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
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