Sangdan Kim

Effects of land use change and water reuse options on urban water cycle

The aim of this article was to study the effects of land use change and water reuse options on an urban water cycle. A water cycle analysis was performed on the Goonja drainage basin, located in metropolitan Seoul, using the Aquacycle model. The chronological effects of urbanization were first assessed for the land uses of the Goonja drainage basin from 1975 to 2005, where the ratio of impervious areas ranged from 43% to 84%. Progressive urbanization was identified as leading to a decrease in evapotranspiration (29%), an increase in surface runoff (41%) and a decrease in groundwater recharge (74%), indicating a serious distortion of the water cycle. From a subsequent analysis of the water reuse options, such as rainwater use and wastewater reuse, it is concluded that wastewater reuse seemed to have an advantage over rainwater use for providing a consistent water supply throughout the year for a country like Korea, where the rainy season is concentrated during the summer monsoon.

Probabilistic Solution to Soil Water Evaporated Flow Equation

A new stochastic model for one-dimensional evaporated soil water flow is proposed with major focus on its probabilistic structure. The newly developed model has the form of the Fokker-Planck equation, and its validity as a model for the probabilistic evolution of the nonlinear stochastic unsaturated flow process is investigated under a stochastic soil-related parameter (i.e., saturated hydraulic conductivity). This model is based on a parabolic type of stochastic partial differential equation, and has the advantage of providing the probabilistic solution in the form of a probability distribution function, from which one can obtain the ensemble average behavior of the flow system. The comparison results with Monte Carlo simulations show that the proposed model can reproduce well the vertically varying soil water wetting front depth. Overall, the ensemble averaging approach using the cumulant expansion method shows good promise for the stochastic modeling of nonlinear hydrologic processes.

An Analysis of the Effect of Climate Change on Flow in Nakdong River Basin Using Watershed-Based Model

To evaluate influence of the future climate change on water environment, it is necessary to use a rainfall-runoff model, or a basin model allowing us to simultaneously simulate water quality factors such as sediment and nutrient material. Thus, SWAT is selected as a watershed-based model and Nakdong river basin is chosen as a target basin for this study. To apply climate change scenarios as input data to SWAT, Australian model (CSIRO: Mk3.0, CSMK) and Canadian models (CCCma: CGCM3-T47, CT47) of GCMs are used. Each GCMs which have A2, B1, and A1B scenarios effectively represent the climate characteristics of the Korean peninsula. For detecting climate change in Nakdong river basin, precipitation and temperature, increasing rate of these were analyzed in each scenarios. By simulation results, flow and increasing rate of these were analyzed at particular points which are important in the object basin. Flow and variation of flow in the scenarios for present and future climate changes were compared and analyzed by years, seasons, divided into mid terms. In most of the points temperature and flow rate are increased, because climate change is expected to have a significant effect on rising water temperature and flow rate of river and lake, further on the basis of this study result should set enhancing up water control project of hydraulic structures caused by increasing outer discharge of the Nakdong River Basin due to climate change.

Estimation of Flood Risk Index for the Nakdong River Watershed

The aim of study is to present how to estimate and use the FRI (Flood Risk Index) for classifying area zones based on regional flooding risk in terms of the integrated flood risk management. To estimate the FRI at a spatial resolution of city/county/town units for the Nakdong River Watershed, the 17 representative flood indexing factors are carefully selected for the three flood indexes, such as PI (Pressure Index), SI (State Index), and RI (Response Index) under the P-S-R (Pressure-State-Response) classification system. Because flood indexing factors are measured at different scales and units, they are transformed into a common domain by the T-Score normalization technique. The entropy weight coefficient method is also applied to calculate the weight of flood indexing factors in order to reduce subjective judgement on the effect of weight coefficients. The three flood indexes of PI, SI, and RI are integrated for an overall value of the FRI to evaluate the flood risk of districts. To examine the practical application of the proposed FRI, the FRI results with/without the weight coefficients are compared with flooding zones of natural disaster risk areas officially announced in 2010. It is expected that the FRI ensured by full verification can make regional protection plans against flooding disasters with respect to causes and characteristics of past floods.

Analytical Derivation of Steady State Soil Water Probability Distribution Function under Rainfall Forcing using Cumulant Expansion Theory

A new stochastic model for the propagation analysis of fluctuations in rainfall to soil water dynamics is proposed with major focus on its probabilistic structure. This model is derived by using cumulant expansion theory from a stochastic differential equation with stochastic rainfall forcing, and has the advantage of providing the probabilistic solution in the form of a probability distribution function, from which one can obtain the ensemble average behavior of the system. Steady state probability distribution function for soil water is obtained analytically and analyzed for different climater and soil conditions.

Analysis of the Effect of Water Budget Elements on Flow Duration Characteristics using SWAT-Nak Dong

본 연구에서는 미계측 유역의 유량 산정 및 평가를 위해 강우, 유출 및 댐 및 물이용 요소를 포함한 유역통합 수문모형(SWAT-Nak Dong)을 낙동강 전체 유역을 대상으로 구축하고, 유역내 댐방류 및 인위적인 물이용 요소를 고려한 물수지 시나리오에 따른 유황변동을 정량적으로 파악하는데 그 목적이 있다. 본 연구에서 적용한 SWAT 모형은 대규모 복잡한 유역에서의 장기간에 걸친 토지관리, 기후 변화 등에 따른 수자원 및 비점오염 평가, 관리를 위해 1990년대초 개발된 연속형 장기유출 모형이다. 구축된 유역통합 수문모형과 다양한 물수지 시나리오를 이용하여 댐 및 유역내 물이용이 하천유량 미치는 영향을 정량적으로 분석하였다. 【In this paper, we constructed the integrated watershed model system, SWAT-Nak Dong that include areal mean precipitaiton, runoff and water balance components in the Nak Dong river basins and with this model system we are capable of estimating streamflows for ungaged river stations and analyzing the variations of the streamflows. SWAT(Soil and Water Assessment Tool) is a conceptual, continous time model that was developed in the early 1990s to assist water resource managers in assessing the impact of management and climate on water supplies and non-point source pollution III watersheds and large river basins. Using the SWAT-Nak Dong system and various scenarios, we analyzed and evaluated the dams and water uses effects on the streamflows.】

An analysis of the effect of climate change on Byeongseong stream's hydrologic and water quality responses using CGCM's future climate information.

For the assessment of climate change impacts for the Byeongseong stream, CGCM 3.1 T63 is selected as future climate information. The projections come from CGCM used to simulate the GHG emission scenario known as A2. Air temperature and precipitation information from the GCM simulations are converted to regional scale data using the statistical downscaling method known as MSPG. Downscaled climate data from GCM are then used as the input data for the SWAT model to generate regional runoff and water quality estimates in the Byeongseong stream. As a result of simple sensitivity analysis, the increase of CO2 concentration leads to increase water yield through reduction of evapotranspiration and increase of soil water. Hydrologic responses to climate change are in phase with precipitation change. Climate change is expected to reduce water yields in the period of 2021-2030. In the period of 2051-2060, stream flow is expected to be reduced in spring season and increased in summer season. While soil losses are also in phase with water yields, nutrient discharges (i.e., total nitrogen) are not always in phase with precipitation change. However, it should be noted that there are a lot of uncertainties in such multiple-step analysis used to convert climate information from GCM-based future climate projections into hydrologic information.

Projection of Korean Probable Maximum Precipitation under Future Climate Change Scenarios

According to the IPCC Fifth Assessment Report, air temperature and humidity of the future are expected to gradually increase over the current. In this study, future PMPs are estimated by using future dew point temperature projection data which are obtained from RCM data provided by the Korea Meteorological Administration. First, bias included in future dew point temperature projection data which is provided on a daily basis is corrected through a quantile-mapping method. Next, using a scale-invariance technique, 12-hour duration 100-year return period dew point temperatures which are essential input data for PMPs estimation are estimated from bias-corrected future dew point temperature data. After estimating future PMPs, it can be shown that PMPs in all future climate change scenarios (AR5 RCP2.6, RCP 4.5, RCP 6.0, and RCP 8.5) are very likely to increase.

Natural Disaster Vulnerability Assessment at Boroughs and Census Output Areas in Seoul Focusing on Socio-economic Perspective

우리나라에서는 매년 호우, 태풍, 대설 등 자연재해로 인하 여 많은 피해가 발생되고 있으며, 2013년도에서는 총 1,721억 원의 재산피해가 발생하였는데 이중 90% 이상이 호우에 기 인하였다. 또한 재해로 인한 피해액과 그에 따른 복구액 역시 점점 증가하고 있는 추세를 보이고 있다(NEMA, 2013). 특히 나 2011년 서울시 우면산 산사태, 2014년 부산·경남 지방에 서 폭우 등으로 인하여 많은 재산 피해와 인명피해가 발생하 였으며, 이러한 사건은 사회적인 관심을 불러일으켰다. 우리나라의 경우 도시지역 인구밀도가 높으며, 이로 인해 도시지역에 재해가 발생되면 치명적인 피해를 입게 된다. 따 라서 도시지역의 자연재해에 대한 대응책 마련이 반드시 필 요하다. 이를 위해서는 어떤 지역에서 자연재해가 발생하였을 경우 얼마나 많은 피해를 입는지에 대한 정량적인 평가가 우 선적으로 진행되어야 한다. Smith and Ward(1998)은 홍수에 Abstract

Improvement of the Empirical Formula for Estimating Stormwater Capture Ratio of WQF Treatment BMPs

비점오염원은 도시, 도로, 농지, 산지, 공사장 등으로서 불특정장소에서 불특정하게 수질오염물질을 배출하는 오염원으로서(MOE, 2013), 주로 강우 시에 발생되는 지표 유출수와함께 쓸려 수계로 유입된다. 지표면에 쌓여있는 먼지, 쓰레기,화석연료 부산물, 타이어 가루, 비료, 농약, 토양침식물, 대기오염물질 등 다양한 종류의 비점오염물질은 광범위한 장소에서 불특정하게 발생하고 시기에 따라 배출량의 편차가 심함에 따라 비점오염물질의 발생량 및 배출량을 예측하고 정량화하기 어려운 특징을 가지고 있다(Kim and Han, 2010). 수질오염총량관리 기술지침(이하 기술지침)(NIER, 2012)에 따르면, 토지계에서 배출되는 오염물질은 비점오염저감시설을 통해 삭감될 수 있으며, 이 때 삭감되는 오염부하량은Abstract