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Thanks REI Co-op for help Improving our clean up efficiency and planning.

This GIS map of shoreline with greatest stormwater impact shows trash, tires and volunteer effort of CJL

Sue King, a graduate student in the Center for Geospatial Analytics at North Carolina State University, carried out the data analysis. She presented her findings at the 2018 Annual Conference of the NC Water Resources Research Institute. View her entire presentation with voice description here.

Sue started with CJL data of all cleanups dating back to 2009. The data set consisted of the number of trash bags, tires and volunteers in 1O5 cleanups conducted by CJL from January 1, 2009 to July 15, 2017. The shoreline length covered the Haw River Arm from the entrance of Robeson Creek to the dam and both sides of New Hope River Channel from the dam northward to New Hope Overlook at Jordan Lake State Park. Of this 24 mi. stretch, about 17 mi. were cleaned at least once. This section was selected because the main source of trash and tires found here is from stormwater flows from the Haw River watershed rather than recreational use of the lake. The spatial variability in intensity of trash and tires and in volunteer effort was defined by dividing the shoreline length into 43 subsections.

Sue Created a Story Map for Easy viewing of GIS maps

As part of Sue's Capstone Project for her MS degree in Geospatial Analysis, Sue's Story Map explains in easily understood terms with photos how Clean Jordan Lake addresses the trash problem. A Users Guide explains how to read through the Story and how to navigate the mappings of trash data for each subsection of shoreline cleaned.

Click here to view the Story Map. For the GIS maps, select the trash measure of interest to view: lb trash per 100 ft, which is the total lb trash removed in all cleanups divided by the total length of shoreline cleaned; lb trash per volunteer-hour assuming an average weight per bag of 20 lb; average lb trash removed in each subsection, which is the lb trash removed in all cleanups divided by the number of cleanups; the number of tires per 100 ft, which is the total tires removed in all cleanups divided by the total length of shoreline cleaned; and the path lengths of each cleanup.

The GIS map of total lb of trash removed per 100 ft of shoreline for all cleanups performed in each of 43 subsections is shown below as example. The circles from smallest to largest represent bin sizes of 6-26.7; >26.7-59; 59-103; and 103-183 lb trash/100 ft. The number of cleanups in each subsection is not the same because the rotation around the shoreline was not systematic. Nevertheless, the larger intensities of trash are consistent with sections of shoreline most vulnerable by their position to accumulation from the watershed. Click on the + sign to see the individual subsections more clearly.

Tips for Navigating for Chromebook Users. Scroll down to the map of interest to position the map so that the buttons on the top right and the Explore button at bottom right are both visible as shown below.

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Click the Explore button and then view the map in Chromebook’s full screen view as shown below. In this example, the Layer List was selected and pounds per volunteer-hour was checked off instead of the default layer of pounds per 100 feet.

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Beyond the Story Map - How much trash comes to the lake with each rainfall?

At least two cleanups were needed along the same length of shoreline to measure the trash amount arriving with rainfall. The first cleanup established a clean state for the shoreline. The trash collected per 100 ft in the next cleanup was divided by the number of significant rainfalls between the first and second cleanups. The same method of calculation applied to subsequent cleanups.

The number of significant rainfalls was determined from the continuous record of lake level kept by the U.S. Geological Survey. We defined a significant rainfall as large enough to cause a lake level rise (LLR) of 2 ft or greater. The data set includes 94 cleanups within 32 subsections where more than one cleanup was done. 

The map below shows the lb of trash per 100 ft of shoreline per LLR. The smallest circle represents a minimum of 0.6 and the largest, a maximum of 38.3. This wide range suggests that not all sections of shoreline along the Haw River Arm are equally vulnerable to trash deposition from rainfall. Flat shorelines with broad and deep coves have been observed to accumulate more trash than steep-sided sections without large coves. Pockets of high deposition were found northward on New Hope Channel, opposite to normal direction of Haw River flow into the lake. During very heavy rainfalls, the flood gates at the dam are nearly closed. This has been shown to force the Haw River flow to travel northward. Typical southwest winds would also aid this movement.

All mappings to include the effect of rainfall on trash and tire deposition are here.

About 1 ton of trash and 36 tires arrive with each significant rainfall!

How did we get these figures? GIS mapping is important to show the pounds of trash and number of tires deposited per 100 ft in each subsection of shoreline. But the impact of rainfall can even be more easily appreciated by a broader interpretation our database. It took our volunteers about four years (2009-2013) to remove trash and tires that had accumulated since the lake was filled in 1981. Starting then with a relativly "clean" shoreline, we summed up the pounds of trash and number of tires removed between 2013 and July of 2017. We divided these totals by 31 lake level rises that occurred in the same time period to obtain a rough estimate of deposition with each significant rainfall.