydrological processes considering the complex surface–groundwater interactions existing in the watershed. Specifically, a spatially explicit land-use change model was coupled with MIKE SHE/MIKE 11, a distributed physically based catchment and channel flow model. Following a rigorous sensitivity analysis along with the calibration and validation of these models, four land-use change scenarios were simulated from 2010 to 2031: business as usual (BAU), new development concentrated within the Rocky View County (RV-LUC) and in Bragg Creek (BC-LUC), respectively, and development based on projected population growth (P-LUC). The simulation results reveal that the rapid urbanization and deforestation create an increase in overland flow, and a decrease in evapotranspiration (ET), baseflow, and infiltration mainly in the east sub-catchment of the watershed. The land-use scenarios affect the hydrology of the watershed differently. This study is the most comprehensive investigation of its nature done so far in the Elbow River watershed. The results obtained are in accordance with similar studies conducted in Canadian contexts. The proposed modeling system represents a unique and flexible framework for investigating a variety of water related sustainability issues.     

Rain Water Harvesting in Bermuda1

Rowe, Mark P., 2011. Rain Water Harvesting in Bermuda. Journal of the American Water Resources Association (JAWRA) 47(6):1219–1227. DOI: 10.1111/j.1752‐1688.2011.00563.x Abstract: Roof‐top rain water harvesting is mandated by law for all buildings in Bermuda and is the primary source of water for domestic supply. The average rate at which rain water is harvested at the typical house with four occupants is, however, insufficient to meet average demand. While just over one‐third of households have access to supplementary water either from mains pipelines or private wells, the majority rely on deliveries from water “truckers” (tankers) to augment their rain water supply. Assuming a reasonably constant daily demand, there is a linear relationship between the “maximum optimum capacity” of a water storage tank and the size of the rain water catchment area, which depends on the characteristics of the rainfall at a given geographic location. A simple spreadsheet model was developed to simulate tank storage levels for various combinations of catchment area, tank capacity, and demand, with an input of actual daily rainfall data for a study period of nearly three years. It was found that for typical cycles of rainfall surpluses and deficits in Bermuda, the tank capacity which there is no benefit in exceeding — the “optimum maximum capacity”— is 0.37 m³ of storage capacity per 1 m² of catchment area. Furthermore, it was concluded that many domestic water storage tanks in Bermuda are larger than necessary, especially so where there is a significant imbalance between rain water supply and demand.     

Habitat Assessment of Non-Wadeable Rivers in Michigan

Habitat evaluation of wadeable streams based on accepted protocols provides a rapid and widely used adjunct to biological assessment. However, little effort has been devoted to habitat evaluation in non-wadeable rivers, where it is likely that protocols will differ and field logistics will be more challenging. We developed and tested a non-wadeable habitat index (NWHI) for rivers of Michigan, where non-wadeable rivers were defined as those of order ≥5, drainage area ≥1600 km², mainstem lengths ≥100 km, and mean annual discharge ≥15 m³/s. This identified 22 candidate rivers that ranged in length from 103 to 825 km and in drainage area from 1620 to 16,860 km². We measured 171 individual habitat variables over 2-km reaches at 35 locations on 14 rivers during 2000–2002, where mean wetted width was found to range from 32 to 185 m and mean thalweg depth from 0.8 to 8.3 m. We used correlation and principal components analysis to reduce the number of variables, and examined the spatial pattern of retained variables to exclude any that appeared to reflect spatial location rather than reach condition, resulting in 12 variables to be considered in the habitat index. The proposed NWHI included seven variables: riparian width, large woody debris, aquatic vegetation, bottom deposition, bank stability, thalweg substrate, and off-channel habitat. These variables were included because of their statistical association with independently derived measures of human disturbance in the riparian zone and the catchment, and because they are considered important in other habitat protocols or to the ecology of large rivers. Five variables were excluded because they were primarily related to river size rather than anthropogenic disturbance. This index correlated strongly with indices of disturbance based on the riparian (adjusted R² = 0.62) and the catchment (adjusted R² = 0.50), and distinguished the 35 river reaches into the categories of poor (2), fair (19), good (13), and excellent (1). Habitat variables retained in the NWHI differ from several used in wadeable streams, and place greater emphasis on known characteristic features of larger rivers.     

Farm-level Economic Modelling within a River Catchment Decision Support System

The diverse distribution of farm categories and objectives found within specific river catchment study areas necessitates a more detailed assessment of individual farm activity than can be provided by a catchment scale economic model. This paper deals with the modelling techniques and the processes of development involved in the construction of a farm-level economic model that can be used within a multi-disciplinary decision support system. Validation procedures show the model to be relatively accurate in estimating historically observed farm activity and also that it may be used with confidence for predicting the likely reactions of farmers to different agricultural policies.     

Distributed Hydrologic Modeling in the Suburban Landscape: Assessing Parameter Transferability from Gauged Reference Catchments1

Mittman, Tamara, Lawrence E. Band, Taehee Hwang, and Monica Lipscomb Smith, 2012. Distributed Hydrologic Modeling in the Suburban Landscape: Assessing Parameter Transferability from Gauged Reference Catchments. Journal of the American Water Resources Association (JAWRA) 48(3): 546-557. DOI: 10.1111/j.1752-1688.2011.00636.x Abstract: Distributed, process-based models of catchment hydrologic response are potentially useful tools for the assessment of Low Impact Development (LID) techniques in urbanized catchments. Their application is often limited, however, by the lack of continuous streamflow records to calibrate poorly constrained parameters. This article examines the transferability of soil and groundwater parameters from a forested reference catchment to a nearby suburban catchment. We use the Regional Hydro-Ecologic Simulation System (RHESSys) to develop hydrologic models of one gauged forested and one ungauged suburban catchment within the Baltimore Ecosystem Study (BES) study area. We use a parameter uncertainty framework to calibrate soil and groundwater parameters for the forested catchment, and discrete measurements of streamflow from the suburban catchment to assess parameter transferability. Results indicate that the transfer of soil and groundwater parameters from forested reference to nearby suburban catchments is viable, with performance measures for the suburban catchment often exceeding those for the forested catchment. We propose that the simplification of hydrologic processes in urbanized catchments may account for the increase in model performance in the suburban catchment.     

Adaptation of a Storm Drainage System to Accommodate Increased Rainfall Resulting from Climate Change

Extreme rainfalls in southern Ontario may increase significantly as a result of climate change. This study was designed to determine the impact of a 15% increase in design rainfall intensities on drainage of a typical urban catchment and to investigate adaptive measures. A calibrated model (PCSWMM 2000) was used to: (1) determine the system performance under current and climate-changed design rainfalls; and (2) calculate the magnitudes of various adaptive measures required to reduce the peak discharge to current levels. For this type of catchment, effective retrofit options that provide the required peak discharge reductions included downspout disconnection (50% of connected roofs), increased depression storage (by 45 m³/impervious hectare), and increased street detention storage (by 40m³/impervious hectare).     

Assessment of deep aquifer groundwater quality in a geographically unique climatic region of Southern Western Ghats,India using water quality indices

Water quality index (WQI) models are generally used in hydrochemical studies to simplify complex data into single values to reflect the overall quality. In this study, deep groundwater quality in the Chittur and Palakkad Taluks of the Bharathapuzha river basin of Kerala, India, was assessed by employing the WQI method developed by the Canadian Council of Ministers of the Environment (CCME). The assessment of overall water quality is indispensable due to the specific characteristics of the study area, such as geography, climate, over-drafting, and prevalent agricultural practices. Forty representative samples were collected from the study area for monsoon (MON) and pre-monsoon (PRM) seasons. The results showed a general increase of contents from MON to PRM. The major cations were spread in the order Ca²⁺>Na+>Mg²⁺>K⁺ and the anions HCO₃⁻>Cl⁻>CO₃²⁻ based on their relative abundance. Among various parameters analysed, alkalinity and bicarbonate levels during MON were comparatively high, which is indicative of carbonate weathering, and 90% of the samples failed to meet the World Health Organization (WHO, 2017)/Bureau of Indian Standards (BIS, 2012) drinking water guidelines. The CCME WQI analysis revealed that nearly 50% of the samples during each season represented good and excellent categories. The samples in the poor category comprised 10% in MON and 15% in PRM. The overall WQI exhibited 15% of poor category samples as well. The spatial depiction of CCME WQI classes helped to expose zones of degraded quality in the centre to eastward parts. The spatial and temporal variations of CCME WQI classes and different physicochemical attributes indicated the influence of common factors attributing to the deep groundwater quality. The study also revealed inland salinity at Kolluparamba and Peruvamba stations, where agricultural activities were rampant with poor surface water irrigation.     

GENETIC PROGRAMMING: A NEW PARADIGM IN RAINFALL RUNOFF MODELING1

ABSTRACT: Genetic Programming (GP) is a domain‐independent evolutionary programming technique that evolves computer programs to solve, or approximately solve, problems. To verify GP's capability, a simple example with known relation in the area of symbolic regression, is considered first. GP is then utilized as a flow forecasting tool. A catchment in Singapore with a drainage area of about 6 km² is considered in this study. Six storms of different intensities and durations are used to train GP and then verify the trained GP. Analysis of the GP induced rainfall and runoff relationship shows that the cause and effect relationship between rainfall and runoff is consistent with the hydrologic process. The result shows that the runoff prediction accuracy of symbolic regression based models, measured in terms of root mean square error and correlation coefficient, is reasonably high. Thus, GP induced rainfall runoff relationships can be a viable alternative to traditional rainfall runoff models.     

Using Regression Tree Analysis to Improve Predictions of Low-Flow Nitrate and Chloride in Willamette River Basin Watersheds

The use of regression tree analysis is examined as a tool to evaluate hydrologic and land use factors that affect nitrate and chloride stream concentrations during low-flow conditions. Although this data mining technique has been used to assess a range of ecological parameters, it has not previously been used for stream water quality analysis. Regression tree analysis was conducted on nitrate and chloride data from 71 watersheds in the Willamette River Basin to determine whether this method provides a greater predictive ability compared to standard multiple linear regression, and to elucidate the potential roles of controlling mechanisms. Metrics used in the models included a variety of watershed-scale landscape indices and land use classifications. Regression tree analysis significantly enhanced model accuracy over multiple linear regression, increasing nitrate R ² values from 0.38 to 0.75 and chloride R ² values from 0.64 to 0.85 and as indicated by the ΔAIC value. These improvements are primarily attributed to the ability for regression trees to more effectively handle interactions and manage non-linear functions associated with watershed heterogeneity within the basin. Whereas hydrologic factors governed the conservative chloride tracer in the model, land use dominated control of nitrate concentrations. Watersheds containing higher agricultural activity did not necessarily yield high nitrate concentrations, but agricultural areas combined with either small proportions of forested land or greater urbanization generated nitrate levels far exceeding water quality standards. Although further refinements are recommended, we conclude that regression tree analysis presents water resource managers a promising tool that improves on the predictive ability of standard statistical methods, provides insight into controlling mechanisms, and helps identify catchment characteristics associated with water quality impairment.     

Human Impacts on Land Cover and Water Balances in a Coastal Mediterranean County

We analyzed the effects of changes in land cover on the water balance in Spain’s Marina Baixa County, on the Mediterranean coast. To reveal how different land management strategies have affected the area’s environment, four municipalities within the same catchment were studied: Benidorm, Callosa d’en Sarrià, Beniardà, and Guadalest. In the municipalities of Callosa and Benidorm, the proportion of the area covered by woodland declined by 4.2% and 30.2%, respectively, and woodland was replaced by agriculture and urban development. The abandonment of farmland produced a 17% increase in the proportion of the area covered by vegetation in Guadalest and Beniardá, where frequent forest fires have exacerbated a decrease in the area of pine woodland. Tourism development in Benidorm has been accompanied by an increase in the transportation infrastructure and by an expansion of areas with an impermeable surface, with the lowest level of infiltration into the aquifer system. These changes have generated a net water deficit in Callosa and Benidorm of more than 6 Mm³/year, creating a high demand for water imported from other municipalities (Guadalest and Beniardá) or from outside of the county to maintain the sustainability of the current water management strategies. The Marina Baixa case study is representative of many of the world’s coastal areas that are undergoing rapid urban development based on an inappropriate understanding of human progress based mainly on economic development and thus provides insights into water management in other areas.     

Assessing Impervious Surface Connectivity and Applications for Watershed Management1

Abstract: Although total impervious area (TIA) is often used as an indicator of urban disturbance, recent studies suggest that the subset of impervious surfaces that route stormwater runoff directly to streams via stormwater pipes, called directly connected impervious area (DCIA), may be a better predictor of stream ecosystem alteration. We evaluated the differences between TIA and DCIA in the Shepherd Creek catchment, a small (1.85‐km²), suburban basin in Cincinnati, Ohio. Imperviousness determinations were calculated based on publicly available geographic information system (GIS) data and parcel‐scale field assessments, and these direct assessments were compared to DCIA calculated from published, empirical relationships. Impervious and semi‐impervious area comprised 13.1% of the catchment area, with 56.3% of the impervious area connected. When summarized by subcatchments (0.26‐1.85 km²), TIA measured in the field (11‐23%) was considerably higher than that calculated from the National Land Cover Data Imperviousness Layer (7‐18%). In contrast, TIA calculated based on aerial photos was similar to TIA calculated from field assessments, thus indicating that photo interpretation may be adequate for catchment‐scale (>25 ha) TIA determinations. While these GIS data sources can be used to calculate TIA, on‐site assessments were necessary to accurately determine DCIA within residential parcels. There was a wide variation in percent connectivity across parcels, and, subsequently, DCIA was not accurately predicted from empirical relationships with TIA. We discuss applications of DCIA data that highlight the importance of parcel‐scale field assessments for managing suburban watersheds.     

EFFECT OF CATCHMENT SIZE ON PHOSPHORUS EXPORT1

ABSTRACT: We tested the common assumption, made when expressing phosphorus export on an areal basis, that this export is a linear function of catchment area and found it wanting. The data show that in agricultural catchments, TP (total phosphorus) export varies as the 0.77 power of drainage basin area, resulting in a reduction in phosphorus delivery per unit area with increasing catchment size. Following further division of catchments according to agricultural practice, we found that this spatial scale effect is restricted to row crops and pastures. We present simple statistical models to allow a comparison of TP export from catchments of different size. Such models are not needed for nonrow crops, mixed agricultural and forested catchments, where TP export is a linear function of catchment size.     

Assessing the Impact of Areal Precipitation Input on Streamflow Simulations Using the SWAT Model1

Masih Ilyas, Shreedhar Maskey, Stefan Uhlenbrook, and Vladimir Smakhtin, 2011. Assessing the Impact of Areal Precipitation Input on Streamflow Simulations Using the SWAT Model. Journal of the American Water Resources Association (JAWRA) 47(1):179‐195. DOI: 10.1111/j.1752‐1688.2010.00502.x Abstract: Reduction of input uncertainty is a challenge in hydrological modeling. The widely used model Soil Water Assessment Tool (SWAT) uses the data of a precipitation gauge nearest to the centroid of each subcatchment as an input for that subcatchment. This may not represent overall catchment precipitation conditions well. This paper suggests an alternative – using areal precipitation obtained through interpolation. The effectiveness of this alternative is evaluated by comparing its simulations with those based on the standard SWAT precipitation input procedure. The model is applied to mountainous semiarid catchments in the Karkheh River basin, Iran. The model performance is evaluated at daily, monthly, and annual scales by using a number of performance indicators at 15 streamflow gauging stations each draining an area in the range of 590‐42,620 km². The comparison suggests that the use of areal precipitation improves model performance particularly in small subcatchments in the range of 600‐1,600 km². The modified areal precipitation input results in increased reliability of simulated streamflows in the areas of low rain gauge density. Both precipitation input methods result in reasonably good simulations for larger catchments (over 5,000 km²). The use of areal precipitation input improves the accuracy of simulated streamflows with spatial resolution and density of rain gauges having significant impact on results.     

A CASE STUDY OF SHALLOW FLOW PATHS IN A STEEP ZERO-ORDER BASIN1

ABSTRACT: Soil water potentials, slope throughflow, runoff chemistry, and isotopic composition were monitored in a 97 m² zero-order basin within the Maimai 8 watershed on the South Island of New Zealand, for a natural rain storm and two artificial water applications. Contrary to results previously reported for other portions of the Maimai catchment, much of the runoff occurred as a shallow subsurface organic layer flow. For the 47 mm natural rain event, pre-storm soil matric potential ranged from ?60 to ?150 cm H₂O. No saturation was produced within the profile, and the majority of storm runoff emanated from flow within the organic horizon perched on the mineral soil surface. Hillslope applications corroborated this interpretation by showing >90 percent new water flushing with negligible mineral soil moisture response. Although the mechanisms cited in the text are not representative of the entire catchment, the study demonstrates: (1) the value of a combined physical-chemical-isotopic approach in quantifying slope processes, and (2) the heterogeneous nature and diversity of slope runoff pathways in a relatively homogeneous catchment.     

SENSITWITY ANALYSIS OF SIMULATED CONTAMINATED SEDIMENT TRANSPORT1

ABSTRACT: A simulation analysis of contaminated sediment transport involves model selection, data collection, model calibration and verification, and evaluation of uncertainty in the results. Sensitivity analyses provide information to address these issues at several stages of the investigation. A sensitivity analysis of simulated contaminated sediment transport is used to identify the most sensitive output variables and the parameters most responsible for the output variable sensitivity. The output variables included are streamflow and the flux of sediment and Cs¹³⁷. The sensitivities of these variables are measured at the field and intermediate scales, for flood and normal flow conditions, using the HSPF computer model. A sensitivity index was used to summarize and compare the results of a large number of output variables and parameters. An extensive database was developed to calibrate the model and conduct the sensitivity analysis on a 6.2 mi² catchment in eastern Tennessee. The fluxes of sediment and Cs¹³⁷ were more sensitive than streamflow to changes in parameters for both flood and normal flow conditions. The relative significance of specific parameters on output variable sensitivity varied according to the type of flow condition and the location in the catchment. An implications section illustrates how sensitivity analysis results can help with model selection, planning data collection, calibration, and uncertainty analysis.     

Integrating Environmental and Socio-Economic Indicators of a Linked Catchment–Coastal System Using Variable Environmental Intensity

Can we develop land use policy that balances the conflicting views of stakeholders in a catchment while moving toward long term sustainability? Adaptive management provides a strategy for this whereby measures of catchment performance are compared against performance goals in order to progressively improve policy. However, the feedback loop of adaptive management is often slow and irreversible impacts may result before policy has been adapted. In contrast, integrated modelling of future land use policy provides rapid feedback and potentially improves the chance of avoiding unwanted collapse events. Replacing measures of catchment performance with modelled catchment performance has usually required the dynamic linking of many models, both biophysical and socio-economic—and this requires much effort in software development. As an alternative, we propose the use of variable environmental intensity (defined as the ratio of environmental impact over economic output) in a loose coupling of models to provide a sufficient level of integration while avoiding significant effort required for software development. This model construct was applied to the Motueka Catchment of New Zealand where several biophysical (riverine water quantity, sediment, E. coli faecal bacteria, trout numbers, nitrogen transport, marine productivity) models, a socio-economic (gross output, gross margin, job numbers) model, and an agent-based model were linked. An extreme set of land use scenarios (historic, present, and intensive) were applied to this modelling framework. Results suggest that the catchment is presently in a near optimal land use configuration that is unlikely to benefit from further intensification. This would quickly put stress on water quantity (at low flow) and water quality (E. coli). To date, this model evaluation is based on a theoretical test that explores the logical implications of intensification at an unlikely extreme in order to assess the implications of likely growth trajectories from present use. While this has largely been a desktop exercise, it would also be possible to use this framework to model and explore the biophysical and economic impacts of individual or collective catchment visions. We are currently investigating the use of the model in this type of application.