Runoff Curve Number Method Research Articles

Estimating the runoff response from hillslopes treated with soil and water conservation structures in the semi-arid Ethiopian highlands: Is the curve number method applicable?

Planning and management of water resources is crucial to enhance agricultural productivity and ensure food security in drylands. For this, adaptable and reliable runoff prediction models are urgently needed to support water harvesting and irrigation development. In this study we explored the potential of the runoff Curve Number (CN) method to estimate daily surface runoff from representative land use types and management conditions in Tigray (north Ethiopia). For this, we use the National Engineering Handbook (NEH-Tables) to derive CN values for runoff plots treated with and without soil and water conservation (SWC) structures. Moreover, the rainfall-runoff data collected from 21 large (600–1000 m2) runoff plots during three years (2010 to 2012) were used to calculate CN-values. Results show that CN values derived from the NEH-Tables are larger by 21% compared to those values calculated from plot data. The calculated CN values vary widely (34 to 91) in response to land use type, slope gradient, and applied SWC structures. Our results show that land use and SWC structures strongly influence runoff production. Considering plots with otherwise similar characteristics, CN values are consistently larger for rangeland sites as compared to those values for cropland sites. Likewise, SWC structures greatly reduce runoff production and their presence also leads to a clearly lower performance of the CN model. The results of this study are relevant contributions towards addressing several goals of agenda 2063 of the African union either directly or indirectly and also international sustainable development goals (SDG). Based on our analysis and field observations, we propose calibrated CN values that may be used for runoff yield assessments in similar environments.

Identifying Potential Sites for Rainwater Harvesting Structures in Ghazi Tehsil, Khyber Pakhtunkhwa, Pakistan, Using Geospatial Approach

Rainwater harvesting is an important step towards maximizing the water availability and land productivity in arid and semi-arid areas. The present study shows that the area of Ghazi Tehsil within Khyber Pakhtunkhwa Province, Pakistan, has great potential for rainwater harvesting due to its feasible climatic and topographic conditions. This area of 348 km2 normally receives high rainfall annually, but, due to hilly terrain, the bulk of rainwater is lost in the runoff process. In order to enhance agricultural output for such a large area, the practice of rainwater harvesting is a sustainable and decisive approach. However, the selection of appropriate sites for rainwater harvesting on a large scale presents a critical challenge. In such areas, geospatial technology has proved very decisive in the identification of potential sites. In this study, we have used the HEC-GeoHMS tool (ArcGIS 9.3) to compute a curve number to represent the effects of rainfall against the hydrological soil group and landcover. Subsequently, the curve number was used as an input parameter in the soil conservation service runoff-curve number (SCS-CN) method to estimate surface runoff potential for different combinations of landcover and hydrological soil groups. It was observed that runoff was higher in mountainous areas and relatively low in plain areas. Finally, to identify the potential sites for rainwater harvesting, weighted overlay analysis-based related thematic map layers were further reclassified, and weights were assigned according to the technical guidelines of suggested international standards and under consideration of the study area’s topographic, hydrological, and climatic factors. As a result, about 20% of the area was found suitable, 52% less suitable, and 29% as not suitable. Furthermore, relative suitability was assigned to the results of suitable sites as an input for the identification of potential sites for different rainwater harvesting storage structures. These results show that 10% of the area was suitable for farm ponds, 5.74% for check dams, 21.5% for Nigarims, and 8.9% was found to be suitable for gully plugs. The comparison of our GIS-derived and field-based results spatially affirms that the analyzed results were agreeably overlaid in the context of spatial results for check dams, gully plugs, and Nigarims.

Determination of accurate baseline representation for three Central Iowa watersheds within a HAWQS-based SWAT analyses

Improving food systems to address food insecurity and minimize environmental impacts is still a challenge in the 21st century. Ecohydrological models are a key tool for accurate system representation and impact measurement. We used a multi-phase testing approach to represent baseline hydrologic conditions across three agricultural basins that drain parts of north central and central Iowa, U.S.: the Des Moines River Basin (DMRB), the South Skunk River Basin (SSRB), and the North Skunk River Basin (NSRB). The Soil and Water Assessment Tool (SWAT) ecohydrological model was applied using a framework consisting of the Hydrologic and Water Quality System (HAWQS) online platform, 40 streamflow gauges, the alternative runoff curve number method, additional tile drainage and fertilizer application. In addition, ten SWAT baselines were created to analyze both the HAWQS parameters (baseline 1) and nine alternative baseline configurations (considering the framework). Most of the models achieved acceptable statistical replication of measured (close to the outlet) streamflows, with Nash-Sutcliffe (NS) values ranging up to 0.80 for baseline 9 in the DMRB and SSRB, and 0.78 for baseline 7 in the NSRB. However, water balance and other hydrologic indicators revealed that careful selection of management data and other inputs are essential for obtaining the most accurate representation of baseline conditions for the simulated stream systems. Using cumulative distribution curves as a criterion, baselines 7 to 10 showed the best fit for the SSRB and NSRB, but none of the baselines accurately represented 20% of low flows for the DMRB. Analysis of snowmelt and growing season periods showed that baselines 3 and 4 resulted in poor simulations across all three basins using four common statistical measures (NS, KGE, Pbias, and R2), and that baseline 9 was characterized by the most satisfactory statistical results, followed by baselines 5, 7 and 1.

Statistical analysis of flash flood events for designing water harvesting systems in an extremely arid environment

AbstractA water harvesting system for research purposes has been established in the Lisan Peninsula of the Dead Sea in the middle of the Jordan Rift Valley, where no authorized guideline is available for designing water harvesting systems. Rainfall and runoff, which occurred as flash floods, were observed at the downstream end of a gorge with a 1.12 km2 barren catchment area from October 2014 through July 2019. Due to the extremely arid environment, runoff from the catchment is ephemeral, and the flash flood events can be clearly distinguishable from each other. Thirteen flash flood events with a total runoff volume of more than 100 m3 were successfully recorded during the five rainy seasons. Pearson and Spearman correlations between duration, total rainfall depths at two points, total runoff volume, maximum runoff discharge, bulk runoff coefficient, total variation in runoff discharge and maximum variation in runoff discharge of each flash flood event were examined, revealing no straightforward relationship between rainfall and runoff. The performance of the conventional SCS runoff curve number method was also deficient in reproducing any rainfall–runoff relationship. Therefore, probability distribution fitting was performed for each random variable, focusing on the lognormal distribution with three parameters and the generalized extreme value distribution. The maximum goodness‐of‐fit estimation turns out to be a more rational and efficient method in obtaining the parameter values of those probability distributions rather than the standard maximum likelihood estimation, which has known disadvantages. Results support the design of the water harvesting system and provide quantitative information for designing and operating similar systems in the future.

Data Construction and Spatiotemporal Trend Attribution of Runoff over the African Continent (1981–2016)

AbstractThe availability of streamflow records in Africa has been declining since the 1980s due to malfunctioning gauging stations and data collection failures. Africa also has insufficient hydrological information owing to the allocation of few resources to research efforts. Unreliable runoff datasets and large uncertainties in runoff trends due to climate change patterns and human activities are major challenges to water resource management in Africa. Therefore, this study aimed to improve runoff estimates and to assess runoff trend responses to climate change and human activities in Africa during 1981–2016. Using statistical methods, monthly gridded runoff datasets were generated for the period of 1981–2016 from a modified runoff curve number method calibrated with river discharge data from 535 gauging stations. According to the cross-validation results, the constructed runoff datasets comprised the Nash and Sutcliffe coefficients ranging from 0.5 to 1, coefficients of determination ranging from 0.5 to 1 and percent biases between ±25% for a large number of stations up to 73%, 80% and 91% of the 535 gauged catchments used as references. Analysis of runoff trend responses to climate change and human activities revealed that land cover change contributed more (72%) to the observed net runoff change (0.30%•a−1) than continental climate changes (28%). These contributions were results of cropland expansion rate of 0.46%•a−1 and a precipitation increase of 0.07%•a−1. The performance and simplicity of the statistical methods used in this study could be useful for improving runoff estimations in other regions with limited streamflow data data. The results of the current study could be important to natural resource managers and decision makers in terms of raising awareness of climate change adaptation strategies and agricultural land-use policies in Africa.

Estimation of initiation thresholds and soil loss from gully erosion on unpaved roads on China's Loess Plateau

AbstractGullies form easily on unpaved road surfaces during heavy rainstorms on China's Loess Plateau. The integrated effect of rainfall, topography, vegetation, land use, and other factors determines where and when gully erosion occurs; however, the mechanisms driving gully erosion on unpaved road surfaces need to be further understood. Repeated gully erosion on some roads during the storm season provides a good opportunity to better understand the mechanisms behind gully erosion. This article aimed to quantify the integrated threshold conditions required for gully initiation in terms of topography, event rainfall, and upslope land use, and to propose an event‐based model to predict the position and magnitude of road gully erosion. Rill and gully erosion on unpaved roads were investigated after an extreme rainstorm of 212.2 mm in 2017 and a regular rainstorm of 83.8 mm in 2018. A digital surface model (DSM) derived from unmanned aerial vehicle (UAV) images was used to analyze the road gradient (S) and upslope area (A). The runoff (QRS) of each road segment (RS) was estimated by the runoff curve number method. The results showed the following: (1) The mean and total gully volumes under the regular rainstorm were only 26.3% and 8.1% of those under the extreme rainstorm, respectively; (2) Gully formation on the surveyed roads under both the regular and the extreme rainstorm could be explained by the threshold relationship (S − 0.056)QRS3.363 ≥ 72.444; and (3) A non‐linear relationship between gully erosion in road segments and event runoff (QRS) and road gradient (S) was found, and was subsequently used to predict road gully erosion on an event basis.

Incorporating a rainfall intensity modification factor [formula omitted] into the [formula omitted]-[formula omitted] Relationship in the NRCS-CN method

The Natural Resources Conservation Service runoff curve number (NRCS-CN) method is widely used to simulate direct runoff, but the impact of rainfall intensity has not been considered. In this study, a rainfall intensity modification factor (γ) was incorporated into the Ia-S relationship of the NRCS-CN method, and the modified method (NRCS–CN–γ) was compared with the NRCS-CN method with λ = 0.2 and λ = 0.05 in three watersheds of the Walnut Gulch Experimental Watershed (WGEW). The results showed that for 2016–2018 period, the simulation performance of the NRCS–CN–γ method was close to the NRCS-CN (λ = 0.05) method and better than the NRCS-CN (λ = 0.2) method. When the new data (2009 data with high variance) was added, the significant improvement was observed by NRCS–CN–γ method with all the evaluation parameters being the best in the three watersheds, indicating a more adapted capability of the modified method with highly uneven rainfall intensities. The covariance between rainfall intensity and the simulated runoff were 19.01, 15.14, and 16.35 for the three methods, respectively. When the optimal CN changed, the relative errors representing CN sensitivity were 6.25, 6.49 and 17.39 for the methods, respectively. It is suggested that the NRCS–CN–γ method outperformed the other two methods and could contribute to a more accurate estimation of direct runoff where rainfall intensity greatly varied, especially in monsoon region or under the context of climate change.

RUNOFF ESTIMATION USING SCS RUNOFF CURVE NUMBER METHOD IN CEBU ISLAND

Abstract. Cebu, with its growing development and increasing demand for water, needs tools and inputs to efficiently understand and manage its water resources. Rainfall runoff models were developed to model surface runoff which may be used to assess water availability. Soil Conservation System (SCS) Runoff Curve Number (CN) method predicts runoff based on an empirical curve number for ungauged watersheds. This study aims to estimate the amount of runoff for the catchments of Cebu Island using the SCS-CN Runoff technique. The data needed for the application of the method in this study were rainfall distribution data, land use/land cover and soil texture for curve number assignment, LiDAR DEM for the delineation of the catchments, and supporting runoff measurements from a different runoff estimation model for assessment of the results. The collected data were prepared by assigning the mean statistics of the rainfall distribution and the composite curve number for each catchment using Geographic Information System (GIS). The calculation of the runoff was also done using the same framework. Maps representing Cebu Island’s catchments’ runoff estimates were produced. Since observed runoff data were unavailable, the results were verified by comparing the SCS-CN estimated runoff to the results of a physically-based distributed hydrologic and hydraulics modelling software, FLO-2D. The SCS-CN estimations were found to coincide with the FLO-2D runoff estimates based on various statistical assessments. Although the results may have higher uncertainties due to the unavailability of observed runoff data, the SCS-CN Runoff method provided relevant results to that of a complex simulation model. Thus, the method may be applied to estimate runoff of ungauged catchments of Cebu Island, the results of which could provide relevant information for water resource management.

Analysis of Rainfall Runoff Pollution Characteristics and Non-point Source Pollution Simulation

In view of the impact of non-point source pollution on the quality of water environment, the campus area of Shenyang Jianzhu University was taken as the research object, and the empirical model---SCS runoff curve number method is used to estimate the annual load of different runoff pollutants generated on the underlying surface of the roof and the underlying surface of the pavement. The results show that the load TSS of annual runoff pollutants in the campus is 38,975.66 kg/a, COD is 10,102.12 kg/a, TN is 454.78 kg/a, TP is 49.1 kg/a, and NH3-N is 171.88 kg/a; In 2015, the annual runoff pollutant TSS loading was 38189.14kg/a, COD was 19293.5kg/a, TN was 833.68kg/a, TP was 77.59kg/a, and NH3-N was 567.89kg/a.

Gully head modelling: A Mediterranean badland case study

AbstractPredicting the location of gully heads in various environments is an important step towards predicting gully erosion rates. So far, field data collection and modelling of topographic thresholds for gully head development has mainly focused on gullies that formed in forested areas, rangelands, pastures and cropland. Such information for gullies in badlands however is very scarce. Therefore, this paper aims to extend the database on gully head topographical thresholds through data collection in a badland area and to improve the prediction of gully heads forming at sites with a very low erosion resistance value. For this, we chose a badland site located in central Italy that is characterized by biancana forms and both active and dormant gullies. The definition of the conditions under which present‐day gully heads developed allowed a better modelling of the gully head threshold equation, with modification of a previous model and the exemplification of how to use the updated model. The model shows that the resistance to gully head retreat depends on slope gradient and drainage area at gully heads, land use at the moment of gully development (as numerically expressed using parameters derived from the Runoff Curve Number method), surface rock fragment cover, presence of joints, pipes, and factors/processes affecting detachment rate. This study attempted to better understand environmental conditions that control the development of gully heads in badlands through a combination of field data collection of gully heads, an analysis of land use changes over 10 centuries, focusing on the period 1820–2005, and land use management through repeat photography and a critical examination of historical documents. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Modelo hidrológico de onda cinemática de la cuenca del río Turbio, Guanajuato, México

Objective: To apply the HEC-HMS methodology based on kinematic wave theory in the Turbio river basin to increase the accuracy of the model in predicting storm runoff. Methodology: Calculations were made for: 1) rainfall depth to runoff depth, through the Soil Conservation Service (SCS) runoff curve number method, 2) runoff depth to hydrograph, for which the SCS unit hydrograph method and kinematic wave (KW) method were used, 3) flood routing in channels, by the Muskingum and KW methods, and 4) flood routing in dams, with the mass balance method. All steps were executed with the HEC-HMS program. Combinations and comparisons of methods 2 and 3 were made, while 1 and 4 remained constant. Results: The hydrologic model that presented the highest Nash-Sutcliffe efficiency index (NSE) was the KW-Muskingum combination, where the runoff depth becomes a hydrograph through the KW and the flood routing in channels is carried out with the Muskingum method, and the lowest value was shown by the KW-KW combination. Study limitations: The models were calibrated for only one event, due to the simultaneous availability of sub-hourly rainfall and flows. This limitation implies that subsequent efforts should focus on validating the kinematic wave model. Originality: The hydrologic model presented here is by events and could be implemented in a flood early warning system. Conclusions: According to the NSE, the three methods were satisfactory; however, the best was the KW-Muskingum combination.

Changes in soil hydraulic properties, soil moisture and water balance in Acacia senegal plantations of varying age in Sudan

The effects of Acacia senegal trees on soil moisture (SM) and hydraulic properties in relation to plantations age and associated changes in soil organic carbon (SOC) were investigated and compared to grasslands at two sites in Sudan. Soil hydraulic properties were computed using pedotransfer functions based on texture and SOC, and SM measured using TDR. The measured SM data was used to parametrize a simple daily water balance model in which Hortonian runoff was calculated using the SCS runoff curve number (CN) method and evapotranspiration calculated using crop coefficients, Kc, adjusted to seasonal values using NDVI. Measured SM was higher in the grasslands than plantations, but increased with plantation age, reflecting a similar trend in plantation SOC and plant available water capacities. The modelling resulted in lower runoff from the plantations, increased infiltration, evapotranspiration, reduced drainage and lower SM, as shown by measurements. Greater SM contents in the grasslands were attributed to lower evapotranspiration and resulted in greater drainage fluxes compared to the plantations. The study highlighted the need for more empirical studies on the effect of tree density and cover on rainfall-runoff relationships, infiltration, evapotranspiration and drainage in drylands, especially those of the drier parts of semi-arid Africa.

Block Level Micro Watershed Prioritization Based on Morphometric and Runoff Parameters

Water is one of the most and essential natural resource in the globe, without which our life cannot exist. The demand of water is increasing with the increase of population day by day. We need water for regular activities, drinking, industry, agriculture, human and cattle consumption. Therefore, it is very important to manage with this resource as a sustainable manner. However, we need proper development and management planning to restore or recharge water where highly runoff exists due to various topographical conditions. In this paper we concern the block based micro watershed study with the help of morphometric and Runoff estimation method. Remote sensing and GIS tools very significant for prioritization of micro watershed studies. NRSC Runoff Curve Number method is a quantitative descriptor of the land use and land cover, soil characteristics of watershed and its computed, runoff through an empirical relation that requires the rainfall and watershed co-efficient namely runoff curve number. These Curve Number approach to runoff volume is typically thought of as a method for generating the storm runoff. Where we also applied the common morphometric analysis method which has been commonly applied to the prioritization of watersheds and sub watersheds. Hence we applied the morphometric parameters where linear and aerial shape have been determined for each micro watershed and assigned rank on the basis of value or relationship with erodibility so as to arrive at a compound value for final ranking of the sub-watersheds. The runoff and morphometric parameters were obtained with the help of Remote Sensing and GIS tools. Based on output results of both parameters the final results revealed of micro watershed priorities are shown into five categorizes very high, high, medium, low and very low priority.

Cartografia digital para estimativa de escoamento superficial visando ao planejamento urbano

RESUMO O trabalho foi desenvolvido na Bacia Hidrográfica do Córrego Caçula, município de Ilha Solteira (SP, Brasil), e teve como finalidade estimar o potencial de escoamento superficial com base em metodologias de cartografia apoiadas em técnicas de tratamento digital de dados objetivando baixo custo e rapidez no processo de análise com vistas a subsidiar o planejamento urbano. O método de curva número (CN), desenvolvido pelo Soil Conservation Service (SCS), foi utilizado para determinação do potencial de escoamento superficial combinando informações de uso e ocupação do solo e tipos de solo presentes na bacia. As cartas de uso e ocupação foram produzidas por meio de imagens de satélite dos anos de 2001 e 2009, possibilitando considerar cenário passado e recente para verificar a influência das mudanças de uso do solo no escoamento superficial. Foi possível averiguar que as modificações no uso e na ocupação ocorridas no período resultaram em mudanças nos índices de escoamento superficial, particularmente em função do crescimento da área urbanizada e de plantio de cana-de-açúcar em substituição a pastagens. Os resultados mostraram forte influência do uso do solo nos valores de escoamento obtidos, e as mudanças de uso, sobretudo de pastagem para cultura de cana-de-açúcar, apontaram fortes variações nos valores obtidos. Em geral, os resultados permitiram avaliar potencialidades e limitações para a expansão urbana, indicando áreas carentes de estudos mais detalhados visando à solução de problemas locais.

GIS-based Approach to Estimate Surface Runoff in Small Catchments: A Case Study

AbstractThe issue of surface runoff assessment is one of the important and relevant topics of hydrological as well as geographical research. The aim of the paper is therefore to estimate and assess surface runoff on the example of Vyčoma catchment which is located in the Western Slovakia. For this purpose, SCS runoff curve number method, modeling in GIS and remote sensing were used. An important task was the creation of a digital elevation model (DEM), which enters the surface runoff modeling and affects its accuracy. Great attention was paid to the spatial interpretation of land use categories applying aerial imagery from 2013 and hydrological soil groups as well as calculation of maximum daily rainfall with N-year return periods as partial tasks in estimating surface runoff. From the methodological point of view, the importance of the paper can be seen in the use of a simple GIS-based approach to assess the surface runoff conditions in a small catchment.

Analýza změn odtokových poměrů pro Českou republiku

One part of the project “Strategy for protection against negative impacts of floods and erosion phenomena by nature­friendly measures in the Czech Republic“ was assessment of actual runoff conditions in the Czech Republic by runoff curve number method.

Decision support tool for the evaluation of landscapes

This paper presents a full SDSS for landscape – its design, algorithmization and practical implementation. The created system allows simultaneous analysis and evaluation of landscape from the perspective of ecological stability, erosion susceptibility, retention capacity and the economic value. The presented system implements products ArcView GIS 3.x, EMDS 2.0 and NetWeaver 1.1. The system implements four methods which are generally accepted for the given analyses and which have been algorithmized and applied in the GIS environment many times. Ecological stability is assessed using the basic coefficients of ecological stability. The susceptibility of soil to water erosion is determined by the RUSLE method. Retention capacity is determined based on the Runoff Curve Number Method and the economic value of the landscape draws on the modified Hessen method. The result includes a filled knowledge base, an algorithmized decision-making scheme for the landscape segment assessment and an optimized data model. The practical solution is applied to the model area of the Trkmanka catchment area.

객체지향성 프로그래밍 방법을 통한 GIS 연계의 수문모델

DEM(Digital Elevation Model) 크기의 변화에 따라 특정 지역에 많은 규격의 수문 데이터가 존재할 수 있기 때문에, 어느 지역, 어느 기상 데이터에도 작동할 수 있는 수문 모형의 개발이 절실히 필요하게 되었다. 이와 같은 필요성을 설명하기 위해서 객체지향(object-oriented)적인 프로그래밍 기술을 적용한 GHISMO(Geographic and Hydrologic Information System Modeling Objects)라는 수문모형(hydrologic model)을 개발하였다. GHISMO의 가장 핵심적인 수문학적 접근방법은 저류-배출(storage-release)과 지표면 유효 강수량을 구하기 위하여 SCS curve number 방법을 사용한 것이다. 이 연구에서 수문모형의 모의실험 결과를 제공할 것이다. With the availability of multi-scale hydrologic data in public domain depending on DEM size, there is a need for a modeling framework that is capable of using these data to simulate hydrologic processes at multiple scales for different topographic and climate conditions for distributed hydrologic model. To address this need, an object-oriented approach, called Geographic and Hydrologic Information System Modeling Objects (GHISMO), is developed. Main hydrologic approaches in GHISMO are storage-release for direct runoff and SCS curve number method for infiltration part. This paper presents conceptual and structural framework of storage-release concept including its application to two watersheds will be presented.

Overflow Risk Analysis for Designing a Nonpoint Sources Control Detention

This paper presents a design method by which the overflow risk related to a detention for managing nonpoint pollutant sources in urban areas can be evaluated. The overall overflow risk of a nonpoint pollutant sources control detention can be estimated by inherent overflow risk and operational overflow risk. For the purpose of calculating overflow risk, the 3-parameter mixed exponential distribution is applied to describe the probability distribution of rainfall event depth. As a rainfall-runoff calculation procedure required for deriving a rainfall capture curve, the U.S. Natural Resources Conservation Service runoff curve number method is applied to consider the nonlinearity of the rainfall-runoff relation. Finally, the detention overflow risk is assessed with respect to the detention design capacity and drainage time. The proposed overflow risk assessment is expected to provide a baseline to determine quantitative parameters in designing a nonpoint sources control detention.

Erratum for “Evolution of the SCS Runoff Curve Number Method and Its Application to Continuous Runoff Simulation” by J. R. Williams, N. Kannan, C. Santhi, X. Wang, and J. G. Arnold

Erratum for “Evolution of the SCS Runoff Curve Number Method and Its Application to Continuous Runoff Simulation” by J. R. Williams, N. Kannan, C. Santhi, X. Wang, and J. G. Arnold