Service Curve Research Articles

Spatio-temporal flood trends & settlement choice in flood-prone areas. A case study of Lubiji micro-catchment, Kampala City

ABSTRACT This study was conducted to establish the spatio-temporal distribution of flash floods and to learn why people prefer to settle in flood-prone areas of Lubiji micro-catchment in Kampala City. Rainfall data were analysed to ascertain Peak Runoff expected for the given flood event based on Soil Conservation Service Curve Numbers. The micro-catchment was delineated in the Arc GIS 10.0 programme, from the Digital Elevation Model. Feature classes were created to obtain the reach extents and river banks. HEC-RAS model was then used to create flood inundation maps in Arc GIS 10.0 between 1983 and 2014. High magnitude flash floods occurred almost after every three years and the spatial extent varied from 4.4 to 6.8 km2. The choice of settlement location in flood-prone areas was influenced by socio-economic ties. The flood hazard maps produced will aid land-use planning, resettlement of the people and setting up a flood forecasting system.

The effect of Sustainable Urban Drainage Systems on outdoor comfort and runoff

Cities are facing numerous challenges such as Urban Heat Island Effect (UHIE) and more frequent flooding events, due to the increasing soil sealing. Greenery and water implemented in urban outdoor spaces have been promoted as effective strategies to counteract UHIE while Sustainable Urban Drainage Systems (SUDS) have been identified as convenient solutions to increase resilience to flooding. However, since many SUDS are green-based, they also benefit urban microclimate and outdoor thermal comfort. In this work, the effectiveness of SUDS as passive strategies to simultaneously improve outdoor thermal comfort and reduce stormwater runoff is assessed. The analysis is carried out on a neighbourhood in Ostia (Rome), selected as representative of Mediterranean climate. The case study area is modelled on ENVI-met in three different scenarios: the current condition is compared with two future developments in which green and water-based mitigation strategies are implemented or in which soil sealing continues based on current trend. Moreover, for each scenario, stormwater runoff has been determined using the Soil Conservation Service curve number method. Results show that the implemented mitigation strategies allow achieving improved thermal comfort conditions and at the same time they can reduce runoff.

Design of Flood Drainage in Golgohar Iron Ore Mine#3

The iron ore minerals reservoir of Golgohar Mine#3 is more than 660 million tons. It is the biggest in Iran and rate of ore extraction is more than 15 million tons per year. The pit takes place on the way of runoff pathway of this watershed and it needs an especial strategy for conserving the pit mine during next imminent floods. The area of Mine# 3 watershed is 20785700 square meters and its general slope in its topography map is 0.59 percent; then initial scheming indicates it can causes a great deal of problems for mining operation n the next floods; particularly, the pit is located into degree 4th sub branch of a main ephemeral river. For this purpose, the Soil Conservation Service Curve Number (SCS) method was employed to estimate intervals period of next floods based on the magnitude, the intensity and the duration of precipitation events data. Conceptual design of runoff drainage of the watershed was designed to lead the flood to a better pathway location. The Mine#3 overburden deposition occupies a huge area on the watershed; and it has been considered and redesigned in terms of size, form, dimensions and location to manage as a physical obstacle against next floods. Hydraulic calculations were applied for designing two essential open channels which can preserve the pit.

Modeling Nakagami Fading channel in Underwater wireless sensor network using Stochastic Network Calculus

Underwater acoustic communication is growing famously day to day because of its important in many applications like offshore search, underwater search. In UWNS while signal is transmitting source to destination the signals are suspected by fading and noise. The QoS guarantees like small backlog, low packet delay are need to be in good condition for Real-time applications. Important role of this designing is Performance evaluation. Analytical models constructed by using (a) queuing theory, (b) effective bandwidth, and (c) deterministic network calculus. These were not adequate to sustain and assess the present packet switched networks. Stochastic Network Calculus is the solution for these issues. The SNC tool can be used to model and network performance assessment, especially for UWSN. In this paper, we have developed an underwater acoustic channel that is subjected to Nakagami fading channel based on SNC to arrive at Stochastic Arrival Curve and Stochastic Service Curve. Backlog bound and delay bounds stochastic performance are derived by using this model.

Spatial Resolution Effect of Remotely Sensed Data on Flood Hydrograph Simulation

The objective of this study is to compare the effect of different spatial resolution of satellite images (Landsat-8, Sentinel-2 and Gaofen-1) for deriving LULC map and its effects on the performance of HEC-HMS lumped and Flood Hydro distributed models in flood hydrograph simulation in the Ammameh Watershed, Iran. The Soil Conservation Service Curve Number method was used for considering the rainfall loss rate in both models. The value of curve number was determined based on hydrologic soil groups and produced LULC maps from the satellite images with respect to soil moisture conditions. The performance of HEC-HMS lumped and Flood Hydro distributed models in flood hydrograph simulation was evaluated for 15 and five rainfall-runoff events, respectively. The simulation results of flood hydrographs in validation phase showed that both models provided acceptable results, and there were no significant differences among the results of three remotely sensed images for simulating the flood hydrographs.

Optimization of Impervious Surface Space Layout for Prevention of Urban Rainstorm Waterlogging: A Case Study of Guangzhou, China.

With the rapid expansion of impervious surfaces, urban waterlogging has become a typical “urban disease” in China, seriously hindering the sustainable development of cities. Therefore, reducing the impact of impervious surfaces on surface runoff is an effective approach to alleviate urban waterlogging. Presently, the development mode of many cities in China has shifted from an increase in urban scale to the improvement of urban quality through urban renewal, which is the current and future development path for most cities. Optimizing the design of impervious surfaces in urban renewal planning to reduce its impact on surface runoff is an important way to prevent and control urban waterlogging. The aim of this research is to construct an optimization model of impervious surface space layout under the framework of a geographic simulation technology-integrated ant colony optimization (ACO) and Soil Conservation Service curve number (SCS-CN) model (ACO-SCS) in a case study of Guangzhou in China. Urban runoff plots in the study area are divided according to the area of the urban planning unit. With the goal of minimizing the runoff coefficient, the optimal space layout of the impervious surfaces is obtained, which provides a technical method and reference for urban waterlogging prevention and control through urban renewal planning. The results reveal that the optimization of impervious surface space layout through ACO-SCS achieves a satisfactory effect with an average optimization rate of 9.52%, and a maximum optimization rate of 33.16%. The research also shows that the initial impervious surface layout is the key influencing factor in ACO-SCS. In the urban renewal planning stage, the space layout of the impervious surfaces with a high–low–high density discontinuous connection can be constructed by transforming medium-density impervious surfaces into low-density impervious surfaces to achieve the flat and long-type agglomeration of the low-density and high-density impervious surfaces, which can effectively reduce the influence of urban development on surface runoff. There is spatial heterogeneity of the optimal results in different urban runoff plots. Therefore, the policy of urban renewal planning for urban waterlogging prevention and control should be different. The optimized results of impervious surface space layout provide useful reference information for urban renewal planning.

Runoff Harvesting Site Suitability Analysis for Wildlife in Sub-Desert Regions

Site selection for runoff harvesting at large scales is a very complex task. It requires inclusion and spatial analysis of a multitude of accurately measured parameters in a time-efficient manner. Compared with direct measurements of runoff, which is time consuming and costly, a combination of a Geographic Information System (GIS) and multi-criteria techniques have proven feasible to address this challenge. Although the accuracy of this new approach is lower than the direct method, conducting in-situ measurements over large scales is not feasible due to its financial issues, a lack of sufficient human resources, and time limitations. To achieve this purpose, climatic, topographic, and soil parameters were used to estimate a runoff coefficient and volume for a single event with the 33%-exceedance probability of maximum daily rainfall in the Kavir National Park of Iran. The main challenges ahead of this research have been a) the large area of the park and the inability to directly evaluate site suitability for runoff harvesting, b) the need for a quick and reliable site evaluation to implement water harvesting measures to address water scarcity, and c) the lack of discharge volume data from water streams (as there are no permanent water streams in the site) and the necessity of reliably estimating runoff in different parts of the park to design water harvesting structures which have been addressed by using GIS and a rainfall-runoff model (Soil Conservation Service Curve Number (SCS-CN)). Site suitability was evaluated for the natural territory of two important wildlife species of the park, namely Gazella dorcas and Ovis orientalis, as the main important food sources of an endangered species named Acinonyx jubatus, commonly known as Persian Cheetah. Saving Persian Cheetah from extinction is currently the top priority for the park managers, which is the main factor behind the species chosen for this research. The Analytic Hierarchical Process (AHP) and fuzzy membership functions were employed to assign weights and standardized thematic layers, respectively. The layers were then integrated using the weighted linear combination method (WLC) to obtain the final suitability map. Accordingly, 38% of the area (846 km2) is suitable or highly suitable for runoff harvesting, while 62% (2623 km2) has a very low potential for this purpose. Afterward, 11 suitable locations were identified to collect runoff. The results indicated that suitable catchments are mainly located on the southern slopes of the Mount Siahkouh as the only major elevation in the area. The storage capacity of the earth embankment in each catchment was estimated based on the upstream area of the catchment and runoff volume. Based on the population of the intended wildlife species and their average water requirement, there is a need for 6500 m3 of drinking water annually. In the best-case scenario and under the circumstance of receiving five rainstorm events a year, only 257 m3 is collectible from all runoff harvesting structures, which is only 4% of the total water demand.

Improved Credit Bounds for the Credit-Based Shaper in Time-Sensitive Networking

In Time-Sensitive Networking (TSN), it is important to formally prove per flow latency and backlog bounds. To this end, recent works apply network calculus and obtain latency bounds from service curves. The latency component of such service curves is directly derived from upper bounds on the values of the credit counters used by the Credit-Based Shaper (CBS), an essential building-block of TSN. In this paper, we derive and formally prove credit upper bounds for CBS, which improve on existing bounds.

A procedure for designing natural water retention measures in new development areas under hydraulic-hydrologic invariance constraints

AbstractIn recent years, in Italy and elsewhere, regional regulations based on hydraulic-hydrologic invariance (HHI) principles have taken hold, especially for new development areas. Natural water retention measures (NWRMs) are among the most interesting options to provide the storage and infiltration capacities that are needed to achieve the HHI objectives. A procedure for the design of NWRMs in new development areas under HHI constraints is presented and is based on a simple combination of Soil Conservation Service Curve Number (SCS-CN) method for determining rainfall excess and lag-time method for simulating runoff propagation. Three types of NWRMs can be considered: rain barrels, drainage wells and drainage trenches; five types of synthetic hyetographs can be selected and three different approaches for the determination of critical storm duration applied. The results obtained by applying the procedure in a new development area located in northern Italy are illustrated and some general conclusions are drawn. It clearly emerges that practitioners should pay particular attention to the correct determination of design storm duration in order to avoid large underestimations of NWRMs size. Moreover, different combinations of the three NWRMs can provide the required reduction of peak of runoff after the transformation, but it appears that drainage trenches are more effective with respect to harvesting systems in reducing the peak runoff value.

Statistical delay bounds for automatic repeat request protocols with pipelining

The recent trend towards low-latency wireless communication requires a notion of non-ergodic capacity that deals with delays. Significant research has contributed such results for relevant physical layer aspects. Less attention has been paid to actual implementations of link layer automatic repeat request protocols. Instead, error-free transmission using instantaneous channel state information, simple stop-and-wait protocols, or instantaneous feedback are frequently assumed. In this work, we investigate protocols with pipelining that deal with packet errors under non-negligible round-trip-times. We define a stochastic service curve model of a general class of automatic repeat request protocols with pipelining and derive statistical waiting time and sojourn time bounds. We discover two regimes: under low to moderate load retransmissions cause the largest part of the sojourn time, whereas under high load the waiting time dominates the sojourn time. Generally, with increasing round-trip-time the basic cases of stop-and-wait protocols or instantaneous feedback neglect relevant effects and provide less accurate estimates.

A Long–Term Response-Based Rainfall-Runoff Hydrologic Model: Case Study of The Upper Blue Nile

This study develops a response-based hydrologic model for long-term (continuous) rainfall-runoff simulations over the catchment areas of big rivers. The model overcomes the typical difficulties in estimating infiltration and evapotranspiration parameters using a modified version of the Soil Conservation Service curve number SCS-CN method. In addition, the model simulates the surface and groundwater hydrograph components using the response unit-hydrograph approach instead of using a linear reservoir routing approach for routing surface and groundwater to the basin outlet. The unit-responses are Geographic Information Systems (GIS)-pre-calculated on a semi-distributed short-term basis and applied in the simulation in every time step. The unit responses are based on the time-area technique that can better simulate the real routing behavior of the basin. The model is less sensitive to groundwater infiltration parameters since groundwater is actually controlled by the surface component and not the opposite. For that reason, the model is called the SCHydro model (Surface Controlled Hydrologic model). The model is tested on the upper Blue Nile catchment area using 28 years daily river flow data set for calibration and validation. The results show that SCHydro model can simulate the long-term transforming behavior of the upper Blue Nile basin. Our initial assessment of the model indicates that the model is a promising tool for long-term river flow simulations, especially for long-term forecasting purposes due to its stability in performing the water balance.

An Event-Based Sediment Yield and Runoff Modeling Using Soil Moisture Balance/Budgeting (SMB) Method

The Soil Conservation Service Curve Number (SCS-CN) method is frequently used for the estimation of direct surface runoff depth from the small watersheds. Coupling the SCS-CN method with the Soil Moisture Balance (SMB) method, new simple 2-parameters rainfall-runoff model and 3-parametrs rainfall-sediment yield models are derived for computation of runoff and sediment yield respectively. The proposed runoff (R2) and sediment yield (S2) models have been tested on a large set of rainfall-runoff and sediment yield data (98 storm events) obtained from twelve watersheds from different land use/land cover, soil and climatic conditions. The improved runoff (R2) and sediment yield (S2) models show superior results as compared to the existing Mishra et al. (S1) and original SCS-CN (R1) models. The results and analysis justify the use of the proposed models for field applications.

Assimilation of Satellite-Based Data for Hydrological Mapping of Precipitation and Direct Runoff Coefficient for the Lake Urmia Basin in Iran

Water management in arid basins often lacks sufficient hydro-climatological data because, e.g., rain gauges are typically absent at high elevations and inflow to ungauged areas around large closed lakes is difficult to estimate. We sought to improve precipitation and runoff estimation in an arid basin (Lake Urmia, Iran) using methods involving assimilation of satellite-based data. We estimated precipitation using interpolation of rain gauge data by kriging, downscaling the Tropical Rainfall Measuring Mission (TRMM), and cokriging interpolation of in-situ records with Remote Sensing (RS)-based data. Using RS-based data application in estimations gave more precise results, by compensating for lack of data at high elevations. Cokriging interpolation of rain gauges by TRMM and Digitized Elevation Model (DEM) gave 4–9 mm lower Root Mean Square Error (RMSE) in different years compared with kriging. Downscaling TRMM improved its accuracy by 14 mm. Using the most accurate precipitation result, we modeled annual direct runoff with Kennessey and Soil Conservation Service Curve Number (SCS-CN) models. These models use land use, permeability, and slope data. In runoff modeling, Kennessey gave higher accuracy. Calibrating Kennessey reduced the Normalized RMSE (NRMSE) from 1 in the standard model to 0.44. Direct runoff coefficient map by 1 km spatial resolution was generated by calibrated Kennessey. Validation by the closest gauges to the lake gave a NRMSE of 0.41 which approved the accuracy of modeling.

SCS Curve Number and Green-Ampt Infiltration Models

AbstractSoil Conservation Service curve number (SCS-CN) and Green-Ampt (GA) infiltration models are probably the most applied equations in practical hydrology to compute the amount of direct runoff...

Revisiting SWAT as a Saturation-Excess Runoff Model

The Soil Water Assessment Tool (SWAT) is employed throughout the world to simulate watershed processes. A limitation of this model is that locations of saturation excess overland flow in hilly and mountainous regions with an impermeable layer at shallow depth cannot be simulated realistically. The objective of this research is to overcome this limitation with minor changes in the original SWAT code. The new approach is called SWAT-with-impervious-layers (SWAT-wil). Adaptations consisted of redefining the hillslope length, restricting downward percolation from the root zone, and redefining hydrologic response units (HRUs) such that they are associated with the landscape position. Finally, input parameters were chosen such that overland flow from variable saturated areas (VSAs) corresponds to the variable source interpretation of the Soil Conservation Service (SCS) curve number runoff equation. We tested the model for the Town Brook watershed in the Catskill Mountains. The results showed that the discharge calculated with SWAT-wil agreed with observed outflow and results simulated with the original SWAT and SWAT-hillslope (SWAT-HS) models that had a surface aquifer that transferred water between groups of HRUs. The locations of the periodically saturated runoff areas were predicted by SWAT-wil at the right locations. Current users can utilize the SWAT-wil approach for catchments where VSA hydrology predominates.

ANN-SCS-based hybrid model in conjunction with GCM to evaluate the impact of climate change on the flow scenario of the River Subansiri

Abstract The River Subansiri, one of the largest tributaries of the Brahmaputra, makes a significant contribution towards the discharge at its confluence with the Brahmaputra. This study aims to investigate an appropriate model to predict the future flow scenario of the river Subansiri. Two models have been developed. The first model is an artificial neural network (ANN)-based rainfall-runoff model where rainfall has been considered as the input. The future rainfall of the basin is calculated using a multiple non-linear regression-based statistical downscaling technique. The proposed second model is a hybrid model developed using ANN and the Soil Conservation Service (SCS) curve number (CN) method. In this model, both rainfall and land use/land cover have been incorporated as the inputs. The ANN models were run using time series analysis and the method selected is the non-linear autoregressive model with exogenous inputs. Using Sen's slope values, the future trend of rainfall and runoff over the basin have been analyzed. The results showed that the hybrid model outperformed the simple ANN model. The ANN-SCS-based hybrid model has been run for different land use/land cover scenarios to study the future flow scenario of the River Subansiri.

A Channel and Queue-Aware Scheduling for the LTE Downlink Based on Service Curve and Buffer Overflow Probability

In this letter, we propose a joint channel and queue-aware resource block allocation algorithm for the long-term evolution (LTE) downlink based on buffer overflow probability estimation. To this end, we first derive an equation for the buffer overflow probability bound. Furthermore, we propose a novel service curve in order to estimate maximum delay for LTE system users considering the Effective exponential signal-to-noise ratio mapping to the SNR values of the LTE sub-bands. Simulation results reveal that in general, compared to other approaches, the proposed scheduling algorithm provides lower delay and buffer overflow rate while maximizing throughput.

An Integrated Hydrological-CFD Model for Estimating Bacterial Levels in Stormwater Ponds

A hydrological model was integrated with a computational fluid dynamics (CFD) model to determine bacteria levels distributed throughout the Inverness stormwater pond in Calgary, Alberta. The Soil Conservation Service (SCS) curve number model was used as the basis of the hydrological model to generate flow rates from the watershed draining into the pond. These flow rates were then used as input for the CFD model simulations that solved the Reynolds-Averaged Navier-Stokes (RANS) equations with k-ɛ turbulence model. E. coli, the most commonly used fecal indicator bacteria for water quality research, was represented in the model by passive scalars with different decay rates for free bacteria and attached bacteria. Results show good agreement with measured data in each stage of the simulations. The middle of the west wing of the pond was found to be the best spot for extracting water for reuse because it had the lowest level of bacteria both during and after storm events. In addition, only one of the four sediment forebays was found efficient in trapping bacteria.

Flash flood schlep ability estimation in vertical distribution law of the precipitation area: a case of Xulong gully, Southwest China

This study focused on the influence of rainfall vertical distribution on the flood schlep ability of Xulong gully, located upstream of Jinsha River. The mountain precipitation vertical distribution formula (MPVDF) was employed to fit the rainfall data, the Soil Conservation Service curve number (SCS-CN) method to calculate the runoff and the isochrone method to calculate the flood peak flow. In addition, the maximum diameter of the gravel transported by flood is used to evaluate the flood schlep ability. The calculation results of the traditional method (TM) and inverse distance weighting (IDW) are also used for comparison. The results show that the maximum error of fitting for rainfall data is 11.58% and the maximum error of the calculated peak flow compared with the calculation of the morphological survey method (MSM) is 3.66%, which highlights MPVDF as more appropriate for the catchments in which the precipitation follows a significant vertical distribution law. The results of the maximum diameter of the gravel transported by flood of MPVDF, TM and IDW were 86 cm, 66 cm and 69 cm, respectively, which means the rainfall vertical distribution has great influence on the schlep ability of flood.

Characteristics of impervious surface and its effect on direct runoff: a case study in a rapidly urbanized area

Abstract In recent years, many cities have experienced serious urban flood and non-point pollution issues due to hydrological process changes in rapidly urbanizing areas. Understanding the relationship between impervious surface and direct runoff is important for urban planning to protect the urban hydrological system. In this study, we used a mixed spectral decomposition method to interpret the long-term series of impervious surface of Shenyang, China. Direct runoff was evaluated by an improved SCS-CN (Soil Conservation Service curve number) model, and the relative influences of five underlying surface factors on the direct runoff of each period were analyzed by boosted regression trees. The overall impervious area was significantly increased in both the study area and built-up area from 1984 to 2015. The impervious ratio showed a decreasing trend in the built-up area and increasing trend in the whole study area. The runoff coefficient of the built-up area showed a significantly decreasing trend. The runoff ratio of the built-up area to the whole study area was increased dramatically, reaching 0.26 by 2015. NDVI (normalized distribution vegetation index), vegetation, and impervious surface were the most important urban surface conditions in the study area for direct runoff generation. The relative influence of impervious surface showed a rapidly increasing trend and then gradually decreased from 2000.