Geog 337 Lab 2


Purpose: 

The Purpose of this lab was to gain a better understanding of the processes involved in delineating watersheds along with real world examples of watershed analysis. This included a case study where flooding risk was calculated in the suburbs surrounding the area of Copenhagen, Denmark. This lab also involved using model builder to structure workflows.

Methods:

The methods for this lab can be divided into two parts.

1. Delineating Watersheds

The first half of this lab focused on delineating watersheds within the boundaries of Adirondack park in New York State. This was done using a shapefile of the park boundaries from the New York State GIS Clearing House and a Hydrology file from the Cornell University Geospatial Information Depository. First, the hydrology files were clipped to the boundaries of the park and a 20km buffer was added to create smoother edges. Next, the coordinate systems for the features were matched and a 30 second raster DEM of North America was added and clipped to the park boundary. The DEM coordinate system was changed to match other features and it was re-projected using a bi-linear re-sampling technique with 60 meter cell output size.

To delineate watersheds, sinks were filled using the hydrology fill tool in the spatial analyst toolbox. Flow direction and Flow accumulation were also determined with hydrology tools. A source raster was created using the conditional expression tool with a cell threshold value of 50,000. Finally, using this source raster and flow direction raster, watersheds were delineated using the Watershed tool in the Hydrology toolset.
Map of Watersheds in the Boundaries of Adirondack Park, New York

This map illustrates how the water flows from the lower value watersheds to the higher value ones.

Part 2: Real World Watershed Analysis

 The second part of this lab was an ESRI online course that had us practice watershed analysis and using model builder with a real world scenario in Denmark. Areas around the city of Copenhagen. In recent years the city experience several cloudburst storms where enormous amounts of rain fell in a short time causing severe flooding. The Danish government established a task force to study the events and determine which areas have the highest risk of flooding.

To first step of the analysis was to determine the location of bluespots, or low lying areas prone to flooding. This was done using a model pre-built in modelbuilder.


Model used for Determining Bluespots
These bluespots were then added to a map to show which areas of the city would be most affected.

A second, more complicated model was then ran which determined how much water each of these bluespots could hold.


Model to Calculate Bluespot Fillup Values.

Using these values a map was created illustrating which buildings were at higher risk of flooding based on nearby bluespots.

Map of Flood Risk 

Additional analyses were performed to determine all buildings at risk, where watersheds are located, and how transportation infrastructure would be affected.


The watersheds were challenging to map due to the large number of features needing to be individually symbolized, making a legend difficult to create. 

Data Sources:

New York State GIS Clearinghouse

Cornell University Geospatial Information Depository, 

University of Copenhagen, Denmark


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