Natural habitats like our forests and native meadows hold valuable soil in place. But when these habitats are disturbed and removed, leaving bare soils, as they are during construction activities, that soil poses a major threat to our local streams and the aquatic life that lives there. Erosion and sediment transport in streams is a natural process, but with so much disturbance (via habitat fragmentation, conversion of natural habitat to housing developments, shopping malls and other human activity), sedimentation in our streams and rivers has become the number one pollutant by volume, nationwide.
What does sediment do to our water bodies? As excess sediment runs off the land and into a stream, it brings with it pesticides, nutrients and whatever else was hitching a ride with the soil particles. Increased sediment in streams creates turbid or cloudy water (turbidity), which means that sunlight cannot penetrate the river and photosynthesis may be limited, thus reducing the growth of food available for aquatic organisms.
Sediment also acts as a heat trap, absorbing sunlight and often increasing stream temperatures. As a result, dissolved oxygen needed for a healthy, diverse aquatic life is diminished, because warmer waters hold less oxygen. Suspended materials in the water can physically clog fish gills, reducing their resistance to disease, lowering their growth rates and negatively affecting development of eggs and larvae. As sediment drops out of the water column, it smothers important riffle habitat, filling spaces between the rocks on the stream bottom and covering habitat, while also smothering the macro-invertebrates and fish eggs that live there that cannot move out of harm’s way.
Streams are dynamic systems, and flooding and bank erosion are natural processes; without these natural events, streams would not meander and change course (this is why it’s never a good idea to build or alter floodplains and instead keep healthy riparian natural buffers and undeveloped flood plains to protect water quality and keep people out of harm’s way). But stream banks themselves are more vulnerable to erosion as we alter and pave over watersheds, causing more stormwater runoff that enters and overwhelms streams with very high flows.
As hard surfaces are constructed and take the place of our natural infiltrating wetlands, forests and other habitats, stormwater runoff increases even during small rain events, scouring stream banks and increasing erosion and sedimentation, often undermining the trees, and unfortunately disconnecting many streams from their floodplain as the stream becomes entrenched. Scientists have shown that streams’ aquatic life diversity begins to suffer and decline when a watershed becomes more developed and exceeds an impervious surface area of 10%. As a stream loses its floodplain, whether due to entrenchment, harmful development or fill, this in turn makes flows even greater, exacerbating erosion and flooding downstream.
The Clean Water Act requires that states keep sediment pollution out of streams. For example, in Pennsylvania, sediment is largely regulated through its Chapter 102 Erosion and Sediment Control regulations. In a nutshell, these laws require that when earth disturbance occurs on land, the construction contractor must develop and use best management practices (BMPs) to minimize the potential for accelerated stream erosion and sedimentation and to manage post-construction stormwater runoff so that the sediment stays on the construction site and does not end up traveling, during rain events, into local streams and water bodies or offsite onto neighboring properties. BMPs include things like installing black fabric silt fences and compost filter socks that one often sees along perimeters of earth disturbance, hay bales to help reinforce these fabrics especially on steeper slopes, and straw mulch that is required to cover raw earth during construction activities. These practices are designed to minimize the amount of disturbed soil at one time, minimize soil compaction, remove sediment from onsite runoff before rainwater leaves the site and generally slow down runoff.
There are also additional BMP protections for high-quality and exceptional-value streams in PA, including preservation of 150-foot natural forest buffers along these streams. The crux of the matter here though can be enforcement and compliance; these BMPs must be maintained and inspected over time to ensure they are not being compromised and are functioning properly. This is where citizen monitors have played an essential role in reporting potential pollution problems to county conservation districts, especially recently on large gas transmission pipeline projects in the Delaware River Basin (DRB).
Citizen watchdogs can make a difference
As you travel around the watershed, citizens can help greatly in determining if erosion and sediment control practices at construction sites are up to par. For example Delaware Riverkeeper Network’s (DNR) Muddy Waters Watch and the recent Pipeline Watch have trained Delaware River residents for over two decades to watchdog construction activities and report pollution, including bad, failing or missing best management practices. DRN’s recent Pipeline Watch was specifically launched to monitor over 13 large natural gas pipeline projects being considered or in some phase of development in the Delaware River Basin, and because these pipelines are linear in nature and impact large swaths of land and many streams and wetlands, keeping sediment out of the water bodies in the path of the pipeline is paramount.
In Pike and Wayne Counties, over 20 local community members and landowners helped watchdog the recent Tennessee Gas Pipeline that cut through forests, wetlands and streams over the past few years. They, as well as the county conservation districts, documented over 60 instances where problems were occurring and compliance was needed. With citizens now having the ability to easily take photos in the field with GPS-enabled phones, this type of visual watch-dogging has become even more effective in the last five years. If you see construction activity that you think may not be following BMPs, or if during a rain event you see sediment laden water entering water bodies, snap a few photos with your phone and contact DRN’s pollution hotline number (800/8-DELAWARE) or your local county conservation district. Or consider coming to one of DRN’s trainings to learn more about how you can help protect streams in your community.
[Faith Zerbe is a biologist with Delaware Riverkeeper Network and directs the organization’s Water Quality Monitoring Program. In her free time she enjoys time in the Upper Delaware – kayaking, camping, snorkeling, and hiking.]