Flows for Floodplain Forests: A Successful Riparian Restoration (original) (raw)
Related papers
Planned Flooding and Colorado River Riparian Trade-Offs Downstream From Glen Canyon Dam, Arizona
Ecological Applications, 2001
Regulated river restoration through planned flooding involves trade-offs between aquatic and terrestrial components, between relict pre-dam and novel post-dam resources and processes, and between management of individual resources and ecosystem characteristics. We review the terrestrial (wetland and riparian) impacts of a 1274 m 3 /s test flood conducted by the U.S. Bureau of Reclamation in March/April 1996, which was designed to improve understanding of sediment transport and management downstream from Glen Canyon Dam in the Colorado River ecosystem. The test flood successfully restored sandbars throughout the river corridor and was timed to prevent direct impacts to species of concern. A total of 1275 endangered Kanab ambersnail (Oxyloma haydeni kanabensis) were translocated above the flood zone at Vaseys Paradise spring, and an estimated 10.7% of the total snail habitat and 7.7% of the total snail population were lost to the flood. The test flood scoured channel margin wetlands, including potential foraging habitats of endangered Southwestern Willow Flycatcher (Empidonax traillii extimus). It also buried ground-covering riparian vegetation under Ͼ1 m of fine sand but only slightly altered woody sandbar vegetation and some return-current channel marshes. Pre-flood control efforts and appropriate flood timing limited recruitment of four common nonnative perennial plant species. Slight impacts on ethnobotanical resources were detected Ͼ430 km downstream, but those plant assemblages recovered rapidly. Careful design of planned flood hydrograph shape and seasonal timing is required to mitigate terrestrial impacts during efforts to restore essential fluvial geomorphic and aquatic habitats in regulated river ecosystems.
EARLY RECOVERY OF AN EASTERN SIERRA NEVADA RIPARIAN SYSTEM AFTER 40 YEARS OF STREAM DIVERSION1
Rush Creek, which feeds Mono Lake, has been diverted below Grant Lake, totally or in part, for over 40 years. In the early 1980 ' s, because of above normal snow packs, runoff was released into the creek. Minimum flow releases have also been established. The riparian vegetation has responded to these releases. In a few areas, riparian trees and shrubs (e.g., black cottonwood and willow) survived the diversion period but with high stem mortality. These plants are resprouting in response to the 1980's floods. In other areas, new plants are establishing within the floodplain; however, on areas away from the floodplain most riparian plants died and are not regenerating. The patterns of riparian regeneration and environmental requirements of each riparian species have been preliminarily determined.
Early recovery of an eastern Sierra Nevada riparian system after 40 years of stream diversion
1989
Rush Creek, which feeds Mono Lake, has been diverted below Grant Lake, totally or in part, for over 40 years. In the early 1980 ' s, because of above normal snow packs, runoff was released into the creek. Minimum flow releases have also been established. The riparian vegetation has responded to these releases. In a few areas, riparian trees and shrubs (e.g., black cottonwood and willow) survived the diversion period but with high stem mortality. These plants are resprouting in response to the 1980's floods. In other areas, new plants are establishing within the floodplain; however, on areas away from the floodplain most riparian plants died and are not regenerating. The patterns of riparian regeneration and environmental requirements of each riparian species have been preliminarily determined.
Freshwater Biology, 2007
1. Riparian vegetation in dry regions is influenced by low-flow and high-flow components of the surface and groundwater flow regimes. The duration of no-flow periods in the surface stream controls vegetation structure along the low-flow channel, while depth, magnitude and rate of groundwater decline influence phreatophytic vegetation in the floodplain. Flood flows influence vegetation along channels and floodplains by increasing water availability and by creating ecosystem disturbance. 2. On reference rivers in Arizona's Sonoran Desert region, the combination of perennial stream flows, shallow groundwater in the riparian (stream) aquifer, and frequent flooding results in high plant species diversity and landscape heterogeneity and an abundance of pioneer wetland plant species in the floodplain. Vegetation changes on hydrologically altered river reaches are varied, given the great extent of flow regime changes ranging from stream and aquifer dewatering on reaches affected by stream diversion and groundwater pumping to altered timing, frequency, and magnitude of flood flows on reaches downstream of flow-regulating dams. 3. As stream flows become more intermittent, diversity and cover of herbaceous species along the low-flow channel decline. As groundwater deepens, diversity of riparian plant species (particularly perennial species) and landscape patches are reduced and species composition in the floodplain shifts from wetland pioneer trees (Populus, Salix) to more drought-tolerant shrub species including Tamarix (introduced) and Bebbia. 4. On impounded rivers, changes in flood timing can simplify landscape patch structure and shift species composition from mixed forests composed of Populus and Salix, which have narrow regeneration windows, to the more reproductively opportunistic Tamarix. If flows are not diverted, suppression of flooding can result in increased density of riparian vegetation, leading in some cases to very high abundance of Tamarix patches. Coarsening of sediments in river reaches below dams, associated with sediment retention in reservoirs, contributes to reduced cover and richness of herbaceous vegetation by reducing water and nutrient-holding capacity of soils. 5. These changes have implications for river restoration. They suggest that patch diversity, riparian plant species diversity, and abundance of flood-dependent wetland tree species such as Populus and Salix can be increased by restoring fluvial dynamics on floodsuppressed rivers and by increasing water availability in rivers subject to water diversion or withdrawal. On impounded rivers, restoration of plant species diversity also may hinge on restoration of sediment transport.
A large-scale environmental flow experiment for riparian restoration in the Colorado River Delta
Ecological Engineering, 2017
Managing streamflow is a widely-advocated approach to provide conditions necessary for seed germination and seedling establishment of trees in the willow family (Salicaceae). Experimental flow releases to the Colorado River delta in 2014 had a primary objective of promoting seedling establishment of Fremont cottonwood (Populus fremontii) and Goodding's willow (Salix gooddingii). We assessed seed germination and seedling establishment of these taxa as well as the non-native tamarisk (Tamarix spp.) and native seepwillow shrubs (Baccharis spp.) in the context of seedling requirements and active land management (land grading, vegetation removal) at 23 study sites along 87 river km. In the absence of associated active land management, experimental flows to the Colorado River delta were minimally successful at promoting establishment of new woody riparian seedlings, except for non-native Tamarix. Our results suggest that the primary factors contributing to low seedling establishment varied across space, but included low or no seed availability in some locations for some taxa, insufficient soil moisture availability during the growing season indicated by deep groundwater tables, and competition from adjacent vegetation (and, conversely, availability of bare ground). Active land management to create bare ground and favorable land grades contributed to significantly higher rates of Salicaceae seedling establishment in a river reach with high groundwater tables. Our results provide insights that can inform future environmental flow deliveries to the Colorado River delta and its ecosystems and other similar efforts to restore Salicaceae taxa around the world.
Effectiveness of environmental flows for riparian restoration in arid regions: A tale of four rivers
Ecological Engineering, 2017
ECOENG-4557; No. of Pages 9 2 E.P. Glenn et al. / Ecological Engineering xxx (2017) xxx-xxx success in restoring the Euphrates poplar forest on the Tarim and germinating new chorts of willows on the Bill Williams has been achieved after 15-20 years of environmental flows, but the Colorado River delta and Murrumbidgee Rivers have only received one or two flows. Success in enhancing native trees in the Colorado delta has been achieved in restoration plots, but the Murrumbidgee will require large overbank flows on a continuing schedule to rejuvenate the red gum forest.
Environmental Management, 2008
Arid zone rivers have highly variable flow rates, and flood control projects are needed to protect adjacent property from flood damage. On the other hand, riparian corridors provide important wildlife habitat, especially for birds, and riparian vegetation is adapted to the natural variability in flows on these rivers. While environmental and flood control goals might appear to be at odds, we show that both goals can be accommodated in the Limitrophe Region (the shared border between the United States and Mexico) on the Lower Colorado River. In 1999, the International Boundary and Water Commission proposed a routine maintenance project to clear vegetation and create a pilot channel within the Limitrophe Region to improve flow capacity and delineate the border. In 2000, however, Minute 306 to the international water treaty was adopted, which calls for consideration of environmental effects of IBWC actions. We conducted vegetation and bird surveys within the Limitrophe and found that this river segment is unusually rich in native cottonwood and willow trees, marsh habitat, and resident and migratory birds compared to flow-regulated segments of river. A flood-frequency analysis showed that the existing levee system can easily contain a 100 year flood even if vegetation is not removed, and the existing braided channel system has greater carrying capacity than the proposed pilot channel.
Post-wildfire riparian forest recovery processes along a regulated river corridor
Forest Ecology and Management, 2020
Riparian forest recovery was monitored over a 23 km study site that encountered a mixed low to moderate severity wildfire on the floodplain that was followed by a sequence of flows ranging from below bankfull to a 50year flood on the regulated South Fork Boise River, Idaho, USA. The goals of the study were to examine the dominant mechanisms of post-wildfire riparian forest regeneration along the river corridor in relation to upstream dam operations. Results are put in context with trends occurring in the regulated river system over the past 70 years that exemplify post-impoundment floodplain dynamics. Aerial imagery and field surveys were used to examine trends in geomorphic and forest response related to flow regulation, riparian wildfire, and a 50-year flood. Additionally, a one-dimensional sediment transport model was employed to assess seedling recruitment related to local and reach-scale erosional and depositional processes over a five-year period following the wildfire. A conceptual model is presented to illustrate riparian forest response to the interacting influences of fire severity and flood disturbance to help guide post-wildfire riparian forest management activities. Aerial imagery between 1957 and 2011 shows that flow regulation after dam closure led to channel narrowing of 62% of historic active channel width and an associated increase in floodplain tree density of 59%. This expansion of forest cover on the floodplain was at the expense of seedling recruitment habitat for pioneer species in the Salicaceae family that require bare sediment, light exposure, and access to the shallow groundwater. A 2013 riparian wildfire led to substantial top kill on the floodplain that provided a disturbance for potential seedling recruitment. However, dam releases during average and wet hydrologic conditions led to only 5% of the total observed seedling recruitment in the system occurring on the floodplain due to the limited magnitude of flood disturbances following the burn, highlighting the importance of the sequence of environmental flows immediately following riparian wildfire. Alternatively, 95% of seedling recruitment occurred within the active channel and was directly related to sediment transport processes. Post-wildfire related debris flows were responsible for providing the requisite sediment supply to the channel in an otherwise sediment supply-limited, regulated river system. Resultant sediment deposition was responsible for providing 100% of seedling recruitment habitat in the active channel during dam releases in average hydrologic conditions, whereas deposition accounted for 84% and erosion accounted for 16% of observed recruitment habitat during wet hydrologic conditions.
Journal of Environmental Management, 2009
River systems have been altered worldwide by dams and diversions, resulting in a broad array of environmental impacts. The use of a process-based, hierarchical framework for assessing environmental impacts of dams is explored here in terms of a case study of the Kootenai River, western North America. The goal of the case study is to isolate and quantify the relative effects of multiple dams and other river management activities within the study area and to inform potential restoration strategies. In our analysis, first-order impacts describe broad changes in hydrology (determined from local stream gages), secondorder impacts quantify resultant changes in channel hydraulics and bed mobility (predicted from a 1D flow model), and third-order impacts describe consequences for recruitment of riparian trees (recruitment box analysis). The study area is a 233 km reach bounded by two dams (Libby and Corra Linn). Different times of dam emplacement (1974 and 1938, respectively) allow separation of their relative impacts. Results show significant changes in 1) the timing, magnitude, frequency, duration and rate of change of flows, 2) the spatial and temporal patterns of daily stage fluctuation, unit stream power, shear stress, and bed mobility, and 3) the potential for cottonwood recruitment (Populus spp.). We find that Libby Dam is responsible for the majority of first and second-order impacts, but that both dams diminish cottonwood recruitment; operation of Corra Linn adversely affects recruitment in the lower portion of the study reach by increasing stage recession rates during the seedling establishment period, while operation of Libby Dam affects recruitment in the middle and upper portions of the study reach by changing the timing, magnitude, and duration of flow. We also find that recent experimental flow releases initiated in the 1990s to stimulate recovery of endangered native fish may have fortuitous positive effects on cottonwood recruitment potential in the lower portion of the river. This case study demonstrates how a process-based, hierarchical framework can be used for quantifying environmental impacts of dam operation over space and time, and provides an approach for evaluating alternative management strategies.
A Managed Flood on the Colorado River: Background, Objectives, Design, and Implementation
Ecological Applications, 2001
The Colorado River ecosystem in lower Glen Canyon and throughout Marble and Grand Canyons was greatly altered following closure of Glen Canyon Dam in 1963, as flood control and daily fluctuating releases from the dam caused large ecological changes. Ecosystem research was conducted from 1983 through 1990, and intensively from 1990 through 1995 when dam releases were modified both for scientific purposes and protection of the river ecosystem. High flows (e.g., beach/habitat building flows) were included in the Glen Canyon Dam Environmental Impact Statement (EIS), which identified a preferred strategy for dam operations and protection of the downstream ecosystem. Use of high flows partially fulfills recommendations of many river and riparian scientists for return of more natural flows, as part of initial efforts in river restoration. In 1996, a seven-day experimental controlled flood was conducted at Glen Canyon Dam to closely study the effects of a high flow event equivalent to those proposed for future dam management. It is an example of modification of operations of a large dam to balance economic gains with ecological protection. Limited to 1274 m 3 /s, the test flood was lower than pre-dam spring floods. The experiment was conducted to (1) test the hypothesis that controlled floods can improve sediment deposition patterns and alter important ecological attributes of the river ecosystem without negatively affecting other canyon resources and (2) learn more about river processes, both biotic and abiotic, during a flood event. Along with an explanation of the planning and background of this flood experiment, this paper summarizes expected and realized changes in canyon resources studied during the flood. Responses of specific resources to the flood are synthesized in the following compendium papers.