Channel Maintenance Research Articles

A CLASSIFICATION METHOD FOR THE PRESENCE OF TIDAL SAND WAVES AND MAINTENANCE DREDGING DESIGN

The study into sand wave dynamics in South Channel commenced after large dune forms were observed in monitoring campaigns following the channel deepening project of the Port of Melbourne. The project involved deepening of the harbor berths and channels, but more importantly, it involved the deepening of South Channel in Port Phillip Bay. South Channel, the main shipping channel, crosses the bay over ≈20km. The growth of bedforms at various locations in South Channel now threatens to impede marine traffic. The dimensions and migration rate of the bedforms in the channel are remarkable, especially in the harsh flow conditions in the narrow channel. Therefore, the bedforms in South Channel cannot be given an obvious classification. In this paper it is shown that the bedforms in South Channel can be classified as a tidal sand wave type with a method that requires only insight in water depth, tidal flow velocity and grain size. Tidal sand waves are large-scale bedforms generated by recirculating flow cells that drive sediment to the top of a crest and are commonly observed on shallow coastal seas such as the North Sea. The bedform concern in the channel illustrates the necessity of an evaluation of the present, and alternative, channel maintenance strategies. A numerical model in Delft3D software is applied, along with a probabilistic calculation that combines insights from the simulations and survey data, to assess different maintenance strategies.

Abundance and Distribution of Blue Elderberry (Sambucus nigra ssp. caerulea) on Lower Cache Creek: Implications for Adaptive Floodplain Management

Author(s): Rayburn, Andrew P.; Rogner, Michael; Frank, Paul | Abstract: Many western U.S. landscapes are managed for multiple objectives, including biological conservation, commodity production, human welfare, and recreation. Effective conservation of special-status species in managed landscapes is challenging when species protection must be balanced with broader land-management objectives. In managed river systems, actions such as channel maintenance, bank stabilization, dam operation, and habitat enhancement are often implemented to achieve objectives related to water delivery, flood control, protection of adjacent lands, public recreation, and biological conservation. However, these actions are often constrained by the presence of special-status species because of regulatory requirements that may supersede implementation of other measures. Strategies to balance special-status species conservation with broader management objectives are directly informed by robust data sets on species abundance and distribution. On lower Cache Creek in Yolo County, California, multi-objective management seeks to balance protection of the federally-threatened Valley elderberry longhorn beetle (Desmocerus californicus dimorphus) and its sole host shrub, blue elderberry (Sambucus nigra ssp. caerulea), with channel maintenance, bank stabilization, and habitat enhancement actions. We conducted a comprehensive field survey from 2015 to 2016 to map all elderberry shrubs across the 904-ha Cache Creek Resource Management Plan area. An estimated 10,296 shrubs that spanned small, medium, and large size classes were mapped, strongly suggesting that the local population has been increasing since in-channel mining ceased in 1996. Analyses of shrub distribution relative to floodplain inundation zones, and associated vegetation, slope, and aspect revealed that most shrubs occurred in association with other woody riparian vegetation and within the ≤ 10-yr floodplain inundation zone. In addition, shrubs occurred more often than expected on intermediate slopes and both westerly and northwesterly aspects. The results of this study are guiding adaptive management and informing project planning and permitting on lower Cache Creek, demonstrating the importance of spatially-explicit abundance and distribution data for special-status species in managed landscapes.

X-band radar as a tool for monitoring natural coastal behaviour and potential development impacts

ABSTRACTThis paper reports ongoing exploration of X-band radar as an operational monitoring tool for coastal infrastructure development. Data have been continually gathered since 2013, helping a major energy developer (EDF Energy) better understand shoreline processes at a proposed new nuclear power station at Sizewell, UK, to inform considerations of engineering design. The continual coverage provided by the radar enables greater confidence in defining natural variability and therefore enhanced assurance to regulators of the integrity or suitability of the site.Sizewell is located on a low-lying, soft coast with at least 1000 years of recorded (net) retreat. The commercial X-band system deployed calculates hydrodynamic data (suitable for managing navigation and vessel access), but this paper illustrates using radar images to establish the pre-construction baseline geomorphic behaviour of the nearshore, including a steep pebbly beach-face, two shore-parallel sub-tidal sandbars, and a large sandbank, 2 km offshore, which significantly affects nearshore hydrodynamics. Data illustrate baseline geomorphic behaviours that were previously unobserved, despite beach profiling records over 20 years. The temporal and spatial scales of natural changes are compared with the potential impacts of the development, including dredging (and spoil deposition) for navigation channel maintenance and the presence of nearshore structures, all of which would affect shoreline processes and so would need to be monitored (and any impacts managed) as development proceeds. Finally, the paper considers where the utility of X-band radar as an operational monitoring tool may surmount the barriers that have limited its uptake outside of academic/research circles.

Spatial, Seasonal, and Sexual Variation in the Diet ofGraptemys flavimaculata, a Threatened Turtle of the Pascagoula River System, Mississippi, USA

The conservation of imperiled species often depends upon conserving their prey. Graptemys flavimaculata (Yellow-blotched Sawback) is an imperiled turtle endemic to the Pascagoula River system of Mississippi, USA. We investigated diet variability of G. flavimaculata relative to site geography, sex, seasons, and size. We captured individuals from May to October in 2007 and 2008 at two distant sites. One site is an inland freshwater tributary (Leaf River, LR) and the other site is coastal and tidally influenced (Pascagoula River, PR). Feces from males (n = 68) and females (n = 74) were collected and analyzed. Using the Index of Relative Importance (IRI; 0–100 scale, 100 = only item present in all samples), we found that G. flavimaculata are primarily sponge specialists for both males (IRILR = 85, IRIPR = 91) and females (IRILR = 84, IRIPR = 65). For both sexes, between-site differences were more varied than within-site differences; for the latter, prey items were typically similar for males and females at a single site, but importance varied. Seasonal comparisons suggest that both LR and PR females shifted diets towards mollusks during the spring and fall, possibly associated with increasing energy and calcium for reproduction. Based on the frequency of wood fragments in feces, submerged deadwood appears important for prey species, and therefore, managers should conserve deadwood along riverbanks (i.e., mature riparian corridors). If channel maintenance is needed, deadwood should be moved toward banks rather than removed to conserve structure for prey species colonization.

Application of remote sensing and GIS for identification of potential ground water recharge sites in Semi-arid regions of Hard-rock terrain, in north Karnataka, South India

Hydro-geomorphological characteristics, together with soil, slope, lineament density and Land use Land cover are signatures of potential ground water recharge areas, and are vital for water harvesting. In the present paper, Fifth order sub-basins in Semi-arid regions of the Varada River basin in South India is studied for selection of suitable area for recharge and prioritize the sub-basins using Indian Remote Sensing satellite (IRS) P6; Linear Imaging Self Scanning Sensor (LISS III) and ArcGIS 9.2. The Fifth order sub-basins of the Varada River spread in Hard-rock terrain and of different agro-climatic zones. The study shows that there are significant spatial variations in the fifth order basins with respect to their morphometric characteristics such as the basin area, drainage density, bifurcation ratio, and circularity ratio, constant of channel maintenance and slope of the basin. These variations reflect the differences in the hydrological process in the different Sub-basins. Based on the variations in the linear, aerial, relief as well as the slope, lineament density, and precipitation pattern rankings are assigned for each parameter with respect to ground water recharge within the Subbasins. Weighted sum overlay for precipitation, Land use, soil and Water table fluctuation are used to select the suitable areas of recharge within the sub-basins. Buffers created for lineaments and drainage networks were intersected with the suitable area of recharge for the probable tank's locations for recharge. The tank locations identified after intersection and having higher stream orders are further filtered for the identification of potential sites for ground water recharge. In the prioritized sub-basins SB-8, SB-10, SB-11 locations have been selected for recharge.

Quantification of Runoff as Influenced by Morphometric Characteristics in a Rural Complex Catchment

This study addresses the critical scientific question of assessing the relationship between morphometric features and the hydrological factors that increase the risk of flooding in Kelantan River basin, Malaysia. Two hypotheses were developed to achieve this aim, namely: the alternate hypothesis (runoff, is influenced by morphometric characteristics in the study watershed) and the null hypothesis (runoff is not influenced by morphometric characteristics). First, the watershed was delineated into four major catchments, namely: Galas, Pergau, Lebir, and Nenggiri. Next, quantitative morphometric characters such as linear aspects, areal aspects, and relief aspects were determined on each of these catchments. Furthermore, HEC–HMS and flood response analyses were employed to simulate the hydrological response of the catchments. From the results of morphometric analysis, profound spatial changes were observed between runoff features of Kelantan River and the morphometric characteristics. The length of overflow that was related to drainage density and constant channel maintenance was found to be 0.12 in Pergau, 0.04 in both Nenggiri and Lebir, and 0.03 in Galas. Drainage density as influenced by geology and vegetation density was found to be low in all the catchments (0.07–0.24). Results of hydrological response indicated that Lebir, Nenggiri, Galas, and Pergau recorded a flood response factor of 0.75, 0.63, 0.40, and 0.05, respectively. Therefore, Lebir and Nenggiri are more likely to be flooded during a rainstorm. There was no clear indication with regard to the catchment that emerged as the most prevailing in all the morphological features. Hence, the alternate hypothesis was affirmed. This study can be replicated in other catchments with different hydrologic setup.

Hydro-geomorphological characterization of Dhidhessa River Basin, Ethiopia

Dhidhessa River Basin is physio-graphically and hydrologically important in the Blue Nile basin, however, its morphometry and hydrology are not well known. This study aimed to characterize hydro-geomorphology of the basin via basin morphometry analysis. SRTM DEM, geological and hydrological maps of the area were used in ArcGIS 10.3 environment for this analysis. Results showed that a 33,468 km total stream length of all orders was found distributed within 28,637 km2 drainage area in a dendritic pattern. According to morphometric parameter classification, total stream length and stream order of the basin were high whereas stream length ratio, bifurcation ratio and hydrologic storage coefficient were low. Furthermore, drainage area was large, drainage frequency was coarse, basin shape was more elongated, drainage density was medium, infiltration number was low, overland flow was long and constant of channel maintenance was high. Moreover, the basin's relief, relief ratio, ruggedness number, gradient ratio and the slope was high. In general, the study asserted that the basin was underlain by uniform resistant rocks, less prone to flooding, with high water resources potential and susceptible to soil erosion. The morphometric analysis approach pursued in this study was cost- and time-effective for basin characterization.

The influence of seasonal climate on the morphology of the mouth-bar in the Yangtze Estuary, China

The geomorphology of the Yangtze Estuary in the Changjiang River Delta in Eastern China has been the subject of extensive research. This study extends previous work to examine the influence of wind-waves on the mouth-bar, where about half of the river-borne material settles to the bed. The site is located just outside of Changjiang River mouth, which is meso-tidal and subject to seasonally varying river flows and wind-wave conditions. Modeling was performed with a coupled wave-current hydrodynamic model using TELEMAC and TOMAWAC and validated against observed data. Bottom Shear Stress (BSS) from river, tide and waves based on the numerical model output was used to infer the respective contribution to the evolution of the subaqueous delta. Our examination did not however extend to modeling the sediment transport or the morphological bed changes. The results suggest that (i) the dominance of river discharge is limited to an area inside the mouth, while outside, the mouth-bar is tide-wave dominant; (ii) considering just the tide, the currents on the shallow shoals are flood dominant and deep channels are ebb dominant, which induces continued accretion over the shallows and erodes the deeper parts of the mouth-bar until the tidal currents become too weak to transport sediment; (iii) whereas waves are very efficient at reshaping the shallow shoals, with the effect being subtly dependent on the depth distribution over the mouth-bar; (iv) the stability of shallow shoal morphology is highly dependent on the presence of seasonal wind-waves and characterized as “summer storing and winter erosion”, while deep channels perform like corridors of water and sediment, exporting sediment all year round. The nature of the mouth-bar response has important implications for coastal management, such as the ongoing deep water channel maintenance, reclamations and coastal defense measures.

Estimating River Bathymetry from Surface Velocity Observations Using Variational Inverse Modeling

AbstractAccurate river bathymetry characterization is important to understanding all aspects of the riparian environment and provides crucial information for ensuring the safe passage of vessels and guiding channel maintenance operations. Verified models based on readily collected physical data facilitate accurate predictions of changes to a riverbed caused by traffic, weather, and other influences. This paper presents a methodology for estimating river bathymetry from surface velocity data by applying variational inverse modeling to the shallow-water equations. The paper describes the mathematical framework for the methodology and the algorithm, and the numerical tools developed to test the methodology. The hydrodynamic modeling uses 2D depth-averaged solvers (under the hydrostatic assumption) and applies a standard empirical correlation that relates depth-averaged velocity to surface velocity. The application of the bathymetry estimation algorithm to water-surface velocity data was tested on a 95-km reach of the Columbia River in Washington State. The root-mean-square error (RMSE) of the estimated bathymetry field relative to the ground truth data is approximately 2 m over the entire reach. The results of the test case indicate that this approach can be used to estimate river bathymetry to a close approximation based on the bank-to-bank surface velocity data on the reach of interest.

Tectonics, lithology and climate controls of morphometric parameters of the Edea - Eseka region (SW Cameroon, Central Africa): Implications on equatorial rivers and landforms

Shuttle Radar Topography Mission (SRTM) - 3 data for Digital Elevation Model through morphometric analyses of the Sanaga, Nyong and Kelle watersheds and landform were correlated with field survey in a Geographical Information System (GIS) model in the Edea-Eseka Region in SW Cameroon; erected on Paleo-to Neoproterozoic crystallophyllian rock types, Cretaceous to Recent sedimentary formations later affected by reactivated and neotectonic faults. This study that aimed to evaluate the lithology, tectonic and climate interactions on operating processes and landform characteristics based on the morphometric parameters of watersheds. Parameters vary from one watershed to another establishing one to three controls. The density drainage (0.05–0.29), the constant of channel maintenance (3.5–19.47) and the drainage pattern; outlines the lithological, the tectonic and the climate controls of the morphology. The Bifurcation ratio (2–5.25), the mean bifurcation ratio (3.67–4.09), the relative relief ratio (0.21–0.27), the watershed slope (5.75–9.35) and the watershed deviation (105–507); highlights the lithostructural controls of the morphology; whilst the wandering ratio (1.54–2.12) individualises both, the structural and climate controls. The stream number (370–2473) and the stream length ratio (0.57–1.91), the elongation ratio (0.47–0.55), the circularity ratio (0.25–0.29), fitness ratio (0.56–0.63), dissection index (0.91–0.99), the concavity index (−0.1-0.56), the hypsometric integral (0.45–0.49) and the stepped longitudinal length profiles, establishes the dominant tectonic controls of the morphology; while the rho coefficient (0.34–0.43) and drainage texture (1.91–4.75) displays the lithological control of the morphology and; the drainage intensity (1.76–7.62) and the length overland flow (1.75–9.74) typified the climate control of the morphology. The Edea-Eseka Region uplift rejuvenates old watershed each time they evolve to equilibrium because of lithological variations, neotectonics, differential erosion and climate variations; overriding its morphology. This geodynamic and climatic control of morphometric processes in the SW Cameroon can be extended to the whole of Central Africa and in Equatorial Regions that display similar evolutions.

Eco-geomorphological approach for environmental flows assessment in monsoon-driven highland rivers: A case study of Upper Ganga, India

Study regionUpper Ganga reaches up to Rishikesh town, India. Study focusEnvironmental Flows (E-Flows) assessment in the upper stretches of the Ganga river has been carried out by integrating ecological and geomorphological parameters with hydraulic analysis to estimate the flow depths and flow volumes necessary for river ecology and channel maintenance. We have used a modified version of Building Block Method (BBM) for computing E-Flows for lean period, for monsoon period and for high floods based on the flow requirements of keystone species for different sites and geomorphic considerations. We define three flow depths, D1, D2 and D3 which correspond to the minimum flow depths required for sustenance of keystone species during lean period, for breeding and spawning of keystone species during monsoon period, and for maintaining lateral connectivity during floods respectively. New hydrological insights for the regionAnnual hydrographs for E-Flows have been developed and compared with the observed flows for each site under natural flow conditions. Our computation shows that for the wet period, which is taken as the period from mid-May to mid-October, monthly E-Flows vary from ∼23% to ∼40% of the monthly natural flows at different sites. However, dry season E-Flows as percentages of natural flows, taken for the period from mid-October to mid-May, vary over a wider range of 29%–53% for these sites.

Characterizing natural riparian vegetation for modeling of flow and suspended sediment transport

Riparian vegetation imposes a critical control on the transport and deposition of suspended sediment with important implications for water quality and channel maintenance. This paper contributes (1) to hydraulic and morphological modeling by examining the parameterization of natural riparian vegetation (trees, bushes, and grasses) and (2) to the design and management of environmental channels by determining how the properties of natural floodplain plant stands affect the erosion and deposition of suspended sediment. Laboratory and field data were employed for enhancing the physical description of flow–plant–sediment interactions with a consideration of practical applicability. A drag force parameterization that takes into account the flexibility-induced reconfiguration, and the complex structure of foliated plants was validated for small natural trees under laboratory conditions, while the data from a small vegetated compound channel demonstrated the approaches at the field scale. Based on the field data, we identified three key vegetative factors influencing the net deposition and erosion on the floodplain. The significance of these factors was evaluated for vegetative conditions ranging from almost bare soil to sparse willows and dense grasses. Overall, the investigated conditions covered flexible and rigid vegetation with seasonal differences represented by foliated and leafless states. The drag and reconfiguration of woody plants were reliably predicted under leafless and foliated conditions. Subsequently, we present a new easy-to-use methodology for predicting vegetative drag and flow resistance. The methodology is based on a physically solid parameterization for five widely used coefficients or terms (Eqs. (2)–(6)), with the necessary parameter values presented for common riparian species. The methodology was coupled with existing approaches at the field scale, revealing that increasing vegetation density and the associated decreasing flow velocity within vegetation significantly increased net deposition. Further, deposition increased with increasing cross-sectional vegetative blockage and decreasing distance from the suspended sediment replenishment point. Thus, longitudinal advection was the most important mechanism supplying fine sediment to the floodplain, but long continuous plant stands limited deposition. The proposed parameterization (Eqs. (2)–(6)) can be readily implemented into existing hydraulic and morphological models to improve the description of natural vegetation compared to the conventional rigid cylinder representation. The approach is advantageous for evaluating, for example, the effects of both natural succession and management interventions on floodplains. Finally, guidance is provided on how floodplain vegetation can be maintained to manage the erosion and deposition of suspended sediment in environmental channel designs.

A Morphometric Analysis of Horan Valley By Using Remote Sensing and Geographic Information Systems

This study was conducted to know the possibility of creating morphometric geo database for Horan valley which is the greatest valley in western desert by using remote sensing and geographic information systems. Digital Elevation Model (DEM) was used to measure the cadastral, morphological or hydrological morphometric properties using the ArcGIS V.10.2 program. These properties considered an important database to make the future planning for dry or wet valleys and rivers basins, which reduce time, expenses and efforts to study the wide area regions. The values of longitudinal section, average of circumference, circularity ratio, circumference compactness factor, elongation factor, form factor, length to width ratio, relief ratio, relative relief, hypsometric integration, basin tissue, the value of rugged, drainage longitudinal density, numerical drainage density, and the Constant of Channel Maintenance, in the Horan valley are 2.562 m km-1, 1307 km, 0.13, 2.77, 0.47, 0.13, 7.3, 2.32 m km-1, 0.64 m km-1, 21.26 km2 m-1, 8 valleys km-1, 0.77, 0.92 km km- 2, 0.61, and 1.08 km2 km-1, respectively.

Sediment Transport into the Swinomish Navigation Channel, Puget Sound—Habitat Restoration versus Navigation Maintenance Needs

The 11 mile (1.6 km) Swinomish Federal Navigation Channel provides a safe and short passage to fishing and recreational craft in and out of Northern Puget Sound by connecting Skagit and Padilla Bays, US State abbrev., USA. A network of dikes and jetties were constructed through the Swinomish corridor between 1893 and 1936 to improve navigation functionality. Over the years, these river training dikes and jetties designed to minimize sedimentation in the channel have deteriorated, resulting in reduced protection of the channel. The need to repair or modify dikes/jetties for channel maintenance, however, may conflict with salmon habitat restoration goals aimed at improving access, connectivity and brackish water habitat. Several restoration projects have been proposed in the Skagit delta involving breaching, lowering, or removal of dikes. To assess relative merits of the available alternatives, a hydrodynamic model of the Skagit River estuary was developed using the Finite Volume Community Ocean Model (FVCOM). In this paper, we present the refinement and calibration of the model using oceanographic data collected from the years 2006 and 2009 with a focus on the sediment and brackish water transport from the river and Skagit Bay tide flats to the Swinomish Channel. The model was applied to assess the feasibility of achieving the desired dual outcome of (a) reducing sedimentation and shoaling in the Swinomish Channel and (b) providing a direct migration pathway and improved conveyance of freshwater into the Swinomish Channel. The potential reduction in shoaling through site-specific structure repairs is evaluated. Similarly, the potential to significantly improve of brackish water habitat through dike breach restoration actions using the McGlinn Causeway project example, along with its impacts on sediment deposition in the Swinomish Navigation Channel, is examined.

Estimate the geomorphological parameters of the Arang watershed in Chhattisgarh region

This study was conducted for the Arang watershed of the Chhattisgarh, India. Several geomorphological parameters of the watershed were determined using standard procedure. The Arang is 3 rd order watershed and comprises of 10 villages. Predominant soil of the watershed is clay loam. The watershed receives an average annual rainfall of 1400 mm, out of which the monsoon season (June to October) contributes more than 85 per cent rainfall. The number of 1 st , 2 nd and 3 rd Order were found to be 20, 4, 1, respectively. The different geomorphometric parameters of watershed were determined and result showed that total length of stream segments were 26.14, 9.37, 8.56 km, respectively. Area of sub-basin for 1st, 2nd and 3rd order streams and of different order streams were to be 32.35, 43.94, and 54.50 km 2 , respectively, for 1 st , 2 nd and 3 rd order streams. The mean bifurcation ratio for the watershed was found to be 4.64. The length ratio, circularity ratio and elongation ratio for the Arang watershed were determined and found to be 2.724, 0.9148 and 0.973, respectively. The hypsometric integral of the watershed was calculated to be 0.998 km. The drainage density, length of over land flow and constant of channel maintenance of the watershed were found to be 0.808 km/km 2 , 0.618 km and 1.237 km, respectively. The main channel slope of the watershed was 0.005 whereas compactness co-efficient of the watershed was 1.093. The stream frequency, basin shape factor, form factor, and ruggedness number of the watershed were 0.458 km 2 , 2.578, 0.387, 0701 and 0.016, respectively. The values of relative relief and relative ratio of the watershed was found to be 1.452×10 -3 and 1.687×10 -3 , respectively. The weighted average slope of the entire watershed was found to be 1.5 per cent. This parameter which indicates that topography of watershed is flat.

Percepción social y comportamiento ambiental de comunidades cercanas a un río urbano tropical en Costa Rica

Las áreas verdes urbanas son de gran importancia para mantener el equilibrio en las ciudades, sin embargo, hay pocos estudios que analicen la percepción social sobre estas áreas. Realizamos una evaluación comparativa de la percepción ambiental que existe en dos comunidades urbanas de San José, Costa Rica. Las comunidades evaluadas se encuentran separadas por el río Ocloro; una presenta un nivel socioeconómico bajo y la otra un nivel medio-alto. Aplicamos encuestas en 40 casas ubicadas a menos de 150 m del río y a los encargados municipales del manejo de los recursos naturales. Realizamos una evaluación cualitativa del estado del río y su área de protección. Además, medimos la cantidad de metros cuadrados de área verde por habitante en imágenes satelitales. Cuantificamos la cantidad de desagües pluviales y de aguas servidas provenientes de cada comunidad y la colindancia de la zona de protección con construcciones, calles y zonas verdes. No encontramos diferencia significativa en la percepción ambiental de las comunidades. Las comunidades identificaron la vegetación y el río como los principales recursos y ventajas, la contaminación y los malos olores como las principales desventajas y, las campañas de educación ambiental, el mantenimiento del cauce y la reforestación como posibles soluciones. Los encargados municipales coincidieron en identificar al vertido de aguas residuales y la invasión de la zona de protección del río como principales problemas ambientales. La percepción ambiental municipal y comunal de la invasión de la zona de protección del río y su entubación fue inconsistente. Por lo tanto, recomendamos adecuar los programas de educación ambiental para que ambas percepciones coincidan y se ajusten a la realidad. La percepción de ambas comunidades es similar, sin embargo, difieren mucho en su comportamiento. La comunidad de nivel socioeconómico bajo vierte más desagües al río, ha invadido el 37,6% de la zona de protección y el 75% de la misma colinda con construcciones. Se recomienda la educación ambiental participativa para modificar el comportamiento de la comunidad de nivel socioeconómico bajo, así como evitar que las construcciones colinden con la zona de protección de los ríos para prevenir la invasión de la misma. Hay desigualdad en la cantidad de áreas verdes por habitante; la comunidad de nivel socioeconómico bajo tiene 19,5 m2 en tanto que la de nivel medio-alto tiene 108,2 m2. Ambos valores son superiores a los recomendados por la Organización de las Naciones Unidas. Sin embargo, esos espacios verdes no siempre son públicos; principalmente en la comunidad de nivel socioeconómico bajo. Por lo tanto, la tasa efectiva de área verde disponible por habitante podría ser menor.

Bed and width oscillations form coherent patterns in a partially confined, regulated gravel–cobble-bedded river adjusting to anthropogenic disturbances

Abstract. Understanding the spatial organization of river systems in light of natural and anthropogenic change is extremely important because it can provide information to assess, manage, and restore them to ameliorate worldwide freshwater fauna declines. For gravel- and cobble-bedded alluvial rivers studies spanning analytical, empirical and numerical domains suggest that at channel-forming flows there is a tendency towards covarying bankfull bed and width undulations amongst morphologic units such as pools and riffles, whereby relatively wide areas have relatively higher minimum bed elevations and relatively narrow areas have relatively lower minimum bed elevations. The goal of this study was to determine whether minimum bed elevation and flow-dependent channel top width are organized in a partially confined, incising gravel–cobbled bed river with multiple spatial scales of anthropogenic and natural landform heterogeneity across a range of discharges. A key result is that the test river exhibited covarying oscillations of minimum bed elevation and channel top width across all flows analyzed. These covarying oscillations were found to be quasiperiodic at channel-forming flows, scaling with the length scales of bars, pools and riffles. Thus, it appears that alluvial rivers organize their topography to have quasiperiodic, shallow and wide or narrow and deep cross section geometry, even despite ongoing, centennial-scale incision. Presumably these covarying oscillations are linked to hydrogeomorphic mechanisms associated with alluvial river channel maintenance. The biggest conclusion from this study is that alluvial rivers are defined more so by variability in topography and flow than mean conditions. Broader impacts of this study are that the methods provide a framework for characterizing longitudinal and flow-dependent variability in rivers for assessing geomorphic structure and aquatic habitat in space, and if repeated, through time.

Underkeel Clearance Reliability Model for Dredged Navigation Channels

This paper presents a reliability measure for selecting marine navigation channel maintenance depth. Resource constraints have resulted in dredging requirements outpacing the funds available to the U.S. Army Corps of Engineers to perform navigation channel maintenance dredging, but navigation managers lack a method to objectively select maintenance depth alternatives to authorized project depths. The reliability of a navigation channel can be determined as the probability that a vessel's net underkeel clearance is greater than or equal to 0. Net underkeel clearance was hindcast from underkeel clearance contributors that include sailing draft, water level, bathymetric elevation, vessel squat, and wave response. This method was tested in Charleston Harbor, South Carolina, with an authorized depth of 45 ft (13.7 m). The harbor includes two-way container, tanker, roll on–roll off, and passenger traffic with maximum drafts exceeding design depth. Vessel squat in transit is calculated on the basis of vessel speed, obtained from Automatic Identification System (AIS) data and a representative block coefficient based on vessel size and type. This study used archival AIS data, bathymetric surveys, observed water level elevations, and information collected by vessel pilots to calculate net underkeel clearance of vessel transits through each dredged location within the harbor in 2011. It was determined that channel reliability ranged from 98.7% to 100%. Channels with 100% reliability had minimum net underkeel clearance between 1.0 ft (0.3 m) and 8.3 ft (2.5 m). The approach provides a potential method to select maintenance depth alternatives to authorized channel depths that may result in maintenance cost savings that arise from avoided dredging and associated material management costs.

Antagonistic Behaviors of NMY-1 and NMY-2 Maintain Ring Channels in the C. elegans Gonad

Contractile rings play critical roles in a number of biological processes, including oogenesis, wound healing, and cytokinesis. In many cases, the activity of motor proteins such as nonmuscle myosins is required for appropriate constriction of these contractile rings. In the gonad of the nematode worm Caenorhabditis elegans, ring channels are a specialized form of contractile ring that are maintained at a constant diameter before oogenesis. We propose a model of ring channel maintenance that explicitly incorporates force generation by motor proteins that can act normally or tangentially to the ring channel opening. We find that both modes of force generation are needed to maintain the ring channels. We demonstrate experimentally that the type II myosins NMY-1 and NMY-2 antagonize each other in the ring channels by producing force in perpendicular directions: the experimental depletion of NMY-1/theoretical decrease in orthogonal force allows premature ring constriction and cellularization, whereas the experimental depletion of NMY-2/theoretical decrease in tangential force opens the ring channels and prevents cellularization. Together, our experimental and theoretical results show that both forces, mediated by NMY-1 and NMY-2, are crucial for maintaining the appropriate ring channel diameter and dynamics throughout the gonad.

Experience of Implementation of Safety and Normal Operation Control Systems at NPP Units

The paper deals with instrumentation and control (I&C) of safety control systems (ESFAS) and normal operation control systems (NOCS) for NPP units. The research contains: general information on I&C of ESFAS and I&C of NOCS; description of design solutions for ESFAS, NOCS and principles of their implementation in I&C versions, description of basic components for design of I&C of ESFAS and I&C of NOCS. Distinctive features of ESFAS and NOCS I&Cs are the following: possibility to design systems with different number of channels in accordance with the design requirements; higher reliability due to redundant structures, including redundancy of analog-digital units and control drive units; minimization of cabling due to optical interface of data transmission using digital devices for remote control, indication and alarm in MCR (ECR); possibility of single redundant channel maintenance of I&Cs without losing operability; continuous monitoring of equipment of I&Cs, including diagnosing of input discrete signal channels and detection of hidden faults “on demand”.