Riverbank Conditions

Suzy Meyer, Landscape Architect
(2001)

This report summary, addressing bank conditions, compliments the 2000 Biotic Assessment and establishes a baseline for the following: riverbank materials, indications of public access, and floodplains along the three rivers within the Pittsburgh Pool (also referred to as the Emsworth Pool). Fifty miles of riverbanks were inventoried between July and August 2000. This inventory is phase one, year one, in a five-year study of the riverbanks of Allegheny County. This study will be useful for contemporary waterfront planning, ecological restoration, as well long term understanding of riverbank changes over time.

Riverbank Materials

A riverbank study documents physical materials that make up riverbank slopes, especially those meeting the water's edge. Along the Pittsburgh/Emsworth Pool, several material types meet the water's edge: stone block, concrete, wood, steel, fill/rubble, gabion, soil, and slag. Humans have placed most of these materials along the riverbanks to form retaining walls or to stabilize steep banks. Steel is often found in the Pittsburgh pool in the form of recycled steel barges (no longer sea worthy) which are sunk and often filled with soil. In a few instances barges are piled one atop another to create a vertical edge of considerable height. These barges create a dramatic visual reminder of Pittsburgh's industrial past. Fill/rubble refers to a variety of man-made materials such as concrete slabs, slag, and stone chunks. These materials are used primarily as urban fill to secure more land for buildings, industry, or transportation above the river's edge. It accounts for approximately 48% of the average material composition of Pittsburgh's riverbanks. Many of the railroad right-of-ways along the river's edge were traditionally stabilized with coarse-grained open hearth slag (an inexpensive byproduct of steel production which was readily available).

The riverbanks in this survey were evaluated in terms of their condition, steepness, height, and material grain size. Natural Riverbanks have a region called berm. Berm is the region adjoining to the water's edge, below the steeper riverbank. Both riverbank and berm areas have been analyzed and described in this study. Condition is a qualitative measurement -- a relative evaluation of quality or characteristics. Material conditions can be subsequently categorized as consolidated, or unconsolidated. They can be even further categorized in terms of slope angle . Slope angle tells us the about a river's capacity to act as a floodplain and also gives us information about accessibility. To better understand the category of angle, the ratings of flat, moderate, steep, and vertical, are used to describe the general morphology (meaning physical characteristics) of a river valley. Slope steepness measurements are also reported in degrees. In the historically industrialized river valleys of Pittsburgh, human activity has greatly altered the riverbanks and changed their natural angles to serve human needs for transportation, flood control, and more usable land. Hence, we find the dominating presence of urban fill along our rivers. Unfortunately it is precisely this, the dominance of urban fill, which renders many of our riverbanks too steep for human access. By measuring height as well as steepness and material condition we are better able to evaluate pedestrian-based, public access.

Furthermore, understanding the bank's material grain size helps us to more accurately determine riverbank slope and understand riverflow. Material grain sizes are described as silt, sand, coarse sand, pebble, cobble, or boulder size. These measurements can help indicate the manner in which riverbank angle is formed. Riverbanks are either eroding, due to the action of waves and current, or being built up by sediment, deposited by the gentle flows of the river over time. Finer grain size is generally an indication of shallower angles (caused by sediment build-up).

Public Access

Public Access is one of the core issues of the 3R2N project. Our study of riverbank access (foot access from the top of the bank to the bottom of the slope, where the land meets the river) builds on existing research to reveal not only formal sites of public access but the informal or "unplanned" points of access which many citizens use. These can often include concrete infrastructure (designed for other purposes such as sewer access) and remnant floodplain. Access is most often indicated by footpaths, firepits, chairs, worn beaches, fishing pole holders, and people. When these indicators are absent access is ranked subjectively in terms of the potential for a person to gain access to the river's edge. Access potential is measured for each 1/10 mile unit in terms of steepness, height, materials, and density of under-story vegetation. Access for the study area is classified in terms of difficulty. Easy Access means there are no impediments to pedestrian access. Moderate Access means that there is some effort in foot placement required to get to the river. Inaccessible means the river is inaccessible due to one or more of the following conditions: retaining walls, steepness, height, or density of under-story vegetation. In order to compliment existing research we also classified access points in terms of use where possible. This is simply a matter of distinguishing between fishing access, boat ramps, private docks, etc.

Our study yielded some surprising results in terms of access. When we looked at research from 1991, utilizing almost identical methods, we noticed a dramatic increase in the number of fishing access points: from 28 in 1991 to 58 in 2000. This means the number of fishing access points has doubled. Local specialists on the subject attribute this change to a shift in public perception about the rivers. This might be, in part, because of the decrease in polluting riverfront industry and subsequent increase in fish population. This shift implies that there is already increased public awareness of the rivers as urban amenities.

Another surprising result we found was that access and steepness are not mutually exclusive terms. Our assumption at the beginning of this study was that steep riverbanks preclude access to the river's edge. This turned out to be false. In eleven study units banks classified as vertical or near vertical still provided relatively easy access because of usable staircases (often provided for the maintenance of sewer infrastructure). This is a commonly used method of river access and an excellent example of the informal or unplanned access which traditionally goes unnoticed in discussions of riverbank use and planning. Informal access points are another important example of the public's appreciation of the rivers as urban amenities.

Floodplains

There is an important relationship between a river's floodplain, public access, and ecological restoration. Usually, in the Pittsburgh area, wide river floodplains areassociated with points of sediment deposit during flood events; these sediments consist of fine grained material, including mud and silt. The steep slopes and soft shale soils of Allegheny county's hillsides are subject to the erosive forces of water and ice. These erosive forces help determine land forms. Steep hillsides and shallow floodplains typify our river corridors. Historically the floodplains of Allegheny County provided the flat base which was ideal for the development of riverfront industry. In the wake of Pittsburgh's industrial age we have an opportunity to integrate development with the remnant ecologies that provide the potential for restoration and preservation. Flooding is a natural aspect of riverbank ecosystems. Our Study examined riverbanks in terms of their potential for flooding. We determine this floodplain potential in terms of height. Any riverbank height of less than ten feet has potential as a floodplain. However, an ecologically relevant floodplain is a mixture of factors, including height, bank shape, and biological and chemical interactions. We hope that ongoing analysis of the riverbank data and the data from the biotic assessment will help determine the number of functioning floodplains in the Pittsburgh Pool. We can currently state that there is significant opportunity to restore ecological floodplain functions to the region, based on the fact that 50% of the study area meets our criteria as floodplains. Floodplains provide special habitats for wetland species, and filter stormwater runoff, providing water quality benefits. Restoring these systems adds beauty and health to our waterfront.

The Riverbank Report Summary

As the above is only a summary it is by no means an exhaustive representation of the data, information, and questions found in the complete Riverbank Conditions Report. We hope this summary provides relevant information for the general reader interested in these issues. Incorporating a broader representation of citizenry into these discussions is one of the goals of 3R2N. Those interested in obtaining a complete copy of the report may do so by contacting 3R2N.