Planning for a Watershed Assessment

The Donaldson Run stream enjoys what seems to be a significantly higher degree of oversight than many such streams in the United States. The county of Arlington has in place a monitoring program for water quality, macroinvertabrates, and bacteria. In addition, the stream was assessed to determine which segments are actively eroding in order to identify where stream channel restoration is necessary.

My approach to defining a watershed assessment plan for Donaldson Run which expands on the good work already being done would be to put in place a multi-faceted assessment protocol that brings together information about the evolution of the broader watershed with the water quality and stream channel assessment. Indicators to correlate with the stream health data would include tree canopy, impervious surface, survey of residential landscape maintenance practices, institutional grounds maintenance practices, and Low Impact Development (LID) storm water management implementations on county and residential properties. Over time, correlating these factors might help to identify and understand those developmental factors that play the biggest role in affecting the health of the stream.

In addition, it would be important to engage each of the constituent bodies that have an impact on the watershed. There are primarily 3 large constituent bodies that reside in and affect the watershed. These include 2 institutional organizations and the residential citizens. The institutional organizations are the Washington Golf & Country Club and Marymount University. The residential citizens subsequently fall into one of 4 different community civic associations. Not only would these groups be critical for gathering the necessary information about impacts on the watershed, but they would also be critical for ensuring that development practices move forward in a direction that is considerate of the needs of the watershed health.

Invasive Species

If you walk Donaldson Run, you’ll find many of the indigenous species of trees, shrubs and forbs that you would expect for an oak-hickory forest in the Piedmont. In a previous post we noted many of the common trees. You’re also likely to find shrubs such as mountain laurel and several types of viburnum. In the lower herbaceous layer, look for Solomon’s seal, Beardtongue, and Jack-in-the-pulpit, among others.

Unfortunately, you’re also likely to find several plant species that have been labeled invasive for our area because of their aggressive growth and adaptation to urban disturbances. These plants threaten to crowd out the native plants that provide the best food and shelter for the fauna in our region. Arlington County has a robust invasive plant management program. If you’re out in Donaldson Run and notice any areas being overrun with any of the plants noted below, give them a call and volunteer to help remove them.

Porcelainberry – Ampelopsis brevipedunculata

The Porcelainberry might look a bit like the native Wild Grape vines in Virginia, with heart-shaped and sometimes lobbed leaves that have course teeth around the edges. However, its tendrils are branching (whereas the native grape vine has non-branching tendrils) and it’s fruit vary in color from yellow to deep purple. It grows extremely quickly, and its porcelain-like shiny fruits are eaten and spread far and wide by birds. It does well in many different light conditions, and prefers moist soils along stream banks.

Asian Bittersweet – Celastrus orbiculata

This woody vine can grow up to 4 inches thick, with the potential to girdle and even kill large trees if left unchecked. The leaves are light green and round. The fruit start green, ripen to yellow, and then split open revealing red berries that birds eat. Like the Porcelainberry, it has a close native cousin called American Bittersweet (Celastrus scandens). In the case of Asian Bittersweet, the two cousins can hybridize and thus threaten the genetic identity of the native species.

Ground Ivy – Glechoma hederacea

In the mint family (and thus spreading quickly via rhizomes just as other mints), Ground Ivy invades low woods and other moist areas. This is one many people might see in their yards as well. The leaves are opposite and heart shaped, and it grows low to the ground.

Japanese Stiltgrass – Microstegium vimineum

Japanese Stiltgrass is a highly shade-tolerant spreading grass that grows up to 3.5 feet tall. It is found most often in flooded or other moist woodlands and can quickly crowd out all other ground-level vegetation. The leaves are pale green and lance shaped, giving it a distinctive bamboo–like look.

Japanese Knotweed – Polygonum spp.: cespitosum, cuspidatum

Stream banks in open areas with more light is where you’ll usually find this highly invasive species; it propagates via seeds as well as rhizomes. It has wide, broad ovate leaves and flowers that are easily distinguishable in late summer. Small, greenish-white flowers develop all along the axils of the leaves.

 

Find more information about these and other invasive plant species at https://www.invasiveplantatlas.org/

 

Water Quality Monitoring

So you have a local watershed that you want to take care of, but don’t know where to start? There are several companies that make getting started with water quality monitoring quite easy. You don’t have to spend a lot of money or have a fancy lab to be able to test all of the basic attributes of the water in your stream, creek, or river.

Several kits that are designed for students make it easy to repetitively test water and build time-series data. Listed below from highest cost to lowest are three popular options.

American Educational makes a $70 kit that allows 60 tests of the following attributes: pH,
dissolved oxygen, turbidity, and coliform bacteria. The kit also provides documentation that helps you to identify the color and odor but these are purely tested by observation. If what you would like to do is test these few attributes many times, then this kit is the one for you.

Next is the LaMotte 5918 Urban Water Quality Test Kit for $61.91. This kit tests several more attributes than the American Educational kit, including heavy metals. You can test chlorine, copper, iron, hardness, nitrate, pH, phosphates, and temperature. As indicated in the title of the kit, this may be more useful for urban environments where metals can be more of an issue in the water supply. The big downside with this kit is that you can only test 2 or 3 samples before ordering more supplies.

Finally you may want to try the Earth Force Low-Cost Water Quality Monitoring Kit for $41. This kit allows you to test more attributes than the American Educational kit as well, but replaces the metals testing with additional oxygen tests. You can monitor coliform , temperature, turbidity, pH, dissolved oxygen, biochemical oxygen demand (BOD), nitrate, and phosphate. With this kit you can do up to 10 samples before ordering new supplies.

As you can see, there may be different reasons why one of these kits may fit your needs better than others. At such low prices, it isn’t prohibitive to try more than one. The main thing is to get out there and get started. There’s a lot you can learn, and the more you study your watershed the closer you become to the systems that sustain us.

Imperviousness

Imperviousness. Is that a word? Spell check doesn’t recognize it but it is becoming a characteristic of land in the urban context that may just be on the verge of having it’s own ‘ness’. I took a closer look at the percentage of impervious land indicated for the Donaldson Run watershed and its implications.

The Arlington County web site page for Donaldson Run indicates that in the 1 square mile of the watershed, 11% of it is impervious. So out of roughly 640 acres, just over 70 acres of the land within the watershed are considered to be of an impervious nature. On the face of it, this percentage did not strike me as particularly alarming or dangerous. The picture that comes to mind is one of many small surfaces spread relatively evenly throughout the watershed, not having any significant negative effect in and of themselves.

Depending upon how the stormwater runoff from these 70 acres of impervious land are managed, the result could be as much as nearly 100% being diverted directly into drains and culverts feeding the stream. The surfaces contributing to the impervious total are made up primarily of buildings (rooftops), driveways, sidewalks and roads. The watershed is small enough that we can imagine a storm falling relatively evenly across the area as it drops its precipitation.

According to the USGS ‘water science school’, 1 inch of rain falling on an acre of land is equal to approximately 27,154 gallons. Therefore, 1 inch of rain falling on the Donaldson Run watershed would be equal to 17,378,560 gallons. From this total then, our impervious area would generate almost 2 million gallons of runoff that has not been slowed in any respect, and will not have any chance of infiltrating the ground or being treated for pollutants before entering the stream.

This is a significant amount of water, and it is an estimate for a relatively small storm. It really adds up fast and puts things into perspective. The need for low impact development techniques upstream is brought into striking relief. According to the EPA analysis of the impact of impervious cover on waterways, “several thresholds of degradation in streams occur at approximately 10–20% of the catchment in impervious area”.