S. K. Mishra

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).

Calibration and validation of a general infiltration model

A general infiltration model proposed by Singh and Yu (1990) was calibrated and validated using a split sampling approach for 191 sets of infiltration data observed in the states of Minnesota and Georgia in the USA. Of the five model parameters, fc (the final infiltration rate), So (the available storage space) and exponent ‘n’ were found to be more predictable than the other two parameters: m (exponent) and a (proportionality factor). A critical examination of the general model revealed that it is related to the Soil Conservation Service (1956) curve number (SCS-CN) method and its parameter So is equivalent to the potential maximum retention of the SCS-CN method and is, in turn, found to be a function of soil sorptivity and hydraulic conductivity. The general model was found to describe infiltration rate with time varying curve number. Copyright

Improved SCS-CN–Inspired Model

AbstractThe present study enhances the Soil Conservation Service curve number (SCS-CN) predictions by improving the model structure, considering the following issues of concern: implementation of antecedent moisture condition procedure, fixation of initial abstraction ratio (λ) at 0.2, usage of the potential maximum retention parameter, and incorporation of storm intensity or duration in runoff estimation. A five-parameter M3 model is proposed, with storm duration and a new parameter Sabs (potential maximum retention), to overcome most of the above limitations prevailing in the SCS-CN model. For simplicity and practical applications obviating storm-duration data, a four-parameter M4 model is also proposed. The performance of the suggested and the available models has been evaluated using the data of 82 small watersheds in the United States of America. As demonstrated, the M3 model performs the best, whereas the conventional SCS-CN model performs the poorest among all the models studied.

A review of the synthetic unit hydrograph: from the empirical UH to advanced geomorphological methods

Abstract This review paper critically examines one of the most popular flood hydrograph modelling techniques for ungauged basins, the synthetic unit hydrograph (SUH), and its recent developments and advances. For this purpose, the SUH models were first grouped into four main classes, as follows: (a) traditional or empirical models; (b) conceptual models; (c) probabilistic models; and (d) geomorphological models. It was found that the geomorphological class is the most useful and interesting, since it is able to employ topographic information, so limiting the role of the calibration parameters. This review is expected to be helpful to hydrologists, water managers and decision-makers searching for models to study the flood hydrograph, modelling techniques and related processes in ungauged basins. It was completed as the International Association of Hydrological Sciences (IAHS) Decade (2003–2012) on predictions in ungauged basins (PUB), drew to a close. Editor D. Koutsoyiannis; Associate editor S. Grimaldi Citation Singh, P.K., Mishra, S.K., and Jain, M.K., 2013. A review of the Synthetic Unit Hydrograph: from the empirical UH to advanced geomorphological methods. Hydrological Sciences Journal, 59 (2), 239–261.

Development of a Modified SMA Based MSCS-CN Model for Runoff Estimation

The Soil Conservation Service Curve Number (SCS-CN) method developed by the USDA-Soil Conservation Service (SCS, 1972) is widely used for the estimation of direct runoff for a given rainfall event from small agricultural watersheds. The initial soil moisture plays an important role in re-structuring of the SCS-CN method and enables us to prevent unreasonable sudden jump in runoff estimation and this has prompted the concept of soil moisture accounting (SMA) procedure to develop improved SCS-CN based models. Applying the concept of SMA procedure and changed parameterization, Michel et al. Water Resour Res 41(2):1–6 (2005) developed an improved SCS-CN model (MSCS-CN), which could be thought of an improvement over the existing SCS-CN method; however, their model still inherits several conceptual limitations and inconsistencies. Therefore, in this study an attempt is made to propose an improved SMA based SCS-CN-inspired model (MMSCS-CN) model incorporating a continuous function for initial soil moisture and test its suitability over the MSCS-CN and SCS-CN model using a large dataset from US watersheds. Using, Nash and Sutcliffe efficiency (NSE) and root mean square error (RMSE) of these models, the overall performance is further evaluated using rank grading system, and it is found that the MMSCS-CN scores highest mark (95; overall rank I) followed by MSCS-CN with 61 (overall rank II), and SCS-CN model with 51 mark (overall rank III) out of the maximum 105. This study shows that the proposed MMSCS-CN model has several advantages and performs better than the MSCS-CN and the existing SCS-CN model.

SCS-CN Method

The Soil Conservation Service Curve Number (SCS-CN) method was developed in 1954 and is documented in Section 4 of the National Engineering Handbook (NEH-4) published by the Soil Conservation Service (now called the Natural Resources Conservation Service), U.S. Department of Agriculture in 1956. The document has since been revised in 1964, 1965, 1971, 1972, 1985, and 1993. The SCSCN method is the result of exhaustive field investigations carried out during the late 1930s and early 1940s and the works of several early investigators, including Mockus (1949), Sherman (1949), Andrews (1954), and Ogrosky (1956). The passage of Watershed Protection and Flood Prevention Act (Public Law 83–566) in August 1954 led to the recognition of the method at the Federal level and the method has since witnessed myriad applications all over the world. It is one of the most popular methods for computing the volume of surface runoff for a given rainfall event from small agricultural, forest, and urban watersheds. The method is simple, easy to understand and apply, stable, and useful for ungauged watersheds. The primary reason for its wide applicability and acceptability lies in the fact that it accounts for most runoff producing watershed characteristics: soil type, land use/treatment, surface condition, and antecedent moisture condition. This chapter describes the existing SCS-CN method, the concept of curve number and factors affecting it, the procedure for its application, sensitivity of its parameters, and its advantages and limitations.

Estimation of design runoff curve numbers for Narmada watersheds (India)

Employing 10 years daily rainfall–runoff data, frequency-based design curve numbers (CNs) of different rain durations and for 2, 5, 10, 25, 50, 100, and 200 years return periods were derived for normal, dry, and wet weather conditions, representing 50%, 10%, and 90% probability of exceedance, respectively. Among the three distributions, Gumble (extreme value) type 1, log normal, and log Pearson type 3, the last performed better than the others. When compared, the design CN-values yielded runoff values quite close to the conventionally derived design runoff, exhibiting the validity of the derived design CN-values.

Performance evaluation of modified versions of SCS curve number method for two watersheds of Maharashtra, India

One of the popular methods for computing the depth of surface runoff for a given rainfall event is the Soil Conservation Service Curve Number (SCS-CN) method. Research conducted on the applicability of the SCS-CN method suggested a need for improvement. Consequently, several modifications of the method have been suggested and reported in literature. The important modified versions of the method include Mishra and Singh (MS) model, Michel et al. model, Sahu et al. model and SME model. These modified models have been reported to perform better than the original method for U.S. watersheds. In the present study, these modified models are applied to two Indian watersheds in Maharashtra and are compared with each other for their performance. The results indicated that the SME and the Sahu et al. model perform equally well compared to each other, and the duo perform consistently better than the original SCS-type method and the others for both the Amba and Kalu watersheds. Further, the performance of the MS model is found to be better than the Michel et al. model.

Improved Storm Duration and Antecedent Moisture Condition Coupled SCS-CN Concept-Based Model

AbstractThe Soil Conservation Service curve number (SCS-CN) method is a well-recognized technique for the estimation of direct surface runoff from a rainfall event. Most of the recently developed SCS-CN–based models including the original one ignore the effect of storm duration or rainfall intensity on surface runoff, an important aspect of the rainfall-runoff model. Some of these models have, however, included the antecedent moisture conditions. In this study, storm duration is incorporated in a recently modified version of the SCS-CN method to derive a more advanced model. This version is found to perform generally better than the other on the data of 60 small U.S. watersheds. The former model performed significantly better than the latter on the watersheds dominated by silty soils and cultivated land uses.

Hypsometric Analysis of Shakkar River Catchment through Geographical Information System

Hypsometric analysis of watershed (area-elevation analysis) has generally been used to reveal the stages of geomorphic development (stabilized, mature and young). The geologic stages of development and proneness of the watersheds for erosion are quantified by hypsometric integral. The estimation of hypsometric integral is carried out from the graphical plot of the measured contour elevation and encompassed area by using empirical formulae. In this study, efforts were made to estimate the hypsometric integral values of Shakkar river watershed which is a tributary of Narmada river located in Madhya Pradesh. The watershed was delineated into eight sub-watersheds and hypsometric analysis was carried out for all of them using digital contour maps, which was generated using Arc/Info GIS. The hypsometric integral values for all the sub-watersheds of Shakkar river ranges between 0.47 and 0.51. In the study area, only mature stage of erosion cycle is identified.