Spatial modeling of land cover change and watershed response using Markovian cellular automata and simulation

A continued challenge in watershed management is information related to future land cover and its impact on watersheds. Changes in land cover can have significant impact on the quality and quantity of water resources, both spatially and temporally. This study evaluates potential implications of land cover change on the hydrology of a regional watershed. Land cover change is evaluated by using Markov Chain analysis and Cellular Automation to assess future land cover based on transitional probabilities and spatial influences. The hydrology of the watershed is simulated using a continuous time simulation model. The land cover change was found to be significant in the watershed with increased urbanization and loss of agricultural and forest cover. Land cover change increased overall surface runoff, stream flow, and sediment loading. Potential land cover changes impact the timing and magnitude of seasonal events. In addition to temporal variation in impacts, spatial impacts varied among subwatersheds and administrative boundaries. Opportunities were identified for mitigating the impacts of land cover change through best management practices and policies that incorporate watershed-scale information to reduce impacts of changing in land cover on water quantity and quality

Integrating stakeholder values with multiple attributes to quantify watershed performance

[1] Integrating stakeholder values into the process of quantifying impairment of ecosystem functions is an important aspect of watershed assessment and planning. This study develops a classification and prioritization model to assess potential impairment in watersheds. A systematic evaluation of a broad set of abiotic, biotic, and human indicators of watershed structure and function was used to identify the level of degradation at a subbasin scale. Agencies and communities can use the method to effectively target and allocate resources to areas of greatest restoration need. The watershed performance measure (WPM) developed in this study is composed of three major components: (1) hydrologic processes (water quantity and quality), (2) biodiversity at a species scale (core and priority habitat for rare and endangered species and species richness) and landscape scale (impacts of fragmentation), and (3) urban impacts as assessed in the built environment (effective impervious area) and population effects (densities and density of toxic waste sites). Simulation modeling using the Soil and Water Assessment Tool (SWAT), monitoring information, and spatial analysis with GIS were used to assess each criterion in developing this model. Weights for attributes of potential impairment were determined through the use of the attribute prioritization procedure with a panel of expert stakeholders. This procedure uses preselected attributes and corresponding stakeholder values and is data intensive. The model was applied to all subbasins of the Chicopee River Watershed of western Massachusetts, an area with a mixture of rural, heavily forested lands, suburban, and urbanized areas. Highly impaired subbasins in one community were identified using this methodology and evaluated for principal forms of degradation and potential restoration policies and BMPs. This attribute-based prioritization method could be used in identifying baselines, prioritization policies, and adaptive community planning

Spatial assessment of conjunctive water harvesting potential in watershed systems

Water harvesting can be used to minimize water loss and to augment water supplies in watershed systems. This effort is increasingly being recognized as critical in regions experiencing urbanization and facing uneven water supplies. Water harvesting requires a careful assessment of geographic locations in a watershed and evaluation of surface and groundwater hydrology. In this paper, we develop a spatially explicit method to evaluate costs of harvesting and potential benefits in water harvesting in the Taunton River Watershed in Eastern Massachusetts, USA. A spatial analysis is used to assess surface storage and groundwater recharge potentials in developed and undeveloped regions of the watershed. Distributed parameters used in the analysis include runoff coefficients, land use, soil properties, precipitation, aquifer, and land price. Prioritization maps were developed to characterize conjunctive harvesting potential that is based on benefits and costs. The results demonstrate that a spatially variable harvesting strategy can be used to minimize runoff loss and to augment water supplies. The potential harvest areas were clustered in specific locations that satisfy feasibility and economic criteria. In some subwatersheds, potential harvest locations were dispersed. A spatially variable approach that incorporates economic criteria to hydrologic assessment can be used to enhance efficiency related to water harvest and supply management. Given the increasing demand for clean water, a distributed and conjunctive harvesting strategy could be effective in several urbanizing watersheds. The model has potential for further extension into complex situations of biophysical and socioeconomic conditions at watershed level

Spatial assessment of conjunctive water harvesting potential in watershed systems

Water harvesting can be used to minimize water loss and to augment water supplies in watershed systems. This effort is increasingly being recognized as critical in regions experiencing urbanization and facing uneven water supplies. Water harvesting requires a careful assessment of geographic locations in a watershed and evaluation of surface and groundwater hydrology. In this paper, we develop a spatially explicit method to evaluate costs of harvesting and potential benefits in water harvesting in the Taunton River Watershed in Eastern Massachusetts, USA. A spatial analysis is used to assess surface storage and groundwater recharge potentials in developed and undeveloped regions of the watershed. Distributed parameters used in the analysis include runoff coefficients, land use, soil properties, precipitation, aquifer, and land price. Prioritization maps were developed to characterize conjunctive harvesting potential that is based on benefits and costs. The results demonstrate that a spatially variable harvesting strategy can be used to minimize runoff loss and to augment water supplies. The potential harvest areas were clustered in specific locations that satisfy feasibility and economic criteria. In some subwatersheds, potential harvest locations were dispersed. A spatially variable approach that incorporates economic criteria to hydrologic assessment can be used to enhance efficiency related to water harvest and supply management. Given the increasing demand for clean water, a distributed and conjunctive harvesting strategy could be effective in several urbanizing watersheds. The model has potential for further extension into complex situations of biophysical and socioeconomic conditions at watershed level.39-5

Watershed-Scale Tradeoffs in Water Quantity and Quality Attributes for Conservation Policy

Information on tradeoffs among water quantity and quality attributes at a watershed scale is important in developing effective watershed conservation policies. Assessment of these multiattribute tradeoffs, a focus of this study, is often a low priority in policy design. A combination of simulation modeling and statistical assessment was used to evaluate the significance of relationships among runoff, sediment, nitrate, and phosphorus loading in 115 subwatersheds of the Blackstone River Watershed in southern New England. We observed high variability in rates of runoff, nitrate, phosphorus, and sediment loading among subwatersheds. Results of the regression analysis indicate a high correlation between nitrate and surface runoff, emphasizing the importance of stormwater management in mitigating nutrient loads. A significant relationship exists between mineral phosphorus and sediment yield in watersheds that could inform strategies to mitigate eutrophication problems in phosphorus-limited systems such as some inland water bodies. The tradeoff analysis proposed can be used in policy design and to assess the implications of various policies to address multiple pollutants

Watershed-Scale Tradeoffs in Water Quantity and Quality Attributes for Conservation Policy

Information on tradeoffs among water quantity and quality attributes at a watershed scale is important in developing effective watershed conservation policies. Assessment of these multiattribute tradeoffs, a focus of this study, is often a low priority in policy design. A combination of simulation modeling and statistical assessment was used to evaluate the significance of relationships among runoff, sediment, nitrate, and phosphorus loading in 115 subwatersheds of the Blackstone River Watershed in southern New England. We observed high variability in rates of runoff, nitrate, phosphorus, and sediment loading among subwatersheds. Results of the regression analysis indicate a high correlation between nitrate and surface runoff, emphasizing the importance of stormwater management in mitigating nutrient loads. A significant relationship exists between mineral phosphorus and sediment yield in watersheds that could inform strategies to mitigate eutrophication problems in phosphorus-limited systems such as some inland water bodies. The tradeoff analysis proposed can be used in policy design and to assess the implications of various policies to address multiple pollutants.347-36

Watershed land use and aquatic ecosystem response: Ecohydrologic approach to conservation policy

Land use activities change the natural functions of a watershed impacting the flow of water and water quality, and impair aquatic ecosystems. Optimal allocation of land use depends on attributes related to terrestrial and aquatic environments. A dynamic model that links land use, overland flow, suspended sediment, and an aquatic species is used to evaluate alternate land use policies. The dwarf wedge mussel that is classified as endangered in the region is used as an indicator species of aquatic health in a watershed in Massachusetts. The simulation model is used to evaluate spatial nature of processes and land use policies. Spatial and temporal changes in runoff, sediment loading, and mussel population are modeled over a period of 4 years. Ten policy scenarios represent combinations of best management practices and development of agriculture and urban land at spatial locations of headwaters, main stem regions, riparian, and entire watershed. Increasing the proportion of agriculture and high density residential land use increased runoff, while increasing the frequency and magnitude of peak flows in the watershed. Sediment loading increased with an increased proportion of agriculture area and decreased with an expansion of high density residential area. Scenarios with an increase in sediment loading above the baseline mean exhibited an irregular recovery of the mussel population from high loading events. Policy implications include the need for best management practices to decrease runoff and sediment loading in the watershed, through education and incentive programs

Multiple criteria dynamic spatial optimization to manage water quality on a watershed scale

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A watershed-based land prioritization model for water supply protection

Water quality management at a watershed scale is important for water supply protection. Escalating costs of water treatment, along with the need for cooperative solutions among various water users in a watershed, reinforce the need for such approach. In a watershed approach, optimum water quality benefits can be achieved by targeting practices to those areas that have the maximum marginal value of water quality protection. To accomplish this, prioritization based on marginal benefits and costs is essential. The information that is crucial for developing an effective prioritization method includes geographic information, relationship between land criteria and effects, and travel-time of runoff water. By integrating these three types of information, a watershed level prioritization model was developed and applied to the Ware River watershed in Massachusetts, USA. It was observed that the time of travel of surface runoff followed a complex spatial distribution. Use of zones based on distance from the outlet or drainage zones may not accurately reflect the spatially explicit nature of travel path and travel-times. The area under each category of travel-time as a function of travel-time followed a nonlinear trend in the Ware River watershed. The distribution of the prioritization index showed that sensitive areas do not clearly fall within the boundaries of any single land characteristic (e.g. riparian buffer, steep slopes, sensitive soils, etc.). Low priority areas covered the highest percent of the watershed and this percentage decreased with increase in land sensitivity. Focusing on fewer areas in the watershed can maximize benefits to water quality and result in lower expenditures. By adjusting criteria and weights, this approach can be adapted to prioritize a wide variety of land-protection and land-use decisions such as preserving prime forestland, protecting critical wildlife habitats, recreational and open space planning, and ecological–economic planning