Effects Of Riparian Vegetation Research Articles

Riparian vegetation's effects on the evolution of an experimental meandering channel driven by an upper vortex flow

AbstractFew investigations of river evolution have incorporated the series of upper vortex flow disturbances induced by quasi‐knickpoints, and it is unclear whether the regulating ability of riparian vegetation in maintaining meandering channel patterns is valid. In this study, we therefore conducted meander evolution experiments to confirm the effects of vegetation species and vegetation strength on this complex system. Two nonleguminous plants with salinity and alkalinity resistance had non‐uniform degrees of normal seedling growth and different root network lengths. Our findings show that braided swales formed between the upstream developing zone of the vortex flow and the nearest bend and the riparian vegetation generally consolidated the single‐thread channel planform without branching outward under the conditions of flooding flow. Transverse point bars on inner banks were replaced by downstream scroll bars in the overall channel for long time, unless riparian vegetation and flood scour were coupled. Shallow‐rooted plants were inadequate to withstand the inner‐banks being cut by the upper vortex flow. Deep‐rooted plants can significantly stabilize bank lines and thalwegs but are vulnerable to locally low vegetation coverage. Using evolutionary spectral analysis based on thalwegs, we found that the streamwise high‐frequency distribution of bed topography was primarily concentrated downstream of the bifurcation interface when a flood was present in the unvegetated scenario, shrank to the isolated turning interface of the upper reach and the large‐scale spiral swale of the lower reach in the shallow‐rooted scenario and stood out along the area disturbed by bare roots in the deep‐rooted scenario. This experimental study broadens our understanding of vegetation effects in hydro‐bio‐geomorphological system engineering.

Has riparian woody vegetation a positive effect on dispersal and distribution of mayfly, stonefly and caddisfly species?

During their adult life stage most EPTs (Ephemeroptera, Plecoptera and Trichoptera) disperse by flying following the riparian corridor. Although it is likely that riparian forest fosters EPT dispersion, this has not been empirically tested in a larger dataset yet and several additional open questions remain. First, it is unclear if the effect of riparian vegetation on EPT community differs and depends on the spatial scale. Second, it is not assessed how the effect of riparian vegetation on EPTs is and how it changes depending on other environmental stressors. Third, the effect potentially depends on riparian vegetation characteristics such as trees species composition and cover.We analysed 98 sites in lowland and lower mountain streams in Northrhine Westfalia, Germany, at two longitudinal and two lateral spatial scales. At each site we calculated the EPT community dispersal ability and quantified other environmental stressors as well as deciduous and coniferous woody cover in the riparian buffer. Generalised Linear Models were used to identify the conditions under which woody riparian vegetation has a significant effect on EPT community dispersal ability.Our results confirmed that the share of weak dispersers increased with deciduous woody riparian cover in low mountain streams, indicating a potential positive effect of natural riparian forest on landscape connectivity. This relationship was only observed at the regional longitudinal scale irrespective of the lateral spatial scale. Tree species composition was relevant as coniferous forests did not contribute to this effect. Finally, there was some indication that the positive effect of deciduous riparian forest occurs at a moderate woody cover and levels off at higher values.This highlights the role of riparian forests not only as habitat but also dispersal corridor in river management and the need to preserve and restore natural woody riparian vegetation to improve EPT communities and macroinvertebrates ecological status.

An improved model of shade-affected stream temperature in Soil & Water Assessment Tool

Abstract. Stream temperatures have been increasing worldwide, in some cases reaching unsustainable levels for aquatic life. Riparian revegetation has been identified as a strategy for managing stream temperatures by blocking direct solar radiation. In this study, the effects of riparian vegetation on stream temperatures were included within the Soil & Water Assessment Tool (SWAT) model through a shade factor parameter. An equilibrium temperature approach was used to integrate the shade factor in an energy balance context. The stream temperature sub-model was improved using the new energy balance equation and integrated into SWAT. Unlike existing models, the modified SWAT model enables improved representation of two processes – mass and heat transfer – that influence stream temperature change and enables simulation of shading and its effects on stream temperatures at sub-basin scales. The updated SWAT model was tested in Dairy McKay Watershed, OR, USA, for four scenarios: current conditions of riparian vegetation, full restoration, efficient restoration, and no vegetation. The model calibration under current riparian vegetation showed good performance (Nash–Sutcliffe efficiency NSE > 0.74). Stream temperature reduction and number of days with stream temperatures above survival limits (NDSTASL) for aquatic species were also evaluated as measures of riparian shade performance. Findings showed average temperature reductions of 0.91 ∘C (SD = 0.69 ∘C) and reductions in NDSTASL of 17.1 d over a year for full riparian restoration and average reductions of 0.86 ∘C (SD = 0.67 ∘C) and 16.2 d for efficient restoration. Notwithstanding the similar benefits, efficient restoration was 14.4 % cheaper than full riparian vegetation restoration.

Rainfall event‐based surface runoff and erosion in small watersheds under dairy and direct‐seeding grain production

AbstractA 3‐year study on erosion and streamflow was conducted in two adjacent paired watersheds that flow into the Passo Real reservoir, one of the largest and most important reservoirs for human water supply and power generation in southern Brazil. The watersheds have similar land use and soil management, but different size and riparian vegetation. The first objective of the study was to monitor and evaluate hydrosedimentological dynamics and effects of riparian vegetation, over a range of rain events, in the two watersheds; the second was to assess the ability of the Limburg Soil Erosion Model (LISEM) to represent these small watersheds in hydrosedimentological terms (runoff and erosion) under individual rain events, in the context of better understanding the role of riparian vegetation and land cover. LISEM is a hydrological model structured on physically based equations that can be used for planning and conservation purposes. Studied rainfall events between 2016 and 2018 had a wide range in total rainfall (10–170 mm), rainfall intensity in 1 h (3–66 mm h−1), stream peak flows (4–5741 L s−1), runoff volume (0.02–40 mm), runoff coefficient (0.1–32%), maximum suspended sediment concentration (20–19 611 mg L−1), and sediment yield (0.002–33.790 Mg km−2). Both watersheds showed a rapid response to rain events with significant runoff generation. Abundance of unpaved roads (often parallel to the slope) promoted high runoff due to channelization effects. South Watershed has 59% more riparian vegetation than North Watershed, but this greater riparian vegetation was not effective in reducing surface runoff and erosion. Furthermore, local adoption of no‐tillage was insufficient to control runoff and sediment yield.

Velocity uncertainty quantification based on Riparian vegetation indices in open channels colonized by Phragmites australis

One of the main purposes of Ecohydraulics is to predict the effects of riparian vegetation on aquatic ecosystems within real water channels. The interaction between water flow and riparian plants significantly affects flow dynamics, hydraulic conveyance, and water quality of vegetated water bodies. This study aimed at quantifying analytically the uncertainty in flow average velocity estimations associated with the uncertainty of Leaf Area Index (LAI) of Phragmites australis (Cav.) Trin. ex Steudel covering a vegetated channel. The impacts of this species on the hydrodynamics of vegetated streams are far to be completely understood. The uncertainty in flow average velocity was assessed through the first-order second-moment statistical method, by comparing direct and indirect LAI measurements of mature Phragmites australis plants. Indirect LAI values were obtained using the LICOR® LAI-2000 Plant Canopy Analyzer device. The results of this study suggest that the uncertainties in flow average velocity estimations are comparable to those associated with experimental measurements of streamwise velocity components retrieved in real vegetated flows fully covered by mature Phragmites australis plants.

Effects of riparian vegetation on evapotranspiration processes and water quality of small plain streams

Riparian vegetation provides a wide range of ecosystem services including water quality regulation, flooding avoidance, and the natural control of stream temperatures. Changes in land use and the increase of anthropogenic activities in the proximity of rivers affect the growth and development of riparian buffers. The aim of the work was to assess the effects of riparian vegetation on the evapotranspiration processes and the water quality of small plain streams using remote sensing resources and in-situ monitoring. The area of study considered two neighboring basins of small plain streams (Glavacioc and Ilfov) from Romania. The data obtained from in-situ monitoring performed in 2019 was used in the Penman-Monteith algorithm to calculate the potential evapotranspiration (PET) based on a series of specific parameters. The Green Normalized Difference Vegetation Index (GNDVI), computed from LANDSAT 8 images, has been used to assess the vegetation status at the basin scale. The GNDVI fluctuations were linked to the variations in precipitation regimes and land use modifications. Remote sensing data have shown changes in GNDVI between June and September 2019 in both riparian areas resulting in an intense spread of cattail (Typha spp.). Surface waters arriving at the entrance control sections had a basic pH and were loaded with nitrates and ammonium ion (NH4+), which had decreased at the downstream section after passing the cattail phytosociological associations and the riparian patches, thus acting as buffer areas. The current anthropogenic pressures on the riparian areas might have degenerative effects on the integrity of the vegetation structure. Thus, for effective and sustainable management, it is essential to identify the main stressors and to assess to what extent they affect the riparian ecosystem as a whole.

Hydraulic and morphological patterns in a riparian vegetated sandy compound straight channel

Emergent vegetation or trees are important riverine features and essential in hydraulic engineering including flood management and river restoration. Clearing up trees along river banks has been pointed out as a contributing factor to the severity of flood damages including financial losses and even fatalities. Thus, the effect of riparian vegetation on river flow must be clearly understood. The hydraulics and morphological patterns in a riparian vegetated sandy compound straight channel were carried out in the Hydraulics Laboratory, School of Civil Engineering, Universiti Teknologi Malaysia. Two-line steel rods with tandem and staggered arrays to simulate as rigid emergent vegetation were placed along the riparian zone of an asymmetrical straight channel. The Manning’s n, depth-averaged velocity, boundary shear stress and morphological changes during shallow and deep floods are discussed in this paper. The findings prevailed that the staggered array riparian vegetation generated 4.5% flow resistance higher than the tandem array. The vegetation also altered velocity distribution which contributed to the boundary shear stress patterns in a compound straight channel. The flow velocity profiles were also related to the morphological changes in the channel.

Morphological traits mediate fish occurrences in oil palm‐impacted tropical streams

Abstract Land‐use change is a leading driver of biodiversity loss, especially in tropical fresh waters where the conversion of natural forest to monoculture plantations impacts freshwater fish assemblages. The environmental pathways underpinning shifts in fish assemblages, however, are poorly understood, but could potentially be inferred from trait–environment relationships. We addressed this knowledge gap using eco‐morphological traits to explain fish occurrences in oil palm‐impacted streams of the Endau drainage in Peninsular Malaysia. We also investigated how traits relate to differences in environmental conditions associated with land‐use change. We then integrate findings from the above to test how potential pathways of land‐use driven environmental changes can impact species occurrences through effects on life history, feeding habits, and mobility. Mixed‐effects models show that fishes with superior (upward‐facing) mouths and low body mass were more likely to occur in oil palm streams than forest streams, and these traits were associated with grass‐dominated riparian zones and reduced woody debris in oil palm streams, respectively. Structural equation models show that mouth positions statistically mediated the effect of riparian vegetation on fish species occurrences in oil palm streams. Specifically, fishes with superior mouths were more likely to feed on terrestrial invertebrates. Our analysis of easily measurable traits revealed pathways of land‐use impact that are potentially more widely applicable than conventional taxa‐based approaches. Fishes with superior mouths tended to occur in oil palm streams as they were able to more effectively exploit inputs of terrestrial invertebrates that are potentially associated with grass‐dominated riparian vegetation. Moreover, shifts in traits may suggest land‐use driven changes in stream ecosystem functioning (e.g. in terms of the role of terrestrial subsidies), thereby informing targeted management actions in land‐use impacted habitats (e.g. retention/restoration of riparian trees).

지형, 개발지역, 수변림과 하천 내 총질소 농도와의 구조적 관계 분석†

Land use in watersheds has been shown to be a major driving factor in determining the status of the water quality of streams. In this light, scientists have been investigating the roles of riparian vegetation on the relationships between land use in watersheds and the associated stream water quality. Numerous studies reported that riparian vegetation could alleviate the adverse effects caused by land use in watersheds and on stream water quality through various hydrological, biochemical and ecological mechanisms. However, this concept has been criticized as the true effects of riparian vegetation must be assessed by comprehensive models that mimic real environmental settings. This study aimed to estimate a comprehensive structural equation model integrating topography, land use, and characteristics of riparian vegetation. We used water quality data from the Nakdong River system monitored under the National Aquatic Ecosystem Monitoring Program (NAEMP) of the Korean Ministry of Environment (MOE). Also, riparian vegetation data and land use data were extracted from the Land Use/Land Cover map (LULC) produced by the MOE. The number of structural equation models (SEMs) were estimated in Amos of IBM SPSS. Study results revealed that land use was determined by elevation, and developed areas within a watershed significantly increased the concentration of Total Nitrogen (TN) in streams and LDI in riparian vegetation. On the contrary, developed areas significantly reduced LPI and PLAND. At the same time, PLAND and LDI significantly reduced the concentration of TN in streams. Thus, it was clear that developed areas in watersheds had both a direct and an indirect impact on the concentration of TN in streams, and spatial pattern and the amount of vegetation of riparian vegetation could significantly alleviate the negative impacts of developed areas on TN concentration in streams. To enhance stream water quality, reducing developed areas in a watershed is critical for long-term watershed management plans, restoration patterns for riparian vegetation could be immediately implemented since riparian areas were less developed than most other watersheds.

Inhibiting Effects of Vegetation on the Characteristics of Runoff and Sediment Yield on Riparian Slope along the Lower Yellow River

Riparian vegetation plays a vital role in soil and water conservation and river health maintenance. However, its inhibiting effects on water and soil loss are limited by different factors, such as slope gradient, vegetation coverage and their interaction. Therefore, this study quantified the inhibiting effect of riparian vegetation on the runoff, sediment and hydraulic characteristics of overland flow, and assessed its relative contribution to slope gradient. Specifically, we selected a riparian slope along the lower Yellow River as a case, and used a field-simulated rainfall experiment under specific rainfall intensity (90 mm/h), different vegetation coverage (0%, 15% and 30%) and slope gradients (5°, 10°, 15° and 20°). The results showed that the presence of vegetation can reduce the slope runoff rate and erosion rate. However, greater slope gradients can result in a lowering of the inhibiting effects of riparian vegetation on sediment yield. There was a critical value of vegetation coverage for inhibiting eroded sediments which was influenced by the degree of slope gradient. At 15% vegetation coverage, vegetation inhibited the slope sediment yield greatly at a slope gradient of less than 8°; while at 30% vegetation coverage, vegetation greatly inhibited the slope sediment yield at slope gradients <11°. Hydraulic characteristics were closely related to the slope gradient and vegetation coverage by the power function. Grey correlation analysis revealed that, with increasing of vegetation coverage, the effect of stream power on slope sediment yield decreased, while the effect of the friction coefficient on slope sediment yield increased. In summary, riparian vegetation can effectively inhibit slope runoff and sediment yield, but its inhibiting effect is notably affected by slope gradient.

Effects of riparian forest buffers and agricultural land use on macroinvertebrate and fish community structure

Although forested riparian buffers can improve stream habitat, there remains debate as to whether biotic integrity can be maintained by buffers in highly degraded watersheds. To determine if forest buffers can ameliorate cropland impacts, we examined macroinvertebrate and fish assemblages in headwater streams categorized into three land use groups (High Buffer-Low Agriculture, High Buffer-High Agriculture, Low Buffer-High Agriculture). Sampling was conducted seasonally over 3 years to explore temporal patterns in biotic assemblages related to land use, instream habitat, and water quality parameters. Macroinvertebrate and fish abundance were higher in low buffer streams due to large numbers of pollution tolerant taxa and herbivores that proliferated with increased periphyton. In contrast, High Buffer-Low Agriculture streams had the best biotic integrity likely due to increased depth and better habitat quality. Non-metric multidimensional scaling ordinations of macroinvertebrate taxa showed no separations, but fish communities were significantly different among all three land use groups. Findings suggest fish community structure is more sensitive than macroinvertebrates to agricultural influences at both the riparian and watershed scales. Our study provides information on the effects of riparian vegetation on agricultural stream communities and highlights the importance of managing riparian forests to conserve stream biotic integrity.

Effect of riparian vegetation clear-cutting on avian community in the Northern Negev

In arid zones, riparian corridors serve as important habitats, offering water, nutrients, shelter and optimal microclimate conditions to many organisms. In the northern Negev desert of Israel, several large rivers cross through the arid landscape, with Saltcedar (Tamarix spp.) being the climax vegetation. Although these rivers have been continuously subjected to management, human control became much more frequent and thorough since the early 2000s. Current management involves vegetation clear-cutting of long riverbed sections. In arid zones such as the Negev, where trees are scarce and restricted to streams, such activity may affect wildlife at all hierarchical levels. Being one of the most successful invasive trees in North America, many aspects of Saltcedar management along rivers have been explored around the USA. Notably, how riparian Saltcedar forests in the old world, where it is native, influence wildlife, has not been studied. We explored the effects of vegetation clear-cutting on bird communities at three sites in the Northern Negev of Israel, comparing bird abundance, richness and diversity between natural and managed riparian transects. All three variables were significantly lower in managed sites. Species composition shifted from tree-dwelling species in natural transects to ground-dwelling species in clear-cut sections. Natural sections were characterized by lower ambient temperature, lower radiation, and higher relative humidity. Our findings may explain the long-term reduction observed in local bird populations in the northern Negev. They also indicate the importance of the Saltcedar forests along major watersheds in the Northern Negev for bird populations.

Experimental study of open-channel flow with partial double-layered vegetation

Many rivers and wetlands have vegetation. The effect of riparian vegetation on ecological and flow process in channels has become increasingly important in river flood risk and aquatic environmental management. Most previous studies have been done on the flow structure of vegetation of the same height which is not realistic in natural rivers. There are only a few studies on flows with a mixing array of short and tall vegetation under either submerged or emergent flow condition. This paper is to undertake a novel experimental study on a flow with double-layered vegetation under submerged and emergent conditions, which often occur in most rivers. Two different heights of dowels, 10 cm and 20 cm, were used in the water flume to represent the short and tall vegetation respectively, and they were allocated on one side of the flume. Experiments in two flow depths were undertaken to represent different submergence ratios of vegetation, and velocities at various locations were measured by Acoustic Doppler Velocimetry (ADV) and propeller velocimetry. Experimental results show that the velocity profile is almost uniform within the depth of short vegetation in different configurations. The velocity starts to increase in the region near the edge of short vegetation, and then followed by a rapid increase through the height of tall vegetation to the free surface. Meanwhile, a strange shear layer exists laterally between vegetation and non-vegetation, showing that the vegetation significantly reduces the velocity of flow.

Effects of Vegetation Density and Arrangement on Sediment Budget in a Sediment-Laden Flow

Understanding the effects of riparian vegetation under sediment-laden flow is becoming crucial due to the increase in frequency of extreme weather events. This study designed three densities and nine random distributions of bent flexible vegetation in flume experiments under sediment-laden flow. Sediments were continually added to the flume at a rate of 21 kg/h to simulate a natural river environment in a sediment-laden flow. The results showed that the evolutionary process of bed form under sediment-laden flow could be divided into four stages: scouring, development, recovery, and deposition stages, forming a dynamic cycle. Dunes were formed and backwater caused them to develop upstream, while structural resistance developed the dunes downstream. Contrary to clear water regime, sediments were deposited upstream of the vegetation area and scour occurred behind the vegetation. In addition, the vertical velocity profile showed to be dependent on the vegetation structure and four clear zones were identified: fixed, bent, canopy, and developed zones. The findings from this study provide crucial information towards river management through understanding the diverse vegetation effects under sediment-laden flows.

Effect of riparian vegetation on stream bank stability in small agricultural catchments

The hydrological processes associated with vegetation and their effect on slope stability are complex and so difficult to quantify, especially because of their transient effects (e.g. changes throughout the vegetation life cycle). Additionally, there is very limited amount of field based research focusing on investigation of coupled hydrological and mechanical influence of vegetation on stream bank behavior, accounting for both seasonal time scale and different vegetation types, and none dedicated to marine clay soils (typically soil type for Norway).In order to fill this gap we established hydrological and mechanical monitoring of selected test plots within a stream bank, covered with different types of vegetation, typical for Norwegian agricultural areas (grass, shrubs and trees). The soil moisture, groundwater level and stream water level were continuously monitored. Additionally, soil porosity and shear strength were measured regularly. Observed hydrological trends and differences between three plots (grass, tree and shrub) were analysed and formed the input base for stream bank stability modeling. We did not find particular differences between the grass and shrub plot but we did observe a significantly lower soil moisture content, lower soil porosity and higher shear strength within the tree plot. All three plots were stable during the monitoring period, however modeling scenarios made it possible to analyse potential differences in stream bank stability under different vegetation cover depending on root reinforcement and slope angle.

Water-quality impacts in semi-arid regions: can natural ‘green filters’ mitigate adverse effects on fish assemblages?

The effective aridity in riparian areas is increasing from climate change and from human water consumption, which exacerbates the impacts of effluents from wastewater-treatment plants and from catchment run-off in rivers. The potential of natural riparian areas to act as ‘green filters’ has long been recognized, but the possible ecological benefits of natural riparian areas over large-scale environmental gradients on fish have not been explored in detail. Using an extensive data-set from northeastern Spain (99,700 km2, 15 catchments, 530 sites), ours is the first study to ask whether natural riparian vegetation can mitigate the effects of pollution on fish in rivers experiencing water scarcity. We used multimodel inference to explore the additive and interactive effects of riparian vegetation with nutrient pollution and water conductivity, which are among the world's worst river stressors, on multiple fish guilds, including widely distributed species and highly invasive alien fish species. Most models (54%) supported the additive effects of water-quality factors on fish, after having accounted for the influence of geography and hydrological alterations. Although many fewer models (7%) included riparian vegetation as an important predictor, riparian vegetation modulated the forms of the associations between fish and pollution. The relationship of nutrient pollution with native and alien fish richness changed from negative to positive with greater riparian structure or species richness. However, we found the opposite effect for the mean body size of sedentary fish, and only positive additive effects of riparian richness for the probability of occurrence of pelagic fish. Ammonium and nitrite concentrations adversely affected fish in these rivers up to 10 years after the enforcement of the implementation of the Water Framework Directive by the European Union. High conductivity also much affects fish, having negatives associations with migratory, pelagic, invertivorous and native fish, and positive associations with sedentary, benthic, omnivorous and alien fish. Therefore, the current status of natural riparian areas is unlikely to fully mitigate water-quality impacts on fish. The conservation of freshwater resources in semi-arid regions, such as north-eastern Spain, requires improved waste-water treatments and better agriculture practices.

Morphodynamic effects of riparian vegetation growth after stream restoration

AbstractThe prediction of the morphological evolution of renaturalized streams is important for the success of restoration projects. Riparian vegetation is a key component of the riverine landscape and is therefore essential for the natural rehabilitation of rivers. This complicates the design of morphological interventions, since riparian vegetation is influenced by and influences the river dynamics. Morphodynamic models, useful tools for project planning, should therefore include the interaction between vegetation, water flow and sediment processes. Most restoration projects are carried out in USA and Europe, where rivers are highly intervened and where the climate is temperate and vegetation shows a clear seasonal cycle. Taking into account seasonal variations might therefore be relevant for the prediction of the river morphological adaptation. This study investigates the morphodynamic effects of riparian vegetation on a re‐meandered lowland stream in the Netherlands, the Lunterse Beek. The work includes the analysis of field data covering 5 years and numerical modelling. The results allow assessment of the performance of a modelling tool in predicting the morphological evolution of the stream and the relevance of including the seasonal variations of vegetation in the computations. After the establishment of herbaceous plants on its banks, the Lunterse Beek did not show any further changes in channel alignment. This is here attributed to the stabilizing effects of plant roots together with the small size of the stream. It is expected that the morphological restoration of similarly small streams may result in important initial morphological adaptation followed by negligible changes after full vegetation establishment. Copyright © 2018 John Wiley & Sons, Ltd.

Effects of Riparian Vegetation on the Transport and Accumulation of Floating Objects in a Meandering River

In order to study and understand the characteristics of transport and depositions of floating objects in real rivers, Large Eddy Simulation (LES) method of real river flows with complex bathymetry, the riparian vegetation and the floating objects has been developed and applied to a meandering river in Perak, Malaysia. The movement and accumulation of floating objects are different for different sizes and the shapes of the objects. The vegetation that may exists on the bed and the banks also are seen to influence the positions where the objects are accumulated and deposited. The results can be used to control the increasing amount of solid objects washed into the rivers and to the ocean.

River pattern discriminant method based on resistance parameter and activity indicators

A new river discriminant system is presented based on resistance law. A parameter characterizing river morphology and indicators reflecting activity of bed and bank are derived. They are defined as river morphology parameter and river activity indicators respectively. By relating river morphology to river activity through a comprehensive resistance factor, the discriminant curves characterizing river patterns, namely resistance thresholds, were derived, which make it possible to calculate the activity of bed and bank by just a few easy-obtaining hydraulic variables. In addition, the effect of riparian vegetation on riverbank strength is incorporated into this study. The discriminant method proposed in this paper has proved to be applicable in distinguishing river patterns by selected data sets of the model and natural rivers and in improving the understanding of patterning process.

Coupling LiDAR and thermal imagery to model the effects of riparian vegetation shade and groundwater inputs on summer river temperature

In the context of global warming, it is important to understand the drivers controlling river temperature in order to mitigate temperature increases. A modeling approach can be useful for quantifying the respective importance of the different drivers, notably groundwater inputs and riparian shading which are potentially critical for reducing summer temperature. In this study, we use a one-dimensional deterministic model to predict summer water temperature at an hourly time step over a 21km reach of the lower Ain River (France). This sinuous gravel-bed river undergoes summer temperature increase with potential impacts on salmonid populations. The model considers heat fluxes at the water-air interface, attenuation of solar radiation by riparian forest, groundwater inputs and hydraulic characteristics of the river. Modeling is performed over two periods of five days during the summers 2010 and 2011. River properties are obtained from hydraulic modeling based on cross-section profiles and water level surveys. We model shadows of the vegetation on the river surface using LiDAR data. Groundwater inputs are determined using airborne thermal infrared (TIR) images and hydrological data. Results indicate that vegetation and groundwater inputs can mitigate high water temperatures during summer. Riparian shading effect is fairly similar between the two periods (−0.26±0.12°C and −0.31±0.18°C). Groundwater input cooling is variable between the two studied periods: when groundwater discharge represents 16% of the river discharge, it cools the river down by 0.68±0.13°C while the effect is very low (0.11±0.01°C) when the groundwater discharge contributes only 2% to the discharge. The effect of shading varies through the day: low in the morning and high during the afternoon and the evening whereas those induced by groundwater inputs is more constant through the day. Overall, the effect of riparian vegetation and groundwater inputs represents about 10% in 2010 and 24% in 2011 of water temperature diurnal amplitudes.