Our rivers are polluted because the land uphill of our rivers, which were once lined with forests and dotted with large wetlands (both of which filter water) have been densely developed or used for agriculture. Development hardens the land, not allowing water to soak in and sends high volumes and velocities of water to run off the land into our streams, carrying pollutants to the river each time it rains.
The rushing stormwater erodes the stream banks, often tearing large chunks of bank off, sending literally tons of dirt into the river, suffocating fish nursery beds and killing off underwater grass. The water running off agricultural lands can carry high amounts of excess nutrients that help cause harmful algae blooms and dead zones.
The Federation’s stream restoration projects aim to slow down and filter the stormwater, thus preventing a significant portion of the dirt and excess nutrients from reaching the tidal creeks. We slow down the water be either temporarily storing it in underground stormwater vaults or in a series of step pools that slowly release the water over time. Another technique is to spread the water out over a floodplain so it loses its force and velocity.
Slowing down the water filters out some dirt and nutrients by allowing them to settle to the bottom of the water column. However, the water is further filtered by by lining the step-pools with wetland plants or by creating wetland habitat in the flood plain. Finally, some of our projects direct water under the step-pools through a thick layer of carbon filled sand that works like a giant charcoal filter to clean the water.
Our most impacted streams often require significant land alteration. A healthy stream should flow at around the same surface elevation as the surrounding flood plain, allowing the water to spill over the banks and slowly spread out across the landscape during rain events. Stormwater-driven streams often look like mini-ravines, with the stream flow several feet below the flood plain elevation. Consequentially, storm water remains trapped in the channel, where it picks up speed and further erodes the bank. We use a variety of construction techniques to fill in or raise up the stream bottom so that it is once more connected to the surrounding landscape.