Engineering Geology 125 (2012) 45–55

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Engineering Geology

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Relationship between observed liquefaction at Kaiapoi following the 2010 Darfieldearthquake and former channels of the Waimakariri River

Liam M. Wotherspoon a,⁎, Michael J. Pender b, Rolando P. Orense c

a EQC Research Fellow in Earthquake Engineering, Dept. of Civil and Environmental Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealandb Dept. of Civil and Environmental Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealandc Dept. of Civil and Environmental Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand

⁎ Corresponding author. Tel.: +64 9 3737599x84784E-mail addresses: l.wotherspoon@auckland.ac.nz (L.

m.pender@auckland.ac.nz (M.J. Pender), r.orense@auck

0013-7952/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.enggeo.2011.11.001

a b s t r a c t

a r t i c l e i n f o

Article history:Received 14 December 2010Received in revised form 6 November 2011Accepted 9 November 2011Available online 13 November 2011

Keywords:LiquefactionLateral spreadingDarfield earthquakeRiver channelsRiver modification

The Darfield earthquake caused widespread damage in the Canterbury region of New Zealand, with themajorityof damage resulting from liquefaction and lateral spreading. One of the worst hit locations was the small town ofKaiapoi north of Christchurch, an area that has experienced liquefaction during past events and has been identi-fied as highly susceptible to liquefaction. The low lying town sits on the banks of the Kaiapoi River, once a branchof the Waimakariri, a large braided river transporting gravelly sediment. The Waimakariri has been extensivelymodified both by natural and human processes, consequentlymany areas in and around the townwere once for-mer river channels.Using historical accounts and maps of the region, areas of land reclamation and old channels that had been cutoff from the river since the beginning of European settlement in the 1850s were identified. These areas corre-lated well with many of the areas having significant liquefaction damage following the Darfield event. Substan-tial lateral spreads and sand boils developed in areas of reclamation along the current river path, causingsignificant damage to stopbanks and structures along the river, with fissures up to 2 m deep and 1 m wide.Much of the residential housing was damaged by lateral spreading, with cumulative displacement offsets upto 3 m parallel to old channel beds that had aggraded over time due to river shifts. In former channel areasthat were free of lateral spreading, large volumes of ejecta were present over wide areas, with depths of upto 400 mm in places. Houses in these regions were damaged as a result of settlement and tilting. In all theseareas underground services and roadways were severely impacted as a result of ground deformation. The sever-ity of this damage indicates the importance of knowing the location of old channels when defining liquefactionprone regions.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Kaiapoi is a small town approximately 17 km north of centralChristchurch in the South Island of New Zealand. It is situated at thenorth eastern end of the Canterbury Plains, a region approximately50 km wide and 160 km long formed by overlapping alluvial fansfrom rivers flowing east from the Southern Alps. In this area inter-bedded marine and terrestrial sediments approximately 100 m deepoverlie 300–400 m of late Pleistocene sands and gravels (Brown andWeeber, 1992). Surficial deposits in the coastal regions east of Kaiapoiconsist of Christchurch formation dune and coastal swamp deposits,with Springston formation silty sand and gravels in the region behindthe coast (Brown andWeeber, 1992). The groundwater table is shallowand varies between 1 and 2 m below the ground surface.

Present day Kaiapoi, shown in Fig. 1 sits on the banks of the KaiapoiRiver, a tributary of theWaimakariri River, a large, steep, braided, gravel

; fax: +64 9 3737462.M. Wotherspoon),land.ac.nz (R.P. Orense).

rights reserved.

bed river that enters the ocean 3 km east of the town. The Waimakaririflows fromwest to the east curving northwards as it passes beneath thetown, but has experienced substantial changes, both natural and man-made, since the times of first European settlement. Historically,floodingof the Waimakariri has caused significant damage to Kaiapoi and thesurrounding area,withfloods regularly entering the city of Christchurchalong old river channels (Logan, 2008). Over time river diversions and anetwork of stopbanks have been constructed to constrain the riveralong its current route and provide flood protection.

At 4.35 am on 4th September 2010 (local time and date), a magni-tude 7.1 earthquake occurred with an epicentre 42 km south-west ofKaiapoi and a focal depth of 10 km. The Kaiapoi North School strongmotion station (KPOC), approximately 900 m north of the KaiapoiRiver, recorded a peak ground acceleration of 0.32 g and a bracketedduration of approximately 20 s (GNS, 2010). The town suffered fromwidespread and severe liquefaction during this event, with largevolumes of sand ejected and extensive lateral spreading. In this re-gion the worst damage was to residential structures, undergroundservices and stopbanks. Prior to this event, the only other recordedcase of liquefaction in Kaiapoi occurred during the 1901 Cheviot

Fig. 1. Map of Kaiapoi with town extent in 2010 and town plan extent in 1858 superimposed.Google Inc., 2010.

46 L.M. Wotherspoon et al. / Engineering Geology 125 (2012) 45–55

earthquake (Berrill et al., 1994). Following the 2010 event, the M6.3aftershock on 22 February 2011 centred 22 km south of Kaiapoiresulted in additional less severe liquefaction damage over a smallerpart of the previously impacted region. In this event the KPOC strongmotion station recorded a PGA of 0.21 g and a bracketed duration ofless than 10 s (GNS, 2011).

Using observations from the 2010 and 2011 events, and records ofthe 1901 event, the relationship between liquefaction at Kaiapoi andthe old channels of the Waimakariri River is presented. An overviewof liquefaction damage from the two events is first summarised, fol-lowed by details of the changing nature of the Waimakariri Riversince the first European settlement. A detailed comparison of areasof liquefaction damage and the old river channels is presented andparallels made with observations in previous events worldwide.

2. Historic liquefaction in Kaiapoi

Well documented evidence of liquefaction in Kaiapoi during the1901 Cheviot earthquake can be found in newspaper reports followingthe event. These detail ejection of sand, lateral spreading and groundsettlement features in an area at the eastern edge of Kaiapoi on both

sides of the Kaiapoi River (then the North branch of the WaimakaririRiver). Reports described fissures opening up in a property between 1and 3 in. (2.5–7.5 cm) wide, and several chains (~40 m) in length inan SW to NE orientation. Water and grey sand deposits were ejectedfrom these fissures, which were probed to a depth of 6 ft (~180 cm).In some areas the water ejected during the liquefaction caused floodingto depths of up to 6 in. (15 cm). Through discussionwith local residents,Berrill et al. (1994) showed that these areas were two properties in theblock bounded by Cass, Sewell, Beswick and Jollie Streets, and the blockbetween Sewell, Jollie and Charles Streets (shaded area at position 1 inFigure 1). Fissures also opened on the other side of the river up to 2 ft(60 cm)wide, while smaller crackswere filled with ejecta. These cracksemerged from out of the river and continued up the river bed into thefarms along the riverbanks. Signs of liquefaction were present in otherareas, but their present day locations could not be defined.

Site investigations were carried out in some of these areas between1986 and 1989 to evaluate their liquefaction potential. Piezoconeprobing and rotary boringwere carried out at four sites, with propertiesencountered indicating a significant liquefaction risk in Kaiapoi, espe-cially of those areas closer to the river (Berrill et al., 1994). Cone resis-tances of approximately 2–3 MPa were encountered at these tests

47L.M. Wotherspoon et al. / Engineering Geology 125 (2012) 45–55

sites in layers from2 to 6 mdeep,whichwere underlain by coarse sandsand fine gravels. The location of these test sites is represented in Fig. 2by the four cross symbols close to the Kaiapoi River. A range of epicen-tres and magnitudes had been reported for the Cheviot event, and byusing site investigation data and liquefaction potential models, Berrillet al. showed that the most likely characteristics were a M6 — 7.5with an epicentre 77 km NE of Kaiapoi.

In 2001 a study of the liquefaction potential of the easternWaimakariri District was carried out that included the area in andaround Kaiapoi (Christensen, 2001). Existing soil information wassupplemented with data from 26 boreholes to define the distributionof soil profile characteristics in the region. The location of these testsites near Kaiapoi is represented in Fig. 2 by star symbols. Each wasdrilled to a depth of 15 m and SPTs performed at one metre intervals,with 29 particle size distribution tests undertaken on representativesamples of potentially liquefiable soil. Liquefaction assessment usedtwo earthquake scenarios, a M7.2 Southern Alps foothills earthquakewith an epicentral distance of 50 km, and a M8 Alpine Fault earth-quake with an epicentral distance of 150 km. Using this data, a mapof liquefaction susceptibility was developed for the region, with the

Fig. 2. Map of Kaiapoi indicating high (H), medium (M) and low (L) liquefaction susceptibievent.Google Inc., 2010.

section of this map from the Kaiapoi area shown in Fig. 2. Three re-gions of high (H), medium (M) and low (L) liquefaction susceptibilityare separated by dashed lines, with areas to the west of town andsouth of the Waimakariri River outside the study area.

3. Liquefaction in Canterbury region following the 2010 Darfieldearthquake

The Darfield event was the most damaging earthquake to occur inNew Zealand since the 1931 Hawke's Bay earthquake. This was a sig-nificant event in terms of liquefaction and lateral spreading, resultingin damage to the built environment in Christchurch and surroundingtowns. The high water table, following the very wet winter season(NIWA, 2010), may have contributed to the widespread extent ofthe liquefaction and lateral spreading.

In Christchurch the worst affected areas were in the suburbs ofDallington, Avonside, Bexley and Halswell located on loose alluvialsand deposits. Dallington and Avonside are located adjacent to themeandering loops of the Avon River, Bexley is situated in old wet-lands at the mouth of the Avon where it enters the Avon-Heathcote

lity zones defined by Christensen (2001) and areas that liquefied during 2010 Darfield

48 L.M. Wotherspoon et al. / Engineering Geology 125 (2012) 45–55

estuary, and Halswell is on the banks of the Halswell River. North ofChristchurch, the towns of Spencerville, Brooklands and Kaiapoi suf-fered extensive damage as a result of liquefaction. Spencerville andBrooklands are located between the coast and the Styx River on youngdunes and loamy sands (Hills, 2002). The characteristics at Kaiapoi,the focus of this paper, have been explained in the Introduction.

Very significant was the extent of lateral spreading and post-liquefaction differential settlement damage to residential structures.Many structures were left uninhabitable as a result of these large move-ments. Damage to the sewer and water supply network was also signif-icant, with lateral movement and floating of the pipes due toliquefaction. While not as extensive, there was also damage to roads,bridges, railroad embankments, and stopbanks. Cracking in roadwaysfrom ground movement and slumping of sections of roads adjacent towaterways was evident, while movement of railroad embankmentscaused buckling of tracks. Road bridge approaches were affected due tolateral spreading, while lower strength footbridges suffered structuraldamage due to the compressive forces generated by the lateral spreadingmovements towards the river channel. Further information about thedamage induced by the earthquake can be found in Allen et al. (2010).

Focusing on Kaiapoi, using data from aerial photographs (NZAM,2010) and ground reconnaissance, the areas that experienced liquefac-tion are shown shaded in Fig. 2. Comparison between this and liquefac-tion susceptibility indicates that much of the area that experiencedliquefaction had been mapped as highly susceptible zones. The onlyarea that seems to be slightlymismatched is the area of extensive lique-faction south east of town that cuts through medium and low suscepti-bility zones. As will be explained in the following sections, this damagecan be correlated with the position of former river channels. The bore-hole in Fig. 2, shown by the star symbol south east of town close tothe banks of the Waimakariri, was drilled outside the former channel,missing the highly liquefiable materials that filled this channel.

4. Waimakariri River since European settlement

4.1. Early history

In the 1860s there were two branches of the Waimakariri River,the north and south branches. These two branches split and rejoinedforming Kaiapoi Island, and Fig. 3 shows the characteristics of theriver and surrounding area (Ward and Reeves, 1865). Kaiapoi Islandwas described as having swampy areas on the northern and southernsides, with a north eastern region that was mainly sand. Europeansettlement at Kaiapoi began in 1853, and it was declared a town in1857 (Wood, 1993).

On the northern side of the river much of the early town was builton sandy deposits, with high sand hills extending as far back as BeachRd (Hawkins, 1957). The southern part of the town was built in the

Fig. 3. Kaiapoi and vicinity in 1865.Adapted from Ward and Reeves, 1865.

swampy northern section of Kaiapoi Island, and this side did not de-velop as fast as the northern side (Hawkins, 1957).

The layout of the town as it existed in 1858 is shown in Fig. 4, withthe extent of the town shown by the dashed line in Fig. 1. The north ofthe town was bordered by Smith, Cass and Hall Streets, with a streetlayout very similar to the present, with the only changes occurring atthe eastern edge of town. The majority of streets on this side of theriver were nothing more than peg lines through the sand at the endof the 1850s (Hawkins, 1957). On the southern side of the river, thetown was bordered on the east by North Road, with the main partof town bordered to the south by Ohaka Rd. At the western edge oftown, the circled area indicated the position of Adams St, which wasconstructed after 1858 and then eroded away by the North branchin 1864–65 (Wood, 1993). The high water mark of the WaimakaririRiver running through the town was along the edge of Charles Stand Raven St on the north and south bank, respectively.

The confluence of the north and south branches of the river was inthe sandy region immediately adjacent to the eastern edge of thetown. Throughout the 1860s, the main flow of the river was alongthe north branch and through the middle of Kaiapoi. As a result, thetown suffered 16 disastrous floods in the first 3 years of its existenceand both Charles and Raven St were subject to scouring (Logan,2008). At this time there were only piecemeal prevention works inplace to protect the town and the island, and many had alreadyproved unsuccessful. Each section had been constructed followingan instance of flooding and the network was neither sufficientlyhigh nor long. On February 4th 1868 the most devastating flood on re-cord hit the town, with many parts 5–6 ft (1.5–2 m) under water. Analmost complete rebuild of the town was required after this event(Wood, 1993).

At the mouth of the river, sand bars extended from both the northand the south and the Waimakariri emptied through a central mouthshown in Fig. 3.

4.2. The first river diversion

In 1867, a canal shown in Fig. 5 at positions 1 and 2 was cut acrossthe island along Maber's Rd from the North to the South branch toserve a flourmill, and this carried a large amount of water from theNorth channel. In an effort to combat the flooding of the town and is-land, local famers carved out a new channel in 1868 from the northbranch to Maber's Rd canal at position 3. This channel started tochoke off the north branch due to the accumulation of shingle, andshifted the flow of the river to this new channel and the south branch(Logan, 2008). Kaiapoi Island was split in half below the point wherethe new channel (3 and 2) and the south branch connected, formingCoutts Island. Downstream from this confluence, the entire flow of theWaimakariri was carried by a single channel.

Just to the east of Kaiapoi, the shift of the majority of the flow tothe South branch resulted in an alteration to the path of the river.Prior to the change, the southern channel turned to the east andjoined up with the northern channel further from town, which isshown in Fig. 3. After the cut, the flow of the river shifted and thesouthern branch joined up with northern branch much closer toKaiapoi.

4.3. Southern branch shift

In 1879–1880, floods eroded the banks and changed the course ofthe south branch along Stewart's Gully at position 4 in Fig. 5, shiftingthemain flow of the river away from the town. The old channel parallelto Stewart's Gully was cut off from the flow of the river, reducing downto a small stream. The network of channels north of the old channelgradually reduced to a single channel through Kaiapoi that connectedup to the Waimakariri at the northern end of Stewart's Gully.

Fig. 4. Plan of the town of Kaiapoi in 1858.Adapted from Wood, 1993.

49L.M. Wotherspoon et al. / Engineering Geology 125 (2012) 45–55

In 1923 there was another substantial flood in Kaiapoi when watersfrom the Camand Eyre Rivers (shown in Figure 3)flowed into theNorthbranch. To better coordinate the flood control efforts, the WaimakaririRiver Trust was established in 1923 (Wood, 1993; Logan, 2008). Bythis time the old north branch was blocked off by stopbanks, and itonly served to drain surrounding swampland. There was also very littleflow in the South branch due to silting.Withmost of the flownowgoingthrough the new channel, the bed level was still being built up withshingle and material eroded from the river banks. This meant that thesystem at that time would be unable to deal with future large floodingevents.

4.4. After 1925 — Hay's No.2 scheme

In response to the 1920s floods, the Waimakariri River Trustimplemented a major river improvement scheme known as theHays No. 2 Scheme, which began construction in 1930. The schemeentailed excavation of a new channel and an overall improvementof the stopbank system along the Waimakariri River. A cut was

Fig. 5. Overview of the characteristics

made at Wrights farm, position 5 in Fig. 5, completing the straighten-ing of the river to its present course (through 3, 5 and 4). Cross bankshave since blocked the flow from the old south branch, which hasbeen reclaimed for other uses. In 1929 the trust diverted the EyreRiver into the Waimakariri, significantly reducing the flood risk inKaiapoi (Logan, 2008). As a result of some excavation and the 1940flood, the river broke through into the ocean just south of Kairaki(Figure 6a), shifting the mouth of the river to its present position.

4.5. Further stopbank construction

Improvements made during the Hay's No.2 scheme were unable tocontain themajor floods in 1940, 1950, and 1957. This resulted in a fur-ther river improvement scheme in 1960, with the stopbanks designedto provide protection against the 100-year flood (Logan, 2008). In1959 the old north branch of the Waimakariri River running throughthe centre of Kaiapoi was renamed the Kaiapoi River (Wood, 1993).

The old positions of the branches of the Waimakariri River aresuperimposed onto the present day map of the region in Fig. 6a, withpresent day Kaiapoi outlined by a dotted line. The old South branchlies beneath a large area on the eastern side of South Kaiapoi, comingfrom the south along the present-day railway line. South of thepresent-day Waimakariri River, the old channel covers a large part ofthe Coutts Island area on both sides of State Highway 1, extendingwest across farms and golf courses on the landside of the present daystopbanks. The old North branch also lies beneath a large area of farm-land, and as it reaches Kaiapoi there is a large region to the northwestthat is within the old river meander. The relation between the locationof the old river channel and the observed liquefaction and lateralspreading that occurred during the Darfield earthquake is discussed insubsequent sections.

5. Comparison of liquefaction damage and location of old riverchannels

In this section we focus on specific areas and the correlation be-tween damage as a result of the Darfield event and the position of oldriver channels near Kaiapoi. The region in and around Kaiapoi is

of the Waimakariri prior to 1935.

50 L.M. Wotherspoon et al. / Engineering Geology 125 (2012) 45–55

reasonably flat, with the largest slopes in the area resulting from stop-bank construction and land reclamation along the Kaiapoi and Waima-kariri Rivers. Looking at the areas near the town, the most extensiveliquefaction damage occurred on the north side and at the easternedge. The areas along the river will be explained in more detail, aswell as the eastern edge of town and the path of the old south branch.These areas are listed below and mapped in Fig. 6a and b.

• Central Kaiapoi (Figure 7)• Western Kaiapoi (Figure 11)• Eastern edge of North Kaiapoi (Figure 13)• Eastern Kaiapoi (Figure 16)• Coutts Island (Figure 18)

Outside these areas of focus, most of the northern section of thetown east of Williams St and south of Beach Rd experienced somelevel of liquefaction following the Darfield event. This seems to be be-cause this area consisted of loose sand hills prior to the constructionof the town. These sand hills were levelled off as the town was con-structed, and the soil in this area is still sandy. The severity of liquefac-tion reduced moving away from the river, and this is probably becausethe elevation of the land increased and thewater tablewas further fromthe ground surface. On the south side of town, the area was more mudand swamp, conditions not as conducive to liquefaction. The south eastpart of the town is described in more detail in the Eastern Kaiapoi sec-tion, as it had soil conditions similar to the north.

5.1. Central Kaiapoi

An aerial view of a section of the Kaiapoi River running through thecentre of the town following the earthquake is presented in Fig. 7, withthe river channel as it existed in 1858 represented by the dashed lines.As explained previously, the river banks at high water ran along theedge of Raven Quay and Charles St, with the riverbed narrowed to halfof what it was in the 1860s. In 1907, the town began to dredge and re-claim ten acres of the foreshore along Charles St and Raven St (Quay) tolessen the effect of flooding and improve the river sights (Wood, 1993).All the parks and stopbanks south of Charles St were built on reclaimedland, while on the south bank a stopbank was constructed along thelength of Raven Quay. Stopbanks along the river were approximately2.5 m above the water line, with slopes in this area approximately2H:1V and 3H:1V on the riverside and landside, respectively (Allen etal., 2010).

Fig. 6. Present day Kaiapoi a) with overlay of former channels of the WGoogle Inc., 2010.

Following the Darfield event, extensive liquefaction and lateralspreading were evident throughout the region shown in Fig. 7 alongboth sides of the river, with large ground fissures parallel to the riverin the area bounded by the 1858 riverbanks. In this area of reclaimedland most of the lateral spreading displacements developed within50 m of the river banks, with total permanent lateral displacements ofup to 3 m recorded (Robinson et al., 2011). Lateral spreading in the vi-cinity of the Kaiapoi Visitors Information Centre and the Coast guardbuilding at position 1 caused both structures to settle and tilt, requiringrepairs to the foundations.

At position 2, large ground cracks up to 100 cm wide and 200 cmdeep were observed on the land side of the embankments, as shownin Fig. 8. These large fissures closer to the river bankswere free of ejecta,while those closer to Charles St were smaller and filled with largeamounts of ejecta. In this grassed reserve area the ground level slopedback gradually to Charles St from the top of the stopbanks. Fig. 4shows that Charles St was close to the level of the river in the past, sothe water table was closer to the ground surface in the regions whereejectawas evident. As indicated by Fig. 9, amuch larger volumeof ejectawas evident at position 3, with ground settlement affecting tanks in thearea and similar large lateral spreadfissures. At this position the slope ofthe land side of the stopbanks was greater, and the reserve area behindthe embankments was much flatter than that at position 2. This meantthe water table was closer to the surface over this area, and could ex-plain why the larger volume of ejecta was present over a wider areaat the surface within the grassed reserve area.

The residential and commercial properties along Charles St and backto Cass St were damaged due to liquefaction induced settlement andground cracking, with settlements of up to 400 mm. Large volumes ofejecta were present in this area, with damage to water/wastewater net-works and roads. There was also lateral spreading damage to the stop-banks along the south side of the river from positions 4 to 3, andsettlement of houses directly behind the stopbanks along Raven Quay.The Mandeville footbridge at position 4 was constructed in 1874, andat that time it reached as far as Charles Street with a total length afterconstruction of 110 m (Logan, 2008). Until 1922, the area occupied byTrousselot Park (position 5 in Figure 7) was a swamp and used as a rub-bish dump, and when the area was reclaimed and the park constructedthe footbridge was shortened to its current length. Sand boils were ev-ident in Trousselot Park following the earthquake, with lateral spreadcracks developing parallel to the river surrounding the park. TheMandeville footbridge in Fig. 10 suffered a buckling failure of the deck

aimakariri post 1850s; b) focus regions of liquefaction damage.

Fig. 7. Aerial photograph of central Kaiapoi River indicating former river channel.NZ Aerial Mapping, 2010.

51L.M. Wotherspoon et al. / Engineering Geology 125 (2012) 45–55

due to compressive forces created by lateral spreading towards the chan-nel of the stopbanks at each end of the bridge, shifting the abutmentsinwards.

5.2. Western Kaiapoi

Fig. 11 shows an aerial view of Kaiapoi River and the Cam Riverwest of the town following the Darfield earthquake. The extent ofthe North branch of the Waimakariri during the 1860s is indicatedin the figure by the dashed black lines, while the centre of the Kaiapoiand Cam River channels in 1941 is shown by the dotted white lines(NZAM, 1941). In the 1960s the Cam River (following the 1 positions)was realigned to its present position during the construction of theCam road motorway access, with the land to the west of thisreclaimed and used to create Wylie Park at position 2 (Wood,1993). From the 1960s onwards, the Cam and Kaiapoi Rivers wereboth realigned to their present positions during the progressive con-struction of the motorway off/on ramp on State Highway 1 (SH1) in-side the 1858 river banks and the twin two lane bridges south of this.

Wylie Park at position 2 experienced widespread liquefaction,with large areas of sand boils developing across the area. At the west-ern end of the park, lateral spreading cracks parallel to the river de-veloped in the park and adjacent roadway. Murphy Park, on theother side of the river at position 3, was also within the meander ofthe river. Here again there was a large volume of ejecta, most of itconcentrated at the eastern end, and extending into the residentialarea behind the park. Sand boils were also evident at position 4 tothe right of the motorway offramp. This area was within the 1865river meander, and adjacent or within the path of the river in 1941.Moving from the onramp towards position 2, there was some evi-dence of liquefaction along the roadway within this meander. Al-though not shown in Fig. 11, Fig. 6a shows a large area of meandersouth of the river channel when it was the North branch of the

Fig. 8. Large lateral spread fissures in reclaimed land alongside Kaiapoi River.NZ Aerial Mapping, 2010.

Waimakariri. In this region there were pockets of liquefaction in res-idential areas and along the rail tracks, with the most severe area inthe bottom right corner of Fig. 11 and the bottom left corner of Fig. 7.

5.3. Eastern edge of north Kaiapoi

Fig. 12 shows the 1858 street plan for Kaiapoi, with Charles St andSewell St both continuing east to Hall St, while in-between Jollie Stand Hall St was Boys St. At this time these streets had only been sur-veyed and little if any permanent works had been undertaken. Fig. 13shows aerial photographs of the area in Fig. 12 following the Darfieldevent, with Charles and Sewell St ending east of Jollie St, and Boys Stnot evident.

When themainflowof theWaimakariri shifted back to the southernbranch following the diversions in 1868, the course of the river in thisarea changed and was directed perpendicular to the northern banksnear the eastern end of town following the arrow in Fig. 12. Thisresulted in progressive erosion of the area east of Jollie St, and in Octo-ber 1878 a commission was set up to try and solve this problem. Ac-counts from the time indicated that the river had encroached by 10chains (200 m) in the soft sandy soil in the area (Wood, 1993). One so-lution was the construction of an embankment along Jollie St, Cass Stand Commercial Rd (Now Askeaton Dr), following points 1 to 4 inFigs. 12 and 13 (Wood, 1993). However, this solution was never putinto place as the shift of themain channel of the river through Stewart'sGully in 1880 reduced the flow at the eastern edge of the town.

To provide a conservative estimate of the erosion, the river banks ataverage water level from 1858 (instead of the high water line along theedge of Charles St) are used as the origin of the 200 moffset to show theextent of erosion at 1878. This erosion would have removed much ofthe planned positions of Charles, Sewell and Boys St shown in Fig. 12.It is also clear from Fig. 13 that the present day river banks are much

Fig. 9. Lateral spread fissures and large volumes of sand ejecta in reclaimed land besideKaiapoi River.NZ Aerial Mapping, 2010.

Fig. 10. Lateral spreading induced damage of the Mandeville footbridge.

52 L.M. Wotherspoon et al. / Engineering Geology 125 (2012) 45–55

closer to the 1858 position, indicating thatmuch of the eroded area waseither aggraded by river sediments or reclaimed since 1878.

All of the area shown in Fig. 13 was affected by liquefaction, withthe region north of the river bend one of the hardest hit due to lique-faction following the Darfield event. Cassia Pl, the cul-de-sac north ofthe river bend and shown in Fig. 14 experienced severe liquefactionresulting in extensive sand boils with ejecta up to 400 mm thick inplaces. Many of the houses in the areas settled as a result of this liq-uefaction, which was damaging in cases with large differential settle-ment. There was also extensive damage to buried services androadways from cracking and ground movement. Lateral spread fis-sures and ejecta were visible along the river banks up the presentday stopbanks in the bend in the river. The fissures that extendedthrough the BMX park adjacent to position 4 in Fig. 13 are shown inmore detail in Fig. 15. Large lateral spread cracks approximately par-allel to the river cut through this area, in conjunction with large vol-umes of ejecta and surface water. This cracking continued east alongthe river following the river banks.

5.4. Eastern Kaiapoi

An aerial view of the eastern edge of Kaiapoi south of the KaiapoiRiver following the Darfield earthquake is presented in Fig. 16, withthe boundary of the old southern channel of the Waimakariri Riverbetween the years 1865–1880 shown by the dashed black line(Cass, 1864; Ward and Reeves, 1865; Logan, 2008). What is

Fig. 11. Aerial photograph of western KaiapoNZ Aerial Mapping, 2010.

immediately obvious is that the regions of liquefaction demonstratea close correlation to the position of the old river channel. Large vol-umes of ejected sand and ground cracking are evident in the fieldseast of Kaiapoi, while heading south, the liquefaction damage followsa more confined path along the former river channel.

On the eastern side of Kaiapoi, the old channel passes underneaththe present day CourtenayDr area shown by position 1, the site of wide-spread damage to residential properties as a result of liquefaction andextensive lateral spreading. This was evident along the eastern side ofCourtenay Dr for a distance of approximately 700 m. Up to 500 mm ofejected sand covered much of the roads and properties in this area fol-lowing the event. Large lateral spread fissures between 0.5 and 1.5 mwide ran through residential areas parallel to the banks of the oldriver channel,withmanyof thesefissuresfilledwith ejecta. This spread-ing resulted in permanent displacements of the ground of between 1.3and 2.8 m towards Courtenay Stream, the present day small watercourse that follows the approximate path of the old river channel. Thecharacteristics of the lateral spreading in this area were different tothose observed elsewhere in Kaiapoi, with themajority of large fissuresdeveloping 120–200 m from the banks of Courtenay Stream in a block-like movement, instead of the larger cracks close to the free face(Robinson et al., 2011). At the free face there were only a few smallcracks evident. The residential one and two storey structures in thisarea, especially on the eastern side of Courtenay Dr, were severely dam-aged due to these large movements. Structural damage was a result oftilting, differential settlement, loss of foundation support, and crackingof foundation slabs (Allen et al., 2010).

Between positions 2 and 3, liquefaction resulted in damage to thetrain tracks. Fig. 17 provides a more detailed aerial view of liquefac-tion and lateral spreading crossing the tracks at position 3 justsouth of Kaiapoi. Using the vehicle in the photo for scale gives agood indication of the considerable size of these cracks and the vol-ume of ejecta. One of the exploratory boreholes from theChristensen study (2001) was at position 4 in Fig. 16, clearly outsidethe path of the old river channel and in an area where no liquefactionwas evident.

5.5. Coutts Island

An aerial photograph of the earthquake damage in the Coutts Is-land Rd is presented in Fig. 18, with ejecta indicated by the grey mot-tled regions in the image. The river channel as it existed in 1865 ishighlighted by the dashed white line in this figure. Following the

i River indicating former river channel.

Fig. 12. Eastern edge of north Kaiapoi in 1858.Adapted from Wood, 1993.

53L.M. Wotherspoon et al. / Engineering Geology 125 (2012) 45–55

diversion of 1868, the new channel joined with the south branch inthis area following a line from the present river channel throughpoints 1 and 3. This is also shown by the intersection of channel 1with the south branch of the Waimakariri in Fig. 5. The fields in thisarea had large volumes of ejecta and lateral spread cracks. AlongCoutts Island Rd, the old river channel passes through an area withwidespread liquefaction near the present day stopbanks. Along thestopbanks, evidence of liquefaction is shown by the long dashedlines, and the area with no evidence of liquefaction is shown by thedotted line. These lines seem to agree well with the length of stop-bank inside and outside the old river channel. Sand boils were evidentalong the base of the stopbanks for the entire length of the dashedline on the land side, with some isolated boils at the base on theriver side.

Liquefaction and cracking on a secondary stopbank following StateHighway One, indicated by the long dashed line at position 2, wereobserved following the earthquake. Liquefaction also resulted indamage to the roadway of the northern onramp at position 4 andthe approaches to the motorway onramp overbridge just north ofthis position. Both these areas were again within the abandonedriver channel.

6. Comparison with observations from other earthquakes

The relation between former river channels and abandoned mean-ders and liquefaction occurrence has been observed in other earth-quakes. Liquefaction-induced damage observed in Dagupan Cityduring the 1990 Luzon, Philippines earthquake (M7.8) correlatedvery well with the locations of former river channels. Dagupan Cityis traversed by the Pantal River, whose meandering nature led to

Fig. 13. Aerial photograph of eastern edge of North Kaiapoi indicating former riverchannel characteristics.NZ Aerial Mapping, 2010.

natural lateral shifting in its course and resulted in channel abandon-ment in some areas (Orense et al., 1991). Moreover, it was reportedthat prior to the 1900's, most of Dagupan City's land areas were fish-ponds and marshlands. As the area developed and became a commer-cial centre, most of these swampy areas were reclaimed by filling onthe flooded areas where shrimp and milkfish farms were located.Thus, the natural land reclamation and the construction of artificialcut-offs account for the loose saturated sediments which make upmost of the city's soil formation (Orense, 2003).

During the 2007 Niigataken Chuetsu-oki Japan earthquake (M6.8),Kashiwazaki City's Garbage Incinerator Plant was damaged due to ex-tensive liquefaction. The road spread laterally towards the river,resulting in massive embankment failure. Based on the locations ofsand boils and ground cracks observed, it was inferred that this sitemay have been a former river channel of the Sabaishi River that wasburied when the road was constructed (Orense et al., 2008). Extensiveliquefaction was also observed at the Suidobashi Park in Nishimoto,Kashiwazaki City. A very long ground crack was observed traversingthrough the entire length of the park, with relative settlements rangingfrom a few centimetres to as much as 20 cm. Further investigationshowed that the region which settled was a former river channel thatwas backfilled and constructed on a sandbar formed by two branchesof the Sabaishi River. As part of the river improvement schemes imple-mented in the 1990s, the river was straightened by backfilling thenorthern branch (Orense et al., 2008). Apparently, the old river channeland portions of the sand bar liquefied during this earthquake, causinglateral spreading towards the existing river channel.

7. Discussion

The situation at Kaiapoi and the other case histories highlight thefact that areas in former river channels and abandoned meanders con-sist of loose deposits of silts and sands, and are therefore susceptibleto liquefaction during earthquakes. The damage resulting from liquefac-tion in these events emphasises the importance of a good understand-ing of the fluvial history of a region. Locations and ages of old riverchannels, lakes and wetlands are an important input in the develop-ment of well informed liquefaction susceptibility estimates.

In the case of Kaiapoi, river channels were very recently abandonedand reclaimed:

• 1850's—Natural shift of the flow from the south to the north channelof the Waimakariri River, eroding north banks to east of town

• 1867— Shifting of flow back to south channel due to channel cutting,reducing flow through Kaiapoi and reduction of river channel

• 1880 — Channel cutting, shifting river east and cutting off channelon eastern edge of Kaiapoi

Fig. 14. Extensive sand boil areas at end of Cassia Pl indicated by darker grey colour.NZ Aerial Mapping, 2010.

Fig. 15. Large lateral spread cracks and sand boils in BMX park adjacent to KaiapoiRiver.NZ Aerial Mapping, 2010.

Fig. 17. Lateral spreading cracks and damage to train tracks southeast of Kaiapoi.NZ Aerial Mapping, 2010.

54 L.M. Wotherspoon et al. / Engineering Geology 125 (2012) 45–55

• 1907 onwards — Reclamation of land along Kaiapoi River, bothCharles St and Raven Quay sides

• 1930 — Wrights cut, straightening and cutting off channel at CouttsIsland

• 1960's — Realignment of Kaiapoi and Cam River and reclamation ofland

Apart from the section of abandoned river channels to the south eastof Kaiapoi, the work of Christensen (2001) was able to provide a goodprediction of the areas affected by liquefaction in and around Kaiapoi.Observed regions of liquefaction were consistent with the estimates ofliquefaction susceptibility during strong seismic shaking using the cri-teria of Youd and Perkins (1978), with river channels expected tohave very high to high susceptibility to liquefaction. Radio carbon dat-ing in the Kaiapoi area outside these channels indicated that depositswere approximately 7000 years old at 9–15 metre depths (Brown,1973). Using the criteria of Youd and Perkins, the interbedded marineand terrestrial sediments of this age outside the old channels wereexpected to have moderate to high susceptibility.

Samples of the ejected material in the Courtenay Drive area ineastern Kaiapoi and adjacent to the Visitors Centre in central Kaiapoiwere collected and laser diffraction analysis used to determine thegrain-size distribution curves (Allen et al., 2010; Pender, 2010). Thematerial was uniformly graded sands, with non plastic fines contentof between 10 and 30% and coefficients of uniformity less than 3.5.Using the grain size criteria of Tsuchida (1971) for sands with low

Fig. 16. Aerial photograph of eastern edge of KaiNZ Aerial Mapping, 2010.

coefficient of uniformity, the grain size distribution of these sampleswas within the region indicating a high possibility of liquefaction.

8. Conclusions

The 2010 Darfield earthquake resulted in widespread liquefactiondamage throughout the Canterbury region, with some of the worstdamage occurring in the town of Kaiapoi. Previous studies have identi-fied the high susceptibility to liquefaction in most areas in and aroundKaiapoi, based mainly on borehole data. This paper has shown thatmuch of themost significant liquefaction damage in and aroundKaiapoiduring the Darfield event occurred in areas where river channels hadbeen reclaimed or in old channels that have had flow diverted away,characteristics observed in past earthquakes in Japan and the Philip-pines. Some areas have been impacted by liquefaction in the 1901Chev-iot, 2010 Darfield, and 2011 Christchurch events. The highly modifiednature of the Waimakariri and its proximity to Kaiapoi meant thatsome of these former channels overlapped areas that have since beendeveloped as the town has grown.

All former channel areas were subjected to some form of liquefac-tion induced damage following the Darfield event. Substantial lateralspreads developed in areas of reclamation along the current riverpath, with sand boils present in cracks in the lower lying areas. Thedamaged stopbanks and caused settlement and tilting of structures inthe area. Residential structureswere severely damaged due to large lat-eral spreads in areas adjacent and within old river channels. In areaswithout lateral spreading, significant volumes of ejecta were still

apoi indicating location of old river channel.

Fig. 18. Overlay of 1865 stream channel on present day Coutts Island.Google Inc., 2010.

55L.M. Wotherspoon et al. / Engineering Geology 125 (2012) 45–55

present over large areas, resulting in house damage due to settlement.In all former channel areas underground services, roads and railwayswere severely impacted as a result of cracking and ground movement.The damage patterns observed in these regions shows the importanceof knowledge of fluvial history and the high liquefaction susceptibilityof abandoned and reclaimed river channels.

Acknowledgments

The authors would like to acknowledge the Earthquake Commis-sion for funding Dr. Wotherspoon's position at the University of Auck-land, and the NZ-GEER reconnaissance team for their work gatheringinformation on liquefaction damage across the Canterbury area fol-lowing the Darfield earthquake.

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