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Abstract:
A watershed is the upslope area that contributes flow generally water to a common outlet as concentrated drainage. It can be part of a larger watershed and can also contain smaller watersheds, called sub-basins. The boundaries between watersheds are termed drainage divides. The outlet, or pour point, is the point on the surface at which water flows out of an area. It is the lowest point along the boundary of a watershed.
In the present study watershed in Satara district of Maharashtra is used for various urban planning work. Geographical Information Systems (GIS) and a high-resolution Digital Elevation Model (DEM) has been utilized for the estimation of watershed. Several hydrological parameters have been computed such as flow direction, flow accumulation, stream order, watershed etc.
Key words: Digital Elevation Model, GIS, Remote Sensing, Satara watershed, Urban Planning
Introduction
Watershed delineation is a crucial process in urban area planning, as it provides an understanding of how water flows through a given landscape, from its highest points to its outlets. A watershed, also known as a drainage basin, is the geographic area that collects rainwater and directs it to a common outlet such as a river, lake, or storm drain. In the context of urban planning, delineating watersheds is essential for managing storm water, preventing floods, and ensuring sustainable development.
Urbanization significantly alters natural hydrological processes. The increase in impervious surfaces like roads, buildings, and parking lots reduces natural infiltration, increasing surface runoff and the risk of flooding. By delineating watersheds, planners can assess how water will flow and accumulate in urban environments, helping to inform critical infrastructure decisions, storm water management, and environmental conservation strategies.
Delineating watersheds helps planners and engineers to:
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Manage Storm water: Properly designed storm water systems, including retention basins, drainage networks, and green infrastructure, rely on watershed analysis to control and manage runoff.
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Mitigate Flood Risks: Identifying flood-prone areas within a watershed helps in the implementation of flood control measures, zoning regulations, and resilient infrastructure design.
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Sustainable Urban Growth: By understanding the flow of water within a watershed, urban planners can develop land-use plans that protect natural resources, reduce erosion, and enhance groundwater recharge.
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Enhance Climate Resilience: Watershed data enables cities to prepare for the effects of climate change, such as increased rainfall and flooding, by guiding adaptive measures and resilient urban design.
Incorporating watershed analysis into urban planning not only enhances the sustainability of urban environments but also improves the safety and quality of life for urban populations by managing water resources effectively.
Study Area: Satara
Satara district is situated in the river basins of the Bhima and Krishna river. The physical settings of Satara show a contrast of immense dimensions and reveal a variety of landscapes influenced by relief,climate and vegetation. The variation in relief ranges from the pinnacles and high plateaus of main Sahyadrians range having height over 4500 feet above mean sea level to the subdued basin of the Nira river in Phaltan tehsil with the average height of about 1700 feet above mean sea level. The climate ranges from the rainiest in the Mahabaleshwar region, which has an average annual fall of over 6000 mm to the driest in Man tehsil where the average annual rainfall is about 500 mm. The vegetal cover too varies from the typical monsoon forest in the western parts to scrub and poor grass in the eastern parts.
Geographical location: North Latitudes 17.5 to 18.11 : East Longitude 73.33 to 74.54
Geographical Area: 10480 (sq.km.)
The main rivers of Satara district are Koyna and Krishna. The Krishna is one of the three largest sacred rivers of southern India. Approx. 172 kms.of the river course falls inside the district. The Krishna river begins on the eastern brow of the Mahabaleshwar plateau and the source is about 4500 ft. above sea level.
Kudali, Urmodi, Venna and Tarali are small feeder rivers of Krishna. Koyna is the largest tributary of Krishna in the district. Neera and Manganga rivers are the two representatives of the Bhima drainage in the north and north-eastern parts of the district respectively. The Satara district in Maharashtra, India has several watersheds, including the Urmodi River
watershed and the Mahabaleshwar-Koyna watershed region:
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Urmodi River watershed: A tropical watershed located in the Satara district
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Mahabaleshwar-Koyna watershed region: A region that includes hill stations and holiday places, such as Mahabaleshwar and Panchgani
[Figure1. Showing Study area Satara]
Methodology:
Delineating a watershed using Digital Elevation Model (DEM) data in ArcGIS Pro is a step-by-step process that involves terrain analysis and the use of hydrology tools to define the boundaries of a watershed.
Below is a detailed guide on how to do this:
Steps to Delineate a Watershed Using DEM in ArcGIS Pro:
1. Prepare DEM Data:
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Acquire DEM: Ensure you have a DEM for the study area. This can be downloaded from sources such as the USGS (for the US), NASA SRTM, or your local government’s geospatial data portal.
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Load DEM into ArcGIS Pro: Open ArcGIS Pro and add the DEM to the map by dragging it into the contents pane.
2. Fill Sinks in the DEM:
Sinks (depressions in the DEM) can create problems when calculating flow direction. The first step is to fill these sinks to create a smooth surface.
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Go to the Geoprocessing Pane and search for the Fill tool.
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Input your DEM as the "Input Surface Raster.
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Run the tool to fill sinks and create a smoothed DEM.
3. Generate Flow Direction:
The next step is to calculate the direction in which water will flow across the surface, based on the filled DEM.
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Search for the Flow Direction tool in the Geoprocessing Pane.
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Set the "Input Surface Raster" to the filled DEM from the previous step.
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Run the tool to generate the flow direction raster.
4. Create Flow Accumulation:
This step calculates the accumulated flow to each cell in the raster based on the flow direction, helping identify potential stream networks.
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In the Geoprocessing Pane, search for the Flow Accumulation tool.
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Input the flow direction raster as the "Input Flow Direction Raster."
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Run the tool to produce a flow accumulation raster.
5. Identify Streams:
To create a stream network, you need to determine which areas have enough accumulated flow to form streams.
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Use the Raster Calculator tool to apply a threshold to the flow accumulation raster. A higher threshold results in fewer, larger streams, while a lower threshold produces more streams.
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Formula: "Flow Accumulation Raster" > threshold_value
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Choose a threshold value based on the scale of your analysis (e.g., 1000 or 5000).
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Run the calculation to get a binary stream network (1 for streams and 0 for non stream cells).
6. Define the Pour Point (Outlet):
The pour point is where water exits the watershed, such as at a river mouth or a designated point on a stream. You can manually create pour points or use existing stream data:
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Add a point feature at the outlet location (the lowest point or where you want to delineate the watershed).
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Snap this point to the nearest stream to ensure accurate watershed delineation.
7. Snap Pour Point to Flow Accumulation:
Ensure the pour point aligns with the highest flow accumulation in its vicinity.
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Use the Snap Pour Point tool:
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Input the pour point feature and the flow accumulation raster.
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Set a snap distance (within which the point will snap to the highest flow accumulation pixel).
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Run the tool to snap the pour point to the nearest high-flow area.
8. Delineate the Watershed:
With the pour point defined, the watershed can be delineated based on the flow direction raster.
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Search for the Watershed tool in the Geoprocessing Pane.
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Set the "Input Flow Direction Raster" to the flow direction raster and "Input Pour Point Data" to the snapped pour point feature.
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Run the tool to delineate the watershed. This will generate a raster representing the watershed area draining to the pour point.
9. Convert Watershed Raster to Polygon:
To make the watershed more manageable for analysis and visualization, convert the raster to a polygon.
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Use the Raster to Polygon tool to convert the watershed raster into a vector format.
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Input the watershed raster and select "Simplify Polygon" to clean up the boundaries.
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Run the tool to create a watershed polygon.
10. Visualize and Analyze the Watershed:
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Symbolize the watershed polygon to distinguish it from other features in the map.
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You can overlay the watershed boundary with other spatial data, such as land use, land cover, or urban infrastructure, to begin your analysis.
By following these steps, you can effectively delineate a watershed using DEM data in ArcGIS Pro, providing the foundation for various environmental, hydrological, and urban planning applications.
Results and Discussion:
[Figure2: Showing FILL DEM]
DEMs may contain small imperfections or sinks, which are areas of lower elevation surrounded by higher elevation. These are often artifacts of data collection and can interfere with hydrological modeling, such as calculating flow direction or watershed delineation. Filling these sinks ensures the surface is continuous, and water flows correctly over the terrain.
A filled DEM is often a prerequisite for accurate hydrological analysis, including flow accumulation, stream network delineation, and watershed analysis. Without filling, you may get erroneous flow patterns, leading to inaccurate results.
[Figure3: Showing Flow Direction]
In ArcGIS Pro, the Flow Direction tool is used to model how water flows across a surface. It determines the direction in which water will flow from each cell in a Digital Elevation Model (DEM) based on the steepest descent to neighboring cells. The tool is commonly used in hydrological analysis to simulate water movement across landscapes. Flow direction is critical for defining watersheds or drainage basins by determining the area that contributes water to a specific point in a stream or river.
How Flow Direction is Represented in ArcGIS Pro:
The Flow Direction tool assigns each cell a unique value that corresponds to the direction of steepest descent to one of its eight neighboring cells. The output is a raster where each cell has a value that represents one of the following directions:
Each number is a power of 2, corresponding to one of the eight cardinal or diagonal directions. These values allow you to trace how water flows across the surface of the DEM.
[Figure 4: Showing stream order and Study area SATARA]
In ArcGIS Pro, stream order is a hierarchical system used to classify streams and rivers based on their connectivity and the number of tributaries. Stream ordering is an essential concept in hydrology and geomorphology for understanding the structure of river networks. It is often used to describe stream size, drainage patterns, and flow paths in watersheds.
There are several methods for determining stream order, but the most commonly used is the Strahler Stream Order system. ArcGIS Pro uses this method in its Stream Order tool to classify streams based on their position within the drainage network.
[Figure5: Showing Watershed area from study area SATARA]
The Watershed tool is used to define the drainage area or catchment region that contributes water flow to a specific point, known as a pour point or outlet. The watershed defines the area where precipitation or runoff flows towards that point based on the surface terrain.
Application Of watershed in Urban Planning:
Watershed analysis plays a crucial role in urban area planning, as it provides critical insights into how water flows through a landscape, helping urban planners make informed decisions to manage storm water, mitigate flood risks, and ensure sustainable development.
Here’s how watershed data is used in urban planning:
1. Stormwater Management
Urbanization typically increases impermeable surfaces (roads, buildings, parking lots), reducing natural infiltration and increasing surface runoff. By using watershed data, planners can:
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Design stormwater infrastructure: Watershed boundaries help in designing stormwater management systems, such as retention basins, detention ponds, bioswales, green roofs, and storm sewers that collect and store runoff.
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Reduce urban flooding: Watershed analysis identifies areas where runoff is most likely to accumulate, helping planners to strategically place stormwater systems and flood control measures.
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Runoff Modeling: Estimating the volume and rate of runoff during rainfall events enables the design of infrastructure that can manage high runoff volumes, preventing urban flooding.
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Use of Low Impact Development (LID): Promote practices that mimic natural hydrology, such as permeable pavements, vegetated areas, and rain gardens, based on the watershed’s flow patterns.
2. Flood Risk Assessment and Mitigation
Watershed data allows urban planners to assess flood risks and develop strategies to protect life and property:
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Floodplain Mapping: By delineating watershed boundaries and using flood models, planners can identify flood-prone areas in the city. This information is essential for guiding land-use decisions.
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Flood Mitigation: Watershed data can be used to create flood mitigation strategies like levees, embankments, and diversion channels in high-risk zones.
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Flood-Resistant Infrastructure: Designing infrastructure with flood resilience in mind, such as elevating roads, constructing bridges over streams, and reinforcing building foundations in flood zones.
3. Water Supply and Drainage Planning
Watershed boundaries help in the planning and management of water supply systems, especially in growing urban areas:
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Water Source Protection: Identifying key recharge zones and protecting natural watersheds helps in safeguarding water sources from urban pollution and overuse.
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Efficient Drainage Systems: Watershed analysis guides the placement of drainage systems and sewage networks to ensure they efficiently handle runoff, reducing the risk of overflowing stormwater systems and sewage backups.
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Rainwater Harvesting: Integrating watershed data into urban design can help planners identify areas where rainwater harvesting systems can be implemented to recharge groundwater and reduce pressure on existing water supply systems.
4. Sustainable Urban Development
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Smart Land-Use Planning: Watershed data helps in zoning decisions by identifying areas that are suitable for development and areas that should be left undeveloped, such as floodplains, wetlands, and natural drainage paths.
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Green Space and Riparian Buffer Zones: Planners can identify areas where green spaces, parks, or natural buffer zones can be preserved or restored to absorb runoff and reduce the urban heat island effect.
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Wetland Conservation and Restoration: Protecting or restoring wetlands within the watershed helps in reducing flooding, improving water quality, and providing recreational spaces within urban areas.
5. Climate Change Resilience
With changing rainfall patterns and increasing storm intensity due to climate change, watershed data is essential for designing resilient cities:
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Flood Resilience Planning: By modeling how climate change will affect rainfall and runoff in the watershed, planners can design urban areas that are more resilient to extreme weather events.
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Urban Heat Island Mitigation: Watersheds that retain natural green spaces and water bodies help mitigate the heat island effect in cities, creating cooler, more livable environments.
6. Erosion and Sediment Control
Watershed analysis helps planners understand areas vulnerable to erosion due to increased runoff from urbanization:
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Erosion Control Measures: Identifying slopes and areas with high erosion potential can guide the placement of erosion control measures like vegetated buffers, silt fences, and check dams.
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Sediment Transport Reduction: Planners can use watershed data to implement strategies that reduce sediment transport to rivers and streams, maintaining water quality and preventing clogging of drainage systems.
7. Environmental Protection and Conservation
Watershed data helps balance urban growth with environmental sustainability:
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Habitat and Wildlife Corridors: Watersheds often contain key ecosystems like wetlands, rivers, and forests that are crucial for wildlife. Identifying these within urban areas helps planners create wildlife corridors or conservation zones.
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Pollution Control: Watersheds provide insight into how pollutants move through urban areas. Planners can target areas with high pollution potential (such as industrial zones) and implement Best Management Practices (BMPs) to control nonpoint source pollution, like oil, chemicals, and heavy metals, from reaching water bodies.
8. Infrastructure and Transportation Planning
Watershed data can inform infrastructure and transportation projects:
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Road and Bridge Design: Knowing the watershed boundaries helps engineers design roads and bridges that can handle large runoff volumes, especially during storms.
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Urban Infrastructure Siting: Infrastructure such as waste treatment plants or industrial zones can be sited outside sensitive watershed areas to minimize environmental impacts and reduce flood risks.
9. Public Awareness and Policy Making
Watershed analysis can be used to develop urban policies and engage the public:
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Public Education: Sharing watershed maps and analysis can raise awareness about how urban development affects water systems and flood risks.
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Policy Development: Data from watershed analysis can inform policies related to stormwater management, floodplain zoning, environmental conservation, and urban growth strategies.
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Community Planning: Watershed data can help create resilient urban communities that are better prepared for natural disasters by planning developments that respect natural water flow and minimize flood risks.
Conclusion
By integrating watershed analysis into urban planning, Satara city can be developed sustainably while mitigating the impacts of urbanization on natural water systems. Planners can balance growth with environmental protection, reduce flood risks, manage water resources, and improve resilience to climate change, ultimately creating safer and more livable urban environments.
Delineating a watershed for Stara urban area planning provides critical insights that can inform infrastructure development, stormwater management, flood control, and sustainable land use decisions. The key conclusions derived from watershed delineation in urban planning help cities balance development needs with environmental protection and resilience to natural hazards like floods.
Reference:-
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Digital elevation modelling available from USGS earth explorer.
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Arun Babu E., Suresh B., Ravichandran S., (2013) ; “Application of SWAT Model to an agricultural watershed in Tamil Nadu, India", Proceedings of SWAT conference 2012, IIT Delhi. , 120-132
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THE STUDY OF WATERSHED DEVELOPMENT PROGRAMME AND AGRICULTURAL LAND USE IN SATARA DISTRICT
Dr. Lingade V. B.1 and Dr. Gharge R. R.2 1Assistant Professor, Department of Geography , S.G.M. College Karad . 2Head & Associate Professor, Department of Geography, S.G.M. College Karad.