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 and 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.
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 AWS did not 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. In order to make this data more understandable and relatable, for the 2014 State of the Anacostia River Report, AWS is using a school grading system.
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 for its data the Stormwater Runoff that is generated excessively because of impervious surfaces. It is not practical to measure the volume of stormwater runoff whenever it rains. 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.
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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