The Hurunui River hapua: geomorphology, sediments, and water quality
Report No. R13/32 ISBN 978-1-927234-93-8 (print) 978-1-927234-94-5 (web)
Report prepared for Environment Canterbury by Dana Mulvany
June 2013
Report No. R13/32 ISBN 978-1-927234-93-8 (print) 978-1-927234-94-5 (web)
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This report represents advice to Environment Canterbury and any views, conclusions or recommendations do not represent Council policy. The information in this report, together with any other information, may be used by staff to guide the design and review of monitoring and investigations programmes.
The Hurunui River hapua: geomorphology, sediments, and water quality
Community Summary
This is a report on the geomorphology, sediment processes and water quality within the Hurunui River hapua. These aspects of the hapua are influenced by river flows and coastal processes.
The tide has a significant influence on the surface area of water within the hapua especially when the mouth opening is at the southern end. An opening at the southern end is caused by high flows in the river. The water surface area, the position of the shorelines, hapua opening location and the width of the barrier are variable over time.
The deposition and scouring of sediment from the hapua shoreline depends on river flow and wind driven circulation of the water
Water quality in the hapua is influenced by the flow of the river, sea storms, the shape of the hapua, and wind driven circulation of the water. Differences in water quality at different locations in the hapua occur when the outlet is at the southern end and there are ponded areas.
Environment Canterbury Technical Report i The Hurunui River hapua: geomorphology, sediments, and water quality
Executive Summary
This report is an up-to-date summary of the contemporary baseline conditions in the Hurunui River hapua, and how they respond to the observed range of fluvial and coastal processes. This includes information on water quality and characteristics, sediment processes, and the geomorphology and characteristics. This report also provides a historical account of the water surface area, the position of the shoreline and lagoonward shorelines of the hapua, and the width of the barrier.
The water surface area can change significantly in response to the tide, especially when the outlet is at the southern end of the hapua. Primary breaches of the Hurunui River hapua barrier appear to be controlled by fluvial rather than coastal processes. The lagoon water surface area, the position of the shorelines and the width of the barrier have been variable historically.
Sediment processes within the hapua depend on the flow of the river and wind driven circulation of the water. Sediment composition along the landward shoreline is variable and can change significantly after floods. Fine sediment can be deposited along the landward shore after floods with a mean daily flow of 20 m3/. Floods with a mean daily flow of 535.6 m3/s scour fine sediment along the landward shore that has been deposited by previous floods.
Water characteristics in the hapua are dependent on the flow of the river, sea storms, the shape of the hapua, and wind driven circulation of the water. The greatest spatial differences occur when the outlet is at the southern end during floods and ponded areas are present.
Management of the Hurunui River hapua must take into account the range of short-term changes that occur such as surface area and the influence of the hapua geomorphology. Additional information on the ecology of the hapua is desirable to increase knowledge of the ecological health of the hapua.
ii Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Table of Contents
Community Summary ...... i
Executive Summary ...... ii
1 Context ...... 1 1.1 Hapua characteristics ...... 1 1.2 Hapua vulnerability ...... 3 1.3 Hapua research ...... 3
2 Methods ...... 4 2.1 Site details ...... 4
3 Geomorphology ...... 6 3.1 Long-term changes ...... 6 3.2 Short-term behaviour and geomorphology ...... 11 3.2.1 Lagoon water surface area ...... 11 3.2.2 Behaviour of the Hurunui River hapua ...... 11
4 Sediment processes ...... 14 4.1 Short-term spatial trends in sediment composition and deposition ...... 14 4.2 Floods and sediment composition ...... 18 4.3 Wind and suspended sediment ...... 18 4.4 Long-term sediment processes ...... 18
5 Water quality ...... 19 5.1 Short-term water quality ...... 19 5.1.1 Water quality in low energy conditions ...... 19 5.1.2 Water quality states ...... 21 5.1.3 Water quality in floods and storms ...... 22 5.1.4 Additional variations in water quality ...... 22 5.2 Long-term water quality ...... 22
6 Periphyton ...... 24
7 Requirements for hapua ecological health ...... 27 7.1 River flow ...... 27 7.2 River water quality ...... 27 7.3 Sea state ...... 28
8 Hapua management ...... 30
9 Suggestions/recommendations for future work...... 33
10 References ...... 34
Environment Canterbury Technical Report iii The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 1: Details of the methods used in this study ...... 36
Appendix 2: Sediment composition data ...... 39
Appendix 3: Sediment deposition (mm) data ...... 40
Appendix 4: Suspended sediment (mg/L) data (low energy event 1: 13 May 2012, low energy event 2: 24 September 2012, flood 1: 25 June 2012, flood 2: 9 August 2012, storm: 7 November 2012) ...... 41
Appendix 5: Water temperature (°C) data taken at the same time as suspended sediment samples ...... 43
Appendix 6: Conductivity (uS/cm) data taken at the same time as the suspended sediment samples ...... 45
Appendix 7: Dissolved oxygen (mg/L) data taken at the same time as the suspended sediment samples ...... 47
Appendix 8: pH data taken at the same time as the suspended sediment samples ...... 49
Appendix 9: Nutrient concentrations (mg/L) data in low energy event 1 (13 July 2012) ...... 51
Appendix 10: Nutrient concentrations (mg/L) data in low energy event 2 (24 September 2012) ...... 52
Appendix 11: Nutrient concentrations (mg/L) data in the flood (2 August 2012) and storm (7 November 2012) events ...... 53
Appendix 12: Graphs showing spatial differences in parameters in different energy conditions and varying positions of the hapua outlet ...... 54
iv Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
List of Figures
Figure 1-1: River mouth classification in Canterbury with regards to the degree of influence from tides, waves, and rivers ...... 2 Figure 1-2: Range of states that hapua experience ...... 3 Figure 2-1: Location of the time lapse cameras and sample sites at the hapua ...... 4 Figure 2-2: Photographs of the different sites at the hapu ...... 5 Figure 3-1: Orthorectified aerial photographs of the hapua ...... 8 Figure 3-2: Aerial photograph of the hapua with the position of the shoreline (right) and the lagoonward side of the barrier (left) on 5 photographed years from 1974 to 2004/2005...... 9 Figure 3-3: Distance of the hapua seaward shoreline from the baseline ...... 10 Figure 3-4: Photograph of the southern end of the hapua close to high tide on the 23rd of September 2012...... 11 Figure 3-5: Photograph of the southern end of the hapua close to low tide on the 23rd of September 2012...... 12 Figure 3-6: High tide (left), and low tide (right) at the hapua on the 9th of May 2012 with circles showing the exposed gravel ...... 12 Figure 3-7: Photograph of the southern end of the hapua showing the water level of the lagoon level with the barrier during a storm on the 15th of June 2012 ...... 13 Figure 3-8: Photograph of a primary breach of the hapua ...... 13 Figure 4-1: Sediment composition at site 2 at the hapua at different locations away from the waterline ...... 14 Figure 4-2: Photographs of the substrate at site 2 after a moderate flood (left), and after a larger flood (right) ...... 15 Figure 4-3: Photographs of limestone chips at site 3 (left), and fine sediment along the shoreline between sites 2 and 3 (right) ...... 15 Figure 4-4: Photographs of the hapua shoreline between sites 3 and B before a flood (left), and after a moderate flood (right) ...... 16 Figure 4-5: Photographs of the landward shore of the hapua at site B in its typical state (left), and after a moderate flood (right) ...... 16 Figure 4-6: Photograph of the shoreline at the northern end of the hapua ...... 16 Figure 4-7: Sediment composition at the hapua outlet at different locations away from the waterline ...... 17 Figure 4-8: Photograph of sediment at the outlet ...... 17 Figure 4-9: Relationship between sediment energy and sources with processes and the resultant export, modification, and sinks of sediment ...... 18 Figure 5-1: Typical states that can exist in the Hurunui River hapua ...... 21 Figure 5-2: Conceptual diagram of external influences on hapua, the effect on internal processes including water quality, and any follow on effects...... 23 Figure 8-1: Photograph of a time-lapse cameras set up at the northern end of the hapua (left), and one at the southern end (right). Both face northwards ...... 31 Figure 9-1: Image of the hapua with a prominent ponded area at the northern end (Source: GoogleMaps) ...... 33
Environment Canterbury Technical Report v The Hurunui River hapua: geomorphology, sediments, and water quality
List of Tables
Table 3-1: Hurunui hapua water body surface area in 5 different years between 1974- 2004/2005 ...... 6 Table 3-2: Details of the frequency of wave overtopping events at the two ends of the hapua ...... 13 Table 5-1: Parameters that exceeded or were within the guideline values...... 20 Table 5-2: The influence of outlet position and energy event on spatial differences in water quality parameters and suspended sediment ...... 20 Table 6-1: Photographs and descriptions the periphyton in different areas of the hapua ...... 24 Table 7-1: Summary of the impacts of river flow on the hapua and ecological health ...... 29
vi Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
1 Context Before this study little was known about the long-term geomorphology, and short-term water quality and sediment processes in the Hurunui River hapua. This report provides an up-to- date account of the present knowledge of the geomorphology, short-term water quality, and sediment processes of the Hurunui River hapua. Based on Mulvany (2013), this report provides information on the:
• change in hapua shape over hourly, and decadal time scales. • sediment composition and processes on the landward side of the hapua and how these can change over time. • water quality in the hapua. • periphyton in the hapua. • controls of ecological health in the hapua.
1.1 Hapua characteristics The Hurunui River mouth has an associated hapua. Hapua are a type of coastal lagoon that are found in high energy wave environments at the end of a range of different river types in New Zealand, especially along the Canterbury coastline (Hart, 2009b; Hart & Bryan, 2008). These include large braided rivers originating in the Southern Alps such as the Rakaia and Waitaki Rivers, braided and meandering rivers originating in the foothills such as the Ashburton River, and small meandering streams that originate in the Canterbury Plains such as the Kowai River (Hart, 2009a; Hart & Bryan, 2008).
Hapua have two distinct characteristics. Firstly, the barrier associated with these lagoons is composed of sand and gravel (Hart & Bryan, 2008). Secondly, the composition of the barrier and its permeability allow water to flow from the lagoonward side of the barrier, through the barrier and to the ocean (Hart & Bryan, 2008).
Hapua geomorphology is dynamic (Hart, 2009b). The shape of the lagoon and barrier can change significantly over a few hours in response to fluvial or coastal processes. As well as fluvial and coastal processes, the geomorphology is also dependent on the characteristics of the barrier (Hart, 2009b). Coastal processes via longshore drift mostly dominate hapua (Figure 1-1).
Environment Canterbury Technical Report 1 The Hurunui River hapua: geomorphology, sediments, and water quality
Figure 1-1: River mouth classification in Canterbury with regards to the degree of influence from tides, waves, and rivers (Hart, 2007, p. 927)
Another characteristic of hapua is, that unlike estuaries, there is no direct tidal action (Kirk, 1991). The only time a temporary tidal influence can occur is directly after a flood when the floodwaters recede and the outlet channel is enlarged (Kirk, 1991).
Tides have an indirect influence on the water level in hapua (Kirk, 1991). At high tide, the hydrostatic pressure between the lagoonward side of the barrier and the seaward side is minimal (Hart, 2007). This causes outflow to decrease and water to back up in the hapua. As a result, the water level in the hapua rises. The difference in pressure between the two sides of the barrier at low tide increases through flow through the barrier. This results in a decline in water level in the hapua (Hart, 2007). Because of the lack of a direct tidal influence, salinity in hapua is from sea spray or from waves that wash over the barrier during sea storms (Hart, 2009b).
Hapua experience a range of morphodynamic states (Figure 1-2) (Hart, 2009b). Primary breaches of the barrier can occur during floods (a), and secondary breaches during sea storms (e). During low energy river and sea conditions, the outlet remains stable (b, c, e). In moderate river and sea conditions, the outlet can elongate (b and c) and the channel can become truncated. Low river flows can result in the closure of some hapua outlets (d) (Hart, 2009b).
2 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Figure 1-2: Range of states that hapua experience (based on the following rivers: Kowhai, Pareora, Waipara, Opihi, Conway, Ashburton, Hurunui, Waiau, Rangitata, Rakaia, and Waitaki Rivers) (Hart, 2009b, p 1357)
1.2 Hapua vulnerability Because hapua are located at the ends of rivers, they are sensitive to activities and changes in their catchments (Hart & Bryan, 2008). Catchment processes such as water development can be more damaging than processes occurring at the coast. Water development can involve dams such as those on the Waitaki River, water abstraction for irrigation which has occurred on the Rakaia River, and flow regulation. Water degradation due to agricultural intensification also pressure hapua. Pressures on the Hurunui River hapua include dam proposals, water abstraction for irrigation, and agricultural intensification.
1.3 Hapua research Hapua research has been on the geomorphology and behaviour (Fifield, 2012; Hart, 1999; Hart, 2007, 2009a, 2009b; Hart & Bryan, 2008; Kain, 2009; Kirk, 1983, 1991; Kirk & Lauder, 2000; McHaffie, 2010; Paterson et al., 2001; Smith, 1995). Few studies have addressed the effects of water development on hapua, and until recently, nothing was known about the sediment and water characteristics, and ecology of these systems.
Environment Canterbury Technical Report 3 The Hurunui River hapua: geomorphology, sediments, and water quality
2 Methods For details of the methods used to obtain the information in this report, refer to Mulvany (2013). See Appendix 1 for a summary of relevant methods.
2.1 Site details Information in this report was collected from five sites located in different areas of the lower Hurunui River and the hapua. Figure 2-1 shows the location of the time lapse cameras, and the location of the sites.
Figure 2-1: Location of the time lapse cameras and sample sites at the hapua
Site 1 is located at the swing bridge upstream of the hapua, and represents the lower section of the river (Figure 2-2). At this site the water is fast flowing compared to the other sites, and the substrate is composed of cobbles.
Site 2 is at the start of the hapua close to the campground. It is shaded, has relatively still water, and the substrate ranges from fine sediment to cobbles.
Site 3 is approximately halfway along the hapua. This site has a soft substrate and is shallow.
4 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Site B is located along the backshore of the hapua in the middle of the ponded area. The position of this site depends on the location of the ponded area. At the time of sampling, this site had a substrate of cobbles and small boulders.
Site O is near the outlet. The exact position of this site was variable, and the substrate is sand and gravel.
Figure 2-2: Photographs of the different sites at the hapua, site 1 (top left), site 2 (bottom left), site 3 (top right), and site B (bottom right). Site O is not included since it changed regularly
Environment Canterbury Technical Report 5 The Hurunui River hapua: geomorphology, sediments, and water quality
3 Geomorphology Five aerial photographs spanning 31 years were used to assess changes in the lagoon surface water area, the position of the shoreline, the position of the lagoonward side of the barrier, and the width of the barrier. The results are presented and discussed in section 3.1. Time-lapse images were used to assess the short-term behaviour and geomorphology of the hapua. The results are presented and discussed in section 3.2.
3.1 Long-term changes The surface area of the hapua, the position of the shoreline, the position of the lagoonward side of the barrier, and the width of the Hurunui River hapua barrier have been variable over the last 31 years. Changes in the surface area can be greater over short time periods such as two years, compared to longer time periods such as 31 years (Table 3-1 and Figure 3-1). The smallest changes in the shoreline position have occurred at the southern end of the hapua (Figure 3-2). The greatest change in the shoreline position has occurred about halfway along the length of the barrier. In contrast, the greatest changes in the position of the lagoonward side of the barrier have occurred at the southern end of the hapua (Figure 3-2). Based on the 5 photographs spanning 31 years, there has been more variation in the position of the lagoonward side of the barrier compared to the seaward shoreline. The width of the barrier has been variable both along its length, and between the recorded years (Figure 3-3).
Table 3-1: Hurunui hapua water body surface area in 5 different years between 1974- 2004/2005, and the change in area between the years (+ for increase in size and – for decrease in size), as well as the error (based on the pixel size and change in the position of the shoreline over a tide. The error can vary up to ±1.33 m of the stated error due to error associated with the GPS.) * Exact date that the image was taken is not known. Table sourced from Mulvany (2013)
Net change Survey Years between Hapua area 2 2 since previous Error (m ) date/photograph photographs (m ) 2 image (m ) 25/12/1974 116,158 ± 3.92 02/07/1993 19 102,642 -13,516 ± 3.92 03/09/1995 2 140,540 +37,898 ± 4.22 2002/2003* 9 135,418 -5122 ± 5.32 2004/2005* 1 (approximately) 141,261 +5,843 ± 6.22
The detection of decadal changes in the surface area of the Hurunui hapua water body, and the position and width of the barrier is hindered by the short-term changes that can occur. The surface area of the lagoon can vary considerably at different stages of the tide, especially when the outlet is at the southern end of the hapua. External influences also have an effect since both storms and floods can increase the surface area of the lagoon and make the barrier appear to be smaller than it actually is. Storms and floods can also result in rapid changes in the geomorphology of the hapua. For instance, primary and secondary breaches of the barrier can occur in response to high-energy events. Therefore, the photographs represent a snapshot in time and it is difficult to make conclusions about the vulnerability of the Hurunui River hapua over decadal or longer time scales.
6 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
a
Environment Canterbury Technical Report 7 The Hurunui River hapua: geomorphology, sediments, and water quality
Figure 3-1: Orthorectified aerial photographs of the hapua (a), aerial photograph digitisations of the hapua water surface area (b), and digitisations of the hapua surface water area from aerial photographs spanning 1974 to 2004/2005 (c)
8 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Figure 3-2: Aerial photograph of the hapua with the position of the shoreline (right) and the lagoonward side of the barrier (left) on 5 photographed years from 1974 to 2004/2005. The scale in the right image applies to both images
Environment Canterbury Technical Report 9 The Hurunui River hapua: geomorphology, sediments, and water quality
400 1974 a
1993 350 1995
2002/2003
300 2004/2005
(m)
250
Distance of of Distance the coastal 200
the baseline from shoreline
150
400 b
350
300
250
200 150 baseline (m) baseline 100 side of barrier from the the from barrier of side of Distance lagoonward 50
0
160
c 140
120 100
80
60
40
(m) barrier of the Width 20
0
1 2 3 4 5 6 7 8 9 10 11 Determination lines
Figure 3-3: Distance of the hapua seaward shoreline from the baseline (a), distance of the lagoonward side of the hapua from the baseline (b), and width of the hapua barrier (c) between 1974 to 2004/2005. Each determination line is spaced at 200 m intervals along the coast from line 1 at the main channel at the southern end of the hapua (Refer to Appendix 1)
10 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
3.2 Short-term behaviour and geomorphology
3.2.1 Lagoon water surface area The hapua water surface area can change significantly in response to the tide. The highest water level and the greatest water surface area occur at high tide when outflow through the outlet is the least (Figure 3-4). The lowest water level occurs at low tide, often resulting in a large area of gravel being uncovered (Figure 3-5).
The greatest change in the surface water area occurs at the southern end of the hapua regardless of the position of the outlet. The greatest difference in surface water area between high and low tide also occurs when the outlet is at the southern end (Figures 3-5 and 3-6). When the outlet is at the northern end, the change in surface area at the southern end of the hapua is smaller (Figure 3-6).
The short-term area of the Hurunui River hapua is also controlled by the flow of the river. The water area is greater during floods compared to low flow conditions. During floods, the influence of the tide on the surface area is eliminated. Floods have an indirect control on the degree of tidal influence by controlling the position of the outlet. In addition to floods, the surface area of the lagoon also temporarily increases during storms as waves wash over the barrier.
3.2.2 Behaviour of the Hurunui River hapua Depending on the shape of the hapua and the flow of the river, some areas of the Hurunui River hapua can be isolated from the main channel of the river at low tide. This occurs when the outlet is at the southern end of the hapua and when the river flow is low (Figure 3-5). It is likely that the river flow has to be lower than 76 m3/s for the main part of the hapua to be isolated from the main current of the river at low tide. This isolation is only temporary and persists for less than an hour. The river flow required for this isolation almost definitely depends on the shape of the hapua, the characteristics of the outlet at the southern end such as outlet width and orientation, and the tide height. It is unknown how the outlet characteristics and the tide height affect the isolation of the main part of the hapua at low tide when the outlet is at the northern end.
Figure 3-4: Photograph of the southern end of the hapua close to high tide on the 23rd of September 2012. Note the large surface area of the lagoon and the small amount of exposed gravel
Environment Canterbury Technical Report 11 The Hurunui River hapua: geomorphology, sediments, and water quality
Figure 3-5: Photograph of the southern end of the hapua close to low tide on the 23rd of September 2012. Note the large area of exposed gravel, and the person to the right of the image for an indication of scale
Figure 3-6: High tide (left), and low tide (right) at the hapua on the 9th of May 2012 with circles showing the exposed gravel
Waves commonly wash over hapua barriers during sea storms (Hart, 2009b). This usually occurs at high tide (Hart, 2009b) and when it happens, the water level in the lagoon increases, sometimes forming a new outlet (Hart, 2009a, 2009b). Although wave overtopping can result in barrier breach of some hapua (Hart, 2009b), this does not appear to occur at the Hurunui River hapua. Despite the barrier becoming virtually engulfed by water during a number of sea storms, and the water level rising to the top of the barrier, the barrier did not breach (Figure 3-7). It is likely that fluvial processes rather than coastal processes control pipe failure and barrier breach at the Hurunui River hapua. During my study flood-induced secondary breaches did occur, but only persisted for 3 to 4 days.
12 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Figure 3-7: Photograph of the southern end of the hapua showing the water level of the lagoon level with the barrier during a storm on the 15th of June 2012 Overtopping of the barrier by waves is more frequent at the northern end than the southern end of the hapua. At the northern end, wave overtopping occurs approximately once every 9 days (Table 3-2). At the southern end of the hapua, overtopping is less frequent, with 1 event every 21 days. Overtopping is sometimes confined to the vicinity of the outlet where the elevation of the barrier is lower.
Table 3-2: Details of the frequency of wave overtopping events at the two ends of the hapua
Camera Camera Number of Number of Overtopping location deployment days of image overtopping events: Length period capture events of deployment Southern 2 May 2012 – 30 104 5 1:21 end January 2013
Northern 22 June 2012 – 30 137 15 1:9 end January 2013
Based on data from the Canterbury Wave Buoy, the maximum significant wave height of the waves that were observed to overtop the Hurunui River hapua barrier ranged from 2.0 m to 8.06 m. Waves that overtoppped the barrier arrived from the east to south-southwest.
Primary breach of the Hurunui River barrier adjacent to the main channel of the river occasionally occurs (Figure 3-8). It is unknown the exact river flow required to induce a primary breach, as this depends on the characteristics of the barrier and the hydraulic head at the time of the flood. Based on Smith (1995) and Mulvany (2013), river flow somewhere between 400 to 536 m3/s is required for this to occur.
Figure 3-8: Photograph of a primary breach of the hapua
Environment Canterbury Technical Report 13 The Hurunui River hapua: geomorphology, sediments, and water quality
4 Sediment processes
4.1 Short-term spatial trends in sediment composition and deposition Sediment grain size composition varies along the landward shore of the Hurunui River hapua and can change rapidly in response to external influences such as floods. Some areas of the hapua are affected by fine sediment deposition after floods.
Sediment grain size at site 1 remains relatively constant with horizontal distance away from the waterline. Approximately 80% of the sediment at this site is coarse pebbles (>32 mm) or larger. This site does not appear to be affected by the deposition of fine sediment by small floods.
The sediment grain size composition at site 2 varies depending on the flow of the river. The sediment at site 2 can be dominated by either gravel sized or fine sized, grains. This site is often dominated by sediment within the very fine pebble to coarse pebble range (2-32 mm), with most of the sediment at the waterline being very fine sand or smaller (< 62.5 µm) (Figure 4-1). Floods can rapidly, and significantly, alter sediment grain size composition at this site. Moderate sized floods, with a mean daily flow of approximately 201 m3/s, deposit fine sediment along the landward shore of the hapua (Figure 4-2). After one such flood, about 95 mm of fine grained sediment was deposited along the shore at site 2, the most of all the sites. Large floods with an approximate mean daily flow of 536 m3/s scour fine grained sediment from the landward shoreline at this site, leaving behind larger grained sediment such as gravel (Figure 4-2).
90.00 high water mark 80.00 70.00 midway between the high water mark and the waterline
60.00 waterline 50.00 40.00 30.00 Percentage 20.00 10.00 0.00 fine sand coarse sand coarse fine pebbles fine medium sand very fine sand < very fine sand fine very < medium pebbles medium > coarse pebbles coarse > very coarse sand coarse very very fine pebbles fine very
Figure 4-1: Sediment composition at site 2 at the hapua at different locations away from the waterline
14 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Figure 4-2: Photographs of the substrate at site 2 after a moderate flood (left), and after a larger flood (right)
Site 3 is dominated by sand and mud, as well as limestone chips from the backshore cliffs (Figure 4-3). Like site 2, this site can become covered in fine grained sediment to an average depth of 25 mm after moderate floods. The landward shoreline from about 100 m further along the hapua from site 2 to site 3, is always composed of sand and mud. Unlike site 2, this area of the hapua shoreline does not lose most of its fine sediment after large floods (Figure 4-3).
Figure 4-3: Photographs of limestone chips at site 3 (left), and fine sediment along the shoreline between sites 2 and 3 (right)
Between sites 3 and B, the shoreline sediment is composed of pebbles (Figure 4-4). This part of the shoreline can become covered in fine sediment after moderate floods.
At the time of sampling, the ponded area was near the northern end of the hapua. As a result, site B sediment was dominated by gravel and boulders (Figure 4-5). For most of the time, 80% of the sediment at this site is coarse pebbles or larger (>16 mm). This site is also covered by a layer of around 15 mm of fine sediment after moderate floods (Figure 4-5). Further northwards, the backshore sediment of the hapua consists of gravel and sand (Figure 4-6).
Environment Canterbury Technical Report 15 The Hurunui River hapua: geomorphology, sediments, and water quality
Figure 4-4: Photographs of the hapua shoreline between sites 3 and B before a flood (left), and after a moderate flood (right)
Figure 4-5: Photographs of the landward shore of the hapua at site B in its typical state (left), and after a moderate flood (right)
Figure 4-6: Photograph of the shoreline at the northern end of the hapua
16 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Sediment at the waterline by the hapua outlet is mostly very fine pebbles (2-4 mm) (Figures 4-7 and 4-8). Because of the constantly shifting substrate and position of the outlet, the strong river flow, and wave action, there is virtually no fine sand or smaller sediment (<125 µm) at the outlet.
90 waterline 80 midway between the high water mark and the 70 waterline 60 high water mark
50 40 30
Percentage 20 10 0 fine sand coarse sand coarse fine pebbles fine medium sand very fine sand < very fine sand fine very < medium pebbles medium > coarse pebbles coarse > very coarse sand coarse very very fine pebbles fine very
Figure 4-7: Sediment composition at the hapua outlet at different locations away from the waterline
Figure 4-8: Photograph of sediment at the outlet
Environment Canterbury Technical Report 17 The Hurunui River hapua: geomorphology, sediments, and water quality
4.2 Floods and sediment composition Fine sediment can be deposited along the landward shoreline of the Hurunui River hapua as floodwaters recede. This occurred after a flood that had a mean daily flow of 201 m3/s. The amount of fine sediment deposited in any given area depends on the size of the flood, and the flow at each site.
Based on Mulvany (2013), floods with a mean daily flow of 536 m3/s are needed to remove fine sediment deposited by previous floods. The amount of fine sediment removed by large floods depends on the shape of the hapua. For instance, if a moderate flood deposits a large amount of fine sediment, and the shape of the hapua changes afterwards to form a ponded area, sediment will not be removed from the ponded area by a subsequent large flood.
4.3 Wind and suspended sediment Where there is fine sediment on the bottom of the hapua, wind driven circulation of the water column results in the re-suspension of this sediment. As a result, suspended sediment and turbidity become elevated. This occurs most commonly at site 3, although can occasionally occur elsewhere along the landward shore of the hapua if there is a significant amount of fine sediment present that has been deposited by previous floods. The mean concentration of suspended sediment at site 3 during low energy conditions is 0.02 mg/L, but when wind driven resuspension of fine sediment from the hapua bottom is significant, suspended sediment can be as high as 0.14 mg/L. Although it is unknown how long the elevated suspended sediment concentration persists for, it will likely be related to: wind strength; wind direction; the persistence of the wind; the amount and composition of fine sediment on the bed of the hapua and water depth.
4.4 Long-term sediment processes Sediment composition and accumulation throughout the Hurunui River hapua over the long- term depends on a number of factors (Figure 4-9). These include: • The source of the sediment - catchment, the eroding backshore cliffs or the coast. • The sediment transport pathways and how these vary over time. eg. river flow. • The shape of the hapua. This is because of its influence on the flow of river water through the hapua.
Figure 4-9: Relationship between sediment energy and sources with processes and the resultant export, modification, and sinks of sediment (Nichols & Boon, 1994, p.163)
18 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
5 Water quality This assessment of the water quality in the Hurunui River hapua is based on field measurements and water samples taken from the sites shown in Figure 2-1. The parameters measured were:
• water temperature • conductivity • dissolved oxygen • pH • suspended sediment • total nitrogen (TN) • ammonia nitrogen (NH3N) • nitrate + nitrite nitrogen (NNN) • total phosphorus (TP) • dissolved reactive phosphorus (DRP)
To assess the quality of the water, measured concentrations of all parameters except water temperature, conductivity, and suspended sediment, were compared to ANZECC (2000) guideline values.
5.1 Short-term water quality
5.1.1 Water quality in low energy conditions All hapua experience short-term floods and storms, although the most common state is low flow conditions (Hart, 2009a). In these conditions, the water quality of the hapua is good as most of the parameters are below or within the guideline values (Table 5-1). However, total nitrogen concentrations are above the guideline value for coastal lakes and lagoons in the Canterbury Region (Environment Canterbury, 2011).
Water quality through the hapua is usually uniform in low energy conditions. However, water quality can vary spatially due to the shape of the hapua and wind. The shape of the hapua has a major control on water quality (Table 5-2). The greatest spatial differences occur when the outlet is at the southern end, and the main part of the hapua is ponded and away from the main flow of the river. When this occurs, conductivity in the ponded area is elevated due to the inflow of seawater with the waves that wash over the barrier during sea storms. If there is a ponded area, the longer the residence time of water the greater the spatial differences in conductivity through the hapua. When the outlet is the northern end of the hapua and no ponded areas are present there are typically no significant spatial differences in water quality. This is because water flow is similar throughout the hapua.
Spatial differences in water quality during low energy conditions can occur because of the influence of wind. Differences in the concentration of total phosphorus and dissolved reactive phosphorus between sites are attributed to wind driven circulation of the water column and re-suspension of fine sediment from the hapua bed (Appendix 12). The resulting exceedence of the guideline value for total phosphorus concentration in this situation is temporary.
Spatial differences in pH in all energy conditions and in different morphological states of the hapua suggests that something other than the shape of the hapua and the flow of the river is controlling pH. It is possible that the limestone cliff along stretches of the backshore is the main influence of pH in this hapua. This cliff is not present in all areas of the hapua, hence is the likely cause for the spatial differences in pH throughout the hapua.
Environment Canterbury Technical Report 19 The Hurunui River hapua: geomorphology, sediments, and water quality
Table 5-1: Parameters that exceeded or were within the guideline values. Table sourced from Mulvany (2013) #ANZECC & ARMCANZ (2000) guideline values * water quality standards for coastal lakes and lagoons in the Canterbury Region set by Environment Canterbury (2011) ** guideline based on the 75th percentile (Ausseil, 2010) mean value within the guideline values mean outside of the guideline values
Parameter Guideline Low energy Floods Storms Dissolved oxygen 6 mg/L#
pH 7.5-8.8**
Total nitrogen 0.614 mg/L# 0.34 mg/L* Ammonia nitrogen 0.9 mg/L#
Nitrate-nitrite nitrogen 0.444 mg/L#
Total phosphorus 0.02 mg/L*
Dissolved reactive # phosphorus 0.01 mg/L
Table 5-2: The influence of outlet position and energy event on spatial differences in water quality parameters and suspended sediment ( spatial differences, X no spatial differences, - not tested for, * the spatial differences in suspended sediment were much greater in the flood conditions when the outlet was located at the southern end compared to the northern end). Table sourced from Mulvany (2013)
Water Dissolved Suspended Conductivity pH temperature oxygen sediment Low energy X X X Outlet at southern Flood * end Storm
Low energy X X X X Outlet at northern Flood X X X end Storm - - - - -
20 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
5.1.2 Water quality states Based on the water quality results in low energy conditions, I have derived three water quality states for the Hurunui River hapua (Figure 5-1). When the outlet is at the southern end, water quality is likely to be poorer than when the outlet is at the northern end. This is due to the differences in water flow through the hapua and the residence time of water in the ponded area. When the outlet is at the southern end, the main part of the hapua can become isolated from the main part of the river at low tide (Figure 3-5). At high tide, water can flow into the ponded area (Figure 3-6). If the river flow is low enough to prevent mixing of water at high tide, water quality could become an issue in the ponded area.
The best water quality within the hapua occurs when the outlet is at the northern end and there are no ponded areas. In this state, water flows through the hapua and the residence time of water is low.
The intermediate water quality state occurs when the outlet is near the northern end of the hapua and ponded areas are present. There is the potential for water quality to be poorer in the ponded areas due to a longer residence time of water. Water temperature and conductivity are likely to be higher in the ponded area than in the rest of the hapua.
Figure 5-1: Typical states that can exist in the Hurunui River hapua (Mulvany, 2013)
Environment Canterbury Technical Report 21 The Hurunui River hapua: geomorphology, sediments, and water quality
5.1.3 Water quality in floods and storms Floods and storms are short-term high-energy events. These events affect water quality in the hapua, however the effects are temporary.
During floods the TN, TP, and DRP exceeded guideline values (Table 5-1), i.e. the water quality within the hapua is poor. Spatial differences in water quality when the outlet is at the southern end are more pronounced than when the outlet is at the northern end and there are low energy conditions. Concentrations of all parameters vary through the hapua during floods when the outlet is at the southern end. Water temperature, conductivity, pH, and the concentration of NNN are higher in the ponded area than non ponded areas that are by the main flow of the river. Dissolved oxygen, suspended sediment, TN, NH3N, TP, and DRP are lower in the ponded area compared to sites by the main flow of the river. Overall, when the outlet is at the southern end during floods, water quality is better in the ponded area than adjacent to the main flow of the river. There is no significant variation in water quality through the hapua during floods when the outlet is at the northern end. It is unknown if nutrient concentrations follow the same trend as the other parameters when the outlet is at the northern end of the hapua during flood conditions. This is because samples for nutrient concentration analysis were only taken when the outlet was at the southern end of the hapua.
During storms when waves wash over the barrier the water quality within the hapua is good as the sea water flowing into the hapua dilutes the concentration of nutrients. However, there are spatial differences in water quality when the outlet is at the southern end of the hapua. It is unknown if there are spatial differences in water quality when the outlet is at the northern end.
5.1.4 Additional variations in water quality It is likely that water quality in the hapua varies seasonally due to variation in river flow through the year. Summer and early autumn is when the lowest flows occur, and the greatest water quality problems occur (Mosley, 2002). Water quality issues are likely to be greater at this time of year, especially when ponded areas are present. Water quality is also likely to be influenced by the variation in sediment and nutrient runoff from agricultural areas during the irrigation season.
5.2 Long-term water quality It is unknown how water quality in the Hurunui River hapua has changed, or will change over decades or longer. Currently, there is a decline in water quality with distance down the Hurunui River (Ausseil, 2010; Hayward, 2001). Numerous pressures from the catchment exist. These include dam proposals, water abstraction, irrigation, and agriculture intensification. Future changes in the water quality in the hapua will depend on these pressures. External influences, in particular the river hydrological regime, have the potential to directly and indirectly affect water quality within the hapua (Figure 5-2). For instance, if the flood regime of the river is altered, the geomorphology of the hapua will be affected, potentially leading to an alteration in the water quality over time. The health of the Hurunui River hapua over decades or longer will depend on the quality of the water entering the hapua.
22 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
External influences Lagoon processes
Floods and storms Geomorphology
Water quality/ characteristics Sea-level rise
Climate change Ecology
Key of major effects: Rapid change Follow on Decadal or longer change effects
Figure 5-2: Conceptual diagram of external influences on hapua, the effect on internal processes including water quality, and any follow on effects. Rapid change is based on changes over hours or days (Mulvany, 2013)
Environment Canterbury Technical Report 23 The Hurunui River hapua: geomorphology, sediments, and water quality
6 Periphyton
No detailed studies of periphyton in the Hurunui River hapua have been done prior to this study. Periphyton species and abundance varies through the hapua. Descriptions of each site, and details of the periphyton (Dr. P.Broady, personal communication, April 18, 2012) at each site are presented in Table 6-1.
Table 6-1: Photographs and descriptions the periphyton in different areas of the hapua Site 1 Site description: • at the swing bridge before the start of the hapua
• swift flow
• in the lower part of the Hurunui River
Periphyton details: • Desmid cf. Cosmarium sp.
• Indicative of freshwater conditions
Site 2 Site description: • at the campground
• still water
• sediment composition can change dramatically
Periphyton details: • 2 species of Oedogonium (Chlorophyta)
• Phormidium
• Abundant single cell diatoms (naviculoid, cymbelloid, nitschioid)
• Melosira filaments (diatom)
24 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Between sites 2 and 3 Site description: • along the backshore of the main part of the hapua at the anglers access
• fine sediment
Periphyton details: • blue-green mats of cyanobacteria
• Phormidium
• Abundant single cell diatoms (nuviculoid, cymbelloid, nitzschioid)
Site 3 Site description: • Soft substrate with limestone chips
• Shallow
Periphyton description: • minimal periphyton
Site B Site description: • gravel and boulders
• at the northern end of the hapua
• usually in the ponded area of the hapua
Periphyton details: • macrophyte Enteromorpha cf. intestinalis
• indicative of brackish water
Environment Canterbury Technical Report 25 The Hurunui River hapua: geomorphology, sediments, and water quality
Site O Site description: • outlet
• gravel and sand
• constantly shifting substrate
• high wave energy and strong river flow
Periphyton details: • sparse single cell diatoms
A brackish algae species occurs along the backshore of the hapua where the water is often ponded. This indicates that this area has a higher salinity than other areas of the hapua. Field measurements found conductivity and salinity in this area is often higher than in other areas of the hapua. This brackish species does not seem to be affected by the scouring effect of floods. This suggests the flow in this location is not sufficient to scour the algae from the substrate.
It is likely that the periphyton between sites 2 and 3 is unaffected by floods and changes in the geomorphology of the hapua. However, if the position of the outlet changes to the southern end and the main part of the hapua drains the periphyton will be affected as areas of the hapua are not covered with water.
The difference in periphyton through the hapua is a function of the substrate composition, substrate stability, river flow, and salinity. The major control on periphyton is river flow due to its influence on the substrate composition, substrate stability, and hapua geomorphology (sections 1.1, 4.2, and 4.4). It is likely that periphyton species and abundance changes in response to the substrate composition. For instance, it is likely that the periphyton at site 2 changes after a significant amount of fine sediment is deposited by moderate floods, or after fine sediment is scoured from the bottom by large floods. It is also probable that some areas of the hapua have a seasonal presence of periphyton. Because observations were made in autumn and early winter, seasonal patterns through the year are as yet unknown.
Approximately 40 years ago, the Rakaia River hapua had extensive areas of macrophytes. It has been speculated that these have since disappeared with the alteration to the hydrological regime of the river due to the intensification of water abstraction, irrigation, and agriculture in the catchment (B. Southward, personal communication, February 17, 2013). Although the Hurunui River hapua does not have significant areas of macrophytes, changes that have occurred in the Rakaia River hapua should act as a caution that the river must be carefully managed to avoid adverse impacts and changes in the hapua.
26 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
7 Requirements for hapua ecological health
7.1 River flow This study has found that river flow is the most important factor influencing the ecological health in the Hurunui River hapua. This is because of its influence on the shape of the hapua and the water residence time. Moderate flows, such as those encountered during this study (37 to 60m3/s) are likely to be the most ideal for maintaining the ecological health through the largest portion of this hapua (Table 7-1). Moderate river flow and wave conditions are required to maintain the outlet at the northern end of the Hurunui River hapua (Hart, 2009). This was observed over 8 months. However, historic aerial photographs show that backwater ponded areas can occur north of the outlet when the outlet is at the northern end of the hapua. The historic river flows, wave conditions, and water quality are not known.
Having the outlet at the northern end is good for water quality as prominent ponded areas are unlikely to be present and there is uniform water flow through the hapua and low water residence time. Based on the water quality in ponded areas in this study, it is likely that below a certain flow, water residence time will increase causing water temperature to increase and dissolved oxygen concentration to decrease. The greatest impact of low river flow on water residence time and water quality would occur when ponded areas are present. This could have a negative effect on the ecological health of the hapua. The migration of the outlets of hapua such as the Rakaia away from the main river channel during low river flow can lead to a degradation in water quality and ecological health (Hart 2009a). However, the river flow and water residence time at which water issues occur in this hapua is unknown.
Floods that result in primary breaches of the barrier have the greatest influence on the presence of ponded areas and on the ecological health of the hapua. Primary breaches occur when the mean daily flow is 536 m3/s, although Smith (1999) predicted that flows as low as 400 m3/s can result in a primary breach. When a primary breach occurs, most of the hapua becomes ponded and isolated from the main current of the river. In this state, water temperature and conductivity are typically higher in the ponded area than the unponded areas. An increase in the water residence time in the ponded area can result in an increase in water temperature and a decrease in dissolved oxygen concentration. This increases the likelihood for a decline in water quality.
Large floods can also disturb the substrate in some areas of the hapua. This is especially evident in the lower river near the entrance of the hapua. Moderate floods (200 m3/s mean daily flow) can also influence ecological health if the landward shoreline of the hapua becomes covered in fine sediment.
More investigation is required to determine at which flow water quality degradation and ecological health becomes compromised. Although the influence of river flow on the hapua shape is important in terms of ecological health, the period that a certain flow persists for, especially low flows, is also important.
7.2 River water quality To maintain the ecological health of the hapua, phosphorus and sediment inputs must be managed. Wind driven circulation and the subsequent suspension of fine sediment from the bed of the hapua naturally occur. When this happens, total phosphorus and dissolved reactive phosphorus become elevated in areas where the hapua bed is fine sediment. Therefore, phosphorus and suspended sediment concentrations are influenced by both river
Environment Canterbury Technical Report 27 The Hurunui River hapua: geomorphology, sediments, and water quality
flow and wind driven circulation in the hapua. These parameters can become elevated in concentration when the river is not in high flow. This could influence the growth of periphyton.
It is possible during low flow conditions large areas of ponded water, river water high in nutrients, and warm conditions occur. If this does occur, biota such as periphyton could benefit, while other biota not adapted to the conditions could be impacted.
7.3 Sea state The sea state influences ecological health in the hapua. During sea storms, waves wash over the barrier into the hapua. This causes conductivity and salinity to increase in concentration. If there are prominent ponded areas present, the water residence time results in a greater persistence of elevated concentrations than in areas that are unponded and close to the flow of the river. It is unknown how long the elevated levels persist for in the ponded areas. Elevated levels of salinity and conductivity would negatively impact biota adapted to freshwater, whereas other species, especially brackish algae species, would benefit.
Because no studies have been done on the ecology of the Hurunui River hapua, the requirements of ecological health are inferred from the response of water quality to the flow of the river and the shape of the hapua. To adequately assess the requirements for ecological health of the Hurunui River hapua, the biota currently present must be known, and how it responds to changes in the river flow, sea storms, and water quality within the hapua. It is possible that biota such as invertebrates also vary spatially in response to the difference in water quality and substrate characteristics when ponded areas are present. With the elimination of microhabitats in response to the ponded areas, species adapted to these habitats could become extirpated. The effect on biota of the position of the outlet cannot be adequately determined without knowing what species are present and what their tolerance ranges to specific conditions are.
28 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Table 7-1: Summary of the impacts of river flow on the hapua and ecological health, based on Mulvany (2013) * flows lower than 37 m3/s were not studied, so the impacts in the hapua and on ecological health during flows < 37 m3/s are predictions
Water Flow What happens in the hapua Effect on ecological health state (m3/s) Large flood > 536 • Primary breach • Change in sediment • Outlet at the southern end composition • Large ponded area • Reduction in fine sediment • Scouring of fine sediment • Decrease in dissolved oxygen, from the hapua bottom and increase in water temperature and conductivity in the ponded area • High water residence time in ponded area, low water residence time in unponded area Moderate ~ 200 • Fine sediment deposition • Change in sediment flood along the landward composition shoreline • Smothering effect of fine • No primary breach sediment deposition • No spatial differences in water quality Moderate 37-60 • Outlet at the northern end • No spatial differences in water flow of the hapua quality, unless ponded areas • Usually no prominent are present ponded areas • Low water residence time
Low flow* < 37 • Outlet at northern end • Increase in water temperature • Increase in water residence time • Higher concentration of nutrients • Increase in periphyton biomass
Environment Canterbury Technical Report 29 The Hurunui River hapua: geomorphology, sediments, and water quality
8 Hapua management
Physical and chemical water parameters should be monitored to provide information of the health of the hapua. Studies of the Hurunui River hapua showed that while some parameters can be within the guidelines, others are outside the guidelines. Parameters used should include: water temperature, conductivity/salinity, dissolved oxygen, pH, total nitrogen, ammonia nitrogen, nitrate + nitrite nitrogen, total phosphorus, and dissolved reactive phosphorous. The monitoring should also incorporate biological aspects including periphyton and macroinvertebrates. Sediment deposition should also be measured. This would provide a holistic approach.
The monitoring program must carefully consider the location of the sampling sites. Sample sites in other hapua would also have to be carefully considered, although the considerations would most likely be different for each hapua. This highlights the importance of conducting a preliminary study before the commencement of any hapua monitoring program. The selection of sample sites will depend on the objectives of the study or monitoring program. At the Hurunui River hapua, significant areas of water can be uncovered at low tide, especially at the southern end of the hapua when the outlet is also at the southern end. When selecting sample sites, the influence of the tide must be considered. Sites that are not uncovered at low tide would need to be chosen. These sites must take into account the potential for geomorphological changes to result in large areas becoming uncovered at low tide.
I recommend the following sampling sites in the Hurunui River hapua. Site 1 by the swing bridge represents the lower river, and the quality of water that enters the hapua. If the quality of water entering the hapua is required, then this site should be included. Water samples should be taken from the true right of the river where there is a concrete block on the bank that allows for easy access. The main channel of the river is also on the true right of the river. For ecological surveys, the true left of the river should be monitored as the flow is less swift and the water is shallow.
Site 2 is located at the campground. If recreational values are important, then this site should be included in a monitoring program or study. The substrate at this site can change significantly in response to floods. This site can change from a substrate covered in fine sediment, to a cobbled and armoured substrate after a flood event. Therefore, visual observations of the substrate must be noted each time that macroinvertebrate or periphyton surveys are conducted. This site also can experience significant changes in the water level and the amount of substrate covered in water at different stages of the tide. This is especially evident when the outlet is at the southern end of the hapua. Therefore, this would need to be taken into account. Because of the backwater effect of the tide at this site, it is suggested that this site only be included in a monitoring program if recreational values are important.
Site 3 should be included in a study or monitoring program as it represents the main part of the hapua. It has a rocky outcrop on the landward shoreline that provides easy access. There is also a minimal amount of fluctuation in the water level at this site compared to other areas of the hapua such as site 2.
The ponded backshore site should also be included as the water characteristics are often different compared to areas that are close to the main current of the river. Because of the dynamic geomorphology of the hapua, this site would need to be shifted depending on where the most prominent ponded area is located.
If the quality of water exiting the hapua is of interest, then the outlet should be included. Because of the safety limitations, this site can only be sampled in low energy conditions.
30 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Periphyton and macroinvertebrate sampling at this site are not useful as the constantly shifting substrate limits the presence of biota.
If the Hurunui River hapua is to be used as an indicator of catchment health, both ponded and unponded areas should be included. This is because there can be distinct differences in the characteristics of the water in the two areas. To investigate the water quality and biota characteristics in the lower river, and in the hapua are to be investigated, it is suggested that site 1 be included. Site 2 could be excluded, and a site representative of the main part of the hapua, and a site representative of a ponded area should be included.
I also suggest that two time-lapse cameras be used in a monitoring program of the Hurunui River hapua. Time-lapse cameras are valuable for providing extra information about the timing of events such as storms and primary breaches. This information can be useful for explaining unexpected and unusual results from water quality measurements.
Two cameras should be used. This is so that the two ends of the hapua can be monitored. The length of the hapua is too long for one camera to monitor the entire lagoon. The greatest changes in the hapua shape and position of the barrier occur in the vicinity of the outlet. Wave overtopping is also most common at the outlet. Therefore, a camera at each end is needed to ensure that the outlet is always photographed. One camera should be placed on the bank on the true right of the river at the southern end of the hapua (Figure 8-1). The other camera should be placed at the road end near the northern end of the hapua (Figure 8-1). The details of these locations are in Appendix 1.
Figure 8-1: Photograph of a time-lapse cameras set up at the northern end of the hapua (left), and one at the southern end (right). Both face northwards Significant areas of the hapua can be uncovered at low tide, especially at the southern end when the outlet is also at the southern end. The influence of the tide must be considered when selecting sample sites. Sites that are not uncovered at low tide must be chosen. Site selection must consider the potential for a change in the area of water uncovered at low tide after significant geomorphological changes and a change in outlet position. This is so that sites remain comparable before and after any significant changes in the geomorphology and characteristics of a site.
Any monitoring program or study at the Hurunui River hapua must consider the number of water samples and the time taken to access each site. Access to some of the sites require walking down a bank (site 3), and walking along the shore for 10 to 15 minutes one way (site B). If these sites are sampled, the number of water samples will be limited by how much
Environment Canterbury Technical Report 31 The Hurunui River hapua: geomorphology, sediments, and water quality
weight the sampler can carry. This would not be an issue if the sites are accessed by boat. However, boat access also has limitations such as the time of the tide and water level in the hapua.
Because of the dynamic nature of the hapua in terms of geomorphology, substrate composition and wind driven circulation, visual observations must be taken each time. This could include wind strength, hapua shape, and outlet location. This would help to explain any unusual results.
The Hurunui River hapua is influenced by the backwater effect of the tide. However, this does not appear to have an influence on the concentration of suspended sediment and nutrients, or water quality parameters including water temperature, conductivity, dissolved oxygen, and pH. Therefore, the time of tide does not need to be considered when taking samples. The time of tide would need to be considered if areas in the hapua that are uncovered at low tide are included in a study or monitoring program. In this instance, samples should be taken at high tide when all of the sites are covered in water.
32 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
9 Suggestions/recommendations for future work
There is currently no information on the animal species that use or live within the hapua. Therefore an Investigation of the species present within the hapua, especially macroinvertebrates, would be a valuable direction of future research. The presence and abundance of species as well as details of where they occur and how the changes in the hapua influence their presence and abundant could be investigated. Periodical mapping of habitat and communities could be a useful method to monitor changes in the Hurunui hapua. Species that are the most vulnerable to a change in fluvial processes and water quality should be identified.
There has not been an extensive long term study of periphyton in the Hurunui River hapua. Such a study is important in understanding the ecology of this ecosystem. Periphyton could potentially be used as an indicator of hapua health and for identifying the effects of changes in the river catchment. It is suggested that its use should be investigated.
It is unknown if there are seasonal differences in the health and water characteristics of the Hurunui River hapua. Further research could investigate this, especially since late summer and autumn is when water quality issues are typically the greatest in the lower river.
It is unknown what the characteristics of the water are when the outlet is towards the northern end and a prominent ponded area is present (Figure 9-1). To further understand the difference in water quality between ponded and unponded areas, water quality in more geomorphological states should be studied.
Figure 9-1: Image of the hapua with a prominent ponded area at the northern end (Source: GoogleMaps)
Environment Canterbury Technical Report 33 The Hurunui River hapua: geomorphology, sediments, and water quality
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Kirk, R. M. (1983). Rakaia river mouth and lagoon system and the adjacent coast. In North Canterbury Catchment Board & Regional Water Board (Eds.), The Rakaia River Catchment: A resource survey (Vol. 2, pp. 67-101).
Kirk, R. M. (1991). River-beach interaction on mixed sand and gravel coasts: a geomorphic model for water resource planning. Applied Geography, 11(4), 267-287.
34 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Kirk, R. M., & Lauder, G. A. (2000). Significant coastal lagoon systems in the South Island, New Zealand: Coastal processes and lagoon mouth closure. Wellington, New Zealand: Department of Conservation.
McHaffie, N. (2010). A GIS based analysis of changes in the Rakaia Hapua, Canterbury. GEOG420 dissertation, Department of Geography, University of Canterbury, Christchurch.
Mosley, M. P. (2002). Hurunui River instream values and flow regime. Environment Canterbury Report R02/1.
Mulvany, D.A. (2013). Contemporary and past conditions in the Hurunui River hapua, Canterbury, New Zealand, and the potential effects of dams on this lagoon. (Unpublished Master’s thesis). University of Canterbury, Christchurch.
Nichols, M. M., & Boon, J. D. (1994). Sediment transport processes in coastal lagoons. In B. Kjerfve (Ed.), Coastal lagoon processes (pp. 157-219). Amsterdam: Elsevier Science Publishers.
Paterson, A., Hume, T., & Healy, T. (2001). River mouth morphodynamics on a mixed sand- gravel coast [Special Issue 34]. Journal of Coastal Research, 288-294.
Smith, S. J. (1995). Morphodynamics of the Hurunui River mouth, North Canterbury. (Unpublished Master’s Thesis). University of Canterbury, Christchurch.
Environment Canterbury Technical Report 35 The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 1: Details of the methods used in this study
Short-term hapua behaviour Time-lapse cameras were installed to capture the two ends of the hapua. Each camera took a photograph every hour. The southern camera took photographs from May 2012 to January 2013, and the northern camera from June 2012 to January 2013. The images were collated into a video sequence which was then downloaded onto a computer. The movie was imported into imovie where the night scenes were eliminated, and the frame speed reduced to approximately one frame per second. The movie was then exported as a quicktime file from which visual observations were made.
Location of time lapse camera Northing Easting South end of hapua on cliff top 5248891.94 1622912.03
At the road end at the northern end 5249499.41 1623550.76
Long-term geomorphology of the hapua Unorthorectified aerial photographs from the years 1974, 1993, and 1995 were scanned at a resolution of 600 dpi. Photographs from 2002/2003 and 2004/2005 were downloaded from the LINZ website. These photos were orthorectified in ArcMap 10 using a Bingmap and New Zealand shoreline shapefile as a basemap. The hapua water area, the position of the shoreline, and the position of the lagoonward shoreline for each of the years were digitised.
Survey Run and Date Scale Source number frame Environment 25/12/1974 SN 5370 L/30 1:26,500 Canterbury Environment 02/07/1993 SN 114 Run A # 83 1:19,000 Canterbury Environment 03/09/1995 SN 12206 DD/32 1:27,000 Canterbury 2002/2003* - - - LINZ
2004/2005* - - - LINZ * Exact date of the image capture is unknown, but it likely to have occurred sometime around Christmas, - unknown
To investigate the width of the barrier, Et Geowizards, an extension of ArcMap 10, was used as it allowed for the position of the shorelines to be measured more accurately than the measure tool function in ArcMap 10. Firstly, a baseline was drawn parallel to the road along the landward shore of the hapua. The ‘split polyline’ tool in Et Geowizards was used to split the baseline into 200m intervals. A perpendicular determination line was then constructed at each interval along the baseline. The determination lines were labelled 1 to 11, with determination line 1 at the southern end, and determination line 11 at the northern end of the hapua. Finally, the distance from the baseline along each determination line to the shoreline and the lagoonward shorelines was calculated.
36 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Sediment composition At each site a transect was laid out from the shoreline to the high water mark which was defined by the debris line. A sample from the top 10 cm of the hapua bed sediment was taken at the waterline, the debris line, and from halfway between the waterline and the debris line. The samples were dried in an oven at 60°C for at least two days. Each sample was placed through a range of sieves down to a size of 4 φ. Samples from site 3 were not sieved as the limestone chips would have broken down during the sieving processes, introducing bias to the results.
Fine sediment deposition To measure fine sediment deposition at each site a transect was laid out perpendicular to the shoreline, from the waterline to the debris line. Twenty random sites were sampled, each at a random point along the transect, and then a random distance away from the transect. Points alternated between the two sides of the transect. A ruler was placed into the sediment to measure the depth at each point. This process was repeated 3 times at each site.
Suspended sediment At each site, an integrated water sampler was used to collect a 1 L sample at knee depth. This was taken upstream of the fieldworker to ensure no disturbed hapua bed sediment was washed into the bottle. The sampler was gently lowered from the surface to the bottom and then up to the surface again. Three samples were collected at two minute intervals. This was done every 2 to 3 hours to investigate the influence of the tide on suspended sediment concentrations. Samples were not taken from site O during floods and storms for safety reasons. The water samples were filtered through a Watman 45 mm pre-weighed filter, and dried at 60°C for at least 24 hours to give the final weight of suspended sediment.
Samples were taken at different stages of the tide in two low energy events and in two floods. Samples were not taken at different stages of the tide during the storm. The location of some of the sites differed slightly between sampling events.
Environment Canterbury Technical Report 37 The Hurunui River hapua: geomorphology, sediments, and water quality
Low energy conditions – 1st event 13 May 2012 (left), and 2nd event 24 September 2012 (right)
Site Northing Easting Site Northing Easting 1 5249389.33 1622376.53 1 5249389.33 1622376.53 2 5249037.75 1622819.87 2 5249037.75 1622819.87 3 5249505.66 1623566.39 3 5249505.66 1623566.39 4 5250052.53 1623913.52 4 5250052.53 1623913.52 5 Was not Was not 5 5249045.07 1623240.09 recorded recorded
Flood conditions 25 June 2012 (left), storm conditions 7 November 2012 (right)
Site Northing Easting Site Northing Easting 1 5249452.78 1622372.71 1 5249446.08 1622366.21 2 5249039.98 1622828.95 2 5249035.43 1622821.07 3 5249505.77 1623563.53 3 5249508.40 1623565.49 4 5250039.06 1623900.45 4 5250044.93 1623904.13 5 na na 5 5249039.02 1623219.27
Water temperature, conductivity, dissolved oxygen, and pH Water temperature, conductivity, dissolved oxygen, and pH were measured when the water samples for suspended sediment concentration were collected. This was done using the multi-parameter Manta2 water quality multiprobe manufactured by Eureka Environmental Engineering. Three measurements were taken at least 2 minutes apart. Measurements were not taken from the outlet during floods and storms for safety reasons.
Nutrients (TN, NH3N, NNN, TP, DRP) Water samples for nutrient analysis were taken at sites 1, 2, 3, B, and O. Samples were taken from knee depth using a water sample pole and an acid-cleaned polyethylene bottle. One sample was taken at each site at low, mid, and high tide in two low energy events. In one of the events the outlet was at the northern end, and the other the outlet was at the southern end of the hapua. Only one sample was taken from each site during a flood and a storm. The outlet site could not be sampled during the flood and storm for safety reasons.
Low energy conditions – 1st event 13 July 2012 (left) and 2nd event 24 September 2012 (right)
Site Northing Easting Site Northing Easting 1 5249452.78 1622372.71 1 5249389.33 1622376.53 2 5249035.76 1622835.08 2 5249037.75 1622819.87 3 5249506.82 1623565.15 3 5249505.66 1623566.39 4 5250057.02 1623910.78 4 5250052.53 1623913.52 5 5250308.05 1624297.71 5 5249045.07 1623240.09
Flood conditions 2 August 2012 (left), and storm conditions 7 November 2012 (right)
Site Northing Easting Site Northing Easting 1 5249389.33 1622376.53 1 5249389.33 1622376.53 2 5249037.75 1622819.87 2 5249035.43 1622821.07 3 5249505.66 1623566.39 3 5249508.40 1623565.49 4 5250151.06 1624075.57 4 5250044.93 1623904.13 5 5250048.93 1623935.89 5 5249039.02 1623219.27
38 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 2: Sediment composition data
(Oc – waterline at site O, Oa – high water mark at site O, Ba – high water mark at site B, Ob – midway between the waterline and high water mark at site O, 1a – high water mark at site 1, 2a – highwater mark at site 2, 2b – midway between the waterline and high water mark at site 2, 2c – waterline at site 2).
Oc Oa Ba Ob 1a 2a 2b 2c Sediment class Φ (%) (%) (%) (%) (%) (%) (%) (%) > - > coarse pebbles 4 0.00 0.00 74.90 5.06 79.62 52.00 18.34 0.00
medium pebbles -3 8.55 15.93 1.85 1.77 5.11 16.25 42.32 5.40
fine pebbles -2 2.77 12.03 4.78 3.94 5.02 4.46 8.65 0.45
very fine pebbles -1 6.90 54.50 5.80 16.70 4.70 3.73 4.24 0.81
very coarse sand 0 18.31 15.72 4.40 24.20 1.30 2.45 2.29 0.80
coarse sand 1 30.27 1.35 2.74 24.20 1.01 2.05 1.94 0.92
medium sand 2 26.92 0.31 3.68 19.32 0.96 2.59 2.19 1.16
fine sand 3 4.30 0.03 0.65 2.19 0.85 3.43 2.93 7.57
very fine sand 4 1.82 0.07 1.04 2.48 0.85 6.40 6.65 48.02
< very fine sand < 3 0.01 0.00 0.13 0.03 0.54 6.59 10.35 34.65 unaccounted sediment - 0.13 0.05 0.04 0.10 0.04 0.05 0.10 0.22
Environment Canterbury Technical Report 39 The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 3: Sediment deposition (mm) data
Site 2 Site 3 Site B 70 90 80 1 2 2 0 2 15 60 70 80 15 12 20 47 40 10 140 125 140 52 55 55 9 5 15 95 100 90 7 10 10 0 5 0 115 110 110 20 0 35 20 55 76 60 90 100 25 40 50 8 0 15 100 100 110 50 35 50 43 70 15 130 130 135 0 2 2 25 10 30 130 130 100 0 15 2 5 0 35 60 75 90 50 55 65 6 0 25 80 70 80 25 35 45 0 0 0 90 85 90 30 25 40 5 20 0 85 90 90 2 2 7 0 52 0 10 40 60 10 15 25 30 0 0 50 75 80 0 10 10 5 10 5 80 110 110 7 0 10 41 0 25 95 90 90 70 50 55 21 72 20 120 120 120 25 0 45 11 2 0 130 135 140 25 20 45 2 0 5 120 115 120 56 20 55 9 0 20
40 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 4: Suspended sediment (mg/L) data (low energy event 1: 13 May 2012, low energy event 2: 24 September 2012, flood 1: 25 June 2012, flood 2: 9 August 2012, storm: 7 November 2012)
Low Low Tide Site Flood 1 Flood 2 Storm energy 1 energy 2 1 0.0018 0.00355 0.21251 0.91415 0.02264 0.0027 0.01535 0.18203 1.1077 0.22244 0.00121 0.0121 0.20237 0.93318 0.02128 2 0.00172 0.02447 0.85402 0.82887 0.01761 0.00261 0.01784 0.26874 0.84892 0.01649 0.00253 0.02294 0.25071 0.85214 0.01974 3 0.00237 0.04356 0.14769 0.13413 0.02171 High tide 0.00439 0.05175 1.13386 0.14108 0.02059 0.00227 0.07856 0.4157 0.13344 0.02031 B 0.00101 0.0087 0.16591 0.10074 0.02911 0.00125 0.00713 0.23045 10262 0.029 0.0018 0.00661 0.19906 0.10073 0.02815 O 0.00177 0.00883 0.90438 0.00187 0.00882 0.02497 0.00182 0.0105 0.02705
1 0.00321 0.01955 0.19399 0.93806 0.00246 0.01584 0.17464 0.76745 0.00235 0.02266 0.17508 0.84774 2 0.00303 0.0298 0.25141 0.75274 0.00234 0.02203 0.73543 0.75068 0.00172 0.02457 0.36335 0.86922 3 0.0057 0.00703 0.20808 0.10049 Mid tide 0.00294 0.00559 0.45924 0.11509 0.00172 0.00584 0.28234 0.08618 B 0.00216 0.14535 0.14592 0.14162 0.00115 0.10855 0.18268 0.08255 0.00598 0.12263 0.16665 0.07814 O 0.00309 0.02033 0.00139 0.02096 0.00175 0.01649
Environment Canterbury Technical Report 41 The Hurunui River hapua: geomorphology, sediments, and water quality
Low Low Tide Site Flood 1 Flood 2 Storm energy 1 energy 2 1 0.00308 0.0156 0.18919 0.79674 0.00193 0.01431 0.17781 0.74611 0.01281 0.01812 0.16183 0.73676 2 0.0021 0.02302 0.36173 0.64262 0.0026 0.01508 0.22414 0.80462 0.00176 0.01744 0.21301 0.75885 3 0.00188 0.11705 0.86707 0.08182 Low tide 0.00212 0.14287 0.18303 0.0849 0.00287 0.1702 0.29258 0.0913 B 0.00271 0.01333 0.15737 0.0758 0.00428 0.00679 0.15403 0.06001 0.0047 0.00705 0.14105 0.15649 O 0.00192 0.03651 0.00224 0.03625 0.00118 0.03502
42 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 5: Water temperature (°C) data taken at the same time as suspended sediment samples
Low energy Low Tide Site Flood 1 Flood 2 Storm 1 energy 2 1 10.95 11.55 6.23 7.72 12.55 10.98 11.55 6.25 7.73 12.51 11 11.54 6.25 7.73 12.47 2 10.83 11.92 6.16 7.73 11.48 10.92 12.02 6.16 7.73 11.36 10.84 12.19 6.16 7.73 11.24 3 10.68 12.13 6.08 8.6 11.2 High tide 10.62 12.13 6.08 8.59 11.33 10.73 12.11 6.1 8.6 11.42 B 10.18 11.88 6.03 8.74 11.06 10.17 11.76 6.01 8.74 11.12 10.64 11.7 6.01 8.74 11.22 O 9.64 11.35 12.32 9.62 11.43 12.47 9.68 11.51 12.66
1 11.47 12.32 6.68 7.97 11.47 12.31 6.68 7.97 11.46 12.29 6.69 7.97 2 11.66 13.09 6.64 7.97 11.62 13.14 6.64 7.97 11.65 13.29 6.65 7.97 3 11.14 11.8 6.45 9.46 Mid tide 11.1 11.67 6.48 9.4 11.17 11.62 6.49 9.31 B 10.25 11.66 6.25 9.06 10.18 11.66 6.26 9.1 10.16 11.59 6.28 9.12 O 10.64 12.69 10.54 12.69 10.6 12.72
Environment Canterbury Technical Report 43 The Hurunui River hapua: geomorphology, sediments, and water quality
Low energy Low Tide Site Flood 1 Flood 2 Storm 1 energy 2
1 11.25 12.18 6.89 7.99 11.24 12.18 6.89 7.98 11.23 12.18 6.89 7.98 2 11.45 12.25 6.89 8.05 11.4 12.2 6.89 8.05 11.39 12.2 6.89 8.04 3 11.54 11.14 6.83 9.51 Low tide 11.43 11.1 6.83 9.54 11.46 11.06 6.83 9.55 B 10.48 11.31 6.67 9.51 10.5 11.27 6.68 9.51 10.41 11.25 6.72 9.54 O 10.99 12.18 11.1 12.16 11.18 12.12
44 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 6: Conductivity (uS/cm) data taken at the same time as the suspended sediment samples
Low Low Tide Site Flood 1 Flood 2 Storm energy 1 energy 2 1 98.2 95 73.3 90.2 94.6 98.2 94.4 73.3 90.7 94.5 98.4 95.1 73.3 90.3 94.6 2 98.4 94.9 72.8 92.3 93 98.2 95.1 73.1 92.4 93.2 98.3 94.6 73.3 92.6 92.7 3 101.8 358.5 72.7 14650 4817 High tide 101.2 355.8 73 14190 4816 100.5 356.2 72.6 14620 4822 B 117.7 970 73.9 18230 9752 117.8 970.3 72.6 18330 9747 115.2 969.4 72.7 18490 9755 O 98.9 96.5 12410 98.9 96.4 12390 100.2 96.4 12330
1 97.9 94.5 73.7 90.6 98.3 94.8 73.3 90.5 98.2 94.8 73.4 90.3 2 98.7 96 73.4 91.9 98.5 95.7 73.5 91.8 98.5 96.1 73.4 91.4 3 100.1 525.9 73.1 17650 Mid tide 100.7 526.2 73 17850 100.1 525.4 73.2 17620 B 108.9 740.8 73.9 17180 108.4 741.3 73.5 17040 107.8 742.1 73.5 17010 O 99.1 103.6 99.3 104.1 99.4 104.8
Environment Canterbury Technical Report 45 The Hurunui River hapua: geomorphology, sediments, and water quality
Low Low Tide Site Flood 1 Flood 2 Storm energy 1 energy 2
1 98.3 94.5 73.5 91 98.4 94.6 73.9 91.6 98.4 94.5 73.6 91.2 2 98.8 95.9 74.1 92 98.5 96.3 74.3 92.1 98.5 96.1 74.2 92.2 3 102.7 603.2 73.9 19010 Low tide 104.5 603.6 73.7 19640 104.2 603.8 73.9 19730 B 101.8 858.3 74.1 17820 102.1 858.3 73.8 17970 102 857.6 74 17970 O 98.7 107 99 106.9 99.4 107
46 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 7: Dissolved oxygen (mg/L) data taken at the same time as the suspended sediment samples
Low Low Tide Site Flood 1 Flood 2 Storm energy 1 energy 2 1 14.6 9.03 20.53 15.17 10.05 14.1 8.62 18.09 13.37 10.04 11.61 8.35 16.98 12.92 10.05 2 11.24 12.65 20.57 14.22 9.6 16.85 12.3 19.24 13.27 9.69 14.54 12.08 18.85 12.81 9.79 3 17.99 11.29 25.01 13.38 8.97 High tide 17.16 10.78 20.31 11.27 8.56 15.54 10.59 18.46 14.73 8.41 B 18.55 10.08 17.41 11.84 10.16 11.37 9.67 16.81 11.45 8.91 18.72 9.39 16.8 11.42 8.55 O 12.44 10.03 9.37 11.49 9.69 9.48 18.91 9.65 9.5
1 11.47 8.17 18.64 13.03 11.47 8.06 17.73 12.56 11.46 8.09 17.46 12.38 2 12.94 10.09 18.36 14.86 12.66 10.05 17.6 13.35 12.55 12.08 17.07 12.82 3 11 11.04 18.64 12.35 Mid tide 10.89 10.37 17.46 11.42 10.19 10.2 16.85 13.7 B 10.34 10.16 19.62 12.05 10.59 9.84 16.31 10.76 10.64 9.69 14.98 10.5 O 30.83 12.63 11.18 11.04 10.89 10.59
Environment Canterbury Technical Report 47 The Hurunui River hapua: geomorphology, sediments, and water quality
Low Low Tide Site Flood 1 Flood 2 Storm energy 1 energy 2
1 15.1 10.51 16.08 13.66 15.07 10.49 15.68 13.05 14.46 10.51 15.69 12.91 2 11.46 9.77 16.6 14.76 11.39 9.16 16.13 13.1 11.36 9.11 15.84 12.87 3 18.33 9.43 17.03 12.16 Low tide 10.57 9.1 16.44 10.86 10.93 9.18 16.03 10.47 B 10.81 9.02 17.54 12 9.15 9.06 17.67 11.01 9.38 9.11 17.31 10.87 O 12.45 10.64 10.96 10.24 10.69 10.01
48 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 8: pH data taken at the same time as the suspended sediment samples
Low Low Tide Site Flood 1 Flood 2 Storm energy 1 energy 2 1 8.17 7.77 7.64 7.91 7.91 8.2 7.76 7.68 7.71 7.86 8.09 7.75 7.64 7.67 7.84 2 8.05 7.83 7.68 7.87 7.79 8.53 7.79 7.65 7.74 7.73 7.84 7.77 7.64 7.7 7.71 3 7.98 7.93 7.9 7.85 8.26 High tide 8.17 7.91 7.79 7.78 8.23 8.01 7.91 7.71 8.15 8.21 B 7.96 8.27 8.22 7.82 8.35 7.64 8.24 7.86 7.83 8.35 7.92 8.23 7.86 7.84 8.35 O 8.08 7.83 8.26 7.88 7.79 8.26 7.69 7.79 8.25
1 8.22 7.82 7.55 7.69 8.23 7.81 7.59 7.66 8.33 7.8 7.59 7.65 2 8.1 7.9 7.57 8.11 7.91 7.84 7.59 7.84 8.12 7.83 7.6 7.75 3 7.99 8.07 7.66 7.83 Mid tide 7.73 8.07 7.86 7.79 7.72 8.07 7.68 8.05 B 7.74 7.94 7.62 7.83 7.74 7.95 7.66 7.8 7.7 7.96 7.66 7.8 O 8.84 7.95 8.1 7.91 8.09 7.91
Environment Canterbury Technical Report 49 The Hurunui River hapua: geomorphology, sediments, and water quality
Low Low Tide Site Flood 1 Flood 2 Storm energy 1 energy 2
1 8.11 7.81 7.59 7.74 8.11 7.8 7.6 7.67 8.09 7.8 7.61 7.66 2 8.09 7.87 7.58 7.92 8.2 7.81 7.6 7.7 8.19 7.81 7.6 7.68 3 8.7 8.17 7.77 7.98 Low tide 8.26 8.17 7.68 7.87 7.96 8.17 7.67 7.86 B 8.11 8.14 7.68 7.85 8.09 8.15 7.81 7.82 8.05 8.16 7.96 7.82 O 8.16 7.99 8.19 7.99 8.21 8
50 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 9: Nutrient concentrations (mg/L) data in low energy event 1 (13 July 2012)
Tide Site TN NH3N NNN TP DRP 1 0.39 0.025 0.4 <0.008 0.001 2 0.43 0.014 0.33 <0.008 0.004 High tide 3 0.32 0.016 0.3 <0.008 0.004 B 0.45 0.02 0.29 <0.008 0.003 O 0.44 0.02 0.28 <0.008 0.003
1 0.4 0.02 0.39 <0.008 0.002 2 0.46 0.029 0.37 <0.008 0.002 Mid tide 3 0.4 0.02 0.39 <0.008 0.002 B 0.44 0.036 0.38 <0.008 0.009 O 0.32 0.021 0.26 <0.008 0.003
1 0.41 0.019 0.4 <0.008 0.002 2 0.39 0.014 0.4 <0.008 0.001 Low tide 3 0.4 0.016 0.37 <0.008 <0.001 B 0.41 0.017 0.39 0.008 <0.001 O 0.42 0.018 0.39 <0.008 <0.001
Environment Canterbury Technical Report 51 The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 10: Nutrient concentrations (mg/L) data in low energy event 2 (24 September 2012)
Tide Site TN NH3N NNN TP DRP 1 0.41 0.011 0.36 0.012 0.002 2 0.4 0.018 0.39 0.009 0.002 High tide 3 0.44 0.016 0.36 0.058 0.019 B 0.36 0.008 0.33 0.004 0.001 O 0.52 0.014 0.35 0.012 0.003
1 0.49 0.009 0.35 0.004 0.002 2 0.4 0.009 0.37 0.004 0.001 Mid tide 3 0.41 0.01 0.41 0.063 0.003 B 0.44 0.012 0.37 0.012 0.002 O 0.45 0.013 0.35 0.02 0.002
1 0.38 0.011 0.39 0.004 0.002 2 0.42 0.012 0.37 0.01 0.003 Low tide 3 0.54 0.008 0.47 0.08 0.003 B 0.52 0.008 0.43 0.004 0.002 O 0.42 0.015 0.35 0.023 0.002
52 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 11: Nutrient concentrations (mg/L) data in the flood (2 August 2012) and storm (7 November 2012) events
Tide Site TN NH3N NNN TP DRP 1 0.87 0.027 0.43 0.91 0.02 2 0.9 0.025 0.38 0.92 0.035 Flood 3 0.88 0.038 0.34 0.73 0.027 B 0.35 0.042 0.18 0.12 0.021 O 0.96 0.044 0.36 1 0.036
1 0.19 0.006 0.2 0.014 0.003 2 0.17 0.008 0.2 0.018 0.007 Storm 3 0.23 0.008 0.15 0.015 0.003 B 0.21 0.009 0.1 0.02 0.004 O 0.19 0.013 0.11 0.018 0.004
Environment Canterbury Technical Report 53 The Hurunui River hapua: geomorphology, sediments, and water quality
Appendix 12: Graphs showing spatial differences in parameters in different energy conditions and varying positions of the hapua outlet
low energy north outlet 1000 low energy north 8.3 low energy south outlet 900 outlet 8.2 800 700 low energy 8.1 600 south outlet 8 500 7.9 400
Mean pH 7.8
300 7.7 200 7.6 Mean conductivity (uS/cm) Mean conductivity 100 7.5 0 1 2 3 B O 1 2 3 B O Site Site
flood north outlet
8 flood south outlet 8.4 storm south outlet 8.3 7.9 8.2
7.8 8.1 8 7.7 7.9
Mean pH 7.8
7.6 Mean pH 7.7 7.6 7.5 7.5 7.4 7.4 1 2 3 B O 1 2 3 B O Site Site
54 Environment Canterbury Technical Report The Hurunui River hapua: geomorphology, sediments, and water quality
flood north outlet flood south outlet flood north outlet
10 73.8 C) 9 ° 73.6 8 73.4 7 73.2 6 73 5 72.8 4 3 72.6
Mean temperature ( Mean temperature 2 72.4 1 (uS/cm) Mean conductivity 72.2 0 72 1 2 3 B O 1 2 3 B O Site Site
flood south outlet 25 flood north outlet 20000 18000 flood south outlet 20 16000 14000 12000 15 10000 8000 10 6000 4000 5 Mean conductivity (uS/cm) Mean conductivity 2000 Mean dissolved oxygen (mg/L) oxygen dissolved Mean 0 0 1 2 3 B O 1 2 3 B O Site Site
0.04 0.1 low energy north outlet low energy north outlet
low energy south outlet 0.032 low energy south outlet 0.08 storm south outlet storm south outlet
0.06 0.024
0.04 (mg/L) 0.016
0.02 0.008 Total phosphorus (mg/L) Total Dissolved reactive phosphorus phosphorus reactive Dissolved 0 0 1 2 3 B O 1 2 3 B O Site Site
Environment Canterbury Technical Report 55 The Hurunui River hapua: geomorphology, sediments, and water quality
0.05 1 flood south outlet flood south outlet
0.04 0.8
0.6 0.03
0.4 0.02
0.2
Total nitrogen (mg/L) nitrogen Total 0.01 Ammonia nitrogen (mg/L) nitrogen Ammonia
0 0 1 2 3 B O 1 2 3 B O Site Site 0.5 1.2 flood south outlet flood south outlet
0.4 1
0.8 0.3
0.6 0.2 0.4 0.1 0.2 Total phosphorus (mg/L) Total
Nitrate + nitrite nitrogen (mg/L) nitrogen nitrite + Nitrate 0 1 2 3 B O 0 1 2 3 B O Site Site 0.04 flood south outlet 1.2 flood south outlet High tide 1 0.032 Mid tide 0.8 Low tide
0.024 0.6 (g/L)
(mg/L) 0.016 0.4
0.008 0.2 Mean suspended sediment sediment Mean suspended Dissolved reactive phsophorus phsophorus reactive Dissolved 0 0 1 2 3 B O 1 2 3 B O Site Site
56 Environment Canterbury Technical Report