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Assessment Protocol and Methodology

Sweepers conducted an assessment of the Rapidan and Robinson River Valleys. Sweepers worked as a team in a canoe, with one person observing and calling out assessment ratings, while the other person recorded the information on handheld Garmin Global Positioning System (GPS) Units. The purpose of the assessment included the following objectives:

  • Identification of emergency access points – the latitude/longitude was recorded on the GPS units.
  • Identification of trash clusters – also recorded on GPS units.
  • River health assessment – see below for protocol and methods.

Note: the word “health” is used to indicate functionality of the riparian ecosystem.

Assessment data for the 2014 season of StreamSweepers was collected in a similar manner to 2013. Like last year, two GPS units were used to mark locations of change in any of the rating categories. One team was assigned to mark only the quality of the left hand side of the river, with the other team assuming responsibility for the right side. One difference in this year’s assessments was the addition of several rating categories. Last year the categories included canopy, bed, bank and bank vegetation. For 2014, the categories and scoring range (low scores indicate lower levels of functionality, high scores indicate higher functionality) are are as follows:

Canopy (0 – 4): An assessment of the amount of shade over either the left or ride side of the river. Each half of the river was given an independent canopy rating of 0%, 25%, 50%, 75%, or 100%. A 0 indicates no canopy, a 4 indicates 100%  canopy coverage over the particular side of the river. To determine the canopy rating, the StreamSweepers assessed the amount of river surface area covered by vegetation.

    •  For the Rapidan River, the majority of the time, the canopy coverage was 25% (37%, river left; 52%, river right), while the canopy coverage was 100% only 1% of the time (river right). Lower canopy ratings correlated strongly with those of buffer, bank erosion, and bank cover. Many species of non-invasive hardwoods were present – primarily Sycamores, Poplars, Hickory, River Birch, Oak and Maple. Invasive Species tended not to affect the canopy but did affect the understory of the bank coverage.

Buffer (0 – 2): An assessment of the amount of the tree buffer on the riverbank. 0 indicates no buffer, 1 generally represents a buffer of a few trees, and 2 indicates dense forest, extending away from the river at least 50 feet.

Bank Erosion (0 – 2): An assessment of the quality of the bank, representing how much erosion has occurred there. A 0 represents no erosion, a 1 represents moderate erosion, and a 2 represents severe erosion.

Bed (0 – 2): Indicates the quality of the riverbed. A 0 indicates roughly 100% sand or silt, 1 indicates a mix of sand and cobbles, and 2 represents a mostly cobblestone bed.

  • Ratings for river bed assessment fell into three categories: cobbled, mixed, and silted (indicators of good, moderate, and poor river health). For the Rapidan River, assessing the bed was perhaps the most subjective measurement because the majority of the time, silt and depth prevented accurate observations of the river bottom.

Bank Cover (0 – 4) : Indicates the type of plant matter covering the bank of the river. A 1 refers to only grass, a 2 represents only  understory (small trees and shrubs), a 3 represents only overstory (large trees), and a 4 refers to the presence of understory and overstory.

  • The StreamSweepers analyzed the river right and left banks for forest stages of succession. Lower ratings were allotted for barren or grass covered areas, while higher ratings were given to areas that had both an understory and an overstory. The majority of the time, the bank cover contained both an understory and overstory. Rarely was the bank completely barren or grassy. The invasive species contributed to greater bank coverage but negatively affected the overall health of the bank vegetation. The most commonly identified invasive species include Kudzu, Tree of Heaven, Bamboo, Garlic Mustard, and Oriental Bittersweet.

Bank Geometry (0 – 2): An assessment of the geometry of the bank, measured by observing the angle of the bank’s ascent from the river. A 2 represents a 0 to 45 degree angle, 1 represents between a 45 and 90 degree angle, and a 0 refers to a bank that is 90 degrees to the river or undercut.

  • Most of the river had moderate bank geometry (around 80% of the time). Good and poor bank geometry sections were few and far between. Steep or undercut banks typically translated into areas with severe erosion. Gently-sloping banks provided great substrate for greater canopy and bank cover ratings.

Bank Height (0 – 3): A measure of the bank’s height. In determining the height of the bank, the StreamSweepers approximated the different heights into four categories: 0-5ft, 6-10ft, 11-15ft, and >15ft.  A 3 refers to a bank that generally does not go much higher than the water and a 0 means about a bank taller than 15 ft.

  • For the Rapidan, despite relatively few changes in bank height (about 70% of the time, the bank was 6-10 ft high), there were greater tendencies toward 0-5ft banks on river right (28% of the time) and toward 11-15ft banks on river left (20% of the time). As the river widened, the banks tended to reach greater heights and vice versa.

Invasive Species (0 – 1): Refers to the presence of invasive species alongside the river. A 0 indicates the presence of invasive species, and a 1 indicates absence.

New assessment data points were recorded each time just one of the variables along the river changed. This means that in visually representing the assessment data on a map, colored lines representing the variables’ score stretch from each data point to the next, changing when the rating changes. As an example, the following map contains the assessment data for the river left (side of river as one floats downstream) side buffer of the Robinson. Red represents a 0, yellow represents a 1, and green represents a 2. Once all of the assessments were carried out, the data was transferred from points the GPS unit to color-coded maps made through use of Google Earth.

As an example, the image below shows the buffer assessment data for the river left side buffer of the Robinson. Red represents a 0, yellow represents a 1, and green represents a 2.

Robinson River Buffer Assessment
Robinson River Buffer Assessment

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