Establishment Of Riparian Vegetation Research Articles

Extracting the Critical Rooting Length in Plant Uprooting by Flow From Pullout Experiments

AbstractThe growth and establishment of riparian vegetation on river bedforms is of hydrological as well as ecological importance as it helps in enhancing spatial heterogeneity and thus the biodiversity of river corridors. Yet, during floods, flow drag and scouring may reduce the rooting length of plants determining plant mortality via uprooting. In order for uprooting to occur, bed scouring must proceed until the rooting length reaches a critical value and drag forces exceed root residual anchorage. Therefore, the critical rooting length of a plant represents a crucial parameter to estimate the probability of plant removal due to flow erosion. However, difficulties in quantifying such length at the field scale have limited so far the performances of biomorphodynamic models for river bed evolution. In this work, we propose to assess the critical rooting length from controlled plant pullout experiments. To this aim, a free‐body model of the forces acting on a flexible plant in a stream at different erosion stages is developed. At incipient uprooting, we conjecture that the root resistance at the critical rooting length equals that of a plant with equal rooting length when pulled out in static conditions. To illustrate our approach, we validate our model on three different data sets obtained from small‐ and real‐scale plant uprooting experiments. A comparison between modeling and experimental observations reveals that the model provides valid results, despite its deterministic approach. The critical rooting lengths are finally used to assess the probability density function of the time to uprooting via a physically based stochastic model.

A Closer Look: Stream Geomorphology and Ecohydrological Interactions in the Minnesota River Basin

A Closer Look: Stream Geomorphology and Ecohydrological Interactions in the Minnesota River Basin

Geomorphological and riparian vegetation responses following a low-head dam removal: a study based on literature review

ABSTRACTMore and more low-head dam structures have deteriorated in recent years. Unlike the large dam, the geomorphological and ecological impacts of a low-head dam removal have not been quantified with insufficient monitoring data on pre- and post-removal. Therefore, this study intends to identify the low-head dam removal impacts on geomorphology and riparian vegetation based on previous studies. The characteristics of stored sediment in the impoundment play a critical role for geomorphological responses on a low-head dam removal creating a knickpoint and promoting a headcut migration. These geomorphological changes often form a new floodplain and create enough room for riparian vegetation establishment. The river geomorphology after a low-head dam removal can be a state of quasi-equilibrium within about a decade. In this state, a newly formed floodplain tends to be colonized by riparian vegetation in many low-head dam removal cases. After a decade to several decades, the riparian vegetation in the floodplain often develops to tree plants.

River channel lateral mobility: metrics, time scales, and controls

Alluvial river channels are intrinsically mobile. We mapped channel planform extent in a series of experiments to measure instantaneous rates of channel motion, loss of planform overlap with the original positions of the channels, and reworking of the fluvial surface over which the channels moved. These experiments comprise two aggrading deltas, one subsiding delta that underwent cyclical base level changes, and one braided channel system that was seeded with vegetation. We find that the amounts of channel planform overlap and remaining unreworked fluvial surface area both decay exponentially with time, and that these metrics and the instantaneously‐measured rates of channel motion scale predictably with one another in spite of the different time scales of the processes they record. Rates of channel planform change increase with increasing sediment flux and bed and planform irregularity, and decrease with the establishment of riparian vegetation. Aggradation does not noticeably affect channel mobility, but induces avulsions that allow the channels to more rapidly rework the fluvial surface. Additional findings include that: (1) sediment flux in the braided experiment equals its rate of bar migration, (2) channel widths are normally distributed with time, and (3) we can use our channel mobility metrics to connect surface processes with the resultant fluvial stratigraphy.

Stratigraphic, sedimentologic, and dendrogeomorphic analyses of rapid floodplain formation along the Rio Grande in Big Bend National Park, Texas

The channel of the lower Rio Grande in the Big Bend region rapidly narrows during years of low mean and peak flow. We conducted stratigraphic, sedimentologic, and dendrogeomorphic analyses within two long floodplain trenches to precisely reconstruct the timing and processes of recent floodplain formation. We show that the channel of the Rio Grande narrowed through the oblique and vertical accretion of inset floodplains following channel-widening floods in 1978 and 1990–1991. Vertical accretion occurred at high rates, ranging from 16 to 35 cm/yr. Dendrogeomorphic analyses show that the onset of channel narrowing occurred during low-flow years when channel bars obliquely and vertically accreted fine sediment. This initial stage of accretion occurred by both bed-load and suspended-load deposition within the active channel. Vegetation became established on top of these fine-grained deposits during years of low peak flow and stabilized these developing surfaces. Subsequent deposition by moderate floods (between 1.5 and 7 yr recurrence intervals) caused additional accretion at rapid rates. Suspended-sediment deposition was dominant in the upper deposits, resulting in the formation of natural levees at the channel margins and the deposition of horizontally bedded, fining-upward deposits in the floodplain trough. Overall, channel narrowing and floodplain formation occurred through an evolution from active-channel to floodplain depositional processes. High-resolution dendrogeomorphic analyses provide the ability to specifically correlate the flow record to the onset of narrowing, the establishment of riparian vegetation, the formation of natural levees, and ultimately, the conversion of portions of the active channel to floodplains.

Propriedades químicas de solo sob reflorestamento ciliar após 20 anos de plantio em área de cerrado

As propriedades químicas do solo variam com a cultura e manejo utilizados. O trabalho teve como objetivos avaliar as propriedades químicas de solo sob reflorestamento ciliar após 20 anos de plantio em área de Cerrado localizada na Fazenda de Ensino, Pesquisa e Extensão, FEPE/UNESP, da Faculdade de Engenharia de Ilha Solteira. Foi realizada a análise química do solo (P, matéria orgânica (MO), pH, K, Ca, Mg, H+Al, Al e S) em 33 módulos, com três repetições em duas profundidades (0,0 - 0,20 e 0,20 - 0,40 m), com delineamento em blocos casualizados em esquema hierárquico. Os resultados indicaram que as propriedades químicas do solo sob o reflorestamento ciliar são semelhantes às propriedades do solo sem perturbação antrópica dessa região. As espécies plantadas no reflorestamento ciliar estão contribuindo com a deposição de material orgânico suficiente para que haja reciclagem de nutrientes, mantendo as propriedades químicas do solo em boas condições para que ocorra o estabelecimento da mata ciliar.

Geomorphic changes upstream of beaver dams in Bridge Creek, an incised stream channel in the interior Columbia River basin, eastern Oregon

AbstractChannel incision is a widespread phenomenon throughout the dry interior Columbia River basin and other semi‐arid regions of the world, which degrades stream habitat by fundamentally altering natural ecological, geomorphological and hydrological processes. We examined the extent of localized aggradation behind beaver dams on an incised stream in the interior Columbia River basin to assess the potential for using beaver, Castor canadensis, dams to restore such channels, and the effect of the aggradation on riparian habitat. We estimated aggradation rates behind 13 beaver dams between 1 and 6 years old on Bridge Creek, a tributary to the John Day River in eastern Oregon. Vertical aggradation rates are initially rapid, as high as 0·47 m yr−1, as the entrenched channel fills, then level off to 0·075 m yr−1 by year six, as the sediment begins accumulating on adjacent terraces. We found that a 0·5 m elevation contour above the stream channel approximately coincided with the extent of new riparian vegetation establishment. Therefore, we compared the area surrounding reaches upstream of beaver dams that were within 0·5 m elevation of the stream channel with adjacent reaches where no dams existed. We found that there was five times more area within 0·5 m elevation of the channel upstream of beaver dams, presumably because sediment accumulation had aggraded the channel. Our results suggest that restoration strategies that encourage the recolonization of streams by beaver can rapidly expand riparian habitat along incised streams. Copyright © 2007 John Wiley & Sons, Ltd.

Historical Changes in Flood Power and Riparian Vegetation in Lower Harris Wash, Escalante River Basin, Utah

This study quantifies historical changes in flood power (measured by boundary shear stress and unit stream power) and riparian vegetation in a narrow stream canyon. Analyses of historical air and ground photographs since 1922 in lower Harris Wash indicate the occurrence of active channel widening, floodplain narrowing, and an 86 percent increase in riparian vegetation growth on the canyon bottom. To quantify temporal changes in flood power at a cross-section, the WinXSPRO channel cross-section analyzer calculated stage and flood power at various return interval flood discharges for 1922 (using a ground photo) and 1998 (using field measurements). Inputs to the program included estimates of Manning's roughness coefficients and channel and floodplain width measurements for both years. Between 1922 and 1998, active-channel flood power values increased 11 to 53 percent, and floodplain flood power values decreased 44 to 97 percent. Of the floodplain power decrease, 20 to 45 percent (at a minimum) is directly attributable to increased hydraulic roughness caused by woody riparian vegetation establishment. This research suggests (1) that historical ground photos may be useful for quantifying temporal changes in flood power in relationship to vegetation, and (2) that riparian vegetation change has dramatically reduced floodplain flood power values in semiarid stream canyons during this century.[Key words: fluvial geomorphology, flood power, riparian vegetation, channel change, Utah.]

Geomorphic implications of glacier outburst flooding: Noeick River valley, British Columbia

An outburst flood from Ape Lake in October 1984 severely affected channel and floodplain morphology of Noeick River. This event, estimated to have exceeded 103 m3∙s−1, was as much as 2.4 times greater than the probable maximum meteorological flood. Storage of water in ponds, lakes, and floodplain margins resulted in attenuation of the flood peak as it progressed downstream. As a result, flood effects were most evident in the alluvial reaches of upper Noeick River, below Ape Lake between km 10 and km 23. Here, the channel zone widened from a preflood average of 75 m to almost 200 m, the area of eroded valley bottom increased by about 2.5 times, and a cumulative length of 2.5 km of valley-side colluvial fans was eroded. Transported sediment stored in the floodplain and along valley margins resulted in aggradation of up to 0.75 m, except in restricted reaches where limited sediment supply and increased stream power caused degradation of up to 3 m. A second, and fractionally larger, outburst flood in August 1986 caused mobilization of sediment and some channel infilling but, overall, further morphological changes were minimal. The first flood in this sequence can be characterized as "catastrophic" because it destroyed the normal (climatic) regime of the river. The event effected an abrupt change in the regime of the river, resetting it to be in equilibrium with channel-forming events of order 103 m3∙s−1, such as the second outburst event. There have been no further outburst floods, resulting in a return to disequilibrium conditions. Ultimate recovery, measured in morphological terms as adjustment to accommodate normal meteorological floods or, in sediment transport terms as a balance between boundary shear stress and available sediment sue, will take on the order of decades to a century. Establishment of riparian vegetation will be an important determinant of the extent and timing of channel and floodplain recovery.

Effects of Regulated Water Flows on Regeneration of Fremont Cottonwood

The reduction in extent of riparian forests in the southwestern United States has been a topic of recent concern. The effect of dams on downstream river flow and the consequent modification of the riparian habitat was studied along the lower Salt River in central Arizona. Dams were found to change the magnitude of river flows and change the seasonal timing of flows in such a way that the habitat appeared less adapted for regeneration ofPopulusfremontii. Modification of river flow patterns, therefore, appears likely to have been a significant factor causing change in vegetation along the Salt River. Riparian forests in the southwestern United States have been reduced in extent in recent history (Johnson and Jones 1977). These habitats provide food and cover for many wildlife species and shade and forage for livestock because of the relatively wet conditions in an otherwise arid to semiarid environment. This study investigated the effects of releasing water from dams on the establishment of riparian vegetation. The hypothesis examined was that dams modify local conditions to the extent that some plant species find the riparian zone less favorable or even unfavorable as habitat. Of particular interest was the effect of dams on patterns of seasonal flooding and how this influences seedling establishment. Seasonal flooding is an important factor in Fremont cottonwood (Populus fremontii) regeneration because of the tree’s short seed viability.’ Research on the effects of dams on riverbed morphology also has been conducted (Priest and Shindala 1969a, 1969b, and 1969~; Black 1973; Blench 1972); however, few studies related changes in riverbed morphology to subsequent vegetative changes (Warren and Turner 1975, Turner and Karpiscak 1980).