Flood Analysis Study of Incheon-Gyo Catchment with SOBEK Model 24 August 2007 BLUE TEAM Advisor : Shie Yui Liong (NUS) Leader : He Shan (NUS) Members : Lee Seung Woo (UI) Lee So Young (UI) Contents INTRODUCTION OF BLUE TEAM INTRODUCTION OF WATERSHED DATA INFORMATION PRE PROCESSING WITH GIS INTRODUCTION OF SOBEK MODEL SOBEK MODEL SET-UP RECOMMENDATIONS INTRODUCTION of BLUE TEAM Advisor : Shie Yui Liong Country represented: Singapore Position : Associate Director, Tropical Marine Science Institute BLUE TEAM Team Leader : He Shan Country represented: Singapore Position : Reserch Engineer, Tropical Marine Science Institute Major : Hydrology BLUE TEAM Member : Lee Seung Woo Country represented: The Republic of Korea Position : Masters Course (National University of Incheon) Major : Environment Hydraulics Member : Lee Seung Woo Country represented: The Republic of Korea Position : Masters Course (National University of Incheon) Major : Environment Hydraulics BLUE TEAM WORK PLAN FROM 20 24 August CONTINUE WITH DATA COLLECTION GIS CONVERTION SIMULATION WITH SOBEK REPORT WRITING PRESENTATION INTRODUCTION to STUDY AREA YELLOW SEA Incheon-Gyo Watershed, Incheon, South Korea This Area was a part of Yellow Sea and is now a reclaimed land (completed in 1985) Area : 34 Length : 8 Mostly urban area Several floods recorded from 1997 to 2001 (except in 2000) INTRODUCTION Linked to the sea through two retention ponds Complicated drainage network There are 4 main drainage networks One drainage network is linked directly to the sea (NOT modeled in this study) The other networks are linked to the reservoir INTRODUCTION Field Trip Retention Pond Drainage System GIS from Incheon City Hall Contour Ground Level Manhole Sewer Network Recorded Flooding Area Rainfall Data Precipitation from raingauge Probability rainfall intensity Formula DATA INFORMATION Other Data CAD file Field Trip Photo Retention Pond Data Tidal Data PRE PROCESSING WITH GIS To generate DEM To produce TIN TIN to Grid (Cell size 50m) Defining the boundary of watershed Set up catchment shape file 7 subcatchments imported to SOBEK TIN file of the Catchment DEM of Grid Size 50x50 (Top to Bottom) Rainfall Data Rainfall event considered: 6:00~9:00 pm on 4 th Aug 1997 A severe rainfall-event which caused significant increase in water level of the retention pond. INTRODUCTION of SOBEK MODEL SOBEK is a 1D and 2D flood numerical model. It incorporates drainage systems, irrigation systems, sewer overflow, ground-water level control, river morphology, salt intrusion and water quality. SOBEK has three basic components covering any fresh water management situation in River, Urban and Rural systems alike. Each component consists of different modules to simulate particular aspects of the water system. These modules can be operated separately or in combination. Data transfer between the modules is fully automatic and modules can be run in sequence or simultaneously to facilitate the physical interaction. SOBEK-Rural 1DFLOW The SOBEK-Rural 1DFLOW module is a module that can be used for the simulation of one-dimensional flow in irrigation and drainage systems. SOBEK-Urban 1DFLOW The SOBEK-Urban 1DFLOW module is a module for the simulation of one-dimensional flow in wastewater and storm water systems. It is a tool that can be used to simulate and solve problems in urban drainage systems. Task block Settings The Rainfall-Runoff module is a module that can be used for the simulation of rainfall-runoff processes. The Rainfall-Runoff module is frequently used in combination with the SOBEK-Rural 1DFLOW and SOBEK-Urban 1DFLOW modules. SOBEK-Urban Rainfall-Runoff Concept The inflow towards the sewer system consists of runoff from rainfall and dry weather flow. The Runoff model of Flow-Manhole and Flow-Pipe, also called NWRW model, describes the dry weather flow and the transformation in time of rainfall into runoff entering the sewer system. The Runoff model is based on the guidelines. Different types of surfaces can be distinguished, depending on surface characteristics and slope. The model distinguishes four types of surfaces (closed paved, open paved, roof, unpaved) and three types of slopes (area with a slope, flat, stretched flat), thus twelve different area types. The slope of the surface and the infiltration capacity largely influence the rainfall-runoff process. The infiltration of rainfall takes place in the open paved areas and unpaved areas. The infiltration capacity depends mostly on the type of surface and moisture condition. Other factors may also play an important role. Rainfall-Runoff Process Rainfall-runoff Process The runoff over the sub-catchment surface to the Manhole is described by the following formula (which is the formula of the Rational Method): q = c. h (1) where q is the inflow into the Manhole (in mm/min), c is the runoff factor (min-1) and h is the rainfall (in mm). The flow in the Pipe is described by the Manning formula (assuming the pipe is rectangular in cross-section): Q = (2) where n is the Manning coefficient, b is the width, H is the water depth and I is the bed slope. Water flow equations The water flow is computed by solving the complete De Saint Venant equations. Dynamic wave Water flow equations Dynamic wave The rainfall-runoff process is conceptualized using the following two network elements in SOBEK: 1.Flow Manhole with Runoff 2.Flow Pipe The Manhole stores the total runoff (or acts as a collection point for the runoff) and the Pipe conveys the stored runoff to the main pipe. 1 Dimensional Flow Model Sub-catchment conceptualization Sewer Network & Manholes Retention Pond Drainage System Recorded Flood Areas (4 th Aug 1997) SIMULATED FLOODED AREA 1 1 SIMULATED FLOODED AREA 2 2 SIMULATED FLOODED AREA 3 3 Retention Pond Drainage System Reservoir Operation CASE 1 CASE 2 CASE 3 CASE 4 Rainfall Data Rainfall event considered: 6:00~9:00 pm on 4 th Aug 1997 A severe rainfall-event which caused significant increase in water level of the retention pond. Total catchment area (m2) : Rainfall in 6 hours (mm) : _________________________________________________ Total rainfall volume (m3) : Total Discharge volume in 6 hours (m^3) : Simulated discharge when the reservoir water level is at EL +2m FLOODED AREA 1 1 Street level FLOODED AREA 2 2 Street level FLOODED AREA 3 3 Street level 1.Sobek model simulation could yield water level time series at any node, and discharge time series at any reach. 2.Simulation results show that SOBEK simulated flooded areas (such as areas 1, 2, and 3) match reasonably well with those recorded/observed. 3.Comparison was also performed to check rainfall volume (of a particular event) with discharge volume at the downstream section. The mass balance is quite satisfactory. Conclusions 4 As 3 main drainage networks link with the reservoir, we put the water level at the reservoir as our model boundary condition. The situation at the reservoir is very important to model simulation, since the real water level at reservoir is unavalible, so it is necessary to study the different water level cases. Besides, we also studied when there is no reservoir, that means, use tide data as boundary condition to simulate. After get the result, we compare and get some conclusion. Conclusions 1 With the result analysis, we can see the different water level at the reservoir has impact to the upstream, especially the flood area water level. We can study more scientific and practical reservoir operation. 2 As there is no real discharge, so this time we did not calibrate. In the future, if the data can be obtained, we need to conduct calibtation. 3 This time we only conducted 1 D simulation as the 2D simulation of sobek has some problem. So later we also will conduct 2 D simulation. Suggestion in the future