Restoration of Physical Integrity of Rivers

Abstract

Physical integrity for rivers refers to a set of active fluvial processes and landforms wherein the channel, floodplain, sediment, and overall spatial configuration maintain a dynamic equilibrium, according to Graf 2001 (cited under Components of Physical Integrity). Physical integrity is achieved when river processes and forms maintain active connections with each other in the present hydrologic regime. The term “physical integrity” was first used in an important piece of legislation in the United States of America, the Clean Water Act of 1977, in which it is stipulated that the nation must restore and maintain the chemical, physical, and biological integrity of the nation’s water. Within the Environmental Protection Agency, the governmental agency charged with carrying out and enforcing the Clean Water Act, and the scientific literature, much of the focus has been on the chemical and biological integrity, with less direct focus on how to restore physical integrity. However, in the late 20th and early 21st centuries, there has been a greater scientific focus on restoration of physical forms and processes in rivers. Restoration of physical integrity encompasses several aspects: reducing fragmentation, ensuring functional physical processes and equilibrium, allowing dynamic processes, and matching restoration to geographic large-scale controls. In practice, restoration of physical integrity can be divided into two main categories—those focused on restoring form by increasing physical heterogeneity or creating a specific planform (e.g., meandering) or bedform (e.g., pool-riffles), and those focused on restoring processes, including sediment transport, flow retention, and flooding in order to maintain forms. Form-based restoration is usually rooted in the assumption that a reference condition can elucidate the forms that best match the processes under similar hydrologic and sediment regimes. Reference conditions can either be historical (i.e., where there is sufficient data on previous channel conditions before the degradation occurred) or geographical—where there is an undisturbed stream reach within the same region with similar climatic, hydrological, geological, and land-use conditions and the reference and degraded reaches have similar drainage areas and valley characteristics (in terms of valley slope and with and hillslope conditions). In addition, process-based restoration goals based on ecosystem functioning or channel classification schemes can be used in designing channel restoration. In areas where the flow regime is heavily altered, by for example dams, flow diversions or land-use conditions, environmental or functional flows have been used to determine which flows (e.g., five-year flood) are necessary to maintain certain physical processes or forms.