Assessment Methods

To evaluate the data for the State of the River report card, the Anacostia Watershed Society employs a variety of scientific methods. Currently there is not a standard grading system to assess Stormwater Runoff Volume, Toxics, and Trash.  These factors are very important to the health of the Anacostia River, so we created our own method, and we explain our scientific process here.

Water Quality Parameters
Stormwater Runoff Volume
Toxics and Trash

Water Quality Parameters

The EcoCheck method developed by the Mid-Atlantic Tributary Assessment Coalition was used to assess the river for water quality parameters as described on the Parameter Trend Analysis page: Dissolved Oxygen, Fecal Bacteria, Chlorophyll a, Secchi Disk Depth (Water Clarity), and Submerged Aquatic Vegetation (SAV).

The link to the manual is here (pdf file, 8.3 MB).

Though AWS uses the EcoCheck protocol to calculate the %Scores for the water quality parameters, unlike other years, in 2014 and beyond AWS did not use the manual’s grading system (A through D and F) because it employs equal interval breaks for grading. Feedback from the public indicated that the EcoCheck grading system is confusing because of its similarity to a school grading system while the interval breaks are different. The EcoCheck grading of C (>=40 and <60 by the EchoCheck %Score) indicates the river is given a passing grade for a swimmable and fishable, but in actuality it is not). In order to make our grading more understandable and relatable to the general public, in 2014 and beyond, AWS is using a school grading system for the State of the Anacostia River Report.

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Stormwater Runoff Volume

Initially, AWS wanted to measure the areas of impervious surfaces throughout the watershed. However, measuring impervious surfaces had various difficulties:

·   AWS relies on government data which is not released on a regular schedule.
·   There are several methods to calculate imperviousness that produce different results.
·   There are 3 jurisdictions in the Anacostia watershed and they do not all use the same methods for calculations.
·   Green infrastructure is continuously being installed and each technique/practice has a different capacity to manage stormwater. It is not clear how those differences will be taken into account as pervious surfaces.

Because of those factors, AWS decided to use peak streamflow data for the Stormwater Runoff Volume analysis because the excessive runoff is generated by impervious surfaces, which will generate sharper peak streamflows when it rains.. It is not practical to measure the volume of stormwater runoff. However, the runoff will be concentrated in streams and it is known that peak stream discharges (flows) have been increasing. United States Geological Survey (USGS) has been measuring stream discharge since 1938 in the Northwest and the Northeast Branches of the Anacostia River. The historic data was used to calculate the Stormwater Runoff Volume %score.

First, the 99th percentile of daily stream discharge was calculated for each year. Then, the values were plotted on a graph as shown below. The reason we use the 99th percentile is to eliminate values from most extreme events such as hurricanes. Using a 99th percentile value for a given year, the highest values for about 4 days will be dropped out.

Click on chart for full size

An average of 99th percentile daily stream discharges for the years 1938 to 1941 and that for 2008 to 2012 were calculated respectively. The former is a tentative target for a 99th percentile peak stream discharge. Because we did not want to have negative values, the average for 2008-2012 was multiplied by 1.5 for use as a baseline. From this baseline of peak stream discharge, we can determine the amount of stream discharge to be reduced (B in the graph).

The tentative goal is still reasonable because in the period of 1938 - 1941, there is documentation of people who swam in the Anacostia River. However, we know that the Anacostia River had been degrading long before then due mainly to agricultural activities, sewage influx, and dumping. As we learn more, we may revise the goal in the future.

The score was then calculated using the target and the baseline.

For example, the 99th percentile peak stream discharge in a given year is indicated as “A” in the graph. Then the score was calculated using this formula:

%Score = (Baseline (current x 1.5 in the graph) - A) / B x 100

With highly fluctuating annual values, to keep an accurate assessment AWS used 5-year moving averages. The score for 2012 is actually an average of scores from 2008 through 2012. The scores were calculated for the Northwest and the Northeast Branches and the average value was used for the Anacostia River's score for Stormwater Runoff Volume.

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Toxics and Trash

Calculating the score for Toxics and Trash is very difficult due to the complexity of assessing a wide ranges of factors. There are many toxic chemicals in the river such as pharmaceuticals, PCB, PAH, pesticide, herbicide, and heavy metals, to name a few. There are about 200 congeners of PCB and numerous chemicals in the group of Polycyclic Aromatic Hydrocarbons (PAHs). The standard toxicity level is different for each chemical. In addition, there are chemicals that even do not have a safe standard for humans and wildlife. Quantifying the amount of trash in the Anacostia River watershed accurately each year is also very difficult, even though unlike chemicals, you can see it plainly with the naked eye!

All of these challenges make interpreting the data and comparing it to a scientifically rigorous standard in a reasonable manner nearly impossible.

Therefore, the Anacostia Watershed Society decided to take a different approach from strictly scientific scoring. AWS decided to apply the Business Confidence Index method to these important parameters. We listed actions to be taken for Toxics and Trash. Then, AWS professionals discussed how much work had been done for each action. It is like an Environmental Confidence Index for Toxics and Trash.

This method produces reasonably understandable and intuitive scores. Also this method gives a good sense to the public about what actions should be taken and where we are to remedy the problems. We will continue to monitor the accuracy of this method, and the system will receive improvements as fit.

The table calculating our scores for Toxics and Trash is shown below.

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