Reference no: EM132322671

Assignment

The Lachlan River in central NSW is approximately 1200 km in length from the head waters to the confluence with another river and a number of small and medium size towns are located along the length of the river. Wyangala is located near the headwaters, and Gooloogong is about 110 km downstream of Wyangala.

The design flow of the river is 30 m3s-1. Your client is the Town Council of Gooloogong, and they have asked you to design a culvert for a road river crossing at Gooloogong. Unfortunately your client does not have very good background information.

Some physical surveys of the river have been done, but the raw data has been lost or is not available. However, some data is presented in tabulated and graphical form in the following paper: Kemp, J., (2010), ‘Downstream channel changes on a contracting, anabranching river: The Lachlan, southeastern Australia’, Geomorphology, 121:231-244.

The tabulated data given in Kemp (2010) (Table 3) is for ‘bankfull’ flows, that is flows at which at some point the stream is about to flood. The cross sections given (Figure 3) also show the location of the bankfull surface.

Note that the design flow is significantly less than the bankfull discharge. You may need to estimate cross sections for flows less than the bankfull discharge. The client has given you the following design parameters: Design Discharge is 30 m3s-1

The maximum allowable velocity in the culvert is to be such that mobilisation of the sediments is unlikely at the design discharge The maximum headwater at the design discharge must be less than the bankfull depth at the first monitoring site upstream (station 7) The road is 10m wide with two traffic lanes and a road crossfall of 3% towards shoulders from the centreline.

The road pavement thickness is 500mm and it is to be the minimum cover over the culvert at any point in the crossing. The allowable headwater at the culvert is 100mm below the road shoulder height to avoid any potential damage to adjacent upstream properties.

The bed slope of the culvert should match the stream bed slope. The channel cross section upstream and downstream of the culvert may be taken as the cross section at Gooloogong The culvert is 15.6m long and is a concrete box of a size specified in the manufacturers catalogue.

Culvert Entrance type to be square edge with headwall. If necessary, more than one barrel may be used. Information on the sediments in the stream can be found Kemp (2010), and the suggested outlet velocities for different sediments in the AusRoads Design Manual.

Question :

Prepare a professional report, outlining the methods and assumptions you have used, the culvert design, and a culvert performance curve (HWL vs Q) for your design.

Use HEC RAS or some other culvert software to help with your design. Discuss the potential for overtopping of the culvert at the bankfull flow.