They want to improve their catchment model to better understand the water quality in Homebush Bay.

Your firm is trying to engage a new client. They want to improve their catchment model to better understand the water quality in Homebush Bay. Previously, a stormwater quality model has been developed for the 8 km2 Powells Creek catchment, which drains into Homebush Bay. The basis of this original stormwater quality model is the US EPA SWMM software.

The SWMM model uses a non-linear reservoir model for surface runoff (pond model) with a kinematic model for flows in the channel. Water quality simulation is based on simulation of the EMC (event mean concentration) rather than a pollutograph or loadograph. The focus of the water quality simulation is on the prediction of the total mass of contaminant transported during the storm event. At present only the flow quantity component of the model is being calibrated. The client would like you to demonstrate the ability to create a water quality model and provide an indicated of the future work that might be required.

The water quality component of the model is yet to be developed. The client has been very generous and shared the previous study. Data available for use in the calibration are:

1. Rainfall data
1. 6 pluviometers (i.e. continuous rain gauges) within the catchment;
2. 6 pluviometers adjacent to the catchment;
3. 1 daily read gauge within the catchment and another 6 in close proximity to the catchment; and
4. Radar images of rainfall over the catchment; these images have not been processed, (i.e. converted to rainfall depths) but they are available for the study. The resolution of these radar images is 1 km x 1 km.

2. Catchment data
1. SRTM and LIDAR based models of the topography;
2. Detailed plans of the stormwater system in the catchment (note that the catchment is serviced by separate stormwater and sanitary sewer systems);
3. Detailed maps in GIS format of land use in the catchment (note that the whole catchment is urbanised);
Soil Maps of the catchment derived from the National Soil Survey

Gauged data at one site in the catchment for 49 years. The client indicated that the approving athorities identied concerns about the rating curve at this gauge station for higher flows. This concern arises from the proximity of railway culverts and the potential for the station to be drowned during higher flows. This gauging station is located in the upper reaches of the catchment and monitors only 2.4 km2 of the catchment.

You are required to provide a detailed proposal to the client (maximum of 20 pages, includive of diagrams, drawings, references and appendices).
The file below contains the details of calibration simulations. Data included in the file for each event (there are multiple events in the file) are:

• Rainfall records from the pluviometer located at the catchment outlet;
• Recorded flow for the event; and
• Predicted flows for alternative sets of parameter values.

To prepare you have had a detailed discussion with your manager. The questions that they would like you to addresss are as follows:
Firstly

i) Select and justify a calibration metric suitable for use to assess the calibration of the quantity component of the model;

ii) Apply this metric to the available data in a manner where all events are considered concurrently. You will need to consider how the different events can be combined and to justify this approach;

iii) Select and justify the best parameter set to be used with the water quality component of the model.
Secondly

i) How the different conceptual components of a catchment model would be used in developing this model.

ii) The sources of error in predictions obtained from a catchment model with reference to the current study. How should knowledge of these errors be considered in the current application?

iii) Whether the selected parameter values would change if a kinematic wave model were to be used in lieu of the non-linear reservoir model of surface runoff.
Finally

You have been asked to improve the current catchment model. To achieve that improvement, you have time and resources available. What would you do?