Application of GIS and Remote Sensing in Watershed Restoration

Transcription

1 Valerie Preler December 15, 2015 NRS 509 final Project Application of GIS and Remote Sensing in Watershed Restoration Over fifty years ago, Lyndon B. Johnson was once said A nation that fails to plan intelligently for the development and protection of its precious waters will be condemned to wither because of its shortsightedness. The hard lessons of history are clear, written on the deserted sands and ruins of once proud civilizations. Unfortunately, not only our nation, but nations throughout the world have failed to heed the warnings of Johnson and history itself. As our world population has grown and civilizations become progressively urbanized, there has been a continuous trend of degradation of waters on a global scale leading to flooding and poor water quality. Alternately, population growth has spurred and ever-increasing need for potable water. This need for clean water coupled with its decreasing availability has made restoring our waters a priority for decision makers across the globe. Although the need for restoring our waters is well established, the task of improving water quality has proved a challenge that is difficult to overcome. Much difficulty appears to lie in the inherent difficulties associated in planning for improvement in a system that is interconnected. Because of this interconnectivity, we must address water quality improvement at the scale of a watershed. Watersheds do not only encompass water functions. Water catchments (watersheds) are functional geographical areas that integrate a variety of environmental processes and human impacts on landscapes (Aspinall and Pearson 2000.) Wetlands within these watersheds provide important functions including providing habitat, decreasing flooding and reducing non-point source pollution (NPS). Strategically planned wetland restoration on a watershed scale has the ability to restore ecosystem level processes that maintain water quality, but wetland restoration is often done on a site by site basis (White and Fennessy 2005). Throughout the journal articles reviewed, there was a continuous assertion of the importance of the restoration of wetlands and the need to consider them within the context of an accurately defined watershed. Further discussion included the difficulties that occurred when decision makers defined watersheds according to guidelines that are not based on scientific accuracy, but rather political considerations (Bhall et al. 2011). Even though it is established that water quality can only be improved if context of an entire watershed, in reading the journal articles, it became increasingly evident that many efforts are being made to restore localized waters, but that throughout the world there has often been either a lack of pertinent current scientific data to support planning and restoration efforts or a lack of consideration for a watershed in its entirety. Remote Sensing and GIS tools can be used to overcome these hurdles as they are able to provide accurate scientific data along with products that can be presented in a manner that are understandable to decision makers and concerned citizens. The studies in the journal articles followed similar processes. They first evaluated and defined the watershed. In order to do so, the drainage area along with the land use and land coverage characteristics must first be determined. To do this, researchers often started with digital elevation models (DEM) derived from Landsat TM data and used digital line graphs (DLG) to create drainage structures from the given topography. However, for smaller scale watersheds that are either too small or have a narrow elongated shape, Landsat TM data needed to be combined with aerial photography and field data to create high resolution mapping (Mwita et al. 2013). Drainage areas (watersheds) are then determined from these maps. Watersheds vary in size. They can be viewed as relatively small catchments draining to a stream or evaluated in the context of the entire watershed. After defining the watershed boundaries within the GIS framework, calculations are used to define watershed characteristics including slope, flow, stream order, and a saturation index. Additional criteria for defining watershed characteristics include land use, land cover, and soil composition. Throughout the studies presented in the journal articles reviewed, land use and land cover are often derived from Landsat TM data or similar remote sensing methods from satellites from the country of origin. Soil data is also taken from data sets such as those derived from Landsat TM imagery. Additionally, data sets can be chosen according to various temporal resolutions which can demonstrate changes to watersheds during varying seasons as well as over longer periods of time allowing the tracking of impacts due to changes in land use (Bhalla et al 2011.) It is from these different variables

2 that the GIS software is able to create the various map layers. After the watershed boundaries and characteristics are defined, researchers are then able to use this data to further evaluate the watershed using additional criteria. Criteria such as water quality data and location of riparian zones can be evaluated and mapped along with the other variables. Other concerns such as the origin of pollutants can also be derived from the evaluation process. Once the watershed characteristics have been determined, researchers can then use this information to create plans for the restoration of the watershed. Many times, the focus is on the restoration of wetlands within the watersheds as wetlands serve the dual purpose of reducing both pollution and flooding. Suitability can be determined through mathematical models that can be run within the GIS software or in another program that can be combined with GIS outputs. When running these models, variables are often weighed according to their importance in providing water quality. This is an important step. Often times the rating scales are based on the opinion of experts in hydrology who are asked to rate variables according to their importance in the watershed and sound scientific solutions can be determined. Although solutions based purely on hydrology would, on the surface, appear to be the best method for restoring water quality, these solutions are not always feasible to implement. Often planners have to account for variables that have little to do with hydrology. The persons in responsible for decision making in regards to watershed restoration often have little scientific background and at times, must assign importance to those very things that may be negatively impacting the watershed. For example, agricultural uses often lead to increased pollution, but decision makers must often consider the economic impact to the farmers as well as the need to feed a population. It is because of these competing needs that those proposing plans for restoration must understand the decision making process. The decision making process can be looked at as the continual process of consultation, decision, evaluation and revision, and, in the context of land-use management and planning, frequently is specifically concerned with adaptive management of change and design of alternative future directions for land use within a given geographic area (Aspinall and Pearson 2000.) GIS is particularly helpful in the area of decision making. GIS is an important tool used to assist decision makers as it can provide a clear representation of problems and solutions when addressing watershed restoration. GIS maps can illustrate the current state of the watershed including any of the variables previously discussed including land use and land cover which can be mapped to demonstrate changes that have occurred over time as satellite imagery is available for over 40 years. The maps themselves create an opportunity to educate the decision makers as to the necessity of restoration throughout the watershed rather than on a site by site basis. Furthermore, the GIS can be used as an adaptive tool allowing researchers and planners to revise the weighting systems assigned by experts to provide maps that reflect the various changes. Once restoration efforts occur, the processes outline previously using remotely sensed images coupled with GIS allow for the continued monitoring of outcomes and ongoing education of the decision makers. Aspinall, R and D. Pearson Integrated geographical assessment of environmental condition in water catchments: Linking landscape ecology, environmental modelling and GIS. Journal of Environmental Management, 59(4), This paper describes watersheds as integrated units that must viewed not only as hydrological units, as well as units that have socioeconomic impacts. The authors create a regional model with sub-basins within GIS that uses ecological and hydrological modeling functions and landscape analysis based on Landsat TM images and GIRAS land cover data set, DEMs, USGS topographic maps, precipitation data from meteorological stations, TIGER roads, and census data for populations within the catchment area. The the upper Yellowstone river is the catchment area used for the case study. The authors assert that studies need to take into account decision makers and begin by defining the decision making process, believing it necessary for the development of goals for handling spatial data in a manner that allows for the understanding of decision makers. The authors discuss the benefits of integrating GIS and eco-hydrological modeling and discuss the difficulties in doing so. The study integrates eco-hydrologic modeling tools into GIS to determine subcatchments and water quality. The authors accomplish the goal of being able to use GIS coupled with modeling to provide outputs in a manner that is understandable to decision makers.

3 Although this paper is somewhat dated, being published in 2000, it provided a clear understanding of the integration of GIS integrated with modeling. Bhalla R, N. Pelkey, D. Prasad K Application of GIS for evaluation and design of watershed guidelines. Water Resource Management 25(1): In this study, the authors analyze the Indian government s guidelines for prioritizing micro-watersheds for restoration from 2003 and 2008 with GIS and spatial statistics. The established governmental guidelines are meant to balance the need for improving watersheds, increasing agricultural productivity, and alleviating poverty and use criteria that are not based on scientifically accurate hydrologic criteria. The authors, however, analyzed these guidelines using GIS and spatial criteria. The authors use GIS to create layers of watershed boundaries, village boundaries, land use, population density, water quality and groundwater depth and then, with GIS, evaluate the efficacy of these guidelines in relation to a small rainfall watershed in southern India. The authors conclude that neither the 2003 or 2008 criteria are appropriate for watershed improvement and that efficient resources based on hydraulic function need to be considered before social and economic concerns. They also argue that a combined GIS and spatial analysis approach is beneficial for evaluating watershed selection criteria and for assessment of outcomes. The authors further concluded that the established guidelines needed to be rewritten using scientifically based criteria. The article was interesting as Bhalla et al. showed that, at times, decision makers use criteria that have little, if anything, to do with science and that these criteria are being used for the foundation of water quality restoration setting the base for future failure. The authors assert that plans need to be based on sound science, but leave the question of how to overcome the barriers to doing so. Dai C, HC Guo, Q Tan, W Ren Development of a constructed wetland network for mitigating nonpoint source pollution through a GIS-based watershed-scale inexact optimization approach. Ecological Engineering. The authors discuss that NPS losses and of nitrogen and phosphorous are degrading water quality especially in rainy mountainous agricultural areas. The authors assert that GIS based approaches are incomplete and instead develop a model that integrates GIS based spatial analysis with fuzzy stochastic two stage programming (FSTP), to better plan for installation of wetlands within a watershed The authors used the Songhuaba watershed in China as their model. By using the created GIS FSTP, they created a model for wetlands within the watershed that would meet multiple targets including maximizing economic benefits and minimizing nutrient loads and could account for multiple processes and factors that can vary which then could be mapped at different confidence levels and demonstrating excess load of N and P under different rainfall conditions according to the established confidence level. The authors note that the GIS technology was used as it allowed smooth communication between the database, the optimization models, and the presentation of results. This article was extremely detailed. The amount of specificity made it at times difficult to wade through, but the detail provided the reader with a clear understanding of the process. López, J. Martnez., F. Carreño, J. A. Palazón-Ferrando, J. Martínez-Fernández and M. A. Esteve (2014) Free advanced modeling and remote-sensing techniques for wetland watershed delineation and monitoring, International Journal of Geographical Information Science, 28:8, The authors assert that enhanced and reproducible methods for modeling land use impact on watersheds needs to be readily available. The authors discuss their use of FOSS (Free and Open Source Software) to meet this objective. The study involves 11 watersheds that drain to semi-arid wetlands in the Murcia province in Spain and compares conditions from 1987 and The authors fully explain how they used FOSS GIS to combine hydrologic modeling and remote sensing to better delineate pressures on wetlands within the watershed. The authors started with DEMs available from the Instituto Geografical Nacional and then used map algebra to create flow

4 accumulation and drainage maps. Next, Landsat images (from winter and late spring to account for seasonal phenology) were enhanced through various methods of supervised classification (again using some open source methods) to create the land use/land cover maps. At the conclusion of the study, the authors determined that the maps of the watersheds created by the chosen methods were more accurate then what was previously available. The study concluded that using Landsat data along with FOSS were methods that were applicable world-wide. The authors were specific and clear in the detailing of their processes. The article appeared to be especially relevant as having reproducible accessible data is often discussed by the authors of the various journal articles that I reviewed. Mwita E, G. Menz, S. Misana, Becker, M., Kisanga, D., Boehme, B Mapping small wetlands of Kenya and Tanzania using remote sensing techniques. International Journal of Applied Earth Observation and Geoinformation 21: The authors discuss small scale wetlands located in Tanzania and Kenya. The authors assert that although there is a need for studies in these areas, they are often overlooked due to their size, diversity, and remote location. The authors discuss the use of remote sensing as the best approach, but that Landsat images are often too poor in spatial resolution to accurately identify these wetlands due to their small size or elongated, narrow shape. Because of this, aerial photography was employed for high resolution mapping. The authors used the Landsat data with ERDAS software in the preliminary stage. They then conducted field studies and gathered aerial photos that were processed with ArcGIS 9.3 to delineate the small wetlands and to indicate the varied types, spatial distribution and land use patterns. Figure 2 in the article was a flow chart of the process which made the process easy to understand. Throughout the article, the authors provide detailed information about the wetlands and their importance. The authors were able to make a strong argument regarding the importance of mapping these as well as other small scale wetlands to help concerned authorities can gain the information needed to make wise choices regarding their management. Ouyang NL, Lu SL, Wu BF, Zhu JJ, Wang H Wetland restoration suitability evaluation at the watershed scale- A case study in upstream of the Yongdinghe river. Procedia Environmental Sciences 10, Part C: Ouyang et al discuss that wetland restoration is necessary as wetlands provide valuable environmental services. However, the authors discuss that wetlands are often studied in isolation and instead need to be evaluated in the context of the entire watershed. The study evaluates the Yongdinghe River at the convergence of the Sanggan River and Yang River. The main data used in the study are DEM, river and soil quality data, and vector data including location of villages, soils, and streams and reservoirs. The authors propose a GIS-based multi-criteria comprehensive evaluation methodology for wetland restoration suitability evaluation (which) includes three steps: criteria information extraction, criteria value assignment and normalization, and integrated evaluation. The article explains each phase of the aforementioned steps in detail. The authors further discuss that the wetland restoration in semi-arid areas is dependent upon water availability and assert that further research should focus on the feasibility of restoration according to water resources available throughout the year. The study does not address any social factors involved in the wetland restoration, but does note that recreational activities may need to be curtailed in during periods of less water. This study would appear to be a first step to wetland restoration and improvement of overall water quality. However, considering the need of water diversion to particular areas, further study involving the impacts of doing so would be necessary. D. White and Fennessy, S Modeling the suitability of wetland restoration potential at the watershed scale. Ecological Engineering 24(4): The authors discuss that often water restoration projects are considered on a site by site basis, but that they need to be considered at the watershed scale. They indicate that restoration on a watershed scale has the ability to restore ecosystem processes that maintain the integrity of the water resources. To this end, the authors develop a suitability model based on multicriteria evaluation theory model within GIS to address wetlands in a spatially explicit manner. The model is applied in a case study of the watershed along the Cuyahoga River in Ohio. The

5 authors target wetlands that can be best restored to mitigate NPS pollution. The study takes a two-phase approach was used. The first is step was to develop indicators identifying all sites suitable for long term sustainable wetland restoration. Criteria used include hydric soils, land use, topography, stream order, and a saturation index based on slope and flow accumulation in each grid cell in the model. The second phase filters and prioritizes sites based on their ability to contribute to the water quality within the watershed once they are restored. This was a well presented paper as the authors clearly outlined the their methods of gathering and modeling data.