LESSON HEC-HMS

Transcription

1 LESSON HEC-HMS Introduction: TEAM 8 SCS method: The input data: Thiessen Polygons: Concentration Lag Time: SCS Method: Calculation of CN: Result figures: CONSTRUCTING HYDROGRAPH WITH HEC-HMS: Rainfall distribution by Theissen polygons: Manage to Run: CONCLUSION Introduction: The objective of this exercise is a general understanding of the theatrical background and application of SCS method and the unit hydrograph in the hydrological analysis of river catchment. It is the main target of this assignment to obtain a suitable hydrograph at the catchment outlet. The hydrograph can be obtained by using either the provided Excel sheet or by applying the software HEC HMS. SCS method: In the Excel file SCS_method.xlsx, there contain 7 different tabs, which are: INPUT_rainfall_daily_1994, INPUT_gis_results, Thiessen Polygons, Concentration_lag_time, SCS_method, result_figures, limb_ratio_peak_factor. The input data: Here we have the recorded daily rainfall data from to at 6 different stations: The following graphic show that the maximum rainfall daily has been measured in ROQUESTERON with mm in January. The picks are also more noted in Levens, Saint-Martin-Vesubie in autumn and winter season. 0

2 We also need the results of GIS analysis from the first exercise, which are categorized by four different sub-catchments: Tinée, Upper Var, Esteron, Vesubie, and Lower Var. Thiessen Polygons: We use the data here to calculate the rainfall distribution for each sub-catchment based on the concept of Thiessen Polygon. In the table THIESSEN Parameter, the percentage of which rainfall station contributes to which sub-catchment is listed. For instance, 0.02 means that the rainfall station Levens contributes 2% to the sub-catchment Tinée. In this respect, the resulted rainfall for the subcatchment Tinée for each hour is: Thiessen parameter of Carros * Rainfall of Carros + Thiessen parameter of Levens*Rainfall of Levens + Thiessen parameter of Roquesteron* Rainfall of Roquesteron + Thiessen parameter of Puget Théniers *Rainfall of Puget Théniers + Thiessen parameter of Guillaumes * Rainfall of Guillaumes + Thiessen parameter of St. Martin Vésubie * Rainfall of St. Martin Vésubie. The variations of the rainfall distribution in Tinee and Lower Var sub-catchment 1

3 Concentration Lag Time: The Concentration Time is the time it takes water to travel from the hydraulically most distant part of the contributing area to the outlet. The Lag Time the delay between the beginning of input and the beginning of the rise of the hydrograph. The result of Concentration and Lag Times are in the following table: SCS Method: To generate the hydrograph using SCS method, several parameters have to be calculated, and they are peak discharge (qp), time to peak (Tp), lag time (Tlag), and recession time (Tr). Some of these parameters (Tp and Tlag) are already calculated in the previous tab concentration_lag_time. To calculate other parameters, we need Curve Number (CN), limb ratio, and peaking factor. The sum of precipitation based on Thiessen calculations to calculate Direct Runoff (Formula I) for each sub-catchment [mm]: Tinee: , Upper-Var: Esteron: Vesubie: Lower Var:

4 Calculation of CN: The Curve Number (CN) is determined by hydrologic soil group (HSG: A,B,C,D), land cover type (forest, artificial sealed surface etc.), and antecedent runoff condition (ARC soil moisture prior to event). We can select our CN number based on the TR-55 table given in the Excel sheet and then, based on the area weight of each land use type within a sub catchment. The representative CN for each sub-catchment is calculated automatically. Result figures: In this step we have used the data which we have been calculated in the previous steps (Lag time, time to peak, recession time, peak discharge). Then, we choose an interval of time, it started from 0.0 hrs then it forward with a step equal to the time to peak and finish with a step equal to the Time to peak + recession time. The results are in the two following table: The graphic presentation of the time (hrs) and the discharge (m3/s) shows the behavior of each sub-catchment according to the discharge and the time. 3

5 CONSTRUCTING HYDROGRAPH WITH HEC-HMS: HEC-Hydrologic Modeling System (HEC-HMS) model components are used to simulate the hydrological response in a watershed. HMS model components include basin models, meteorologic models, control specifications and input data. After creating a new project and setting up all SCS properties for each sub-basin: Hydrologic Elements, Sub-basin, Loss, Transform (see figure) we can add the meteorology model by creating time series data for each rainfall station. Rainfall distribution by Theissen polygons: In this step we will build the meteorologic model manager, after that we will specify the followings Tab meteorology model and the tab bassins. Then, we will add the proper ratios (Thiessen parameters) from the xlsx file. We manage our rainfall distribution through the built-in "Meteorologic Model Manager". After the meteorologic data are setting, the model is ready for simulation. Manage to Run: In this step we will prepare the control specification through: Component Control specifications Manager. We specify the proper name, the basin model, the meteorological model, the control specification. After creating the control specification and précising the simulation specifications, we specify the period. Then we start the simulation by selecting RUN. The results obtained are representing below: The table contains a representation of the peak discharge in each sub-catchment, the time of peak and the volume of water drained. 4

6 Output value at the junction 2 Output value at Vesubie Basin CONCLUSION Output value at Outlet of the Basin In this assignment we learned to use two methods to construct hydrograph, we firstly have used Excel to calculate the discharge starting by calculating the rainfall distribution by using the Thiessen polygons, then we calculate the Lag time and CN in each sub-catchment that we used to calculate the direct runoff and the peak discharge for each sub-catchment: The result is the graphic of the discharge of each-subcatchment and the outlet. In the second method we started with creating the HEC-HMS project and using the data of the Var catchment of the previous assignment 1 (.shp). Then we input the data in HEC-HMS (Area, CN, Name), we have created the own time series. After that, we have defined the Rainfall distribution by using the Thiessen Polygons. Also, we have created a specification manager and created a simulation run. The result is a graphic representation of the flow and the depth according to the time. Then we finish and conclude the discharge (m3/s) in each sub-catchment and in the outlet of the Var catchment. 5