11/11/2022 0 Comments Class b flow hec rasNormal depth is the depth of flow in a channel or culvert when the water surface slope equals the channel bottom slope and the water depth keeps in constant (Swamee, P. Usually, normal depth is an alternative option if there is no observed data (Sredojevic, D., & Simonovic, S. Since no investigated flow data is available for water surface of study area, it was necessary to choose appropriate Steady Flow Boundary Conditions. For this project, simulation was performed under two flood return periods.ĭefining boundary conditions was the next step after flow data input. The calculation results in Table 4 was inputted into HEC-RAS as estimated flow data. According to the three trend lines of each hydrometric station, estimated 100-year and 200-year magnitude in Chilliwack River upper reach, lower reach and Slesse Creek are shown on the table below: R2 of each trend line of Flood Frequency Analysis is approximately equal 1, which statistically shows a strong relationship between recurrence interval and the peak flow. Line Graph 1,2,3 converted by the historic flood frequency Analysis results in Recurrence Analysis Page indicate the relationship between the recurrence interval and peak flow rates and forecast the tendency of changing in the future on each station. The results of the historic flood frequency analysis on each year are presented in the Recurrence Analysis Page including the discharge data collect by the government for corresponding station. M., 1987):īased on the equation mentioned above, the flood frequency analysis of each station is able to be done, and the line graph generated by the frequency analyses can estimate the discharge rates of corresponding flood return period. Recurrence interval (T) can be calculated according to the Gringorten plotting position formula (Hirsch, R. It’s rigorous to estimate flood recurrence interval with latest data so that results can eliminate the potential error from climate changes on discharge rates, since the most recent estimate of the same flood is significantly higher (Drew Brayshaw, 2016). The table below provides a summary of available flow data for different parts of the river.įlood return period is the concept of the recurrence interval of occurrence of a given flood in a given year (Gumbel, E. Since the trend of climate change Consequently, for this project, 100-year flood and 200-year flood will be calculated, which is able to involve various climate scenarios. Based on the tendency of historic flood, flow rates for different food return periods can be approximately estimated. The figure below indicates the location of three hydrometric stations. The discharge data for flood frequency analysis were downloaded from three different hydrometric stations, CHILLIWACK RIVER AT VEDDER CROSSING (08MH001), SLESSE CREEK NEAR VEDDER CROSSING (08MH056), and CHILLIWACK RIVER ABOVE SLESSE CREEK (08MH103) at the Canada Wateroffice Historic Data site (BC MFLNRO, 2016). For this project, the stream in Chilliwack River is assumed as the steady flow and is analyzed with subcritical flow regime. Within steady flow analysis, it can be resembled subcritical, supercritical or mixed flow regime. Conversely, if the depth, discharge and velocity of flow at some point changes with time, the flow is considered as the unsteady flow (Sredojevic, D., & Simonovic, S. Flow in an open channel is steady if the channel depth, discharge, and average velocity of flow at a particular location does not vary with time, or if it can be assumed constant during a given time period (Sredojevic, D., & Simonovic, S. Besides, It can handle the presence of bridges, culverts, and Manning's roughness coefficients, flow rate, depth, and velocity as well. HEC-RAS system is composed of a graphical user interface, separate hydraulic analysis components, data storage and management capabilities, and graphing and reporting facilities, and it is currently capable to supports one-dimensional steady flow calculations, one and two-dimensional unsteady flow calculations, sediment transport computations, and water temperature analysis (USACE, 2002 b). HEC-RAS is a software package, developed by USACE and designed for executing one-dimensional water surface calculations.
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