127
2017). Land use in the valley bottom replaced riparian forests with agricultural
lands and settlements, which led to more than 50% reduction in the spatial extent of
the river corridor. Restoration designed to decrease flood risk and increase sustainable river habitat was undertaken during 2013–2015, with a focus on widening the
active channel, decreasing the steepness of the banks along the incised channel, and
removing grade-control structures (Fig. 4.10). Observed changes thus far include
greater longitudinal connectivity for sediment transport, increased instream habitat
diversity, and increased size and abundance of riparian vegetation patches (Moritsch
2017).
In North America, basin-scale restoration programs have included reconnecting
channels with portions of the river corridor disconnected through channel engineering and/or flow regulation. Examples come from the Kissimmee River in Florida,
USA and the Colorado River in the southwestern United States and northwestern
Mexico.
The Kissimmee River is the headwaters of the Everglades ecosystem and the
primary tributary to Lake Okeechobee. The river drains ~6100 km
2
of low-relief
terrain with extensive wetlands (Warne et al. 2000). The highly sinuous Kissimmee
was channelized and regulated with six water-control structures between 1962 and
1971. Nutrient loading to Lake Okeechobee increased, the river became anoxic, and
habitat and wildlife populations declined. Public outcry led the Florida legislature
to pass the Kissimmee River Restoration Act in 1976 with the goal of restoring
ecological integrity as judged by energy source (organic matter inputs), water quality, habitat quality, hydrology, and biological interactions (Koebel 1995; Wohl
2004). Restoration included recreating a more natural flow regime by removing two
of the water-control structures. Restoration also included enhancement of natural
spatial heterogeneity via backfilling portions of the channelized canal and reexcavating buried portions of the original channel and removing barriers to connectivity created by artificially cutoff meanders (Fig. 4.11). Although the original
hydrologic regime has not yet been restored and this limits full recovery of the river
ecosystem (Toth et al. 1993), restoration activities completed thus far have produced
the expected effects (Koebel and Bousquin 2014).
The Colorado River drains ~637,000 km
2
of the southwestern United States and
northwestern Mexico, entering the Pacific Ocean in the Gulf of California. The river
is intensively altered from the headwaters to the delta. Alterations include numerous
dams for water storage and diversions for consumptive water uses within and
beyond the drainage basin. The lower portion of the drainage basin is channelized.
Agricultural return flows and salinity create water quality problems. Most of the
flow regulation infrastructure was built during the second half of the twentieth century. By the end of the twentieth century it was clear that ecosystems throughout the
river network were in serious decline. Restoration programs have focused on four
portions of the river network: the Upper Colorado River basin upstream from the
Grand Canyon; the Colorado River within the Grand Canyon; the Lower Colorado
River basin downstream from the Grand Canyon; and the river’s delta.
The Upper Colorado River endangered fish recovery program (http://www.coloradoriverrecovery.org/) emphasizes conservation and restoration of four endangered
4.6 Changing Perceptions of River Health and Naturalness
2017). Land use in the valley bottom replaced riparian forests with agricultural
lands and settlements, which led to more than 50% reduction in the spatial extent of
the river corridor. Restoration designed to decrease flood risk and increase sustainable river habitat was undertaken during 2013–2015, with a focus on widening the
active channel, decreasing the steepness of the banks along the incised channel, and
removing grade-control structures (Fig. 4.10). Observed changes thus far include
greater longitudinal connectivity for sediment transport, increased instream habitat
diversity, and increased size and abundance of riparian vegetation patches (Moritsch
2017).
In North America, basin-scale restoration programs have included reconnecting
channels with portions of the river corridor disconnected through channel engineering and/or flow regulation. Examples come from the Kissimmee River in Florida,
USA and the Colorado River in the southwestern United States and northwestern
Mexico.
The Kissimmee River is the headwaters of the Everglades ecosystem and the
primary tributary to Lake Okeechobee. The river drains ~6100 km
2
of low-relief
terrain with extensive wetlands (Warne et al. 2000). The highly sinuous Kissimmee
was channelized and regulated with six water-control structures between 1962 and
1971. Nutrient loading to Lake Okeechobee increased, the river became anoxic, and
habitat and wildlife populations declined. Public outcry led the Florida legislature
to pass the Kissimmee River Restoration Act in 1976 with the goal of restoring
ecological integrity as judged by energy source (organic matter inputs), water quality, habitat quality, hydrology, and biological interactions (Koebel 1995; Wohl
2004). Restoration included recreating a more natural flow regime by removing two
of the water-control structures. Restoration also included enhancement of natural
spatial heterogeneity via backfilling portions of the channelized canal and reexcavating buried portions of the original channel and removing barriers to connectivity created by artificially cutoff meanders (Fig. 4.11). Although the original
hydrologic regime has not yet been restored and this limits full recovery of the river
ecosystem (Toth et al. 1993), restoration activities completed thus far have produced
the expected effects (Koebel and Bousquin 2014).
The Colorado River drains ~637,000 km
2
of the southwestern United States and
northwestern Mexico, entering the Pacific Ocean in the Gulf of California. The river
is intensively altered from the headwaters to the delta. Alterations include numerous
dams for water storage and diversions for consumptive water uses within and
beyond the drainage basin. The lower portion of the drainage basin is channelized.
Agricultural return flows and salinity create water quality problems. Most of the
flow regulation infrastructure was built during the second half of the twentieth century. By the end of the twentieth century it was clear that ecosystems throughout the
river network were in serious decline. Restoration programs have focused on four
portions of the river network: the Upper Colorado River basin upstream from the
Grand Canyon; the Colorado River within the Grand Canyon; the Lower Colorado
River basin downstream from the Grand Canyon; and the river’s delta.
The Upper Colorado River endangered fish recovery program (http://www.coloradoriverrecovery.org/) emphasizes conservation and restoration of four endangered
4.6 Changing Perceptions of River Health and Naturalness