M3 Of Sediment Research Articles

Meander chute cutoff at an alluvial river facilitated by gypsum sinkholes

Collapse sinkholes are common in areas where gypsum strata underlie rock that is incompetent to bridge the cavities created by the groundwater dissolution of gypsum. On floodplains these can be obscured due to fill by overbank deposits, and channels tend to migrate towards larger enclosed depressions. This study utilises GIS to analyse the influence exerted by small collapse sinkholes on the channel dynamics of the alluvial River Ure, UK. At Ripon Loop, a large compound meander bend, sinkhole area and channel dynamics have been tracked over >160 years from multiple datasets, including historic maps, aerial imagery, lidar and a Structure-from-Motion photogrammetry dataset acquired for this study. This indicated two distinct populations, firstly long-lived, constant-sized sinkholes and secondly dynamically growing holes aligned with the contact of bedrock and unconsolidated materials of a buried valley at depth where artesian water saturated with sulphate enters the latter. Frequent overbank flows of the River Ure across the neck of the bend have interacted with sinkholes, e.g. by deposition of bedload in the down-valley end of the holes and localised headward incision on the opposite side due to the relatively high gradient between holes and the downstream limb. The location of holes has conditioned the incision of small shallow channels over at least 7 years, before cutoff occurred over several floods in 2019. Initially overbank flow traversed the neck via the chain of sinkholes before widening and deepening of the channel captured all the surface flow of the River Ure, resulting in the mobilisation of more than 20,000 m3 of sediment. Allogenic influences on fluvial systems in relation to meander dynamics are often neglected and this study is the first to link floodplain sinkholes with detailed mechanisms of a chute cutoff, hereby indicating a potential feedback to sinkhole dissolution processes.

Geomorphologic Recovery of North Captiva Island from the Landfall of Hurricane Charley in 2004

Hurricane Charley made landfall on the Gulf Coast of Florida on 13 August 2004 as a category 4 hurricane, devastating North Captiva Island. The hurricane caused a breach to occur to the southern end of the island, which naturally healed itself over the course of three years. By 2008, the cut was completely repaired geomorphologically. LiDAR data analysis shows the northern half of the island has been subjected to persistent erosion from 1998–2018, while the southern half experienced accretion since 2004, including the complete closure of the “Charley cut”. The maximum volume of sediment erosion in the northern sector of the island (R71–R73) from 2004–2018 was −85,710.1 m3, which was the source of southern accretion. The breached area of the island (R78b–R79a) obtained 500,163.9 m3 of sediments from 2004–2018 to heal the cut made by Hurricane Charley. Along with LiDAR data analysis, Google Earth Pro historical imageries and SANDS volumetric analysis confirmed the longshore transport of sediments from the northern to the southern end of the island. Winter storms are mainly responsible for this southerly longshore transport and are hypothesized to be the main factor driving the coastal dynamics that restored the breach and helps in widening the southern end of North Captiva Island.

Geomorphic effects of recurrent outburst superfloods in the Yigong River on the southeastern margin of Tibet

Landslide dam outburst floods have a significant impact on landform evolution in high mountainous areas. Historic landslide dams on the Yigong River, southeastern Tibet, generated two outburst superfloods > 105 m3/s in 1902 and 2000 AD. One of the slackwater deposits, which was newly found immediately downstream of the historic dams, has been dated to 7 ka BP. The one-dimensional backwater stepwise method gives an estimate of 225,000 m3/s for the peak flow related to the paleo-stage indicator of 7 ka BP. The recurrence of at least three large landslide dam impoundments and super-outburst floods at the exit of Yigong Lake during the Holocene greatly changed the morphology of the Yigong River. More than 0.26 billion m3 of sediment has been aggraded in the dammed lake while the landslide sediment doubles the channel slope behind the dam. Repeated landslide damming may be a persistent source of outburst floods and impede the upstream migration of river knickpoints in the southeastern margin of Tibet.

Human Impacts on Estuarine Erosion-Deposition in Southern Central Vietnam: Observation and Hydrodynamic Simulation

This paper aims to identify the causes and sources of erosion and deposition at small estuaries in southern central Vietnam under human intervention. The jetty built at the Tam Quan river mouth (Binh Dinh Province, Vietnam) serves as the base for the study. After its completion at the end of 2009, the hydrodynamic and erosion-deposition processes in the region have been significantly altered. Inside the estuary, the waves are not influenced, but the currents are increased during the ebb tide period and decreased during the flood tide timeframe. During the southwest monsoon, the jetty could cause an increase in the deposition process in both frequency and area, whereas the erosion process tends to narrow the area and increase the frequency on the north coast. In contrast, both deposition and erosion processes are increased on the southern coast. About 5859 m3 of sediments are deposited in the channel gate mainly by local sources. During the northeast monsoon, both deposition and erosion processes are located over a narrow area with frequency increased on the north coast, whereas the deposition process is narrowed with higher frequency on the southern coast. The total amount of sediment deposited at the estuary is 56,446 m3, of which 74.2% is from the onsite erosion material, 15.8% from the river and 10% from the longshore transportation. Generally, due to mainly erosion-deposition processes, sediment volume is accumulated during the northeast monsoon with amount 9.6 times more than that the southwest monsoon. The erosion-deposition processes are contributed to by poor practical management and local human activities inland and in the coastal regions, as well as the natural situation, resulting in serious impacts on society, the economy and the environment. Hence, the governance of the erosion-deposition processes and sediment load in small estuaries appear to contribute to the master plan for the local sustainable development of society and the economy.

Transformation of high-relief canyon topography by an ancient rock avalanche, Hop Valley, Zion National Park, Utah, USA

Zion National Park preserves a rich geological record of Holocene landslide-dammed canyons in its deeply incised topography, with 11 hypothesized valley-blocking deposits within the park boundaries. Despite consistent stratigraphic, tectonic, and climatic settings, the occurrence of and subsequent landscape response to these natural dams varies. As such, the region provides a unique natural laboratory for quantifying the effect and evolution of landslide dams in high-relief canyon topography. Here we present a detailed study of a rock avalanche deposited at the mouth of Hop Valley in Zion National Park, describing its age, size, emplacement conditions, impact on local geomorphology and sedimentology, as well as the subsequent usage of the valley by native Ancestral Puebloans. Topographic reconstructions indicate the original deposit was ~75 million m3 and 1.5 km long with a maximum thickness of 180 m. New ages from cosmogenic 10Be surface exposure dating indicate a single-event failure at 6.7 ± 0.7 ka. The rock avalanche impounded ~55 million m3 of sediment, transforming Hop Valley from a relatively narrow gorge to a broad flat-floored canyon. Stratigraphic sections of accumulated upvalley sediments, calculated sedimentation rates (averaging 8.2 ± 0.8 m/ky), and paleoclimate records suggest the deposit primarily dammed sediment, rather than water, to produce an extensive alluvial plain. This detailed case-history analysis, together with our review of other Holocene landslide dams in Zion National Park, helps clarify the legacy of valley-blocking mass movements in steep canyon topography.

Detailed Characterization and Monitoring of a Retrogressive Thaw Slump from Remotely Piloted Aircraft Systems and Identifying Associated Influence on Carbon and Nitrogen Export

Ice-rich permafrost landscapes are sensitive to ongoing changes in climate. Permafrost retrogressive thaw slumps (RTSs) represent one of the more abrupt and prolonged disturbances, which occur along Arctic river and lake shorelines. These features impact local travel and infrastructure, and there are many questions regarding associated impacts on biogeochemical cycling. Predicting the duration and magnitude of impacts requires that we enhance our knowledge of RTS geomorphological drivers and rates of change. Here we demonstrate the utility of remotely piloted aircraft systems (RPAS) for documenting the volumetric change, associated drivers and potential impacts of the largest active RTS along the Old Crow River in Old Crow Flats, Yukon, Canada. RPAS surveys revealed that 29,174 m3 of sediment was exported during the initial evacuation in June 2016 and an additional 18,845 m3 continued to be exported until June 2019. More sediment export occurred during the warmer 2017 summer that experienced less cumulative rainfall than summer 2018. However, several rain events during 2017 were of higher intensity than during 2018. Overall mean soil organic carbon (SOC) and total nitrogen (TN) within sampled thaw slump sediment was 1.36% and 0.11%, respectively. A combination of multispectral, thermal and irradiance (derived from the RPAS digital surface model) data provided detailed classification of thaw slump floor terrain types including raised dry clay lobes, shaded and relatively stable, and low-lying evacuation-prone sediments. Notably, the path of evacuation-prone sediments extended to a series of ice wedges in the northern headwall, where total irradiance was highest. Using thaw slump floor mean SOC and TN values in conjunction with sediment bulk density and thaw slump fill volume, we estimated that 713 t SOC and 58 t TN were exported to the Old Crow River during the three-year study. Findings showcase the utility of high-resolution RPAS datasets for refining our knowledge of thaw slump geomorphology and associated impacts.

Geomorphological impact of Hurricane Irma on Marco Island, Southwest Florida

Hurricane Irma caused significant damage on Marco Island, where it made landfall on September 10, 2017. Pre- and post-hurricane beach profiles were analyzed for an arched spit, “Tigertail,” along the northwestern side of the island, and volumetric quantification of its evolution was estimated using SANDS software. LiDAR data from 2008 to 2017 and Google Earth historical imagery dating back to 1995 were used to compare landscape-level changes as a consequence of the storms that affected the region. The data show that the sand spit evolved dramatically from a relatively small sand bar in 1995. The impact of Hurricane Irma appears to be most significant on the northern end of the spit, where nearly 200,000 m3 of sediment was added by the storm between R-monuments V-311 and V-314. About 95,000 m3 of sediment was removed by Hurricane Irma from the mid-island southward, between V-316 and R-133. Overall, the impact of Hurricane Irma was significant for Tigertail Beach and its surroundings, when compared to previous hurricanes, with a net gain from transport and redeposition of 118,000 m3 of sediment on the barrier island and its surroundings.

Geomorphic insights from eroding dredge spoil mounds impacting channel morphology

A number of large rivers across the world are dredged for navigation. Dredging removes sediment from the channel, creates spoil mounds in the adjoining floodplain, and disposes sediment along the channel margin on a bar, or in open water. Retrospective studies that examine the placement and fate of this disposed material can provide guidance for other localities where dredging is practiced, and better elucidate the impacts associated with disposal at different types of sites. Many studies exist for impacts and benefits of dredging in the coastal environment, particularly to ecosystems and water quality. Few studies have examined disposal site selection and the fate of dredge spoil placed along a river corridor from a geomorphic and retrospective perspective.The Apalachicola River in Florida was dredged from the 1950s for several decades, with disposal on sand bars, in open water on the channel margins, and on the floodplain. Numerous large and small floodplain dredge-spoil mounds are a legacy from this navigation project. One of the larger mounds, disposal site 40 (DS 40), which locals call “Sand Mountain,” stands ~22 m high and extends ~10 ha in area. This disposal site originated in an artificial cutoff created in 1968–69 and grew to hold >625,000 m3 of sediment. Because this section of river was a problem for navigation when dredging was being conducted, detailed historical survey sheets with topographic and bathymetric data exist. The purpose of this paper was to analyze the local floodplain and channel geospatially, coupled with dredging and disposal data, to interpret the geomorphic changes of DS 40 and the adjoining river. Poor placement has resulted in this and other dredge spoil mounds returning sediment to the river through lateral erosion and mass wasting. Intermittent sediment pulses have altered channel morphology adjacent to the spoil mound with the channel becoming wider and shallower than originally, mean bed and thalweg elevations increasing by ~1.5 to 2 m, and width-depth ratio increasing three-fold.Although dredging of this river has not been conducted for nearly two decades, study of historical dredge spoil mounds in this reach suggest poor placement of spoil can continue to stress and alter a river in the decades that follow. Based on our findings, dredging downstream of distributaries will have poor outcomes. Dredge spoil placement in cut-off channels close to the river can be problematic because the river will regain sinuosity. Further, sites on the outer bend of meanders are more subject to erosion, and sites immediately upstream of problem or shallow areas will feed sediment to the problem reach. Findings of this study have implications to other settings, such as intensively mined rivers where unused unconsolidated material is often left on floodplains.

Determination of water erosion in Kowsar catchment area and evaluation of Gabion structures in its control

Water erosion is one of the problems in the country that reduces soil fertility, environmental degradation, food security threats, and the filling of dams’ reservoirs. Therefore, the use of sedimentation control methods such as Gabion structures is considered important. The purpose of this study was to evaluate the geotechnical structures of Kowsar watershed in the Khuzestan province with an area of 64.81 km2, located in the longitude 48°25′36″ to 48°33′27″ east, and the latitudes 32°40′54″ to 32°45′38″ north. In this basin, 279 structures with a volume of 13,374.35 m3 were studied in 2017. The results of this study showed that the specific erosion and sediment production in this basin were 5742 m3 km−2 and 145,130 m3 year−1. Based on the area of each of the sub-basin and based on PSIAC factors, it was found that 76.12% of the basin area was in the very erosive class, 0.3% in the erosion class and 23.58% in the moderate erosion class. In general, it was expected that 13,442.99 m3 of sediment would be inhibited in this sub-basin, but due to the destruction of some structures, the trapped sediment rate was determined to be 79,421.8 m3. Therefore, the structures constructed in the Kowsar basin with an efficiency of 59% had a relatively good ability to contain sediments in this basin.

MORPHOLOGICAL EVOLUTION OF THE BOTTOM OF THE POTOU LAGOON OVER THE LAST TEN YEARS (COASTAL ZONE OF COTE D'IVOIRE)

This study with a morphology and hydrosedimentology character was done to carry out a with an understanding the evolution of the channels and sedimentation in Potou lagoon in Ivory Coast starting from the realization of the bathymetric map. The bathymetry of this lagoon avered that the depths are lower than 2.11 m out of 22 km2, and presente three types of channels. In fact the channels in "U" represent a balance between the agents of accumulation and erosion. Channels resulting from processes of erosion which are in "V" and channels intermediate indicating an evolution of the type "V" in "U". In particular during these fourteen last years the Potou lagoon has sudden great phenomenon of deposit is a volume of +66791000.18 m³of sediments deposed on a surface which is thus estimated at 65.2 % of chenal surface. These deposits are certainly causes of full high funds in this lagoon. The mean velocity of sedimentation on Potou lagoon is thus estimated at 26.5 cm/year. As for the erosion, it could be estimated at-8487601 m³ a volume of on a surface wich is thus estimated at 34 % of chenal surface. The sedimentary budget would be thus estimated at+58303398.68449 m³ on a surface of 12.45 m2. A surface which is thus estimated at 0.8 %hasn’t sudden phenomenon of deposit or erosion. The bathymetric chart and the sedimentary budget of Potou lagoon are tools necessary for use of the stretch of water by the users. Thus, the zones at the risks determined on the bathymetric chart, such as the high bottom and the points of swirl generated by the depressions, will be easily avoided.

Modeling the geomorphic response to early river engineering works using CAESAR-Lisflood

Landscape Evolution Models (LEMs) simulate the movement of water and sediment over the landscape. Although much progress has been made in the development of LEMs, few have been tested in rivers subject to anthropogenic impacts that produce high energy flows, transporting large amounts of sediment and causing significant geomorphic changes. As such, it remains uncertain if LEMs are useful and stable under relatively short term ‘extreme’ geomorphic conditions. To shed light on this topic we use a LEM (CAESAR-Lisflood) and historical documents to develop a detailed reach scale model of the Kander river (Switzerland). This model was used to simulate the unintended impacts of engineering works, occurring in 1714, that deviated the Kander river into a lake and resulted in a large decrease in base level of the river. In 10 years, the model simulates knickpoint propagation that rapidly erodes 2.5 million m3 of sediment and produces a remarkable 27 m of channel erosion. Simultaneously, the model develops the formation of a delta via frequent avulsions. Model testing is performed by comparing model predictions against historical observations of channel incision, knickpoint location, and delta spatial extent. Overall, model error is low and the model remained stable as results do not contain erratic erosion or deposition. Importantly the model suggests that downstream processes occurring at and near the delta have an effect on upstream channel erosion. We also recommend that studies replicating historic landscape changes with LEMs reduce uncertainty in hydrological inputs.

Paraglacial adjustment of sediment slopes during and immediately after glacial debuttressing

Daily time lapse imagery and pixel tracking was used to monitor and track spatial and temporal changes in sediment-mantled hillslopes, during and immediately after glacier retreat in the Fox Glacier/Te Moeka o Tuawe valley, New Zealand. Observations from 2014 to 2018 of the Fox Glacier and surrounding hillslopes show hillslope failure is primarily coincident with, and triggered by, glacier retreat with rainfall accelerating movement of the hillslope. During glacier retreat, failure of the hillslope primarily occurred through sediment sliding, internal deformation of the sediment and occasional surficial debris falls, flows and avalanches delivering approximately 9.2 M m3 of sediment directly to the underside of the glacier over the study period with a maximum daily averaged movement of 0.4 m per day of the main sediment mass. Following debuttressing, hillslope failure became dominated by localised rainfall-induced debris flows which initiated gullying of the sediment-mantled slope. Ongoing instability of the slope and associated movement is maintained by toe erosion from the Fox River and melting dead ice, while continued rapid failure is facilitated through localised debris flows. The tracking of temporal and spatial changes of sediment-mantled hillslopes during glacier retreat has shown broad-scale hillslope response to occur quickly within days of rainfall or accelerated glacier retreat, particularly during summer. Debris flows, commonly thought to be a dominant erosion process within paraglacial environments, only occur following complete debuttressing and are supply-limited, only occurring after sediment sliding has occurred. Unlike many other case studies, sediment connectivity immediately following glacier retreat is high due to a lack of storage space and high rainfall inducing mass movements, efficiently delivering hillslope sediments to the proglacial stream channel. Attempts to quantify displaced volumes of sediment from paraglacial systems are likely underestimated due to a) a lack of focus on the early and latter stages of debuttressing b) a reliance on debris flows being a primary transport mechanism, and c) sediment being delivered sub-glacially rather than supra-glacially, further enhancing connectivity.

Sediment export and impacts associated with river delta channelization compound estuary vulnerability to sea-level rise, Skagit River Delta, Washington, USA

Improved understanding of the budget and retention of sediment in river deltas is becoming increasingly important to mitigate and plan for impacts expected with sea level rise. In this study, analyses of historical bathymetric change, sediment core stratigraphy, and modeling are used to evaluate the sediment budget and environmental response of the largest river delta in the U.S. Pacific Northwest to western land-use change beginning in ~1850. An estimated 142±28 M m3 of sediment accumulated offshore of the emergent Skagit River delta in Washington State between 1890 and 2014 and ~68% of which was found in sand deposits. The fraction of sediment retained in sand reservoirs represents 83% of the expected fluvial sand delivery over this time suggesting their potential utility to evaluate the relative contribution of different land uses to sediment runoff through time. A significantly higher ratio of sand retention to delivery during the period 1890–1939 coincided with extensive watershed denudation (clear-cut logging) and channel dredging, relative to the period 1940–2014, which was characterized by improved forest practices and sediment management to protect endangered species but also more extensive river channelization. Retention in the delta foreset of 78% of the sand delivered by the river between 1890 and 1939 was associated with extensive sediment bypassing and delta progradation that is shown to be 5–10x higher than rates over the Holocene. Comparable offshore sand retention over time and higher nearshore retention subsequent to 1940 after normalizing for the assumed reduction in sediment runoff with improved forest practices, suggests that channelization has continued to influence sediment export at a magnitude equivalent to the effects of early logging. Adverse impacts of the bypassing sediment regime to natural hazards risk and ecosystem management concerns are discussed, including the role of the lost sediment as a resource to mitigate subsiding coastal lands vulnerable to flood impacts. The sediment budget and coastal change analyses provide a framework for evaluating opportunities to achieve greater resilience across several sectors of coastal land use important in low-lying deltas worldwide.

Landslide evolution assessment based on InSAR and real-time monitoring of a large reactivated landslide, Wenchuan, China

The upper Minjiang catchment is frequently affected by a significant number of large to giant landslides. In one such massive older landslide, approximately 2 million m3 of sediment was reactivated, threatening the safety of a pylon on the landslide and the safety of the only route that allows high-speed travel from Wenchuan to Maoxian. To trace the deformation evolution history and analyze the current deformation of the new landslide, we examined SAR data since 2007, carried out geological and UAV surveys, and designed and installed real-time monitoring equipment. This paper presents the main spatial and temporal characteristics of the landslide. We found that the landslide has experienced creep deformation in the past five years and its sensitivity to rainfall. The development process of the landslide from the formation of tensile crack at the trailing edge to the gradual pushing forward of the crack propagation was revealed. The innovation of this paper is to reveal the whole process of the spatial-temporal evolution from its beginning to large deformation of a real case of creep landslide, which can provide a very good reference for the analysis and monitoring of such creeping landslide evolution process. This representative case also shows how to combine remote sensing and in situ monitoring methods to carry out continuous monitoring and the establishment of a warning system for potential landslide sites, so as to trace the evolution history, derive activity maps and analyze development trend, which can significantly reduce landslide risk. Additional mitigation procedures can be put into place if continuous monitoring of the Minjiang River Canyon occurs, resulting in a reduction of direct losses. In particular, modeling of the slope deformation and failure, damming process, and prospective flooding can be done in advance. Therefore, it is expected that this report can strengthen the case for the deployment of systematic monitoring of potential landslide sites by integrating earth observation methods and in situ monitoring systems as an approach to reduce risk.

Effects of dredged sediment dumping on trace metals concentrations and macro benthic assemblage at the continental shelf adjacent to a tropical urbanized estuary

This study assesses trace metals and macro benthic fauna in a dumping area for dredged material in the continental shelf of Guanabara Bay (Rio de Janeiro), southeast Brazil. Sampling of the study area was made after the last dredging of Rio de Janeiro, in 2017, removing 2.9 × 106 m3 of sediments that were disposed at a recurrent dumping site. The trace metals Cu, Zn, Pb, Cr and Ni exhibited a pattern of increasing concentrations towards the disposal site. Geoaccumulation index (NIgeo) and pollution load index (PLI) classified the dumping area as extremely polluted. The benthic macrofauna was composed by Nemertinea, Nematoda, Sipuncula, Annelida-Polychaeta, Mollusca, Crustacea, Brachiopoda and Echinodermata groups. The central station at the dumping site presented a single taxon Corbula patagonica. The benthic diversity decreased towards the disposal site, as observed by richness and diversity indexes that were markedly different among stations. Results presented preliminary data of trace metals in the dumping area revealing severe pollution in the continental shelf of Guanabara bay. Dumping of dredged material seems to negatively affect the macrobenthic community in the study area since richness and diversity increase with distance from the central spot.

Rotation, sedimentary deficit and erosion of a trailing spit inside ria of Arousa (NW Spain)

Based on the analysis of a large set of remote images, bathymetric studies and acoustic profiles, we studied the causes of erosion of a small island inside a ria of the NW coast of Spain. The island consists of a rocky sector to the south and a trailing, or comet-tail, spit to the north, which, until 1980, was in an equilibrium between the waves of the open ocean propagated inside the ria and the local wind waves. The development, in the 1970s, of a large park of floating rafts for mussel farming was identified as the factor triggering a period of disequilibrium and severe erosion on the island. The area covered by the floating rafts was the cause of the attenuation of local wind waves and the reinforcement of waves propagated from the open ocean. The spit underwent a period of approximately 38 years of disequilibrium characterized by a rotation movement with several phases. During the first period (1980–1989), a submarine lobe was formed, sequestering approximately 9000 m3 of sediment. Between 1989 and 2015, the spit maintained a rotation of 24° of amplitude and a phase of severe erosion, with rates of up to 6.6 m/yr, began in 2000. Since 2015, the spit has entered a new phase of stabilization, reducing the rotation to a small amplitude of 5°. The rates of erosion have also decreased, although they are still active.

Gully erosion susceptibility modelling to support avoided degradation planning

ABSTRACT Restoration resources are usually limited and strategic information on and erosion susceptible areas are required to avoid further degradation. This study has potential in the Mzimvubu River Catchment, South Africa, where two large reservoirs are planned on the Tsitsa tributary. The Tsitsa River Catchment, however, consists of highly erodible soils with widespread gully erosion evident. It is important to prevent further gully erosion in the catchment due to the presence of duplex and dispersive soils. Therefore, this study modelled areas that are susceptible to gully development in the Tsitsa River Catchment, as well as estimated the sediment yield potential from the susceptible areas if gully development occurs. This was achieved by mapping gully-free areas in a GIS that have the same DEM-derived topographical variables, soil associations and land cover as gullied areas, followed by scenario analysis of the potential sediment yield. More than 30 000 ha (7%) of the catchment is intrinsically susceptible to further gully development, consisting of drainage paths with a large contributing area and erodible duplex soils. If not protected, these susceptible areas could contribute an additional 300 million m3 of sediment to the river network, reducing the volumes of both reservoirs by more than 50%.

Produção de água com a aplicação de práticas mecânicas e vegetativas de conservação do solo e água em área de pastagem degradada

A perda de solo e água em terrenos que apresentam pastagens degradadas é um fator comprometedor da sustentabilidade de inúmeras propriedades rurais do Brasil. O presente estudo teve por objetivo conter o solo erodido e água do escoamento superficial proveniente da área de encosta dentro do Instituto Federal Minas Gerais, campus Governador Valadares. A área total da encosta é de aproximadamente 43125 m2, que para fins operacionais foram divididas em cinco áreas (denominadas 1 a 5). A intervenção deu-se nas áreas 1 a 4, totalizando 29675 m2. Os resultados a partir da intervenção nos 4 pontos de exutório, sendo especificamente três novas barraginhas e limpeza de outras duas existentes, além da instalação de 18 paliçadas, complementarmente com o plantio de 742 mudas de capim vetiver em pontos críticos da bacia, onde o solo estava exposto, culminou com a capacidade de 265 m3 de armazenamento de água pelas barraginhas. No período de setembro de 2018 a abril de 2019 houve precipitação de 853,9 mm de chuva e estima-se que aproximadamente 70% do volume escoado ficou retido pelas barraginhas, além de conter 20 m3 de sedimentos as paliçadas possibilitaram a retenção de cerca de 10,9 m3 de sedimentos. A sobrevivência das mudas de capim vetiver foi de 50%. Como o custo total do projeto, exceto mão de obra, foi de R$4.645,80, considera-se que tais intervenções foram exitosas para produção de água e mitigar o aporte de sedimentos nos canais de drenagem localizados à jusante da área de intervenção.

Tropical Cyclone Impacts on Headland Protected Bay

The response of headland protected beaches to storm events is complex and strongly site dependent. In this study, we investigated the response of several headland protected beaches in Noosa, Australia to a tropical cyclone event. Pre and post topographical surveys of all beaches were completed using both pole-mounted RTK-GNSS and structure-from-motion (SfM)-derived elevation models from survey-grade drone imagery to assess sediment volume differentials. Coastal imaging was used to assess shoreline development and identify coastal features while a nearshore wave model (SWAN) was used to project waves into the study site from a regional wave buoy. Obliquely orientated swells drive currents along the headland with sediment being eroded from exposed sites and deposited at a protected site. Elevated sea-levels were shown to be a strong force-multiplier for relatively small significant wave heights, with 10,000 m3 of sediment eroded from a 700 m long beach in 36 h. The SWAN model was adequately calibrated for significant wave height, but refraction of swell around the headland was under-represented by an average of 16.48 degrees. This research has coastal management implications for beaches where development restricts natural shoreline retreat and elevated sea states are likely to become more common.

Effects of amendments of PCB-containing Hudson River sediment on soil quality and biochemical and growth response of cucumber (Cucumis sativus L. cv ‘Wisconsin SMR 58’)

Approximately 200 million m3 of sediments are dredged every year in the United States. Of this amount, 2.3–9 million m3 are contaminated to the extent that they require special, and often costly, handling. Therefore, there is a pressing need to develop appropriate technology for the safe utilization of these sediments, especially in the case of the Hudson River, which is well known to demonstrate significant polychlorinated biphenyls (PCBs) contamination. Hence, the aim of the present study was to examine the influence of different doses of Hudson River sediments (10%, 25%, 50%, 75% and 100% admixtures) on soil quality and on the biochemical and growth response of cucumber (Cucumis sativus L. cv ‘Wisconsin SMR 58’), used as potential phytoremediation tool for sediment-borne PCBs. A sediment/soil admixture was found to significantly decrease the nitrogen (N) content in the substratum; in addition, phosphorus (P) content was significantly increased by 50–100% sediment, while potassium (K) content was significantly increased by 10% sediment, and significantly decreased by >50% sediment. Although sediment treatment resulted in a gradual increase in PCB content in the soil-sediment substratum, exceeding the threshold effect concentration (TEC) for the ≥50% sediment admixture, the Microtox assay did not suggest toxicity to microorganisms. The results demonstrated also that admixture of 10–25% Hudson River sediment increased cucumber growth; however, higher doses led to growth inhibition, manifested as lower biomass and smaller leaves. Also, chlorophyll a and b content decreased with increasing doses of sediment. Phenylpropanoid and flavonol contents were significantly higher in plants grown in soil amended with 10% of sediment, but significantly lower in soil treated with a 100% sediment admixture. The anthocyanin content in plants was lower at admixtures of 50% and higher. The obtained results corresponded with the decreasing content of N and K.