'Cheon' is one of four categories with 'Ki'(氣), 'Do'(道), ‘Ri'(理). Specially 'Cheon' meaned sky is so important that most of philosophers have referred to it. 'Cheon' is widespread, so it has been the object of the astronomers and subject of the philosophers. All recognize the conception definitely and consistently, in the other hand some vaguely, someone give different conceptions. Therefore this paper is written with a view to right recognition of the conception and relationships with the human by the study of significance changes by the times.

Ki is the important conception of Chinese philosophy, many of philosophers have discussed it. So the meaning of it is various in accordance with the times and the scholars. And it has been discussed not only in the sphere of philosophy but medicine, astronomy, g eography, society and culture ; therefore we can't understand the Oriental studies without the comprehension of it. Above all, the Oriental-medicine is based on the principles of it, that is to say 'Ki-medicine'. There are Ki of a letter, Ki of a philosophy, Ki of a nature and Ki of the human body according to the recognition process from that time on the ancient. This paper is written with the view of the right understanding about it by the comparison of various theories dealed with it.

A number of projects for development have been done continuously due to the increase of tourist in Jeju Island. However flood disaster countermeasure due to urbanization is not considered during this development projects. This study is to make basic process for the flood estimation in Han stream of Jeju Island. The variation of stream discharge due the every 5 years' land use change from 1980 to 2005. Data for flood events (rainfall and discharge) were collected for HEC-HMS model. Clark method was used for unit hydrograph analysis. For the estimation of Clark unit hydrograph parameters, Kraven II and Sabol’s empirical equations were applied. The peak discharge increased 9.9~33.67% and total discharge amount increased 12.53~30.21%. Also, time of concentration for peak discharge was reduced by 10 minutes for each event.

As global warming has accelerated to weather in recent years, and The frequent floods are creating heavy rains and typhoons followed by considerable damage in Jeju. This study estimated design flood discharges and flood stage in Jeju, considering climate change in connection with RCP scenario, the 5th IPCC Report recently published. It also analyzed the period which might be subject to the risk of flooding in downstream of Oedo Stream. As a result, it has analyzed that there might be a risk of flooding when there were 80 years or more rainfall events in 35 years that rainfall would have increased by 10%, 69 years that 100 years or more heavy rain and rainfall would have increased by 20%, and 104 years that 100 years or more heavy rain and rainfall would have increased by 20%. It is expected that this study results of rainfall increasing trend caused by climate change will be helpful to minimize the damage of floods which will secure the future of Jeju.

Rainfall-runoff model of Jeju Oedo Stream was used to compute the optimal unit hydrograph by HEC-HMS model that reflecting on watershed characteristics. Each rainfall event was comparatively analyzed with the actual flow measurement using Clark, Snyder and SCS synthetic methods for derived unit hydrograph. Subsequently, the null hypothesis was established as p-value for peak flow and peak time of each unit hydrograph by one-way ANOVA(Analysis of variance) was larger than significance level of 0.05. There was no significant difference in peak flow and peak time between different methods of unit hydrograph. As a result of comparing error rate with actual flow measurement data, Clark synthetic unit graph best reflected in Oedo Stream as compared to other methods, and error rate of Clark unit hydrograph was 0.02~1.93% and error rate at peak time was 0∼2.74%.

As occurrence of gradually increasing extreme temperature events in Jeju Island, a hybrid downscaling technique that simultaneously applies by dynamical method and statistical method has implemented on design rainfall in order to reduce flood damages from severe storms and typhoons.As a result of computation, Case 1 shows a strong tendency to excessively compute rainfall, which is continuously increasing. While Case 2 showed similar trend as Case 1, low design rainfall has computed by rainfall in A1B scenario. Based on the design rainfall computation method mainly used in Preventive Disaster System through Pre-disaster Effect Examination System and Basic Plan for River of Jeju Island which are considering climatic change for selecting 50-year and 100-year frequencies. Case 3 selecting for Jeju rain gage station and Case 1 for Seogwipo rain gage station. The results were different for each rain gage station because of difference in rainfall characteristics according to recent climatic change, and the risk of currently known design rainfall can be increased in near future.

Jeju Island, a volcanic island, is the region that shows the biggest rainfall and has a big elevation-specific deviation of precipitation, but Jeju Island River Maintenance Plan doesn't reflect the characteristics of Jeju Island as it only calculates probable precipitation from four weather stations with elevation less than 100m. Therefore, this study uses AWS observational data in four Jeju Island weather stations and other regions to calculate location-specific probable precipitation, review the elevation-probable precipitation correlation in southern and northern regions, and create a probable precipitation map for all regions of Jeju Island, in order to produce better outcomes. This study is expected to be the most basic data to establish a safe Jeju island from flood disaster in preparation for the future climate changes and widely used for Jejudo Basin Dimension Planning, River Maintenance Plan, Pre-Disaster Impact Review, etc.

This study Analyzed four of seven runoffs which had happened in 2012 in comparison with the runoffs shown in Kalesto data, using the fixed surface image velocimetry (FSIV) installed at Oedo stream, Jeju Island. As a result of identifying a runoff curve graph, it was analyzed that the flood runoffs calculated with two observation devices were almost equivalent. As the differences in peak flows were 10 m3/s, 0.7 m3/s and 3 m3/s, the very similar result values were calculated. Even though there were errors in RMSE(Root Mean Square Error) made by two observation devices according to the degree of the peak flow, the values of R² by flood event were 0.89, 0.87, 0.86 and 0.82, showing the result values almost close to 1. Therefore, there was a very high correlation in flood runoffs calculated with two observation devices. This research method was considered to be a very suitable method to measure unexpected flood runoffs which could happen in the island area such as Jeju island during bad weather.

The water resources system of Jeju-do Island entirely depends on groundwater. This study is making a precision observation of baseflow, surface water, water shortage that might be vulnerable to climate change and drought in future. The field observation of baseflow discharges in Akgeuncheon stream has regularly been made with ADCP and ADC and Flowmate every two weeks for twenty-two (22) months (July 8, 2011 to April 27, 2013). This paper represent the results of calculating discharge of a number of hydraulic structures (broad-crested weirs) with comparing and has been calculated more accurate discharges with suitability of different observation methods. The average discharge has been observed 0.851 m3/s, whereas the average ADC and Flowmate is 0.709 m3/s. Meanwhile, stream discharge has been calculated 0.709 m3/s through the broad-crested weir equation. The discharge has calculated with the weir equation greatly changed according to even a small change in the water level. However, it showed a similar trend to one of the observed discharge. Although, in past there were generating errors caused by observers’ strides, vertical and horizontal flow velocity distribution when the average flow velocity had been measured, non-prismatic flow, turbulent flow and others in ADC. This study comes up with the weir equation is more suitable for the characteristics of Jeju-do could be presented through an observations of baseflow discharge.

The rainfall-runoff characteristics in Jeju Island significantly differ from those in inland, due to highly permeable geologic features driven by volcanic island. Streams are usually sustained in the dry conditions and thereby the rainfall-runoff characteristics changes in terms of initiating stream discharge and its types, depending highly on the antecedent precipitation. Among various the rainfall-runoff characteristics, lag time mainly used for flood warning system in river and direct runoff ratio for determining water budget to estimate groundwater recharge quantity are practically crucial. They are expected to vary accordingly with the given antecedent precipitation. This study assessed the lag time in the measured hydrograph and direct runoff ratio, which are especially in the upstream watershed having the outlet as 2nd Dongsan bridge of Han stream, Jeju, based upon several typhoon events such as Khanun, Bolaven, Tembin, Sanba as well as a specific heavy rainfall event in August 23, 2012. As results, considering that the lag time changed a bit over the rainfall events, the averaged lag time without antecedent precipitation was around 1.5 hour, but it became increased with antecedent precipitation. Though the direct run-off ratio showed similar percentages (i.e., 23%)without antecedent precipitation, it was substantially increased up to around 45% when antecedent precipitation existed. In addition, the direct run-off ration without antecedent precipitation was also very high (43.8%), especially when there was extremely heavy rainfall event in the more than five hundreds return period such as typhoon Sanba.

Fixed Electromagnetic Wave Surface Velocimetry (Fixed EWSV) has been started to be used to measure flood discharge in the mountain stream, since it has various advantages such that it works well to continuously measure stream discharge even in the night time as well as very strong weather. On the contrary, the Fixed EWSV only measures single point surface velocity, thus it does not consider varying feature of the transverse velocity profile in the given stream cross-section. In addition, a conventional value of 0.85 was generally used as the ratio for converting the measured surface velocity into the depth-averaged velocity. These aspects could bring in error for accurately measuring the stream discharge. The capacity of the EWSV for capturing rapid flow velocity was also not properly validated. This study aims at conducting error analysis of using the EWSV by: 1) measuring transverse velocity at multiple points along the cross-section to assess an error driven by the single point measurement; 2) figuring out ratio between surface velocity and the depth-averaged velocity based on the concurrent ADCP measurements; 3) validating the capacity of the EWSV for capturing rapid flow velocity. As results, the velocity measured near the center by the fixed EWSV overestimated about 15% of the cross-sectional mean velocity. The converting ratio from the surface velocity to the depth-averaged velocity was 0.8 rather than 0.85 of a conventional ratio. Finally, the EWSV revealed unstable velocity output when the flow velocity was higher than 2 m/s.

The streams in Jeju Island have very distinctive hydrological and geological properties and there are a lot of limits in applying the general flood estimation method. This study presented parameters dominant in the Hancheon stream of Jeju Island by analyzing the sensitivity of parameters of HEC-HMS model regarding rainfall events in the target basin, and extracted the optimal parameter(Time of Concentration of Clark Unit Hydrograph: KravenⅡ method, Storage Coefficient: Sabol method) by analyzing and comparing it with the flood runoff data observed in the site and Jeju Island's observation data.

Jeju island, which is located along the moving path of typhoon, suffers from flooding and overflow by torrential rain. So abrupt runoff occurring, damages of downstream farm field and shore culturing farms are increasing. In this study, Oaedo stream, one of the mountainous streams on Jeju island, was selected as the basin of study subject and was classified into 3 sub-basins, and after the characteristics of subject basin, the soil erosion amount and the sediment delivery of the stream by land usage distribution were estimated with the use of SATEEC ArcView GIS, the sediment yield amount of 2000 and 2005 was analyzed comparatively. As a result of estimating the sediment yield amount of 2000, the three sub-basins were respectively 12,572.7, 14,080 and 157,761 tons/year. and sediment yield amounts were estimated as 35,172.9, 5,266 and 258,535 tons/year respectively in 2005. The soil erosion and sediment yield amount of 2005 using single storm rainfall were estimated high compared with 2000, but for sub-basin 2, the values rather decreased due to changes in land use, and the land coverage of 2005, since there are many classifications of land usage compared with 2000, enabling to reflect more accurate land usage condition, could deduce appropriate results. It is anticipated that such study results can be utilized as basic data to propose a direction to predict the amount of sediment yield that causes secondary flooding damage and deteriorates water quality within detention pond and grit chamber, and take action against damages in the downstream farm field and shore culturing farms.

For Kangjeong stream and Akgeun stream in the central part of the southern Jeju Island, on-site discharge estimation was carried out for approximately 10 months (July 2011-April 2012) twice a month on a regular basis by using ADCP (acoustic doppler current profiler) and long term rate of discharge was calculated by using SWAT (soil and water assessment tool) model. The discharge was 0.28-1.30 m 3 /sec for Kangjeong stream and 0.10-1.54 m 3 /sec for Akgeun stream. It showed the maximum in the summer and the minimum in the winter. As a result of parameter sensitivity analysis of SWAT model, CN (NRCS runoff curve number for moisture condition Ⅱ), SOL_AWC (available water capacity of the soil layer), and ESCO (soil evaporation compensation factor) showed sensitive responses. By using the result, the model was corrected and the rate of discharge was calculated. As a result, the annual discharge rate was 27.12-31.86(%) at the Akgeun basin and 23.55-28.43(%) at the Kangjeong basin.

Jeju Island, the heaviest raining area in Korea, is a volcanic Island located at the southernmost of Korea, but most streams are of the dry due to its hydrological/geological characteristics different from those of inland areas. Therefore, there are limitations in applying the results from the mainland to the studies on stream run-off characteristics analysis and water resource analysis of Jeju Island. In this study, the SWAT(soil & water assessment tool) model is used for the Hwabuk stream watershed located east of the downtown to calculate the long-term stream run-off rate, and WMS(watershed modeling system) and HEC-HMS(hydrologic modeling system) models are used to figure out the stream run-off characteristics due to short-term heavy rainfall. As the result of SWAT modelling for the long-term rainfall-runoff model for Hwabuk stream watershed in 2008, 5.66% of the average precipitation of the entire basin was run off, with 3.47% in 2009, 8.12% in 2010, and root mean square error(RMSE) and determination coefficient(R2) was 496.9 and 0.87, respectively, with model efficient(ME) of 0.72. From the results of WMS and HEC-HMS models which are short-term rainfall-runoff models, unless there was a preceding rainfall, the runoff occurred only for rainfall of 40mm or greater, and the run-off duration averaged 10～14 hours.

Acoustic Doppler Current Profilers (ADCPs) are increasingly popular in the river research and management communities being primarily used for estimation of stream flows. ADCPs capabilities, however, entail additional features that are not fully explored, such as morphological representation of river or reservoir bed based upon multi-beam depth measurements. In addition to flow velocity, ADCP measurements include river bathymetry information through the depth measurements acquired in individual 4 or 5 beams with a given oblique angle. Such sounding capability indicates that multi-beam ADCPs can be utilized as an efficient depth-sounder to be more capable than the conventional single-beam eco-sounders. The paper introduces the post-processing algorithms required to deal with raw ADCP bathymetry measurements including the following aspects: a) correcting the individual beam depths for tilt (pitch and roll); b) filtering outliers using SMART filters; d) transforming the corrected depths into geographical coordinates by UTM conversion; and, e) tag the beam detecting locations with the concurrent GPS information; f) spatial representation in a GIS package. The developed algorithms are applied for the ADCP bathymetric dataset acquired from Han-Cheon in Jeju Island to validate themselves applicability.

Due to the difficulties for measuring flood discharge in the dangerous field conditions, conventional instruments with relatively low accuracy such as float still have been widely utilized for the field survey. It is also limited to use simple stage-discharge relationship for assessment of the flood discharge, since the stage-discharge relationship during the flood becomes complicated loop shape. In recent years, various non-intrusive velocity measurement techniques such as electromagnetic wave or surface images have been developed, which is quite adequate for the flood discharge measurements. However, these new non-intrusive techniques have little tested in the flood condition, though they promised efficiency and accuracy. Throughout the field observations, we evaluated the validity of these techniques by comparing discharge and velocity measurements acquired concurrently during the flood in a mountain stream. As a result, the flood discharge measurements between electromagnetic wave and surface image processing techniques showed high positive relationship, but velocities did not matched very well particularly for the high current speed more 3 m/s. Therefore, it should be noted here that special cares are required when the velocity measurements by those two different techniques are used, for instance, for the validation of the numerical models. In addition, authors assured that, for the more accurate flood discharge measurements, velocity observation as well as stage height is strongly necessary owing that the unsteady flow occurs during the flood.

Different from the main land of South Korea, Jeju Island has been in difficulties for measuring discharge. Due to high infiltration rate, most of streams in Jeju Island are usually in the dried state except six streams with the steady base flow, and the unique geological characteristics such as steep slope and short traveling distance of runoff have forced rainfall runoff usually to occur during very short period of time like one or two days. While discharge observations in Jeju Island have been conducted only for 16 sites with fixed electromagnetic surface velocimetry, effective analysis and validation of observed discharge data and operation of the monitoring sites still have been limited due to very few professions to maintain such jobs. This research is sponsored by Ministry of Land, Transport and Maritime Affairs to build water cycle monitoring and management system of Jeju Island. Specifically, the research focuses on optimizing discharge measurement techniques adjusted for Jeju Island, expanding the monitoring sites, and validating the existing discharge data. First of all, we attempted to conduct discharge measurements in streams with steady base flow, by utilizing various recent discharge monitoring techniques, such as ADCP, LSPIV, Magnetic Velocimetry, and Electromagnetic Wave Surface Velocimetry. ADCP has been known to be the most accurate in terms of discharge measurement compared with other techniques, thus that the discharge measurement taken by ADCP could be used as a benchmark data for validation of others. However, there are still concerns of using ADCP in flood seasons; thereby LSPIV would be able to be applied for replacing ADCP in such flooded situation in the stream. In addition, sort of practical approaches such as Magnetic Velocimetry, and Electromagnetic Wave Surface Velocimetry would also be validated, which usually measure velocity in the designated parts of stream and assume the measured velocity to be representative for whole cross-section or profile at any specified location. The result of the comparison and analysis will be used for correcting existing discharge measurement by Electromagnetic Wave Surface Velocimetry and finding the most optimized discharge techniques in the future.