Determination of clark unit hydrograph parameters for estimating probable maximum flood

다국어 초록 (Multilingual Abstract)

The estimation of the exact probable maximum flood is very important for the design or evaluation of dams. The probable maximum flood was defined as the flood generated from the probable maximum precipitation. The probable maximum flood is estimated by using a unit hydrograph with the probable maximum precipitation as input. Recently, Clark unit hydrograph, which have time of concentration and storage coefficient as parameters, has been used in Korea. Until now, due to short observation period and lack of reliability verification of hydrological data, Clark unit hydrograph parameters were estimated with only a small number of storm events in a gaged basin, and no procedures have been presented for determining the parameters in an ungauged basin. In this dissertation, a method to determine unit hydrograph parameters for estimating the probable maximum flood was proposed. The summary for the total of five chapters conducted in this dissertation is as follows.

First, the method for determining the time of concentration and the storage coefficient using peak velocity was examined and applicability of the method was confirmed through the observation data. Secondly, downstream variations of velocity in a storm event was theoretically derived and examined from the observation data. Third, the application method of rational formula for estimating the peak discharge for time-distributed rainfall was reviewed and examined from the observed data. Fourth, the possibility of estimating the velocity at an ungaged point in a rainfall event was inspected and the applicability of it to the downstream point was examined. Finally, a method to determine unit hydrograph parameters for estimating the probable maximum flood was proposed and evaluated. The results from the method were compared with those from the existing researches. Furthermore, consistency was examined by comparing them with the peak discharge obtained from the probability rainfall.

The results from this dissertation would enable the determination of sufficiently objective unit hydrograph without subjective judgment based on the experience of each technician. Furthermore, it is expected that this method will help in the process of determining and reviewing parameters even for a gauged basin. Through this, it is expected that the methodology in this dissertation would be actively used in the new dam construction plans or safety evaluations.

목차 (Table of Contents)

• 1. Introduction 1
• 1.1 Background 2
• 1.2 Objectives and Organization of the Dissertation 9
• 1.2.1 Research Objectives 9
• 1.2.2 Organization of the Dissertation 13
• 2. Determination of Clark Unit Hydrograph Parameters Using Velocity 16
• 2.1 Introduction 17
• 2.2 Theoretical Background 20
• 2.2.1 Time of Concentration and Peak Velocity 20
• 2.2.2 Storage Coefficient and Time of Concentration 23
• 2.3 Relationship Between Peak Velocity and Parameters Identified by Observation Data 25
• 2.3.1 Study Area and Rainfall-Runoff Data 25
• 2.3.2 Selection of Rainfall Events with Observed Peak Velocity 27
• 2.3.3 Parameter Estimation for Rainfall Events 29
• 2.3.4 Variation of Parameters According to Peak Velocity 31
• 2.3.5 Ratio of Parameters According to Peak Velocity 37
• 2.4 Comparison of Representative Parameters from Observation Data and Parameters from Empirical Formulas 43
• 2.4.1 Estimation of Representative Parameters 43
• 2.4.2 Comparison with Parameters Estimated by Empirical Formulas 46
• 2.5 Examination of Applicability on Ungauged Basin Using Empirical Formulas and Velocity 50
• 2.5.1 Determination of Parameters Using Empirical Formulas and Velocity 50
• 2.5.2 Examination of Applicability on Ungauged Basin 53
• 2.6 Conclusion 57
• 3. Downstream Variations of Velocity During a Rainfall Event 59
• 3.1 Introduction 60
• 3.2 Theoretical Background 65
• 3.2.1 DHG Analysis Using Entropy Theory 68
• 3.2.2 DHG Analysis Using MSTC Theory 77
• 3.3 Derivation of Theoretical Downstream Variations of Velocity Using MSTC and Entropy Theory 83
• 3.4 Analysis for Rainfall Events of Major Dam Basins in Korea 95
• 3.4.1 Study Basin and Data 95
• 3.4.2 Variation of Peak Velocity According to the Distance 101
• 3.4.3 Variations of Velocity, Width, and Depth According to Discharge 107
• 3.5 Conclusion 121
• 4. Application of Rational Formula to Time-Distributed Rainfall 124
• 4.1 Introduction 125
• 4.2 Theoretical Background 128
• 4.2.1 Rational Formula and Modified Rational Formula 128
• 4.2.2 Application Method of the Rational Formula and Modified Rational Formula to Time-Distributed Rainfall 132
• 4.3 Comparison Using Virtual Basin 146
• 4.3.1 Virtual Basin and Rainfall Event 146
• 4.3.2 Application of Rational Formula to Time-Distributed Rainfall 151
• 4.3.3 Application of Modified Rational Formula to Time-Distributed Rainfall Event 158
• 4.3.4 Comparison and Discussion 166
• 4.4 Application of Rational Formula to Actual Rainfall Event 171
• 4.4.1 Study Basin and Rainfall Event 171
• 4.4.2 Application Results 174
• 4.5 Conclusion 179
• 5. Estimation of Velocity due to Probable Maximum Precipitation 182
• 5.1 Introduction 183
• 5.2 Theoretical Background 187
• 5.2.1 Estimation of Peak Discharge Using Rational Formula 187
• 5.2.2 Establishment of Discharge-Velocity Relationship Using Manning Formula 193
• 5.3 Application 201
• 5.3.1 Study Area and Basin Characteristics 201
• 5.3.2 Selection of Observation Data and Target Rainfall Event 204
• 5.3.3 Application to Gauged Basin assuming Ungauged Basin 206
• 5.3.4 Application to Upstream Ungauged Basin and Comparison with Downstream Observed Velocity 227
• 5.3.5 Estimation of Velocity due to PMP 243
• 5.4 Conclusion 246
• 6. Proposal of Determination Method of Unit Hydrograph Parameters for Estimating Probable Maximum Flood 249
• 6.1 Introduction 250
• 6.2 Determination of Unit Hydrograph for Estimating PMF 254
• 6.2.1 Method of Determining Unit Hydrograph in Existing Studies 254
• 6.2.2 Overview for Proposing Method to Determine PMF Unit Hydrograph Parameters 262
• 6.3 Study Area and Data 271
• 6.3.1 Study Area and Basin Characteristics 271
• 6.3.2 Data for Analysis 275
• 6.4 Proposal of the Method for Determining Unit Hydrograph Parameters for Estimating PMF 284
• 6.4.1 Estimation of Velocity for Upstream Point 284
• 6.4.2 Proposal of Method for Determining PMF-UH Parameters Through Comparison with Rep-UH parameters 308
• 6.5 Application and Evaluation of the Proposed Method 313
• 6.5.1 Analysis Overview 313
• 6.5.2 Determination of PMF-UH Parameters 314
• 6.5.3 Comparison of PMF 321
• 6.6 Conclusion 327
• 7. Summary and Discussion 329
• References 335