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<br />HABITAT REHABILITATION
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<br />RIVER-FLOODPLAIN RESTORATION
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<br />Restoration, in the perfect sense, requires recreating both the structure and function of damaged ecosystems
<br />(Cairns, 1991). Because the complete reversal of anthropogenic disturbances is usually unattainable, or
<br />undesirable (Petts, ]989; Cairns, 1991), Gore and Shields (1995) use the term rehabilitation 'meaning the
<br />restoration of some of their ecological functions and values' in their recommendations regarding the ability
<br />to restore large rivers.
<br />Stream rehabilitation efforts are widespread and great strides have been made towards evaluating project
<br />design, effectiveness, and sustainability (Gore and Bryant, 1988; Swales, 1989; Frissell and Nawa, 1992).
<br />Large river restoration, conversely, is poorly understood (Regier et al., ]989; Gore and Shields, 1995). There
<br />are, however, several examples of projects that attempt various scales of river rehabilitation ranging from
<br />complete restoration of the former floodplain (Toth et al., ] 993), to reconnecting historic side-channels
<br />(Bravard et al., 1986; Amoros, 1991), to the isolation of floodplain lakes to reduce sedimentation and
<br />manipulate water levels (Sparks, 1992).
<br />Recognizing that complete restoration is usually unattainable, large-scale river rehabilitation efforts must
<br />strive to enhance the eco]ogical integrity (Angermeier and Karr, 1994) of the system within its mu]tiple
<br />demands. Planning large-scale restoration, therefore, requires expertise from resource managers (ecologists,
<br />hydrologists, river engineers, realtors, planners) and resource users (commercial navigation and recrea-
<br />tionists) affected by the proposed restoration efforts (Petts, 1989).
<br />Success in Upper Mississippi River-floodplain restoration wiJ] ]argely be defined by (I) the ability to
<br />restore abiotic controls (Regier et al., 1989; Ward and Stanford, 1989; Bayley, 1991, 1995; Angermeier and
<br />Karr, 1994); and (2) the acquisition of floodplain property (Sparks et al., 1990; Bayley, 1991). Project
<br />performance evaluation is a matter that requires extensive physical and ecological monitoring of pre-
<br />improvement characteristics and then following their change through time with respect to restoration efforts
<br />(Gore and Bryant, 1988; Kelly and Harwell, 1990; Angermeier and Karr, 1994). Monitoring attention
<br />should focus on ecological processes (Angermeier and Karr, 1994) and lower trophic levels (Gore and
<br />Bryant, 1988) in the restored project. Knowledge gained from completed projects should be used to refine
<br />future restoration design.
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<br />UPPER MISSISSIPPI RIVER HABITAT REHABILITATION
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<br />Habitat rehabilitation on the Upper Mississippi River Navigation System is being implemented in many
<br />locations (Figure 1) as discrete projects designed to improve or protect aquatic habitats. Projects are
<br />typically designed using a special interest (i.e. game species) oriented management approach that sometimes
<br />precludes the utility of an area for non-target species (Bayley, 1991; Sparks, 1992). The primary objectives of
<br />the projects are to counteract side-channel and backwater sedimentation. The three most common
<br />techniques include: (1) introduced flow to counteract oxygen depletion in backwaters or side-channel
<br />isolation; (2) isolation of backwaters to reduce sediment inputs; and (3) island construction to reduce wave
<br />energy and sediment resuspension. Dredging is a component of most projects.
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<br />Introduced flow projects
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<br />Introduced flow projects are proposed or recently completed at seven locations (Figure I; triangles).
<br />Aquatic habitats isolated by dams, dikes or natural obstructions were selected because they are likely to
<br />become anoxic when isolated from river flow. An example offlow introductions through the earthen portion of
<br />a dam is presented in Figure 3. Side-channel projects either remove obstructions or construct dikes with water
<br />control structures in projects requiring water management capability. Early results indicate that introduced
<br />flow projects have been successful in raising backwater oxygen levels, but cold water intrusion during winter
<br />may decrease backwater temperatures and increase current velocities. All three parameters (oxygen, flow and
<br />temperature) are important determinants of overwintering habitat quality for fish (Bodensteiner and Lewis,
<br />1992). Projects have not been completed long enough to assess sedimentation rates, but increased flow through
<br />an area will introduce more sediment laden river water than before project implementation.
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