Parameter Adjustment to Prevent the Overestimation of Peak Discharge in a Small Watershed

We revisit empirical methods to prevent the overestimation of peak discharge in a small watershed, in particular investigating the time-area method, which has not been considered in the overestimation problem of peak discharge. To avoid misapplying the same inlet time between the unit hydrograph and rational formula, distinct parameter adjustments for each method are proposed. We adopt the secondary basin response time for the unit hydrograph, rainfall duration for the rational formula, and time of concentration for the time-area method, as suitable parameters to adjust the estimation of peak discharge. In conclusion, adding 10 minutes to secondary basin response time, 20 minutes to rainfall duration, and 30 minutes to time of concentration, respectively, yields estimates within a reasonable range of specific discharge in a small watershed.

Effective Length Prediction and Pullout Design of Geosynthetic Strips Based on Pullout Resistance

In this study, pullout tests were conducted on geosynthetic strips which can be applied to a block-type front wall. Based on the test results, the effective length is predicted, and the pullout design results are presented. In other words, the pullout displacement–pullout load relationship of all geosynthetic strips was analyzed using the pullout test results, and their effective lengths were predicted. It was found that the reinforcement width affected the pullout force for the geosynthetic strips at the same tensile strength. The pullout behavior was evidenced within a range of approximately 0.45 L of the total length of the reinforcement (L) and hardly occurred beyond a certain distance from the geosynthetic strips front regardless of the normal stress. Based on these pullout behavioral characteristics, a method is proposed for the prediction of the effective length (LE) and maximum effective length (LE(max)) of a geosynthetic strip. The pullout strength was compared using the total area and effective area methods in accordance with the proposed method. In the case of the total area method, GS50W (width: 50 mm) and GS70W (width: 70 mm) exhibited similar pullout strengths. The pullout strength by the effective area method, however, was found to be affected by the soil-reinforcement interface adhesion. The proposed method used for the prediction of the effective length of a geosynthetic strip was evaluated using a design case. It was confirmed that the method achieved an economical design in instances in which the pullout resistance by the effective length (LE) was applied compared with the existing method.

Estimation of Flood Discharge in Complex Basins and Assessment of Downstream Conveyance in Development Areas

The rainfall-runoff characteristics of urban and rural areas differ. Hence, major domestic design standards recommend using the rural basin rainfall-runoff models (the unit hydrograph method) for rural areas and the urban rainfall-runoff models (time-area method) for urban areas when estimating the amount of floods. Further, the guidelines for consultations on disaster impact assessment in Korea describe the selection of rainfall-runoff models according to basin types such as urban and rural areas. However, in complex watersheds where rural and urban basins coexist, the type of rainfall-runoff model is selected based on the modeler’s (or business operator’s) experiences rather than model selection guidelines. This study aims to analyze the impacts of uncertain design standards on disaster impact assessment in Korea. To this end, the parameters for each model (the unit hydrograph method, time-area method) were optimized using the measured datasets. The accuracy of the models was evaluated, as well as the appropriateness of flood reduction measures based on whether there was an assessment of downstream conveyance in development areas. The results of this study are expected to contribute to improving the reliability of the evaluation of flood reduction measures by assessing the accuracy of results in hydrological modeling and supplementing the uncertain flood estimation guidelines.

CONSTRUCTION CASH FLOW AND RISK S-CURVES DEVELOPMENT APPROACH, AND AREA METHOD ANALYSIS AT THE PRECONSTRUCTION STAGE FROM CLIENT PERSPECTIVE IN THE UNITED ARAB EMIRATES

Purpose – Understanding construction cash flow estimation is crucial for project success. Experts are concerned about project’s cash-flow and risk estimation and control. Latest construction studies concentrated on modelling and estimating construction costs and risks. Methodology – This article aims to approach pure quantitative mathematical modelling to develop the S-Curves (i.e., cash-flow and risks) and to develop the cash-flow simple area method. This research referred to the mathematical definitions of construction cash-flow and risks, integrating a clear systematic approach to develop the s-curves and to build the simple-area-method. Findings – This research paper reviled that construction cash-flow and risk s-curves can be developed at the preconstruction stage, mathematically, without the need for having cost historical data of similar completed projects. In addition, this article has provided a simple area method approach mathematically, for construction cash flow analysis, using the basic developed cash-flow s-curve and the actual cost data of, at least, 2 completed similar projects. The simple area method is proved effective to provide a better understanding of cash-flow behaviour of the analysed projects’ type. However, the s-curves development can be generalised to cover construction cost and risk simple s-curves, while the area method is restricted with the projects’ characteristics (i.e., type, size, location, etc.) used in developing the simple area. Unique contribution to theory, practice and policy – The significance of this study is to provide an S-Curve development approach for both cashflow and risk percentages from client perspective at the preconstruction stage, using solely the tender contract value. And to provide a simpler stochastic area method approach for project management professionals/researchers, who do not have large amount of historical similar projects’ cost data. Originality, theoretical-implications, practical-implications, and limitations are presented in the conclusion for future research.