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1

The use of asymptotic functions for determining empirical values of CN parameter in selected catchments of variable land cover

Wałęga A., Młyński D., Wachulec K.

Studia Geotechnica et Mechanica

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2017

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Vol. 39, nr 4

111--120

EN

The aim of the study was to assess the applicability of asymptotic functions for determining the value of CN parameter as a function of precipitation depth in mountain and upland catchments. The analyses were carried out in two catchments: the Rudawa, left tributary of the Vistula, and the Kamienica, right tributary of the Dunajec. The input material included data on precipitation and flows for a multi-year period 1980-2012, obtained from IMGW PIB in Warsaw. Two models were used to determine empirical values of CNobs parameter as a function of precipitation depth: standard Hawkins model and 2-CN model allowing for a heterogeneous nature of a catchment area. The study analyses confirmed that asymptotic functions properly described P-CNobs relationship for the entire range of precipitation variability. In the case of high rainfalls, CNobs remained above or below the commonly accepted average antecedent moisture conditions AMCII. The study calculations indicated that the runoff amount calculated according to the original SCS-CN method might be underestimated, and this could adversely affect the values of design flows required for the design of hydraulic engineering projects. In catchments with heterogeneous land cover, the results of CNobs were more accurate when 2-CN model was used instead of the standard Hawkins model. 2-CN model is more precise in accounting for differences in runoff formation depending on retention capacity of the substrate. It was also demonstrated that the commonly accepted initial abstraction coefficient λ = 0.20 yielded too big initial loss of precipitation in the analyzed catchments and, therefore, the computed direct runoff was underestimated. The best results were obtained for λ = 0.05.

2

Direct runoff assessment using modified SME method in catchments in the Upper Vistula River Basin

Wałęga A., Rutkowska A., Grzebinoga M.

Acta Geophysica

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2017

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Vol. 65, no. 2

363--375

EN

Correct determination of direct runoff is crucial for proper and safe dimensioning of hydroengineering structures. It is commonly assessed using SCS-CN method developed in the United States. However, due to deficiencies of this method, many improvements and modifications have been proposed. In this paper, a modified Sahu–Mishra–Eldo (SME) method was introduced and tested for three catchments located in the upper Vistula basin. Modification of SME method involved a determination of maximum potential retention S based on CN parameter derived from SCS-CN method. The modified SME method yielded direct runoff values very similar to those observed in the investigated catchments. Moreover, it generated significantly smaller errors in the direct runoff estimation as compared with SCS-CN and SME methods in the analyzed catchments. This approach may be used for estimating the runoff in uncontrolled catchments.

3

Usefulness of the Modified NRCS-CN Method for the Assessment of Direct Runoff in a Mountain Catchment

Wałęga A., Rutkowska A.

Acta Geophysica

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2015

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Vol. 63, no. 5

1423--1446

EN

The aim of this study was to evaluate the usefulness of modified methods, developed on the basis of NRCS-CN method, in determining the size of an effective rainfall (direct runoff). The analyses were performed for the mountain catchment of the Kamienica river, right-hand tributary of the Dunajec. The amount of direct runoff was calculated using the following methods: (1) Original NRCS-CN model, (2) Mishra- Singh model (MS model), (3) Sahu-Mishra-Eldho model (SME model), (4) Sahu 1-p model, (5) Sahu 3-p model, and (6) Q_base model. The study results indicated that the amount of direct runoff, determined on the basis of the original NRCS-CN method, may differ significantly from the actually observed values. The best results were achieved when the direct runoff was determined using the SME and Sahu 3-p model.

4

SCS-CN method. Part 1: Derivation of SCS-CN -based models

Mishra S., Singh V.

Acta Geophysica Polonica

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2002

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Vol. 50, nr 3

457-477

EN

This part of the paper, in a sequence of two, provides an analytical treatment of the Soil Conservation Service Curve Number (SCS-CN) method including its derivation from a) early rainfall-runoff methods, such as the Mockus and Zoch methods, using the Horton method and b) first (linear)- and second (non-linear) -order hypotheses. After a critical review of the available analytical derivations, SCS-CN-based models are proposed for depression, interception storage, and initial abstraction, which forn parts of the SCS-CN method. The performance of the existing and modified versions of the SCS-CN method is evaluated using field data.