Morphological and Hydrological Aspects of the Three Reaches of the Sullivan Creek in Canberra, Australia. A Student's Overview

TABLE OF CONTENTS

1. Introduction
1.1.General Description of Sullivan Creek and Catchment
1.2. Previous Studies
1.3. Aim and Objectives of the Study
1.3.1. Aim
1.3.2. Objectives

2. Study Sites
2.1. Description of the Sites
2.2. Type and Form of Channel
2.3. Bed Materials
2.4. Flow Condition
2.5. Vegetation
2.6. Field Description of Topography and Land Use

3. Methodology
3.1. Sampling Program
3.2. Equipment
3.3. Procedures

4. Results
4.1 Stream Morphology (Shape and Structure)
4.1.1 Cross-sectional Measurement
4.1.2. Cross sectional measurement of channel in Reach 1
4.1.3. Cross sectional measurement of channel in Reach 2
4.1.4 Cross sectional measurement of channels in Reach 3
4.1.5. Cross sectional measurement of rectangular channels in Reach 3
4.1.6 Composition of bed and bank material (clay, silt, sand, gravel, cobbles, boulders)
4.1.7 Bed slope (as a reach mean)
4.2. Flow characteristics
4.2.1 Estimation bed roughness for Manning’s n
4.2.2 Estimation of velocity using Manning’s equation
4.2.3 Measurement of velocity
4.2.4 Measurement of discharge using cross sectional area method
4.2.5 Estimation of discharge with reference to the derived value of velocity from Manning’s equation
4.3 Water Quality
4.3.1 Water Quality Parameters in Reach 1
4.3.2 Water Quality Parameters in Reach 2
4.3.3 Water Quality Parameters in Reach 3

5. Discussion
5.1. Stream Morphology
5.1.1. Channel Shape and Structure
5.1.2. Bed and Bank Material
5.1.3. Bed slope (gradient)
5.2. Flow Characteristic
5.2.1. Disparity between direct measurement and estimation of flow
5.3. Hydrological variability of reaches in the creek
5.3.1. Hydrological characteristics of Reach 1
5.3.2. Hydrological characteristics of Reach 2
5.3.3. Hydrological characteristics of Reach 3

6. Conclusion

References

1. Introduction

1.1.General Description of Sullivan Creek and Catchment

The area of this study, which is known as Sullivan Creek has a length of 13 Km and constitutes the major hydrological system particularly in the northern part of Australian Capital Territory (ACT). It serves as an important stream flowing to Lake Burley Griffin, as well as water replenishment for the 53 Km[2] catchment area surrounding it (Beavis, 2008).

The creek catchment area is bounded by Mount Ainslie and Majura Ridges in the east and Black Mountain and O’Connor ridges in the west. Laid along these ridges are a number of vital conservation areas. Geological formation of the catchment varies from sandstone (Black Mountain and O’Connor ridges), shale, limestone and silt stone (O’Connor and most of the valley floor), volcanic (Mount Ainslie, Mount Majura and the northern hills of the catchment) and quaternary alluvium (adjacent to Sullivan Creek and its tributaries) (Dyer, 2000) (See Figure 1).

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Figure 1. The Map of the Sullivan Creek

Source: adapted from Dyer, 2000

The creek’s catchments consist of urban areas (40%), rural areas (40%) and conservation sites (11%). The number of people residing within the catchment is approximately 31,142 (ABS, 1996 cited in Dyer, 2000). Land use type within the catchment is assorted, predominantly single family housing, playground, sports ground, University precinct and grazing areas.

1.2. Previous Studies

The previous study with regard to Sullivan Creek was the one commissioned by ANU Division of Facilities and Services, and conducted by Fiona Dyer in 2000. This study was aimed at investigating composition and source of nutrients, particularly Nitrogen and Phosphorous, which the creek contains. There are a number of information that can be derived from this study for instance:

- Sullivan creek is aberrantly high with nutrients, exceeding aquatic ecosystem standard (for Nitrogen and Phosphorous).
- Concentration of nutrients in the creek is highly influenced by seasonal variation of flow.
- Temperature has a significant influence to concentration of particular nutrient or particular form of nutrient within the creek.

1.3. Aim and Objectives of the Study

1.3.1. Aim

This study is aimed at familiarizing students with sampling techniques for water quality and stream flow (inclusive flow velocity), and analysis of the data collected.

1.3.2. Objectives

The main objectives of this field observation:

1. To assess the stream condition based on its water quality and loading ability of the stream.
2. To understand various factors that may contribute to the water quality (physical, biological and chemical properties) and stream flow (surface flow, base flow, vegetative covers, anthropogenic factors, channel, shape and structure, etc)
3. To compare water quality parameters in the 3 reaches, namely at constructed and instream wetland at David Street O’Connor, the concrete line section from David Street wetlands to Barry Drive Gross Pollutant Trap (GPT) and the earthen channel from Barry Drive to Lake Burley Griffin.

2. Study Sites

2.1. Description of the Sites

This study was carried out in 2 lines. Sampling line 1 located at midstream of the Sullivan Creek and sampling line 2 located downstream, with Gross Pollutant Trap (GPT) located near Barry Drive as the reference point. The first sampling line starts from Barry Drive GPT further up to the artificial wetlands at David Street O’Connor, while the second sampling line begins from GPT further down to the earthen channel alongside the Australian National University (ANU) and ending at Lake Burley Griffin (See Figure 2).

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Figure 2. The Sketch of Distribution of Sampling Sites (a. Sampling line 1; b. Sampling line 2)

Source: Adapted from Dyer, 2000

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Figure 3. Barry Drive Gross Pollutant Trap as the reference point

Source: photo by Meisya

A number of sampling sites are installed across 2 lines. At first line, two sites are located downstream of GPT, two sites spread around O’Connor channel, and the rest lied down at intersection between O’Connor channel and mainstream. While for second line, seven sampling sites were placed randomly, represent representing particular characteristic of downstream, midstream and upstream of the section.

Description of position of each of sampling site is presented in the following table.

Table 1. Description of position of sampling sites

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2.2. Type and Form of Channel

Channel the Sullivan Creek can be divided into constructed and semi-constructed channel. In sub-urban section of the catchments, most channels are fully engineered and made from concrete. Main channel in this midstream section of the creek is observed to be similar in terms of form, size, slope and pattern. They are generally in trapezoidal form, 4-5 meter bed width, 30% slope and tend to be straight. Sub-channels, on the other hand, are fairly different. They are much more diverse in terms of shape (rectangular and pipe), smaller in size (bed width and depth), flatter in slope (flatter) and rather curved in pattern (meandering).

These kind of variation are probably common in irrigation construction. Main channels are generally designed to occupy greater amount of discharge/run off/debris and higher rate of transportability. In contrast, inflow channels are in a particular sense designed to occupy smaller portion of discharge from specific sub-section of a catchments (for example a particular urban housing area) and expected to be lower in stream flow.

In earthen reach of the creek that crosses through the ANU precinct, most channels are slightly engineered (except one medium size in stream channel downstream ANU Avenue). Typically, the channel banks are rough stone wall, while the bed portion is left natural. Form of the channel within this specific catchments is generally trapezoidal, with slope of around 30% and larger size (bed width and depth) compare to channeled lined upstream of Barry Drive GPT.

The reasons why this section is maintained naturally, is to support the biological activity of biotic components within the catchments, as well as to encourage supplementary groundwater recharge. With such preservation, in addition, it is also likely to improve the aesthetic value of the scenery in surrounding area.

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Figure 4. Different types of channel along the Sullivan Creek (top left: trapezoidal channel with an artificial instream wetland at David Street O’Connor; top right: concreted trapezoidal channel prior to Barry Drive Gross Pollutant Trap; bottom left: Earthen channel downstream of Barry Drive; bottom right: In stream channel at downstream of Canberry Bridge with rectangular form.

Source: photo by Meisya

2.3. Bed Materials

Generally, bed materials of channels within the creek may consist of debris of abiotic component (such as sand, clay, silt, gravel, cobble and boulders), and/or biotic component (such as leaves, grasses). The predictable composition of bed materials at each section can be described as follow:

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2.4. Flow Condition

Flow condition of channels in the creek is highly variable and responsive to seasonal variation of rainfall and storm water production. Hydrological variation of the creek can be described as follow:

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Source: adapted from Beavis (2008)

2.5. Vegetation

Vegetation structure which constructs ecosystems in surrounding area of the creek is generally a combination of native and exotic species of either trees or grasses. Vegetative cover in each section of the creek is highlighted in the table underneath.

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2.6. Field Description of Topography and Land Use

General description of topography and land use at each reach of the creek is highlighted in the following table.

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Figure 4. Vegetative covers of each section of the channel (a) and b): a mixture of trees and grasses nearby constructed and in stream wetland at David Street O’Connor; c) and d): Sclerophyllous vegetation and exotic grasses along concreted line upstream of GPT; e) and f): introduced tree species that construct ecosystem in surrounding earthen channel.

Source: photo by Meisya

3. Methodology

3.1. Sampling Program

Sampling was carried out for 2 days, with the interval of five days. The first sampling conducted at the first sampling line, started at Barry Drive GPT up to constructed and in stream wetland at David Street O’Connor. The second sampling conducted at second sampling line, begun from grassy area prior to Toad Pond down to Creek’s mouth at Lake Burley Griffin.

Sampling program consists of water quality testing and stream flow measurement (stream morphology and flow characteristic). Water quality testing was achieved through gauging of physical parameters such as Electrical Conductivity (EC), temperature (°C), and turbidity, and chemical parameters for example pH and Dissolved Oxygen (DO)¹. Stream flow measurement was conducted by characterizing cross-sectional areas, bed slope, bed and bank material, and flow characteristic.

The specific role of each parameter taken in this practical is described in Table².

Table 2. Description of parameters measured

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Source: compiled from Davie (2003)

3.2. Equipment

Equipment used in this practical consist of multiprobe meter, turbidity meter, distilled water, flow meter, clino meter (suunto), stopwatch, large and small tape meter, stopwatch, tape meter (long and short one), marking stick (with red and white strips), floating stick, pocket camera and notebook. The use of each of these is presented in Table 3.

Table 3. Equipment engaged in observation and their use

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3.3. Procedures

A. Water Quality Testing

1. Determine the number of sampling sites to be taken in each of the lines, and define carefully how can these particular points help in analysing channel characteristic. Remark the possible constraints that would be faced by having these points.
2. Take exact sampling location by drawing a sketch derived from a formal topographic map or Google earth.
3. Record earth coordinates by using a GPS (if possible) and put it into the sketch
4. Begin the readings of EC, temperature, pH, DO and turbidity in each sampling site, and record them accurately. In order to approach actual value of each indicator, reading may be taken more than one time (e.g. three or four times).³
5. Take some notes on depth, clarity, odor, flora and fauna in surrounding sampling site.

[...]

¹ DO was not tested in this practical due to a technical problem (unable to get reading with meter consistently submerged in stream flow during a 5 minute time period). Data was taken from the other graduate student’s group

² This tool was only introduced in terms of its usage, but was not actually used because of low flow condition

³ turbidity in this practical was only read once per sampling site