Service Curve Number Method Research Articles

VEGETATION AND LAND USE ANALYSIS FOR RUNOFF ESTIMATION IN SMALL FORESTED CATCHMENT: A CASE STUDY OF TAJOVSKÝ BROOK IN SLOVAKIA

Flash floods have been in the centre of attention for numerous hydrological studies recently and their magnitude and frequency are projected to increase due to the changing climate. This is especially important in small catchments where a local storm event can cause rapid increase in damage causing discharges. To estimate the possible impacts of a rainfall event, it is necessary to understand the precipitation/runoff conditions. Soil Conservation Service Curve Number (SCS CN) method is widely used and discussed to estimate the effect of land cover and soil moisture conditions on runoff. In this paper, we implement this standard method in the Tajovský brook catchment in Central Slovakia. The individual land cover classes were identified, and weighted CN numbers were established. Forest accounted for 67% of the entire area, grasslands for 19% and built-up areas for 10%. The final CNII number was computed as 60.8. Seven initial abstraction ratio values were tested on a monthly hydrograph data and optimal value was set to 0.01. This suggests the possible most suited regional value of the abstraction ratio that could be used for this type of small (<50 km) forested catchments, but further testing on other catchments and precipitation events would be beneficial.

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.

A spatially distributed Clark’s unit hydrograph based hybrid hydrologic model (Distributed-Clark)

ABSTRACTA hybrid hydrologic model (Distributed-Clark), which is a lumped conceptual and distributed feature model, was developed based on the combined concept of Clark’s unit hydrograph and its spatial decomposition methods, incorporating refined spatially variable flow dynamics to implement hydrological simulation for spatially distributed rainfall–runoff flow. In Distributed-Clark, the Soil Conservation Service (SCS) curve number method is utilized to estimate spatially distributed runoff depth and a set of separated unit hydrographs is used for runoff routing to obtain a direct runoff flow hydrograph. Case studies (four watersheds in the central part of the USA) using spatially distributed (Thiessen polygon-based) rainfall data of storm events were used to evaluate the model performance. Results demonstrate relatively good fit to observed streamflow, with a Nash-Sutcliffe efficiency (ENS) of 0.84 and coefficient of determination (R2) of 0.86, as well as a better fit in comparison with outputs of spatially averaged rainfall data simulations for two models including HEC-HMS.

Runoff Depth Estimation using SCS-CN Method in Jhargram Community Development Block - A Remote Sensing and Geographic Information System Approach

Jhargram Community Development blocks which is situated on a watershed divider of Kansabati river basin and Dulung river basin. At a glance the area is suffering for water resource in some of the major parts. Surface runoff is one of the most important indicators of surface water availability, ground water recharge, soil practice etc. In this regard, estimation of runoff is highly needed for water resource planning, management and environment impact analysis. And Geographical Information System (GIS) and Remote Sensing (RS) techniques are used to calculate the runoff depth, it is one of the most time consuming way in recent days. The US Department of Agriculture (USDA), Soil Conservation Service Curve Number (SCS-CN) method which is the most widely used method is very effective in this study. In fact, the model is a quantitative description of land use-land cover and soil complex characteristics of a watershed and their impact on surface water flow. ERDAS Imagine 2014 and ArcGIS 10.1 are the platform which generate the input maps like sub watershed & micro watershed delineation, drainage map, soil map & hydrological soil map, classification of land use/ land cover, elevation & slope map, Rainfall map, area calculation for each class. The rainfall map is prepared from the rainfall data of different stations. After sequentially used the equations of SCS-Curve Number method the different years from 2010 to 2014, the final prioritization map has been generated which shows the value of runoff depth from high to low. Similarly, there has been shown the runoff-rainfall relationship over the last five years. Wherever the runoff depth is high, the infiltration rate is low due to soil and slope. With seeing the results of this case study, this can be used for further management of water resources as well as water scarcity of this area.

Influence of coarse soils with high hydraulic conductivity on the applicability of the SCS-CN method

ABSTRACTThe impact of the existence of coarse soils with high hydraulic conductivity on the applicability of the Soil Conservation Service curve number (SCS-CN) method is investigated in a heterogeneous catchment in the Zagros mountain region, southwest Iran. The findings indicate that curve numbers (CN) decline steadily as rainfall depths increase, showing no evidence of reaching stable CN values. This is attributed to a small low permeability area in the catchment, although most parts of the region are covered by high to very high permeability soils. Although this behaviour has been attributed mainly to forested areas by some researchers, it is shown here that it can be observed in mountain regions with coarse soils. The results also reveal that a linear rainfall–runoff formula of the form Q = CP provides more accurate results than the SCS-CN method, and the runoff coefficient (C) can be taken as equal to the low-permeability area fraction, meaning that these parts can be considered to be the main runoff-producing areas.

Effectiveness of BIOECODS for peak flow attenuation: an appraisal using InfoWorks SD

ABSTRACTThe Bio-Ecological Drainage System (BIOECODS) is a sustainable drainage system, which adopts a “control at source” approach for urban storm water management in Malaysia. This study attempts to model a small-scale BIOECODS using InfoWorks SD. New modelling techniques are used to fully integrate the surface and on-line subsurface conveyance system, in which overland flow routing is described by a storm water management model that uses a nonlinear reservoir method and the kinematic wave approximation of the St Venant equation, and subsurface flow is described by the Horton method in conjunction with the Soil Conservation Service (SCS) curve number (CN) method. The observed water levels at primary outlets are compared with those obtained from model simulation. The modelling approach has been proven successful as the hydrographs (predicted and observed) match each other closely, with a mean error in the range of 4.58–7.32%. Results from the model showed that the BIOECODS is able to attenuate peak flow by 60–75%, and increase the lag time by 20 min within an area of <28 300 m2 when compared with a traditional drainage system.

HYDROLOGICAL MODELLING OF UNGAUGED ARID VOLCANIC ENVIRONMENTS AT UPPER BATHAN CATCHMENT, MADINAH, SAUDI ARABIA

Hydrological modelling of ungauged catchments is still a challenging task especially in arid regions with a unique land cover features such as highly fracture volcanic basalt rocks. In this study, upper Bathan catchment (103 km2) in Madinah, western of Saudi Arabia is selected. The aim of this paper is to simulate the hydrological responses of volcanic catchment to daily design storm events. The weighted areal average of two daily design rainfall depth scenarios are computed, which are 50 years and 100 years return period and correspondent predicted rainfall are 80.6 mm and 94.1 mm, respectively. SCS Type II temporal synthetic distribution of daily rainfall is selected to disaggregate the daily rainfall into smaller time interval. Excess rainfall is computed using Soil Conservation Services Curve Number (SCS-CN) method based on Land Cover and Land Use (LCLU) and hydrological soil groups (HSG) maps, while direct runoff hydrograph is developed using Soil Conservation Services dimensionless unit hydrograph (SCS-UH) method using lag time equation. HEC-HMS software is used, and it showed that the runoff volumes of the two rainfall scenarios are 50% and 54% of the total rainfall depth, and the peak discharges are 123 m3/sec and 158 m3/sec. This study provided an indication of the hydrograph characteristics of basaltic catchments and the result of this paper can be used for further flood studies in arid ungauged volcanic catchments.

Investigating practical alternatives to the NRCS-CN method for direct runoff estimation using slope-adjusted curve numbers

The Natural Resources Conservation Service (NRCS) Curve Number (CN) method is generally applied to estimate direct runoff from watersheds. However, its utility in estimating direct runoff in South Korean watersheds is limited due to steep slopes, shallow soil layers, less infiltration losses and sudden peak flow generation. The CN is the primary parameter used in the method and varies with watershed characteristics and measured rainfall runoff data. In this study, we evaluated the performance of NRCS-CN models employing weighted average CNs and watershed slope-adjusted CNs. Furthermore, various combinations of alternatives were investigated to determine the proper watershed average CN. Direct runoff was estimated using different CN approaches and these estimates were compared to the observed values. The results obtained in this study indicated that the slope-adjusted CNs were higher than the NRCS tabulated CNs. Similarly, the Weighted Runoff (WQ) method provided higher runoff estimates than the weighted CN (WCN) method. In conclusion, the runoff estimated using the combination of the WQ method and slope-adjusted CNs showed better agreement with the observed direct runoff compared to other methods.

Evaluating the Accuracy of Common Runoff Estimation Methods for New Impervious Hot-Mix Asphalt

AbstractAccurately predicting runoff volume from impervious surfaces for water quality design events is an important step to meet water quality and infiltration design targets for green infrastructure stormwater control measures. The objectives of this research were to quantify abstraction from a recently paved impervious hot-mix asphalt (HMA) parking lot surface and evaluate the accuracy in modeling runoff volume from small events using the following runoff estimation methods: the Soil Conservation Service Curve Number (SCS-CN) method, the Simple Method (SM), and the Small Storm Hydrology Method (SSHM). A 4,000 m2 (0.4-ha) parking lot in Edison, New Jersey, was designed with impervious HMA driving lanes evenly draining onto parking lanes constructed with permeable pavement. Ten lined permeable pavement sections that capture all infiltrating water and route it to collection tanks were included in this study. Using a water balance approach on an event basis, the measured infiltrate volume was compared to ...

Evaluation of Three Models for Simulating Pesticide Runoff from Irrigated Agricultural Fields.

Three models were evaluated for their accuracy in simulating pesticide runoff at the edge of agricultural fields: Pesticide Root Zone Model (PRZM), Root Zone Water Quality Model (RZWQM), and OpusCZ. Modeling results on runoff volume, sediment erosion, and pesticide loss were compared with measurements taken from field studies. Models were also compared on their theoretical foundations and ease of use. For runoff events generated by sprinkler irrigation and rainfall, all models performed equally well with small errors in simulating water, sediment, and pesticide runoff. The mean absolute percentage errors (MAPEs) were between 3 and 161%. For flood irrigation, OpusCZ simulated runoff and pesticide mass with the highest accuracy, followed by RZWQM and PRZM, likely owning to its unique hydrological algorithm for runoff simulations during flood irrigation. Simulation results from cold model runs by OpusCZ and RZWQM using measured values for model inputs matched closely to the observed values. The MAPE ranged from 28 to 384 and 42 to 168% for OpusCZ and RZWQM, respectively. These satisfactory model outputs showed the models' abilities in mimicking reality. Theoretical evaluations indicated that OpusCZ and RZWQM use mechanistic approaches for hydrology simulation, output data on a subdaily time-step, and were able to simulate management practices and subsurface flow via tile drainage. In contrast, PRZM operates at daily time-step and simulates surface runoff using the USDA Soil Conservation Service's curve number method. Among the three models, OpusCZ and RZWQM were suitable for simulating pesticide runoff in semiarid areas where agriculture is heavily dependent on irrigation.

Assessment of Surface Runoff from Sub Basin of Kodayar using NRCS CN model with GIS

Objectives: To estimate the runoff from the sub basin of Kodayar, Tamilnadu using Natural Resources Conservation Service Curve Number (NRCS-CN) method with GIS and Remote sensing techniques. Methods: The GIS and remote sensing techniques facilitate accurate estimation of surface runoff from watershed. Thematic maps such as soil map, land use and hydrologic soil group (HSG) maps have been generated with GIS environment. Weighted CN value for the basin was obtained and the runoff for the selected rainfall event was estimated. Findings: In the HSG map, the region predominantly comprises of group B (56%) followed by group C (27.4%), group D (12.4%) and A (3.9%) respectively. In order to calculate the CN value of the basin, it is divided into 12 sub basins of which each sub basin has area less than 150km2 which gives more accurate result than considering the whole basin. The CN values for these 12 sub basins are ranging from 69 to 80. Composite curve number value for each sub-basin was calculated by multiplying weights according to the area occupied by each land use class and the corresponding curve number. Weighted CN value and the storage retention (S) for the entire basin are estimated as 75 and 85 respectively. Runoff values are estimated on four different rainfall events selected during the study period in this basin. Conclusion: The study ultimately leads to the development of the rainfall runoff model based on NRCS-CN-GIS technique. The runoff for any rainfall event occurred can be estimated by feeding the inputs into this corresponding model which would in turn be helpful on significant conservation of water in the study area.

Soil loss estimation through MUSLE using Kirpich and Williams times of concentration using RS and GIS techniques: a case study

Water is one of the most vital requirements for sustenance of life. Water, along with soil, is the most essential natural resource for economic and social development. A study of soil and water dynamics at a watershed level can facilitate a scientific approach toward their conservation and management. The present study is an attempt to apply the Modified Universal Soil Loss Equation (MUSLE) along with the Soil Conservation Service Curve Number (SCS-CN) method for runoff estimation and comparison of soil loss estimates for the catchments of Baindur Hole and Yedamavina Hole in the Udupi District of Karnataka State, India, obtained by times of concentration calculated by the Kirpich equation and the Williams equation. The base map and thematic maps were prepared using Indian Remote Sensing satellite 1C (IRS-1C) LISS-III (Linear Imaging Self-Scanning Sensor) image for land use/land cover and from Survey of India topo sheet in a GIS environment for overlaying and extraction of results. The time of concentration estimated by the Kirpich formula is lower in all cases; hence, the corresponding soil loss is 1.4 times higher than that determined with Williams formula. Catchments 23 and 17 with a lower drainage length show comparatively higher values of soil loss in case of the Williams equation, which can be attributed to the greater importance of drainage length in the equation.

KIRPICH AND WILLIAMS TIMES OF CONCENTRATION IN MUSLE: A CASE STUDY

ABSTRACT Water is one of the most vital requirements for sustenance of life. Water, along with soil, forms the combination of the most essential natural resource for economic and social development. A study of soil and water dynamics at a watershed level can facilitate a scientific approach to a conservation and management plan for them. The present study is an attempt to implement Modified Universal Soil Loss Equation (MUSLE) using Soil Conservation Service Curve Number (SCS-CN) method for runoff estimation and comparison of soil loss results for the catchments of Baindur Hole and Yedamavina Hole in Udupi district of Karnataka state obtained by times of concentration calculated by the Kirpich equation and the Williams equation. Preparation of base map and thematic maps was carried out using IRS-1C, LISS-III image for LU/LC and from SOI toposheet in a GIS environment for overlaying and extraction of results. The time of concentration estimated by the Kirpich formula is lower in all cases; hence the corresponding soil loss is higher by 1.4 times in comparison to Williams' formula. The catchments 23 and 17 with a lower drainage length show comparatively higher values of soil loss in case of the Williams equation which can be attributed to the higher importance given to drainage length in the equation.

Rainfall-Runoff Modeling: Comparison of Two Approaches with Different Data Requirements

Among several hydrological models developed over the years, the most widely used technique for estimating direct runoff depth from storm rainfall i.e., the United States Department of Agriculture (USDA) Soil Conservation Service’s (SCS) Curve Number (CN) method was adopted in the present study. In addition, the Muskingum method, which continues to be popular for routing of runoff in river network, was used in the developed model to route surface runoffs from different subbasin outlet points up to the outlet point of the catchment. SCS CN method in combination with Muskingum routing technique, however, required a detailed knowledge of several important properties of the watershed, namely, soil type, land use, antecedent soil water conditions, and channel information, which may not be readily available. Due to this complexity of semi-distributed conceptual approach (SCS CN method) and non-linearity involved in rainfall-runoff modeling, researchers also attempted another less data requiring approach for runoff prediction, i.e., the neural network approach, which is inherently suited to problems that are mathematically difficult to describe. The purpose of this study was to compare the rainfall-runoff modeling performance of semi-distributed conceptual SCS CN method (in combination with Muskingum routing technique) with that of empirical ANN technique. The models were coded in C language and to make them user friendly, a Graphical User Interface (GUI) was also developed in Visual Basic 6.0. The developed models were tested for Kangsabati catchment, situated in the western part of West Bengal, India. Monsoon data of 1996 to 1999 were used for calibration of the models whereas they were validated for another four years (1987, 1989, 1990, and 1993) monsoon data. Modeling efficiency (ME) and coefficient of residual mass (CRM) were used as performance indicators. Results indicated that for Kangsabati catchment, the empirical runoff prediction approach (ANN technique), in spite of requiring much less data, predicted daily runoff values more accurately than semi-distributed conceptual runoff prediction approach (SCS CN method).

Evaluation of NRCS curve number and MODIS time-series proxies for antecedent moisture condition

Soil moisture plays a vital role in a watershed's hydrologic response to a precipitation event. Soil moisture condition antecedent to an event in empirical runoff estimation models, such as the 5-day antecedent moisture model for natural resources conservation service (NRCS) curve number (CN) method, is generalised and spatially inexplicit. This study assesses the potential to parameterise a statistical streamflow estimation model utilising next generation weather radar (NEXRAD) precipitation records and time-series biophysical proxies for soil moisture from moderate resolution imaging spectroradiometer (MODIS) on board Terra satellite. This study is conducted on a 1420 km2 rural watershed in the Guadalupe River basin of southcentral Texas, a basin prone to catastrophic flooding from convective precipitation events. A least squares regression model, accounting for 83% of the variance of observed streamflow for calendar year 2004, was developed based on radar precipitation estimates, land surface temperature, and a vegetation index, on an 8-day interval. Estimated 8-day mean streamflows from the remote sensing model represented an improvement over CN modelled streamflows, developed with the standard and a continuum-based 5-day antecedent moisture condition model. Assessment of remotely sensed proxies of soil moisture has potential for complementing traditional CN method and for estimating streamflow in watersheds for which the CN or other empirical methods are limited by data constraints.

A generalized relation between initial abstraction and potential maximum retention in SCS‐CN‐based model

Soil Conservation Service curve number (SCS‐CN) method estimates direct surface runoff from given amount of rainfall. The initial abstraction coefficient (λ), which largely depends on the climatic conditions, is taken as a constant value of 0.2 in the method and it is perhaps the most ambiguous parameter to be considered for modification. Though the Mishra and Singh (MS) [14] model allows variation in λ and, in turn, initial abstraction Ia, it obviates its dependence on the antecedent moisture M. In fact, larger the antecedent moisture, lesser will be the initial abstraction, and vice versa. This study presents a modification to the initial abstraction (Ia)‐potential maximum retention (S) relationship of the existing SCS‐CN method and MS model for M. In an application to a large set of data from 84 small watersheds of U.S.A., the proposed modified model for varying λ is found to perform much better than the existing one and other considered variations. The proposed method advantageously obviates sudden jumps in the curve number with antecedent moisture condition, an unreasonable and undesirable feature of the existing SCS‐CN model. Finally, a better one‐parameter model is also suggested for field applications.

PCN BASED METAL PARTITIONING IN URBAN SNOWMELT, RAINFALL/RUNOFF, AND RIVER FLOW SYSTEMS1

ABSTRACT: Drawing an analogy between the popular Soil Conservation Service curve number (SCS‐CN) method based infiltration and metal sorption processes, a new partitioning curve number (PCN) approach is suggested for partitioning of heavy metals into dissolved and particulate bound forms in urban snowmelt, rainfall/runoff, and river flow environments. The parameters, the potential maximum desorption, ψ, and the PCN analogous to the SCS‐CN parameters S and CN, respectively, are introduced. Under the condition of snowmelt, PCN (or ψ) is found to generally rely on temperature, relative humidity, pH, and chloride content; during a rainstorm, ψ is found to depend on the alkalinity and the pH of the rainwater; and in the river flow situation, PCN is found to generally depend on the temperature, pH, and chloride content. The advantage of using PCN instead of the widely used partitioning parameter, Kd, is found to lie in the PCN's efficacy to distinguish the adsorption (or sorption) behavior of metals in the above snowmelt, rainfall/runoff, and river flow situations, analogous to the hydrological behavior of watersheds.

A Modified SCS-CN Method: Characterization and Testing

The Soil Conservation Service Curve Number (SCS-CN) method (SCS,1956) is modified by accounting for the static portion ofinfiltration and the antecedent moisture. A volumetric analysisshows that the ratio of the potential maximum retention (S) tothe precipitation amount versus the runoff factor relation isequivalent to the average suction pressure-moisture contentrelation for a unit rainfall amount and a given soil porosity. Asimple spreadsheet procedure is suggested for determining S withuse of a 5-day antecedent precipitation amount. The modifiedmethod is found to perform well on the same data sets as used inthe National Engineering Handbook (SCS, 1971).

Hydrologic response of a watershed to land use changes: a remote sensing and GIS approach

In the arid and semi-arid tropics, low annual rainfall together with high intensity rains has resulted in excess runoff, soil erosion and low moisture intake leading to poor crop yields. Therefore, adoption of soil and water conservation measures is necessary for the optimal utilization of natural resources and to increase the productivity of land on a sustainable basis. Remote sensing and GIS techniques can be used for generating development plans for the watershed area in consonance with the production potential and limitation of terrain resources, and can also be used for assessing the impact of these measures before actual implementation in the field. This paper describes a case study for the Jasdan taluka (district) of Rajkot in Gujarat, India. The aims are to prioritize watersheds on the basis of runoff generated, expressed as yield, due to existing land use conditions; to suggest soil and water conservation measures; and to evaluate the hydrologic response of these measures on runoff. The Soil Conservation Service Curve Number (CN) method was used for computing the runoff; subsequently runoff yield in percentage was calculated for prioritizing the watersheds. Satellite and other collateral data were used to identify the problems and potential in the watersheds and recommend measures for soil and water conservation. The impact of these measures was assessed by computing runoff under alternative land use and management practices. It was found that the runoff yield decreased by 42.88% of the pre-conservation value for the watershed.

Hydrologic response of a watershed to land use changes: A remote sensing and GIS approach

In the arid and semi-arid tropics, low annual rainfall together with high intensity rains has resulted in excess runoff, soil erosion and low moisture intake leading to poor crop yields. Therefore, adoption of soil and water conservation measures is necessary for the optimal utilization of natural resources and to increase the productivity of land on a sustainable basis. Remote sensing and GIS techniques can be used for generating development plans for the watershed area in consonance with the production potential and limitation of terrain resources, and can also be used for assessing the impact of these measures before actual implementation in the field. This paper describes a case study for the Jasdan taluka (district) of Rajkot in Gujarat, India. The aims are to prioritize watersheds on the basis of runoff generated, expressed as yield, due to existing land use conditions; to suggest soil and water conservation measures; and to evaluate the hydrologic response of these measures on runoff. The Soil Conservation Service Curve Number (CN) method was used for computing the runoff; subsequently runoff yield in percentage was calculated for prioritizing the watersheds. Satellite and other collateral data were used to identify the problems and potential in the watersheds and recommend measures for soil and water conservation. The impact of these measures was assessed by computing runoff under alternative land use and management practices. It was found that the runoff yield decreased by 42.88% of the pre-conservation value for the watershed.