Chapter 6: Monitoring Floodplain Restoration
George R. Pess, Sarah A. Morley, Julie L. Hall, and Raymond K. Timm
River corridors are naturally dynamic and ecologically complex components of a watershed and often contain a disproportionately high amount of the total regional biodiversity (Naiman et al. 1993; Ward et al. 2001). Unaltered river corridors have heterogeneous landscape features, dominated by dynamic conditions, and exhibit scale-dependent biophysical patterns and processes (Ward et al. 2001). A prominent feature within river corridors is the floodplain (Figure 1). Geomorphologists traditionally define a floodplain as a flat, depositional feature of the river valley adjoining the river channel, formed under the present climate and hydrologic regime and during times of high discharge (Leopold et al. 1964; Dunne and Leopold 1978; Leopold 1994). Hydrologists and engineers view the floodplain either as land subject to periodic flooding or the area flooded by the 100-year flood event (Dunne and Leopold 1978). Ecologists have defined the floodplain and accompanying habitats as areas that are periodically inundated by the lateral overflow of river or lakes, or direct precipitation or groundwater; the resulting physiochemical environment causes the biota to respond by morphological, anatomical, physiological, phonological, or ethnological adaptations, and produce community structures (Junk et al. 1989).
Some of the most common features and terms associated with the definition of floodplains regardless of discipline include main channels; oxbow lakes; point bars; meander bends; meander scrolls; floodplain channels, such as sloughs, beaver ponds, surface and groundwater-fed tributaries, natural levees, or raised berms above the floodplain; wetland areas created by finer sediment overbank deposits; coarser sand deposits called sand splays; accumulations of wood deposits, such as logjams; mid-channel islands created by obstructions, such as wood deposits; and unique vegetation patterns determined by flows, obstructions within the floodplain, and small changes in elevation (Figure 2; Table 1; Leopold et al. 1964; Dunne and Leopold 1978; Wohl 2000). These floodplain-associated features are unique and are needed to help maintain river dynamics, watershed processes, and community structure and function (Ward et al. 2001).
The objective of our chapter is to describe how to monitor the effectiveness of floodplain-associated projects that attempt to reconnect isolated habitats. First, we identify and briefly review common effects of anthropogenic disturbance to floodplains and restoration techniques used to reconnect floodplain habitats isolated by anthropogenic disturbance. Next, we discuss how developing a monitoring plan based upon clear restoration goals and objectives can be used to help guide the monitoring of individual or multiple floodplain reconnection projects. Then, we discuss the selection of physical and biological study parameters and sampling protocols that can be applied to different types of restoration approaches. Finally, we provide recommendations for applying these monitoring techniques to temperate rivers.