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CVEN9612 – Catchment Modelling

Assignment 1 Part 1– Rainfall-Runoff Modeling and Routing

This part of the assignment is worth 15% of the total grade for CVEN9612. The assignment

answers are to be submitted online in Moodle as a short report.

Assignment 1 Part 1 is due 10pm 30th September (Week 4)

Total marks available for each part are listed below.

Question 1 – Runoff routing (15 marks)

There was a large flood on the Richmond and Wilsons Rivers in February 2024, which led to

extensive damage in Lismore and surrounding areas. The flood hydrograph on the Richmond

River was measured at Wiangaree (EL. 91m AHD) and we would like to be able to model the

hydrograph at the town of Kyogle, 21km further downstream (EL 71m AHD). The observed

streamflow hydrographs at Wiangaree and Kyogle are available on Moodle.

Using Manning’s Equation calculate a representative wave velocity for flow down the channel

assuming that the hydraulic radius of the channel is R=5.2 and it has a Manning roughness n of

0.05. Assume the wave celerity is 1.7 times the Mannings velocity.

Employ the Muskingum method to determine the best estimate of the flood hydrograph at Kyogle,

assuming that an approximate value of K can be calculated by dividing the reach length by the

wave speed. Calibrate your model to estimate the best value for x by minimizing the sum of

squared error of the prediction.

Provide a short report (less than 2 pages), with appropriate figures to answer the following

questions. Show your working where appropriate and justify any assumptions that are required.

a) What time step did you use for your calculations (in hours) and how do you know if it is

appropriate? (1 mark)

b) What is the peak of the calculated flow hydrograph at Kyogle? (5 marks)

c) What value of x did you use and how did you know this was the optimum value?

Demonstrate with the use of an appropriate figure. (3 marks)

d) What is the RMSE of the calculated outflow hydrograph compared to the observed data at

Kyogle? (2 marks)

e) What is the impact of changing the value of x to 0? What is the practical meaning of x =

0? (2 marks)

f) If there was interest in investigating Nature Based Solutions in the Richmond catchment

and riparian zone was revegetated and as a result Mannings n was 0.1, what is the new

peak flow at Kyogle? Explain how revegetation affects the routing of flows. (3 marks) 2

Question 2 – Model Calibration (15 marks)

Model aim

In this part of the assignment, you need to model the runoff and Lake Werri Berri in the Thirlmere

Lakes National Park wetland system using GR4J. The model is to be set up to understand

1. how often the lake is suitable for water sports and

2. the risk of bushfires affecting the sensitive peat ecosystem of the lake.

Water sports can only occur when the lake is more than 2 m deep and bushfire risk is too high if

water levels in lakes are less than 0.1 m for more than 30 consecutive days. The management plan

for the lakes requires decisions to be supported with 8 years of data hence why a model is required

as flow data is only available since 2011. The management plan requires the frequency of these

two events (i.e. water sports and bushfire risk) to be documented.

The aim of the modelling exercise is twofold:

(i) to understand the implications of choices in modelling such as objective function and

data transformation on lake water level predictions and what the most appropriate

choices are given the aims of the model.

(ii) To assess an alternative GR4J model for the same catchment which uses satellite

retrieved surrogates using the SRM methodology of Yoon et al., 2023 (week 3 lecture).

Assignment details

Use the AirGR and SRM packages in R to model the catchment. Instructions for AirGR and a

short video on setting up a model in AirGR are provided on Moodle. Please be aware that in the

Surrogate River discharge Model (SRM), only one objective function is available, which is

focused on minimizing the Surrogate River discharge Model Error (SRME).

Data, code, and the SRM Package can be downloaded via this link: https://deciduous-camp995.notion.site/Sharing-SRM-for-CVEN9612-e7a48b40de9b4f38a16915d1c6a07a4d

Rainfall, evaporation and streamflow data is provided for the catchment on Moodle. Data in all

files is provided in mm/day. The catchment area is 84 ha.

You can assume that the wetlands have a plan area of 10.5 ha and that water levels can range

between 0 m and 5 m. Assume that the catchment average rainfall and evaporation also apply

directly to the wetland water balance. Assume that there are no groundwater interactions and that

if water levels are higher than 5 m that all flow is lost instantaneously on that day.

You will have to select an appropriate calibration period given the data available for the catchment.

It is up to you to decide on how best to use the data that is available in setting up the model. You

will also have to decide what objective function and data transformation is the most appropriate

given the model aims.

In your short report (less than 3 pages), you need to assess at least two objective functions and two

data transformations and comment on the sensitivity of your conclusions to the modelling choices

you made when calibrating using observed flow data. You also need to compare the SRM

calibration with that for the model version where observed flows are used for calibration, noting

key similarities and differences. Provide suitable figures and tables of results to support your

conclusions. 3

Part 2 marking rubric

1 mark 2 marks 3 marks 4 marks

Description of

model set up

No details

provided and

unclear if

correct set up

used

Some details

provided or

obvious

problems with

simulations

Clear description of

set up, parameter

values and model

results

Clear and

detailed

description of

set up,

modelling

choices and

summaries of

results

Modelling 2

data

transformatio

n, 2 objective

functions,

comparison

with SRM

Only one set of

model

simulations

provided

Either two

transformations

or 2 objective

functions not

tested

4 combinations of

model set up with

discussion of

differences/similariti

es and best choice

As before, plus

an assessment

of similarity and

differences in

model with

respect to the

SRM version

Conclusions

on risk of not

meeting flow

requirements

Incorrect

recommendatio

n, no discussion

on model

limitations

Either incorrect

recommendatio

n or no

discussion on

model

limitations

Clear and correct

recommendation.

Only limited

discussion of model

limitations

Clear and

correct

recommendatio

n. Thorough

discussion of

model

limitations and

their

implications for

recommendatio

n.

Reporting

quality

Poor quality

figures/tables,

poorly

structured, hard

to understand

Acceptable

presentation

quality, with

potential for

improvements.

Well structured,

tables and figures

labelled,

grammatically

correct