Abstract:Most runoff analyses using a grid-based distributed model use one parameter group calibrated at the outlet of a watershed, instead of dividing the watershed into subwatersheds. Significant differences between the observed value and the simulation result of the subwatersheds can occur if just one parameter group is used in all subwatersheds that have different hydrological characteristics from each other. Therefore, to improve the simulation results of the subwatersheds within a watershed, a model calibrated at every subwatershed needs to be used to reflect the characteristics of each subwatershed. In this study, different parameter groups were set up for one or two sites using a distributed model, the GRM (Grid based Rainfall-runoff Model), and the evaluations were based on the results of rainfall-runoff analysis, which uses a multi-site calibration (MSC) technique to calibrate the model at the outlet of each site. The Hyangseok watershed in Naeseong River, which is a tributary of Nakdong River in Korea, was chosen as the study area. The watershed was divided into five subwatersheds each with a subwatershed outlet that was applied to the calibration sites. The MSC was applied for five cases. When a site was added for calibration in a watershed, the runoff simulation showed better results than the calibration of only one site at the most downstream area of the watershed. The MSC approach could improve the simulation results on the calibrated sites and even on the non-calibrated sites, and the effect of MSC was improved when the calibrated site was closer to the runoff site.

The assembly of the micron-sized Si/CNT/carbon composite wrapped with graphene (SCG composite) is designed and synthesized via a spray drying process. The spherical SCG composite exhibits a high discharge capacity of 1789 mAh g -1 with an initial coulombic efficiency of 84 %. Moreover, the porous architecture of SCG composite is beneficial for enhancing cycling stability and rate capability. In practice, a blended electrode consisting of spherical SCG composite and natural graphite with a reversible capacity of ~500 mAh g -1 , shows a stable cycle performance with high cycling efficiencies (> 99.5%) during 100 cycles. These superior electrochemical performance are mainly attributed to the robust design and structural stability of the SCG composite during charge and discharge process. It appears that despite the fracture of micro-sized Si particles during repeated cycling, the electrical contact of Si particles can be maintained within the SCG composite by suppressing the direct contact of Si particles with electrolytes.

In this study, we estimate parameters of a distributed hydrologic model, GRM (grid based rainfall-runoff model), using a model-independent parameter estimation tool, PEST. We implement auto calibration of model parameters such as initial soil moisture, multipliers of overland roughness and soil hydraulic conductivity in the Geumho River Catchment and the Gamcheon Catchment using radar rainfall estimates and groundobserved rainfall represented by Thiessen interpolation. Automatic calibration is performed by GRM-MP (multiple projects), a modified version of GRM without GUI (graphic user interface) implementation, and "Parallel PEST" to improve estimation efficiency. Although ground rainfall shows similar or higher cumulative amount compared to radar rainfall in the areal average, high spatial variation is found only in radar rainfall. In terms of accuracy of hydrologic simulations, radar rainfall is equivalent or superior to ground rainfall. In the case of radar rainfall, the estimated multiplier of soil hydraulic conductivity is lower than 1, which may be affected by high rainfall intensity of radar rainfall. Other parameters such as initial soil moisture and the multiplier of overland roughness do not show consistent trends in the calibration results. Overall, calibrated parameters show different patterns in radar and ground rainfall, which should be carefully considered in the rainfall-runoff modelling applications using radar rainfall.

No abstract

Rainfall characteristics are changing due to climate change in Korea, as they are across the rest of the world. While the average annual rainfall is increasing, the number of rainy days is decreasing and that results in the increase of rainfall intensity. Because of the increase in rainfall intensity, the frequency of abnormal rainfall and floods is also increasing and can lead to extensive damage. It is necessary to establish reasonable alternatives to mitigate flood damage. In order to establish suitable disaster mitigation alternatives to overcome abnormal flooding, the following methods are used. Firstly, a test basin which has a big city in downstream vulnerable to flood damage is selected. Secondly, flood vulnerability is evaluated by a variety of scenarios and flood mitigation alternatives. Finally, the goal is to find out the best flood mitigation alternative that can protect the city located downstream. Since the Namhangang River basin selected for the test basin has only one reservoir, Chungju Reservoir, the flood control capability is relatively small considering the basin area. Therefore, in the case of flood occurrence which exceeds the flood control capacity of Chungju Reservoir, Yeoju which is located downstream of Chungju Reservoir, may have flood damage. In July of 2006, the flood was close to the design flood that actually occurred in Yeoju. The July of 2006 flood event is first analyzed, and the rainfall which is 1.2, 1.3, 1.4, 1.5 times greater than the actual rainfall is generated and analyzed for the safety of Yeoju. On the basis of the analyzed flood vulnerability of Chungju Reservoir, five alternatives are considered to reduce the flood damage in Yeoju. As a result, the alternative of constructing a new reservoir is found to be the most efficient alternative to mitigate the flood damage in Yeoju.