The word "riparian" comes from the Latin ripa, meaning "river".  Today the word is commonly used to refer to a freshwater stream, streambanks, and the land surrounding the stream.  "Riparian restoration" refers to landscape and land management activities designed to return the natural integrity and function of our stream systems, many of which have become impaired as a result of upstream development, mismanagement, or deliberate channelization.  Restoration efforts often concentrate on restoring the vegetated "buffer" strip next to the stream bank; this riparian buffer is an essential component of a healthy freshwater ecosystem as well as a key element of urban stormwater management.  Other, more intensive restoration activites involve re-engineering the channel morphology of an impaired stream, with the goal of changing the stream's "behavior", or the way the water flows.  Restoring our streams is important to the health of our drinking water supply, the richness of our recreational resources and the well-being of native plant and animal communities.

The Paper Mill Run is a small stream that collects from a watershed area of 3 square miles (8 square km) before emptying into the Wissahickon Creek, a major recreational and drinking water resource for the Philadelphia region of southeastern Pennsylvania.  The last quarter-mile of the Paper Mill Run flows through the Morris Arboretum's lower meadows.  For decades, the Arboretum's section of the Paper Mill Run was impaired as a result of mismanagement and increased stormwater runoff (which is caused by impervious structures upstream, such as buildings and pavement).  This sort of impairment is fairly common for an urban stream:   The stream channel was getting scoured and becoming deeper with every flooding event, and there was no vegetation holding the banks in place, so the banks had become seriously eroded.  The grass had been mowed right up to the edge of the water for many years, and there was no riparian buffer to speak of.

The Pennsylvania Department of Environmental Protection (DEP) provided grant funding for the Morris Arboretum to design and install streamside landscapes demonstrating to visitors how they can improve water quality.  During the summer of 1998, over 900 feet (275 meters) of the Paper Mill Run were revitalized through a combination of soft engineering techniques and the planting of hundreds of native plants, shrubs and trees.  These efforts are helping to reduce the scouring effects of urban storm waters and help filter out pollutants from water that runs off the land.  The intent of the "demonstration" part of the Demonstration Project was to show that impaired waterways can be effectively rehabilitated by using a combination of vegetation and regrading.  The PA DEP has recently partnered with American Forests, Inc., Global Releaf 2000 initiative, to produce a statewide program called Stream ReLeaf.  The goal of Stream ReLeaf is to help mitigate development-related environmental degradation by replanting many of the Commonwealth's streamside buffers.  This is part of an overall initiative to restore 2,010 miles (3,235 km) of riparian forest buffers in the greater Chesepeake Bay watershed by the year 2010.

Interpretive signs tell the story of the demonstration project.  (photo credit: Brice Dorwart)

 

The geology and topography of the Paper Mill Run (PMR) Demonstration Project site are quite distinctive.  From a high point of ~400 feet (120 m) above sea level in Chestnut Hill and the Wissahickon gorge, quartzite and schist geologic formations fall rapidly to a rolling limestone plain, at an elevation of ~120 feet (35 m), at the Morris Arboretum.  The gorge constricts the flow of the Wissahickon Creek causing flood waters to back up in the low-lying areas upstream.  Almost all of the PMR site is within this floodplain.  Consequently, the upper soil layer is comprised of river sediments and deposits.  Soils are "sweet" (pH ~7.5) and fertile.  These conditions were key considerations in developing the plant list for the PMR Demonstration Project.

Phase I of the Paper Mill Run Demonstration Project is completely within the floodplain of the Wissahickon Creek, meaning that the site experiences periodic inundation.  For the majority of the year, however, the areas at or above the average bank height can be quite dry.  Within the context of the limestone Wissahickon floodplain, the PMR site was divided into three sub-areas reflecting the most common zones of soil moisture.  At the "toe" of the bank slope, where the soil meets the water, is a zone of saturation.  Plants selected for this narrow strip generally require water-saturated soils, and are at least partially submerged through most of the year.  Moving up the bank to a slightly higher elevation is a second zone that wicks moisture from the stream or groundwater table, and is subject to frequent flooding from small storm events.  Plants selected for this area tolerate short periods of inundation.  The third and final zone experiences inundation in only the largest storm events.  These plants have higher tolerances for dry conditions.

Dozens of native plant species were planted as part of the restoration effort.  Click here to see a full plant list from the project.

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