GEOG 309 10-52
Group 5ix
The role of land use in the
sedimentation of the Lyttelton Harbour
basin
Prepared for: Lyttelton Harbour/Whakaraup6 Issues Group
By: Justyna Giejsztowt, Melissa Shearer, David Gainsford, Roseanna Dale and James Parsons.
College of Science
Department of Geography
15th October 2010
GEOG309 Project Report Disclaimer
DCWUNIVERSITY OFCANTERBURYTe Whare l~-al1attga 0 WaitahaCHRISTCHURCH l'EW ZEALAl'D
This project report has been completed as part fulfilment of the requirements for GEOG309Research Methods in Geography. This is an undergraduate course offered at the University ofCanterbury in New Zealand.
The intended audience for the project report is GEOG309 academic staff and Community Groupmembers. The report discusses the project aims, methods, key findings and conclusions.
It is important to recognise that the report is the outcome of an undergraduate learning experiencerather than a piece of professional consultancy.
As such, the following clauses apply to the project report and its use:
(a) the project report is offered in good faith but, reflecting its origins in a student learning exercise,no responsibility can be taken for any errors of fact or interpretation herein, nor for any loss ordamage arising from use or interpretation ofthe project material;
(b) the views presented are not the official position of the University of Canterbury;
(c) the project report is not intended or suitable for use as evidence in planning or other forms oflegal negotiations;
(e) the project report and its component parts are not, under any circumstances, to be reproducedin any form for commercial gain;
(f) if paper copies of the report or its parts are made for particular purposes by the community groupfor which it is intended, then a copy of this disclaimer page (or an appropriate summary thereof)should be included with any excerpts.
Table of Contents
Executive Summary
1.0 Introduction
2.0 Methodology
3.0 Results
4.0 Discussion
5.0 Limitations
6.0 Recommendations
7.0 Conclusion
8.0 Acknowledgements
References
1
3
7
11
15
21
22
24
25
25
"
Executive Summary
• Since European settlement, drastic changes in land uses have occurred
resulting in accelerated rates of sediment accumulation within the harbour.
This is affecting shipping access to the port and degrades the harbour as a
habitat for aquatic life. Therefore an assessment of the sources of sediment
from different land uses is required to enable targeted mitigation of the rate
of sedimentation.
• Research questions posed for this project were: which combinations of land
uses within the Lyttelton Harbour catchment produce and deliver the
greatest amount of suspended sediment into the harbour? What practical
management changes can the Lyttelton Harbour Issues Group implement to
decelerate and mitigate sedimentation?
• Research on sediment flow into Lyttelton Harbour from catchments
incorporating a variety of land uses was undertaken, in order to investigate
the relationship of these land uses to sediment outputs from streams.
Quantitative measurements of sediment outputs were obtained using water
sample and turbidity analysis. Stream and catchment characteristics including
land uses were obtained qualitatively through personal observations and
digital analysis. Land uses within catchments were classified as urban,
agriculturat quarrying and forest.
• We have determined there are noticeable differences in the sediment
outputs from different catchments within Lyttelton Harbour. Te Wharau
stream which drains a predominantly agricultural catchment is providing the
highest amount of sediment to the harbour followed by Foleys Stream which
is adjacent to an active quarry site. Forested and urban catchments are
contributing the least amount of sediment into the harbour. Weather within
the harbour has a major control over characteristics of streams.
1
"
• Our research indicates a future remedial measure for high sediment flows
into streams could be the utilisation of riparian buffer zones, as these result
in a function similar to the natural forested condition of the harbour.
• A major limitation for this research were the difficulties in sampling stream
flow rates during storm events, which would gauge the level of sediment
outputs during high flow conditions which are most significant for erosion
rates. In addition, sampling of ephemeral streams, which flow during storm
events, would strengthen our findings. As this work was only completed over
a small time frame, the small sample sizes obtained pose difficulties in
making reliable inferences about the harbour as a whole.
• Future research should therefore focus on sediment outputs during high
rainfall events in both permanent and ephemeral stream networks. A wider
range of streams should also be sampled over a longer time period to gain a
better understanding of the system as a whole.
2
1.0 Introduction
This report aims to explore and quantify the sources of sediment to into Lyttelton
Harbour attributing to the sedimentation issues. Research questions and objectives
we intend to answer are:
• Which combinations of land uses within the Lyttelton Harbour catchment
produce and deliver the greatest amount of suspended sediment into the
harbour?
• What practical management changes can the Lyttelton Harbour Issues Group
implement to decelerate and mitigate sedimentation?
Starting with a literature review, our methods and results are then presented and
discussed, followed up by our recommendations to Lyttelton Harbour Issues Group.
Rapidly increasing rates of sediment transport from the land into coastal systems via
fluvial networks (streams and rivers) is a global phenomenon which has been
increasing in magnitude since the advent of permanent agricultural practice (Walling
2006). The processes of sediment erosion and delivery have pronounced effects on
the Earth's surface and the well being of its inhabitants. The destabilisation of soils is
an issue globally; however solutions must be tailored to local conditions (Scheurer et
al. 2009). Physical considerations such as the climate and regional soil and
vegetation types must be considered together with the economic and social values
of land (Stutter et al. 2007). Therefore, when we looked to combat sedimentation
issues in a local harbour, a holistic approach had to be adopted.
1.1 Study Site
Lyttelton Harbour, located on Bank's Peninsula, New Zealand is a topographical
feature with many contrasting uses, both culturally and economically. A ring of steep
hills feed numerous streams which transport large quantities of sediment into the
harbour. European settlement in c. 1830 AD resulted in the peninsula undergoing
3
drastic changes in land use (Goff 2005). This long history of modification to the land
surface and subsequent destabilization has led to the present day sedimentation
issues within the harbour. Historically, Banks Peninsula was covered in dense native
podocarp forest, which has been all but completely felled. The development of road
networks, small settlements, farming blocks and a quarry further compounded the
fundamental changes to Banks Peninsula and Lyttelton Harbour. Goff (2005)
completed a preliminary core study of the upper Lyttelton Harbour and found a clear
correlation between European settlement and an increase in sediment accumulation
rates. Prior to human settlement, accumulation of sediment was occurring at
0.08cm/year. A subsequent acceleration in accumulation rates occurred with a peak
of 0.85cm/year in the early 1900's. During this time, $$ transition occurred from the
sediments being less than 20% silt to nearly 100% silt and enriched with organic
material. The present accumulation rates are similar to that of the initial stages of
colonisation (Goff 2005). It is now widely accepted that the enhanced sedimentation
is not attributed to natural depositional processes but the modification to land use
(Hart 2004, Goff 2005, ECan 2007). It has been estimated that 44300ta-1 (tonnes per
annum) of soil is eroded (Goff 2005) which over time has resulted in 47 metres of
sediment deposited within the harbour and the creation of the mudflats in the upper
harbour which cover an area of llkm 2 (ECan 2007).
Sedimentation is a persistent issue within this shallow harbour as it alters
bathymetric water flow within the basin (Jaffe et al. 2007) and hinders shipping
access to the port. Moreover, rapid sedimentation is having drastic effects on
harbour ecology, altering community structure by smothering benthos and
degrading habitat (Walling 2006). Little is understood about long- term erosional and
depositional patterns in Lyttelton Harbour, making effective management difficult to
implement (Jaffe et al. 2007). The Lyttelton Harbour Issues Group, a local community
group, has identified a need to discern the processes by which streams contribute to
harbour sedimentation. More specifically, stakeholders must have a grasp of the
effects that a number of current land uses are having on sediment outputs from
streams.
4
1.2 Effects of land uses on erosional processes
Erosional processes have a profound effect on the way in which land uses contribute
to sedimentation. Soil type, soil moisture content, and underlying geology are pivotal
in determining susceptibility (Russell et al. 2001). Carling et al. (2001) states that "the
vulnerability of soils to erosion depends not only on such factors as climate,
topography and soil characteristics, but also on the type and intensity of land use".
Water is a particularly dominant transport agent. A protective vegetative cover can
decrease erosion rates by lowering the water table, reducing surface water velocity
and intercepting raindrop impact. Impermeable urban surfaces will also decrease
sediment erosion due to a lack of ground infiltration; however they may result in
larger peak discharges (Nelson and Booth 2002). The transport of eroded sediment
into deposition zones leads to sedimentation which is problematic for aquatic
systems. Benthic organisms and fish are suffocated by mud layers being laid down on
the sea bed and delicate gills and mouthparts of fauna are damaged by sediment
remaining in suspension (Niyogi et al. 2007).
Connectivity of the eroding land to fluvial systems is fundamental to sediment
delivery (Outeiro et al. 2010). Small catchments, like those on Bank's Peninsula, have
particular sediment export issues because of high inputs from steep slopes and no
floodplains which normally act as a sediment sink. Trends in erosion are complicated
by climatic factors. Soil concentrations in runoff vary with rain intensity (Mwendera
and Saleem 1997) and frequency (Kreutzweiser et al. 2009) therefore storm events
can have profound impacts. Variations in climate between the bays of Lyttelton
Harbour could therefore have an influence on the amount of sediment produced
within each catchment.
Suspended sediment is a diffuse rather than point source type pollutant, meaning
that to remedy the issue the root must be dealt with (Stutter et al. 2007), as land use
is the root of the issue in Lyttelton Harbour, its effects must be mitigated. Land use
5
within Lyttelton Harbour is a mixture of extensive agriculture, urban settlements,
forested blocks and a small quarry. Each land use has fundamentally different
surface characteristics which results in clear differences between the rates of
sediment output from these land uses.
1.3 Literature Review
The literature concerning erosion and sedimentation as a consequence of land use
change is extensive. Initial literature searches were performed to obtain an idea of
knowledge about the role of land use in sedimentation in a range of New Zealand
and international examples. The results of searches into urban, agricultural, forested
and quarrying land uses have been incorporated into the discussion section below.
Knowledge about the erosional process, ephemeral streams and how weather
variations can affect erosion was also obtained from a wide range of sources.
Detailed information specific to each landuse type is elaborated further under the
Discussion section in relation to our results. Answering our research questions
encompassed using this existing knowledge in addition to our findings in the field.
6
2.0 Methodology
2.1 Theoretical Analysis
Desk studies for quantifying and classifying the catchments in the harbours consisted
of aerial photo and topographic map interpretation, which were our first steps in
focussing our research. Reviewing and analysing literature of relevance was also
important in order to gain a grasp of concepts being dealt with in the project topics
and research process.
2.2 Field Methods
Five streams were chosen around the inner harbour area (Fig. 1), which were chosen
as representative of typical catchments in that region of the harbour.
Figure 1: Locations of
samples taken in streams in
the upper harbour basin.
The colours of the symbols
denote the stream
catchment name and are
also used in Table 1. Full
size image is in Appendix.
7
We aimed to encompass the range of land uses which we had previously determined
by map and aerial photo interpretation to be predominant in Lyttelton Harbour,
these being limited to agriculture, forest, urban and quarry (Table 1). Each of the five
streams was sampled in two locations, with a site in both the upper and lower
catchment. Sites were chosen preferentially at land use boundaries, so as to
encompass the effects of different land uses. A site specific description was noted at
each sampling site for purposes of individual comparison and repeatability.
Table 1: The five streams sampled during this study and the land uses present within each of their
catchments broken down into local land use and predominant catchment land use. Site 1 was in the
lower catchment while site 2 was in the upper catchment.~ ....................,... ,........................ ~............................... ..................................................................................................
Sample : Predominant Site 1 local land use : Site 2 local land useStream iCatchment land use (lower catchment) (upper catchment)
!
, Corsair Bay i Forest Urban Forest ,Stream
! Rapaki Agriculture Urban AgricultureStream
!i , ...
i Foleys : Agriculture Quarry Agriculturei Stream ,
!Te Wharau ! Agriculture Orton Bradley Agriculture: Stream facilities
.".....".".
Church Gully Forest Forest Forest .Stream
...............
A water sample was taken from the stream at each site in a jar for subsequent
laboratory analysis. A turbidity meter was used multiple times at each site, giving
instant indications of turbidity (clarity) of the water. Care was taken to ensure no
light from outside sources entered the test chamber and that the machine was
calibrated correctly at the start of each test. Turbidity measurements and water
samples were taken first to ensure we had not disturbed the stream bed.
A flow probe was used to measure the water velocity; the convention in using this is
8
to move it throughout the velocity profile (Fig. 2). When the water level was too
shallow to immerse the propeller, averaged timed floats over a set distance were
used to obtain the velocity.
UpstreamRiver Right /
I
/ Ri,erLe"
Downstream
Lamina Plowa fayeted Row of w.alerwhich the slower l~ay~'f:S
push again!it lhe banks andboltom The Fastest layllrs at-Il on top in mid siloam
'''albl ~lGVl:
ACorkscteW trli:l~OI1
downstream
Figure 2: A generic stream cross section indicating the variation of water velocity through the stream profile. NEEDS SOURCE
Cross-sectional analysis was based on measuring the wetted perimeter. Data
obtained allowed the group to investigate and plot trends of turbidity, stream
discharge and suspended sediment concentration.
2.3 Laboratory Methods
Lab work consisted of analysing water samples where sample jar volume was noted
to obtain a measure of sediment per volume of water for each site. Samples were
passed through pre weighed 250llg filters using a vacuum pump. Each filter was
placed in an oven at 40·C to dry for a minimum of 24 hours. Dried filters were
reweighed to obtain a weight of suspended sediment from each site, per litre of
discharge. Thus, sediment concentrations were standardised so that catchment area
9
"
did not confound the results.
2.3 Digital Tools
Extensive use was made of geospatial information systems (GIS). Proprietary
programs and tools from the ESRI ArcGIS™ and TopoMapTM range were used on
satellite images obtained from Environment Canterbury and NASA. A summary of
the techniques used included:
• Multi-band Radiometric Analysis and Remote Sensing land Classification,
which measured the electromagnetic radiation signature of land cover, and is
a measure of the free water content. This allowed different land use types to
be accurately identified (Martinez 2004, Deloach et al. 2010).
• Stream Profiles -long sections drawn as the course of a stream to illustrate
elevation and topography - were created from an inbuilt tool in the
proprietary TopoMapTM software.
2.4 Statistical Analysis
Statistical analysis was completed with Minitab lS™ software, and involved multiple
regressions, analyses of variance, and analyses of covariance. All data was tested
with inbuilt tools for normality and equality of variances.
10
3.0 Results
3.1 Influences of Water Level and Microclimate Patterns
The actual day that sampling took place was a significant determinant of suspended
sediment concentrations as well as total sediment output in fluvial systems. Day Two
samples - which were collected after a period of persistent rainfall - had the highest
suspended sediment averages (F= 8.96; P=O.002; df=24). Data collected from a
number of weather stations in different locations within the harbour showed that
annual weather patterns differed substantially over small scales (Fig. 3).
Microclimate data showed that precipitation highs were greater in catchments in the
southern half of the basin (such as Diamond Harbour) than those in the northern or
eastern harbour (Lyttelton Port and Charteris BaYI respectively). AdditionallYI
Diamond Harbour meteorological station data indicated higher variability of
precipitation maxima.
- Charteris Bay
- Lyttelton Harbour
- Diamond Harbour
180 -I160 -1---------1--+-----
E 140 +---------11----+---
.§. 120
§ 100'';:;.~ 80 -J--\--------+-:I---Vl---+--+-Q,'y 60 -J-.-\----,I-=.........----+l---'I<-I-=----\-Qlct 40 +-~_I_---'lt----::--tH__"\.--_H'_PIl---
20 I~~~~~~-'W_~ro +--,---,-.....,.
Figure 3: Variation in monthly precipitation highs in the Lyttelton Harbour Basin area from October
2009 to September 2010
11
Agriculture Fo est
3.2 Influence of Land Use on Sediment Transport
The analysis of variance results proved, as expected, that the predominant
catchment land use had a strong and significant effect on suspended sediment
weights (F=12.84; P= 0.001; df=24). Substantially higher totals were recorded in
streams located in catchments with predominantly agricultural management such as
Foleys, Rapaki and Te Wharau (mean= 0.92 grams of sediment per litre discharge, se
= 1.16) than those from primarily forested catchments such as Corsair Bay and
Church Gully (mean = 0.09{g/L), se= 0.18) (Fig. 4).
1.6~ 1.4S_ 1.2c(I) 1E" 0.8(I)
III 0.6
"~ 0.45i 0.2Q.III 0;:,
en -0.2
-0.4
-0.6
Predominant catchment land use
Figure 4: Disparity of suspended sediment concentration between 5 sampled streams in catchments
of predominantly agricultural and forested land use in LyUelton Harbour Basin, 2010.
Likewise, land use directly upstream of the sample site, irrespective of the area
covered, was a good predictor of suspended sediment concentrations in streams
(F=5.72; P= 0.006; df=18) (Fig. 5). Particularly of note was the large contribution of
the quarry in the Foley's Stream catchment which was below the upper catchment,
but above our lower catchment sample site as seen in Fig. 1. Te Wharau stream
(which lies in an agricultural catchment) had a higher sediment load in the lower
catchment, which has an extensive road network. Corsair Bay Stream, the upper
12
catchment of which is a mixture of plantation forest and native grassland, drops
some of its sediment load as it moves through an established urban setting.
1.8-...JC, 1.6-- 1.4t:(1)
E 1.2'0 1(1)til'0 0.8(1)
'0 0.6t:
8. 0.4til~ 0.2
o
•
Upper Catchment
•
Lower Catchment
-+-Corsair
~Foleys
Church Gully
Te Wharau
-Rapaki
Figure 5: Variation in suspended sediment concentrations as a result of different land uses in the
upper and lower catchment in 5 sampled streams in Lyttelton Harbour Basin, 2010.
Generally, agriculture or quarry land use directly upstream of a sample site resulted
in higher sediment concentration than those sections of a stream which were placed
within urban or forested land - even if the urban or forested land was relatively small
in area (Fig. 6).
Figure 6: Variation in average suspended sediment concentrations as a result of different local land
uses in 5 sampled streams in Lyttelton Harbour Basin, 2010.
13
Predominant catchment land use and day of sampling interacted significantly in an
analysis of covariance (F=3.64; P=0.042; df=24). On sampling days with higher
discharge, erosion susceptible land uses such as agriculture had proportionally larger
increases in concentrations of suspended sediment than forested catchments (Fig.7).
- 2.5..J-C)-- 2s::::CI)
E1.5"0
CI)tn"0 1CI)"0s:::: 0.5CI)Q,tn::]
0UJ
~Agriculture
Forest
None Very little Moderatelevel of precipitation in preceding days
Figure 7: Level of precipitation in days preceding sampling had a variable effect on suspended
sediment concentrations, dependant on predominant catchment land use in 5 sampled streams in
Lyttelton Harbour Basin, 2010.
14
,,
4.0 Discussion
4.1 Agricultural Land Use
Agriculture is a particularly dominant land use type in Lyttelton Harbour. All levels of
grazing pressure increase soil and solute runoff (Mwendera and Saleem 1997),
however impacts increase with the intensity of agriculture such as increased
livestock numbers (Outeiro et al. 2010). This is because grazing reduces vegetative
cover (Russell et al. 2001) and vegetation complexity (Greenwood and McKenzie
2001). Livestock also cause higher erosion because they trample the soil and
decrease infiltration, particularly in fine textured soils such as loess (Mwendera and
Saleem 1997) as found in Lyttelton Harbour. In addition to stock impacts, human
construction works like roads, drains and tracks, can result in a large input of
sediment (Outeiro et al. 2010). Our results have indicated that predominantly
agricultural catchments contribute the highest levels of suspended sediments into
the harbour. Te Wharau stream runs through a typically agricultural catchment,
Orton Bradley Park. It has a mixture of uses including extensive grazing of sheep and
cattle, small native bush remnants and recreational facilities such as picnic areas and
a golf course. Te Wharau appears relatively clean; despite this our results indicate
high suspended sediment loads, which are probably a result of runoff from the
sparsely vegetated hillsides. It has been illustrated that the highest erosion rates
occur where surface runoff results in structures such as sheet and rill/gully erosion
(Walling et al. 2002; Capra et al. 2009; Valentin et al. 2005) and there is clear
evidence of this in Te Wharau catchment and other agricultural catchments of
Lyttelton Harbour such as Rapaki (Fig. 8A and 8B). Consequently, Rapaki Stream also
had the one of the highest suspended sediment discharges. In comparison with Te
Wharau Stream, there was ample evidence within the Rapaki catchment to indicate
extensive soil erosion such as the slumping and gullying on the hillsides and thick silt
deposits on the streams edges as the result of a recent storm event (Fig. 8C).
15
A
Figure 8: Evidence of larges-scale soilerosion in agricultural catchments inLyttelton Harbour 2010. (A) Depictsrifling and (B) slumping. (C) is showingsediment deposition on stream banks.Photographer: Melissa Shearer26/8/2010
4.1.1. Forests
Lyttelton Harbour contains a mixture of both native forest and plantation forestry
blocks. Generally, forest cover is important in limiting erosion, mass wasting, soil
degradation and sediment deposition. Afforestation increases rainfall interception,
adds strength to erosion-prone land (Carlton 2001), and reduces overland flow thus
reducing the potential for sediment erosion and transport (Trimble 2003). In
plantations however, there is a large short term erosion risk during and after harvest
until canopy closure, and heavy machinery and road networks can result in
sedimentation of adjacent streams (Boothroyd et al. 2004). This effect can take
decades to be remedied by reforestation, depending on individual tree growth rates
(Parkyn 2004). The presence or absence of riparian buffer zones is also vital in
controlling the amount of sediment reaching streams in a production forest. This will
be especially noticeable on the headland between the Head of the Bay and Charteris
Bay where forestry blocks extend to the shoreline (Fig. 9).
16
sediment when being harvested if a riparian buffer were not established. Photographer David
Gainsford 26/9/2010.
Church Gully stream which is a small ravine type catchment is representative of the
natural forested condition of Bank's Peninsula. Suspended sediment contributions
from Church Gully were minute in comparison to agricultural catchments. It is clear
that the dense vegetation within this catchment is successful at minimising transport
of sediment into the stream channel. This highlights the importance and
effectiveness of riparian buffer zones. The upper reaches are bordered by farmland,
and from anecdotal evidence it is clear when cattle are being grazed in proximity of
the stream as the outflow into Church Bay is noticeably tainted with sediment (pers.
obs.). However maintaining a riparian buffer zone between the paddocks and the
stream would minimise this effect.
4.2 Quarrying
Mining and quarrying activities within a river or harbour catchment can have
significant sediment contributions (Nelson and Booth 2002). There are two quarries
present in Lyttelton Harbour (one active and one converted to a landfill) (ECan
2007), and although they take up a minor proportion of the land area, the active
17
road metals quarry site may provide significant sediment contributions because of its
close proximity to Foleys Stream. The Foleys stream catchment was also dominated
by extensive agriculture, but possibly more significant sediment inputs are derived
from the quarry. This stream was the second highest producer of suspended
sediment in our study, and considerably more would be carried during flood events.
There were profound differences between the stream morphology and suspended
sediment loads above and below the quarry. Above the quarry, the stream was
relatively rapidly flowing with pool and riffle complexes. Below the quarry, the water
was lethargic, highly turbid and the stream banks and bed were comprised of thick
silt and mud (Fig. 10). It can therefore be assumed that a significant amount of
sediment is being introduced to the stream and therefore the harbour from this
quarry. Past studies on the sources of sediment into the Harbour have indicated that
the quarry is of high risk and priority for management (ECan 2007).
Figure 10: The impact of quarry sediment outputs on morphology in Foleys Stream (lyttelton
Harbour, 2010) is visible in these photos. (A) is a photo taken above the quarry in a stream section
which is not impacted by quarry outputs, conversely, (B) shows downstream impact. Photographer:
Melissa Shearer 26/8/2010
4.3 Urban Areas
Urban land surfaces include an impervious stormwater drainage network which is
designed to intercept and rapidly discharge any excess water, which can mean
greater erosion of the stream channel receiving the stormwater discharged during
18
these events (Corbett et al. 1997). However/ the greatest potential for sediment
discharge is during the construction phase of urban development (Nelson and Booth
2002; Wotling and Bouvier 2002; Chin 2006)/ as they often consist of unprotected
soils (Roberts and Pierce 1974). There are currently 10 subdivision developments in
various stages of completion/ such as at Cass Bay. In addition to these current
subdivision developments/ proposed changes to land use zoning allowing for further
development represents the potential for enhancing sedimentation rates in the near
future (ECan 2007). After the construction phase is complete the impervious nature
of urban surfaces such as roofs/ car parks and roads mean sediment levels are
actually relatively low (Nelson and Booth 2002). Catchments which contain urban
settlements such as Corsair Bay have been found to contribute very small amounts
of sediment in our study.
Due to the lack of infiltration/ little or no pollutant filtering occurs before water is
discharged into streams (Corbett et al. 1997). Hydrocarbons and heavy metals are
abundant in urban runoff and are detrimental to marine and freshwater aquatic
communities (Corbett et al. 1997; Walker et al. 1999; Goodwin et al. 2003; Rodriguez
et al. 2003). Riparian Buffer Zones or engineering works such as mesh fences and
settling ponds and grassed swales can improve water quality in urban streams in
terms of both suspended sediment and chemical composition (Parkyn 2004).
4.4 Weather Influences
Variations in climate between the bays of Lyttelton Harbour can have an influence
on the amount of sediment produced within each catchment. As we have illustrated
there is variation in the amount of rain/ and also wind direction and speed. This
variation is due to different aspects of the bays and the prevalent direction of
incoming weather systems and their entailing wind and precipitation patterns.
Higher exposure of vulnerable land surface to erosive agents in the form of adverse
weather increases erosion potential. Both wind and rain are erosive agents/
therefore catchments with higher precipitation such as those in Diamond Harbour
may be more vulnerable. The intensity and frequency of storm events will have
19
significance for the production of sediment within the different catchments
(Kreutzweiser et al. 2009) fhj
The temporal variation in weather patterns therefore influences the sediment
output of streams. We have found that discharge varies significantly from day to day,
as a result of the amount of rainfall received in the catchment within the few days
prior to sampling. We have also found that this variation has resulted in a significant
difference in sediment levels between sampling days. In relatively low rainfall
periods, very little water occupied the area available in stream channels in our study
(the 'wetted perimeter'). This means that there is less kinetic energy to erode the
bed sediments and then transport them downstream. Conversely, periods of high
flow (such as during rain storms) have the potential for greater erosion as higher
water levels mean a greater proportion of the stream channel is subject to erosion.
Higher energy levels of the faster flowing water also enable greater erosion and
transport. Storm events also affect overland flow as excess precipitation creates
surface runoff. Soils will hold moisture up to a threshold, above which water will
flow down slope over the land surface entraining and transporting sediment into
stream channels and the harbour (Bryan 2000, Russell et al. 2001).
20
5.0 Limitations
Several limitations are present within our study which may have an effect on the
research undertaken.
5.1 Timing
A major limitation to our study was that we were unable to sample during high
rainfall events. This was due to time constraints and difficulties in organising group
outings on short notice to coincide with peak sediment fluxes. We therefore do not
have suspended sediment data for occasions which are typically the most
responsible for significant total sediment discharge.
5.2 Ephemeral Streams
We intended to quantify the contribution of ephemeral streams to sedimentation, as
they are regarded as important sediment transport agents in literature. As these
characteristically only flow during storm events we were unable to sample
ephemeral stream discharge, so decided to discount this from our overall research.
5.3 Sample Size
Despite several sampling occasions, we still have a relatively small sample size due to
the small number of samples taken at each site within the different streams. This
may result in difficulty in making inferences about the total catchment system of the
harbour. In addition to this, we must extrapolate the results from our small selection
of streams around the inner harbour to the harbour as a whole.
5.4 Currency of Data
A discrepancy existed between 2004 land use maps and current satellite imagery
used to obtain land use by inspection and digital analysis. This however could be
overcome by on site judgment of land use percentages during our field sampling
occasions although this too has inherent interpretive inaccuracies.
21
6.0 Recommendations
6.1 Riparian Buffer Zones
A riparian buffer zone is a strip of trees and other vegetation surrounding water
bodies such as rivers and lakes (Fig. 11). This vegetated stream margin has a number
of important influences on in-stream physical and chemical characteristics such as
water temperature, coarse and fine organic nutrient inputs and turbidity (Boothroyd
et ai, 2004; Lee et al. 2004). These factors can influence the community structure
within the stream system including invertebrates, fish, terrestrial birds and mammals
and aquatic plant life (Boothroyd et ai, 2004; Lee et al. 2004). In addition to this,
vegetation reduces the velocity of the water flowing both overland and within
channels, weakening its power to erode and transport sediment (Langer et al. 2008).
Figure 11: A pastoral example of a riparian buffer zone which could be employed as a sediment trap in
Lytellton Harbour. Source: Agriculture and Agri-Food Canada (2010).
Sparovek et al. (2002) clearly outline the factors that need to be considered when
calculating a forested buffer width. Several authors including Greynoth (1979) have
determined that a riparian buffer zone in a plantation forest, consisting of trees,
ferns and shrubs and with a width of 30 metres was sufficient. New Zealand's native
plants have been recognised as excellent bank stabilisers (Boothroyd et al. 2004,
Langer et al. 2008) making them a favourable option for riparian species.
22
We recommend the use of riparian buffer zones around all streams in urban,
agricultural and forested catchments, including the continued planting of seedlings
around Te Wharau Stream in Orton Bradley Park. Additionally, in Orton Bradley Park
and other agricultural catchments, we suggest shelter belts should be established if
not already present. Russell et al. (2001) illustrated the large potential for sediment
delivery reduction from paddocks as a result of shelter belts intercepting both
subsoil and surface water flow. A faster-acting alternative is possible with geotextile
fine mesh netting fixed across stream beds to 'catch' sediment whilst allowing
filtered water pass through (Elliot 2010).The implementation of riparian buffers
should also be a high priority around the quarry site which is a major contributor of
sediment.
6.2 Ephemeral Streams
Further investigations of ephemeral stream outputs in the context of the lyttelton
Harbour are necessary to quantify their contribution to sedimentation as it can be
assumed they are significant contributors both from overseas work (for example
Reid and laronne 1995) and personal observations of local people.
6.3 Urban Development
Planning for proposed subdivisions needs to include stringent controls on sediment
outputs. This can include the use of grass swales to intercept fine sediment (Deletic
2005) and other development strategies such as riparian buffers and low Impact
Development subdivisions (LID). For more information on LID and its effectiveness,
see Dietz and Clausen (2008).
6.4 Stream Modelling
Further modelling of stream flow rates and sediment inputs needs to be quantified
and mapped to form additional base data to our findings. This will be essential for
future decision making and to understand the behaviour of the catchments under a
23
broader range of conditions over longer time periods. Regular surveys of the
bathymetry of the harbour will also help improve understanding of the issues facing
the harbour as the result of sedimentation. We understand that Environment
Canterbury has taken steps to initiate such work, and this should be supported and
encouraged to help maintain progress and momentum.
24
7.0 Conclusion
The rate of sediment accumulation in water bodies is an increasingly important issue
world-wide, and has been attributed to changes in land use, in particular the
removal of forest cover to make way for agricultural land. The removal of native
forest by European settlers has been correlated with acceleration in sediment
accumulation rates within the Lyttelton Harbour. However, contributions of
different catchments and land use related trends are confounded by microclimate
patterns within the Lyttelton Harbour basin. Sedimentation has significant impacts
on both economic and environmental aspects of the harbour environment as port
access has to be maintained by expensive dredging, while aquatic communities face
habitat destruction and water contamination.
It has been established that this issue is a result of land use change rather than
natural processes, it is therefore important to establish how the different land uses
are contributing to sedimentation. From this study, it has been identified that
agricultural land use is producing the greatest amount of sediment. This is possibly
due to the effects of livestock induced soil compaction and the loss of vegetation
diversity, which reduces soil cohesion and exposes soils to erosion by wind and rain.
The second largest contributor of sediment is the road metals quarry adjacent to
Foleys Stream. The sediment from this source flows directly into the stream with no
intercepting riparian buffer. In contrast to agricultural and quarrying land uses,
forested and urban catchments are producing the smallest quantity of sediment.
However, planned subdivisions have the potential to be significant sediment sources
in the future. We strongly recommend the use of riparian buffer zones around all
streams. These aim to imitate the historic natural forested condition of many of the
streams in Lyttelton Harbour, by forming a barrier between the land and the stream
system and thus reduce the rates of sediment export. This should be a step towards
mitigating the sedimentation issue of Lyttelton Harbour.
25
8.0 Acknowledgements
The group would like to thank Claire Findlay, Justin Harrison, Michele Stevenson,
Paul Pritchett and GEOG309 teaching staff for their advice, assistance and helpful
suggestions.
9.0 References
Agriculture and Agri-Food Canada (2010), 'Riparian Buffer Zone' [Image], retrieved 17/10/2010 from
http://www4.agr.gc.ca/AAFC-AAC/display-afficher.do?id=1235756863870&lang=eng.
Boothroyd, IKG, Quinn, JM, Langer, ER (Lisa), Costley, KJ and Steward, G (2004), 'Riparian buffers
mitigate effects of pine plantation logging on New Zealand streams 1. Riparian vegetation structure,
stream geomorphology and periphyton', Forest Ecology and Management, vol. 194, pp. 199-213.
Bryan, RB (2000), 'Soil erodibility and processes of water erosion on hillslope', Geomorphology, vol.
32, pp. 385-415.
Capra, A, Porto, P, Scicolone, B (2009), 'Relationships between rainfall characteristics and ephemeral
gully erosion in a cultivated catchment in Sicily (Italy) Soil and Tillage Research, vol. 105(1), pp. 77-87.
Carling, PA, Irvine, BJ, Hill, A and Wood, M (2001), 'Reducing sediment into Scottish streams: A review
of the efficacy of soil conservation practices in upland forestry', The Science of the Total Environment,
vol. 265, pp. 209-227.
Carlton, J (2001), The effects offorestry on sediment production in the Coalgate Forest, Malvern Hills,
inland Canterbury. MSc Thesis, University Of Canterbury.
Chin, A (2006) 'Urban transformation of river landscapes in a global context', Geomorphology, vol. 79,
pp.460-487
Corbett, CW, Wahl, M, Porter, DE, Edwards, D and Moise, C (1997), 'Nonpoint source runoff
modelling. A comparison of a forested watershed and an urban watershed on the South Carolina
coast', Journal ofexperimental marine biology and ecology', vol. 213, pp.133-149.
26
Deloach Sand Ellis S (2010), 'Subsurface Soil Moisture with Passive Microwave Radiometry', retrieved
14/10/2010 from http://proceedings.esri.com/library/userconf/proc98/proceed/to850/pap845/p845.htm.
Deletic, A (2005) 'Sediment transport in urban runoff over grassed areas', Journal ofHydrology, vol.
301, pp. 108-122.
Dietz, ME and Clausen, JC (2008) 'Storm water runoff and export changes with development in a
traditional and a low impact subdivision', Journal of Environmental Management, vol. 87, pp. 560
566.
Elliot, C (2010) [Course notes] GEOG340: Field Based Geomorphic Applications, Department of
Geography, University of Canterbury, Christchurch.
Environment Canterbury (2007), lyttelton Harbour Potential Contaminant Sources Study, Report No.
U08/17
Goff, J (2005), Preliminary core study - Upper lyttelton Harbour, National Institute of Water and
Atmospheric Research ltd., Christchurch, New Zealand.
Goodwin, TH, Young, AR, Holmes, MGR, Old, GH, Hewitt, N, leeks, GJl, Packman, JC and Smith, BPG
(2003), 'The temporal and spatial variability of sediment transport and yields within the Bradford Beck
catchment, West Yorkshire', The Science of the Total Environment, vol. 314-316, pp. 475-494.
Graynoth, E (1979), 'Effects of logging on stream environments and faunas in Nelson', New Zealand
Journal ofMarine and Freshwater Research, vol. 13, pp. 79-109.
Greenwood, Kl and McKenzie, BM (2001), 'Grazing effects on soil physical properties and the
consequences for pastures: A review', Australian Journal of Experimental Agriculture vol. 41(8),
pp.1231-1250.
Hart, DE (2004), 'Mapping of the bathymetry, soft sediments and biota of the seabed of Upper
lytellton Harbour', University of Canterbury Departments of Geography and Biology, Report to
Environment Canterbury and DTEC Consulting ltd.
Jaffe, BE, Smith, RE and Foxgrover, AC (2007), 'Anthropogenic influence on sedimentation and
intertidal mudflat change in San Pablo Bay, California: 1856-1983', Estuarine, Coastal and Shelf
Science, vol. 73, pp. 175-187.
Keim, RF and Schoenholtz, SH (1999), 'Functions and effectiveness of silvicultural streamside
management zones in loessial bluff forests', Forest Ecology and Management, vol. 118, pp. 197-209.
27
Kreutzweiser, 0, Capell, S, Good, Kand Holmes, S (2009), 'Sediment deposition in streams adjacent to
upland c1earcuts and partially harvested riparian buffers in boreal forest catchments', Forest Ecology
and Management, vol. 258, pp. 1578-1585.
Kreutzweiser, 0, Capell, S, Good, Kand Holmes, S (2009), 'Sediment deposition in streams adjacent to
upland c1earcuts and partially harvested riparian buffers in boreal forest catchments', Forest Ecology
and Management, vol. 258, pp. 1578-1585.85.
langer, ER (lisa), Steward, GA and Kimberley, MO (2008), 'Vegetation structure, composition and
effect of pine plantation harvesting on riparian buffers in New Zealand', Forest Ecology and
Management, vol. 256, pp. 949-957.
lee, P, Smyth, C and Boutin, S(2004), 'Quantitative review of riparian buffer width guidelines from
Canada and the United States', Journal of Environment Management, vol. 70, pp. 165-180.
Martinez, E(2004), 'Remote Sensing Techniques for land use classification of Rio Jauca watershed
using IKONOS images'[ Journal Article], retrieved from http://gers.uprm.edu/geoI6225/research.html
on 12/10/10.
Mwendera, EJ and Saleem, MAM (1997), 'Infiltration rates, surface runoff, and soil loss as influenced
by grazing pressure in the Ethiopian highlands', Soil Use and Management, vol. 13(1), pp. 29-35.
Nelson, EJ & Booth, OB (2002) 'Sediment sources in an urbanizing, mixed land use watershed', Journal
of Hydrology, vol. 264, pp. 51-68.
Niyogi, OK, Koren, M, Arbuckle, CJ and Townsend, CR (2007). 'Stream communities along a catchment
land-use gradient: Subsidy-stress responses to pastoral development.' Environmental Management,
vol. 39(2), pp. 213-225.
Outeiro, l, Ubeda, X and Farguell, J (2010), 'The impact of agriculture on solute and suspended
sediment load on a Mediterranean watershed after intense rainstorms', Earth Surface Processes and
Landforms, vol. 35(5), pp.549-560.
Parkyn, S, (2004). 'Review of Riparian Buffer Zone Effectiveness' [Technical Policy Report]. Wellington:
New Zealand Ministry of Agriculture and Forestry and National Institute of Water and Atmospheric
Research.
Personal Communication. Paul Pritchett, lyttelton Harbour Issues Group Member, 25/09/2010.
28
Reid, I and Laronne, JB (1995). 'Bed load sediment transport in an ephemeral stream and a
comparison with seasonal and perennial counterparts.' Water Resources Research, vol. 31(3), pp. 773
781.
Roberts, WP and Pierce, JW (1974) 'Sediment yield in the Patuxent River (MD.) undergoing
urbanisation, 1968-1969', Sedimentary Geology, vol. 12, pp. 179-197.
Rodriguez, F, Andrieu, Hand Creutin, J-D (2003), 'Surface runoff in urban catchments: morphological
identification of unit hydrographs from urban databanks', Journal ofHydrology, vol. 283, pp.146-168.
Russell, MA, Walling, DE, Hodgkinson RA (2001), 'Suspended sediment sources in two small lowland
agricultural catchments in the UK, Journal of Hydrology, vol. 252(1-4), pp.1-24.
Scheurer, K, Alewell, C, Banninger D, and Burkhardt-Holm P (2009). 'Climate and land-use changes
affecting river sediment and brown trout in alpine countries-a review.' Environmental Science and
Pollution Research, vol. 16(2), pp. 232-242.
Sparovek, G, Ranieri, SBL, Gassner, A, De Maria, IC, Schnug, E, Ferreira dos Santos, Rand Joubert, A
(2002), 'A conceptual framework for the definition of the optimal width of riparian forests',
Agriculture, Ecosystems and Environment, vol. 90, pp. 169-175.
Stream Cross Section [Image] 2006, 'Rivers', retrieved 27/9/2010 from
http://www.vcsar1.org/images/swiftwater/river cross-Section. jpg.
Stutter, MI, Langan, S, and Demars BOL (2007), 'River sediments provide a link between catchment
pressures and ecological status in a mixed land use Scottish River system', Water Research vol. 41(12),
pp. 2803-2815.
Trimble, SW (2003). Environmental Hydrology Second Edition. Washington, D.C: Lewis Publishers.
Valentin, C, Poesen, J, Yong Li (2005), 'Gully erosion: Impacts, factors and control', Catena, vol. 63,
pp.132-153.
Walker, WJ, McNutt, RP and Maslanka, CK (1999), 'The potential contribution of urban runoff to
surface sediments of the Passaic river: Sources and chemical characteristics', Chemosphere, vol. 38,
pp.363-377
Walling, DE (2006), 'Human impact on land-ocean sediment transfer by the world's rivers',
Geomorphology, vol. 79(3-4), pp. 192-216.
29
Walling, DE, Russell, MA, Hodgkinson RA, Zhang, Y (2002), 'Establishing sediment budgets for two
small lowland agricultural catchments in the UK', Catena, vol. 47(4), pp.323-353.
Weather data from professional and amateur weather stations in various locations in the Lytellton
Harbour basin [Primary Data] 2008-2010, retrieved throughout September and October 2010 from
http://www.wunderground.com/cgi-
bin/fmdweather/getForecast?query=Christchurch,%20New%20Zealand&wuSelect=WEATRER.
Wotling, Grvdrr and Bouvier CH (2002), 'Impact of urbanization on suspended sediment and organic
matter fluxes from small catchments in Tahiti', Hydrological Processes, vol. 16, pp.1745-175690
30