Home About us Contact
|
Home About us Contact | ||
|
|
||
Delivery Ratio (delivery + ratio)
Selected AbstractsAODV-RIP: improved security in mobile ad hoc networks through route investigation procedureCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 7 2010Byung-Seok Kang Abstract Most routing protocols in mobile ad hoc networks (MANETs) place an emphasis on finding paths in dynamic networks without considering security. As a result, there are a number of attacks that can be used to manipulate the routing in MANET. A malicious node that sends a modified control message to an intermediate node can disturb the network using a control message. To solve this problem, we introduce AODV protocol with route investigation procedure (AODV-RIP). It uses two additional control messages to defeat security attacks that can occur in AODV routing protocol. When an intermediate node that is on the path between the source node and the destination node receives a control message, it sends a Rroute Investigation Request (IREQ) message to the destination node in order to check the reliability of the control message. According to the existence of Route Investigation Reply (IREP), the intermediate node decides whether it transmits the control message to the source node or not. Consequently, the intermediate node that receives the control message confirms that it is using two additive control messages: IREQ and IREP. Through this investigation procedure, the source node can obtain a reliable path for transmitting data packets to an intentional destination node. The simulation results show an improvement in the packet delivery ratio and end-to-end delay at the expense of a moderate increase of the control message overhead compared with the current routing protocols. Copyright © 2009 John Wiley & Sons, Ltd. [source] Short-term erosion rates from a 7Be inventory balanceEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2003Christopher G. Wilson Abstract Detailed soil erosion studies bene,t from the ability to quantify the magnitude of erosion over time scales appropriate to the process. An inventory balance for 7Be was used to calculate sediment erosion in a 30·73 m2 plot during a series of runoff-producing thunderstorms occurring over three days at the Deep Loess Research Station in Treynor, Iowa, USA. The inventory balance included determination of the pre- and post-storm 7Be inventories in the soil, the atmospheric in,ux of 7Be during the event, and pro,les of the 7Be activity in the soil following the atmospheric deposition. The erosion calculated in the plot using the 7Be inventory balance was 0·058 g cm,2, which is 23 per cent of the annual average erosion determined using 137Cs inventories. The calculated erosion from the mass balance is similar to the 0·059 g cm,2 of erosion estimated from the amount of sediment collected at the outlet of the 6 ha ,eld during the study period and the delivery ratio (0·64). The inventory balance of 7Be provides a new means for evaluating soil erosion over the time period most relevant to quantifying the prediction of erosion from runoff. Copyright © 2003 John Wiley & Sons, Ltd. [source] Sediment production in large gullies of the Mediterranean area (NE Spain) from high-resolution digital elevation models and geographical information systems analysisEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2003J. A. Martínez-Casasnovas Abstract Recent studies in the Mediterranean area have shown gully erosion to have a very significant contribution to total soil loss. In the Penedès vineyard region (NE Spain), between 15 and 27% of the land is affected by large gullies and gully-wall retreat seems to be an ongoing process. Multi-date digital elevation model (DEM) analysis has allowed computation of sediment production by gully erosion, showing that the sediment production rates are very high by the, up-to-date, usual global standards. Here, we present a study carried out using large-scale multi-date (1975 and 1995) aerial photographs (1 : 5000 and 1 : 7000) to monitor sediment yield caused by large gullies in the Penedès region (NE Spain). High-resolution DEMs (1 m grid) were derived and analysed by means of geographical information systems techniques to determine the gully erosion rates. Rainfall characteristics within the same study period were also analysed in order to correlate with the soil loss produced. Mass movement was the main process contributing to total sediment production. This process could have been favoured by rainfalls recorded during the period: 58% of the events were of an erosive character and showed high kinetic energy and erosivity. A sediment production rate of 846 ± 40 Mg ha,1 year,1, a sediment deposition rate of 270 ± 18 Mg ha,1 year,1 and a sediment delivery ratio of 68·1% were computed for a gully area of 0·10 km2. The average net erosion within the study period (1975,95) was 576 ± 58 Mg ha,1 year,1. In comparison with other methods, the proposed method also includes sediment produced by processes other than only overland flow, i.e. downcutting, headcutting, and mass movements and bank erosion. Copyright © 2003 John Wiley & Sons, Ltd. [source] Close range digital photogrammetric analysis of experimental drainage basin evolutionEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2003J. Brasington Abstract Despite the difficulties of establishing formal hydraulic and geometric similarity, small-scale models of drainage basins have often been used to investigate the evolution and dynamics of larger-scale landforms. Historically, this analysis has been restricted to planform basin characteristics and only in the last decade has the topographic similarity of experimental landscapes been explored through explicitly three-dimensional parameters such as the distributions of cumulative drainage area, area,slope and catchment elevation. The current emphasis on three-dimensional morphometry reflects a growing awareness of the descriptive paucity of planform data and the need for more robust analysis of spatial scaling relationships. This paradigm shift has been significantly facilitated by technological developments in topographic survey and digital elevation modelling (DEM) which now present the opportunity to acquire and analyse high-resolution, distributed elevation data. Few studies have, however, attempted to use topographic modelling to provide information on the changing pattern and rate of sediment transport though an evolving landscape directly by using multitemporal DEM differencing techniques. This paper reports a laboratory study in which digital photogrammetry was employed to derive high-resolution DEMs of a simulated landscape in declining equilibrium at 15 minute frequency through a 240 minute simulation. Detailed evaluation of the DEMs revealed a vertical precision of 1·2 mm and threshold level of change detection between surfaces of ±3 mm at the 95 per cent confidence level. This quality assurance set the limits for determining the volumetric change between surfaces, which was used to recover the sediment budget through the experiment and to examine local - and basin-scale rates of sediment transport. A comparison of directly observed and morphometric estimates of sediment yield at the basin outlet was used to quantify the closure of the sediment budget over the simulation, and revealed an encouragingly small 6·2 per cent error. The application of this dynamic morphological approach has the potential to offer new insights into the controls on landform development, as demonstrated here by an analysis of the changing pattern of the basin sediment delivery ratio during network growth. Copyright © 2003 John Wiley & Sons, Ltd. [source] Spatial analysis of instream nitrogen loads and factors controlling nitrogen delivery to streams in the southeastern United States using spatially referenced regression on watershed attributes (SPARROW) and regional classification frameworks,HYDROLOGICAL PROCESSES, Issue 16 2009Anne B. Hoos Abstract Understanding how nitrogen transport across the landscape varies with landscape characteristics is important for developing sound nitrogen management policies. We used a spatially referenced regression analysis (SPARROW) to examine landscape characteristics influencing delivery of nitrogen from sources in a watershed to stream channels. Modelled landscape delivery ratio varies widely (by a factor of 4) among watersheds in the southeastern United States,higher in the western part (Tennessee, Alabama, and Mississippi) than in the eastern part, and the average value for the region is lower compared to other parts of the nation. When we model landscape delivery ratio as a continuous function of local-scale landscape characteristics, we estimate a spatial pattern that varies as a function of soil and climate characteristics but exhibits spatial structure in residuals (observed load minus predicted load). The spatial pattern of modelled landscape delivery ratio and the spatial pattern of residuals coincide spatially with Level III ecoregions and also with hydrologic landscape regions. Subsequent incorporation into the model of these frameworks as regional scale variables improves estimation of landscape delivery ratio, evidenced by reduced spatial bias in residuals, and suggests that cross-scale processes affect nitrogen attenuation on the landscape. The model-fitted coefficient values are logically consistent with the hypothesis that broad-scale classifications of hydrologic response help to explain differential rates of nitrogen attenuation, controlling for local-scale landscape characteristics. Negative model coefficients for hydrologic landscape regions where the primary flow path is shallow ground water suggest that a lower fraction of nitrogen mass will be delivered to streams; this relation is reversed for regions where the primary flow path is overland flow. Published in 2009 by John Wiley & Sons, Ltd. [source] SEDIMENT TRAPPING WITHIN FORESTRY STREAMSIDE MANAGEMENT ZONES: GEORGIA PIEDMONT, USA,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2004Jason M. Ward ABSTRACT: The effectiveness of streamside management zones (SMZs) was assessed for reducing sediment transport from concentrated overland flow draining two Georgia Piedmont clearcuts that had undergone mechanical and chemical site preparation and planting. Silt fences were used to trap sediment transport from zero-order ephemeral swales at the edge of and within SMZs. Four control swales and nine treatment swales were studied. A double mass curve approach was used to graphically compare sediment accumulation rates at the edge of SMZs to accumulation rates within the SMZs at a distance consistent with current recommendations for SMZ width in Georgia. SMZ efficiencies for trapping sediment transported by concentrated flow ranged from 71 to 99 percent. No statistical model was found to explain how SMZ efficiencies varied with SMZ and contributing area characteristics. Measured sediment accumulations at the SMZ boundary were compared to Revised Universal Soil Loss Equation (RUSLE) predictions of up- slope erosion, and a delivery ratio of 0.25 was calculated. SMZs had a quantifiable and substantial ameliorating effect on sediment transport from concentrated overland flow on the clearcut study sites. [source] TOWARDS A UNIFORM CONCEPT FOR THE COMPARISON AND EXTRAPOLATION OF ROCKWALL RETREAT AND ROCKFALL SUPPLYGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2007MICHAEL KRAUTBLATTER ABSTRACT. Rates of rockwall retreat and rockfall supply are fundamental components of sediment budgets in steep environments. However, the standard procedure of referencing rockwall retreat rates using only lithology is inconsistent with research findings and results in a variability that exceeds three orders of magnitude. The concept proposed in this paper argues that the complexity inherent in rockfall studies can be reduced if the stages of (i) backweathering, (ii) filling and depletion of intermediate storage on the rock face and (iii) final rockfall supply onto the talus slopes are separated as these have different response functions and controlling factors. Backweathering responds to preweathering and weathering conditions whereas the filling and depletion of intermediate storage in the rock face is mainly a function of internal and external triggers. The noise apparent in backweathering rates and rockfall supply can be reduced by integrating the relevant controlling factors in the response functions. Simple conceptual models for the three stages are developed and are linked by a time-dependent ,rockfall delivery rate', which is defined as the difference between backweathering and rockfall supply, thus reflecting the specific importance of intermediate storage in the rock face. Existing studies can be characterized according to their ,rockfall delivery ratio', a concept similar to the ,sediment delivery ratio' used in fluvial geomorphology. Their outputs can be qualified as trigger-dependent rockfall supply rates or backweathering rates dependent on (pre-)weathering conditions. It is shown that the existing quantitative backweathering and rockfall supply models implicitly follow the proposed conceptual models and can be accommodated into the uniform model. Suggestions are made for how best to incorporate non-linearities, phase transitions, path dependencies and different timescales into rockfall response functions. [source] Spatial patterns of suspended sediment yields in a humid tropical watershed in Costa RicaHYDROLOGICAL PROCESSES, Issue 12 2001Jagdish Krishnaswamy Abstract An Erratum has been published for this article in Hydrological Processes 16(5) 2002, 1130,1131. Humid tropical regions are often characterized by extreme variability of fluvial processes. The Rio Terraba drains the largest river basin, covering 4767 km2, in Costa Rica. Mean annual rainfall is 3139±419sd mm and mean annual discharge is 2168±492sd mm (1971,88). Loss of forest cover, high rainfall erosivity and geomorphologic instability all have led to considerable degradation of soil and water resources at local to basin scales. Parametric and non-parametric statistical methods were used to estimate sediment yields. In the Terraba basin, sediment yields per unit area increase from the headwaters to the basin mouth, and the trend is generally robust towards choice of methods (parametric and LOESS) used. This is in contrast to a general view that deposition typically exceeds sediment delivery with increase in basin size. The specific sediment yield increases from 112±11·4sd t km,2 year,1 (at 317·9 km2 on a major headwater tributary) to 404±141·7sd t km,2 year,1 (at 4766·7 km2) at the basin mouth (1971,92). The analyses of relationships between sediment yields and basin parameters for the Terraba sub-basins and for a total of 29 basins all over Costa Rica indicate a strong land use effect related to intensive agriculture besides hydro-climatology. The best explanation for the observed pattern in the Terraba basin is a combined spatial pattern of land use and rainfall erosivity. These were integrated in a soil erosion index that is related to the observed patterns of sediment yield. Estimated sediment delivery ratios increase with basin area. Intensive agriculture in lower-lying alluvial fans exposed to highly erosive rainfall contributes a large part of the sediment load. The higher elevation regions, although steep in slope, largely remain under forest, pasture, or tree-crops. High rainfall erosivity (>7400 MJ mm ha,1 h,1 year ,1) is associated with land uses that provide inadequate soil protection. It is also associated with steep, unstable slopes near the basin mouth. Improvements in land use and soil management in the lower-lying regions exposed to highly erosive rainfall are recommended, and are especially important to basins in which sediment delivery ratio increases downstream with increasing basin area. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||