Mr Sean

Topics: Fluid dynamics, Volumetric flow rate, Force Pages: 9 (2500 words) Published: June 18, 2013
The projects objective is to design a bridge spanning across the Murrumbidgee River located near Gundagai. Through the use of hydrological data and hydraulic analysis we will determine the required height of the bridge corresponding to a specific frequency of flood. To design a bridge capable of spanning the Murrumbidgee River and flood plain will require hydrological analysis which takes into account all upstream data that is required for the catchment area of the river that will pass Gundagai. Once the hydrological data has been found we can continue with determining the hydraulic analysis. The hydraulic analysis is used to determine the flow rate at the bridges location, and in the scenario of the Gundagai region we will be using a 1 in 100 year event which is chosen per the Australian Standards. Throughout the Hydrology segment of CIVL444 there will be 2 different methods used to determine flow rate, these are the Flood Frequency Analysis (FFA) and the Watershed Bounded Network Model (WBNM). The first method relies simply on past history of floods that have occurred in the past, and the second method is a computer program that analysis a flood based on gauge data. Once the flow rate of the river is determined we can begin hydraulic analysis on the bridge. The cross sectional area of the river and the soffit level are other factors required when working out the hydraulic analysis. The soffit is the under surface of the bridge superstructure, it has to be a required height in relation with the Roads and Traffic Authority (RTA) NSW. In a 100 year event there has to be an allowance of 300mm gap from the top of the water level to the lowest part of the bridge deck. The hydraulic analysis will look at the forces on the bridge piers as a result of debris crashing into them and the forces of the water. The foundations of the piers will also be investigated for local scouring. The bridge will be designed in relation to the Australian Standards and the RTA NSW.

Flood Frequency Analysis
Flood Frequency Analysis (FFA) is an analytical technique that involves the use of historical annual peak flow data to calculate statistical information. With the historical information provided for the Gundagai region we were able to accurately calculate the mean discharge, standard deviation, skewness, hydrographs and recurrence intervals. The flood frequency analysis provides a peak discharge based on the history of the past peak discharges. The more historical data the more chance we have of creating a probability of a certain size flood will occur. Hence this lets us calculate a 1 in 100 year flood which this size of flood should only take place once in any 100 year period. This yearly estimate corresponds to an Annual Exceedence Probability of 0.01. Using FFA we will determine the size of the one in hundred year flood so we can then use the figure to further research the hydraulic analysis. The analysis of the discharge data from the correct area is crucial as it plays a vital role in determining the height level of the bridge. The Murrumbidge River at Gundagai is where the bridge is to be located. The annual peak discharge data was collected over a period of 125 years (from 1887 to 2011) and is presented in a table (include table no.). The effect of two major dams in this analysis is not considered and should be using temporary storage for the flood results recorded. When the design is complete the bridge will be capable of surviving extreme floods that occur once in every one hundred years. Data

The flood was given in ML/Day which was converted into Q m3/s which gave us a new value which we could then continue to analysis the data, once this was completed the new Q value was placed in an ascending order from smallest to largest. This mean we could then find the mean, standard deviation and skewness which eventually resulted in us finding the flow rate for the Murrumbidgee River.

Hydraulic Analysis
The height and...
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