Phase 1 - Water Resources Board - State of Oklahoma
4 BACKGROUND In Oklahoma, development and implementation of a comprehensive wetland monitoring program is a high priority. Wetland-focused projects recently conducted in the state include development of a probabilistic monitoring design, creation of an interactive wetland mapping system, development of procedures to evaluate use attainability in wetlands, and development of indices of biotic integrity using different biotic assemblages. The majority of this work has focused on closed depressional wetlands, although Oklahoma’s wetland resources include a number of other important wetland types. Oxbow systems are unique natural lakes/wetlands that have not been assessed in Oklahoma. These systems are unique in that they have attributes of both lakes and wetlands. Oxbow systems provide several key ecosystem services such as floodwater retention, nutrient and sediment retention, nursery grounds for fish, and habitat for local and migratory waterbirds, amphibians and macroinvertebrates. Although oxbow systems are highly variable in their physical and chemical characteristics, many of these systems are considered wetlands because they have relatively shallow depths, large amounts of sediments and nutrients, characteristic riparian and emergent plant assemblages, and seasonal hydroperiods. These systems form when a U-shaped meander is cut off from the main portion of river by process of erosion and deposition. Erosion occurs as sediment is scoured from the outer bank of the meander. As erosion is occurring sediment is deposited on the inner bank of these bends. The area of deposition is called a “point bar.” Figure 1 shows this process occurring in two areas – bend A and bend B. This process continues, causing bend A and bend B to move closer to one another. Eventually the two bends meet forming a bypass of the meander. In time, deposition of sediments will cause the meander to be essentially cut off from the rest of the river. This new cut-off portion forms a lake that often exhibits a distinctive “bow” shape. Sometimes a small connection is kept between the oxbow and the river called a “tie-channel.” This allows for an exchange of water and sediments. These tie channels can remain active for hundreds to thousands of years (Rowland and Dietrich, 2005). However, not all oxbows exhibit tie channels. Often oxbows only receive water from its parent river by seepage, rainfall, runoff, and during times of high flow. Bend A Erosion Bend B Deposition Deposition Deposition Figure 1: Oxbow formation showing erosional and depositional processes in a meander over time.
5 The amount of time this process occurs can vary depending on various factors such as sediment type and flow. The following aerial photographs (Figure 2) show the formation of an oxbow in Oklahoma. Pottawatomie County, 2003 Pottawatomie County, 2006 Pottawatomie County, 2008 Pottawatomie County, 2010 Figure 2: Oxbow formation in Pottawatomie County from 2003 to 2010. The development of assessment/monitoring schemes to evaluate habitat quality is an important part of managing Oklahoma’s surface water resources. The Beneficial Uses Monitoring Program (BUMP) conducted by the Oklahoma Water Resources Board currently monitors over 130 reservoirs in the state. This monitoring program is based on Use Support Assessment Protocols (USAP) that are designed to determine attainment of beneficial uses designated for Fish and Wildlife Propagation, Agriculture, Industrial and Municipal Process and Cooling Water, Primary Body Contact Recreation, Secondary Body Contact Recreation, and Aesthetics. According to OAC 785:45, separate protocols exist in Oklahoma to assess attainment of assigned beneficial uses based on the type of waterbody. There is one set for streams, another for lakes, and at this time none for wetlands. As oxbow systems are a meld of streams, lakes and wetlands, the application of current USAP would likely not be appropriate for wetlands since