water

Article Near-Bed Monitoring of Suspended during a Major Event Highlights Deficiencies in Existing Event-Loading Estimates

Alistair Grinham 1,*, Nathaniel Deering 1, Paul Fisher 1, Badin Gibbes 1, Remo Cossu 1, Michael Linde 2 and Simon Albert 1

1 School of Civil Engineering, The University of Queensland, Brisbane, QLD 4072, Australia; [email protected] (N.D.); p.l.fi[email protected] (P.F.); [email protected] (B.G.); [email protected] (R.C.); [email protected] (S.A.) 2 The Port of Brisbane Pty Ltd., Brisbane, QLD 4178, Australia; [email protected] * Correspondence: [email protected]; Tel.: +61-412057941

Received: 15 November 2017; Accepted: 17 January 2018; Published: 23 January 2018

Abstract: Rates of fluvial sediment are notoriously difficult to quantify, particularly during major flood events. Measurements are typically undertaken using event stations requiring large capital investment, and the high cost tends to reduce the spatial coverage of monitoring sites. This study aimed to characterise the near-bed suspended sediment dynamics during a major flood event using a low-cost approach. Monitoring nodes consisted of a total suspended sediment (TSS) logger, a single stage sampler, and a time-lapse camera for a total cost of less than US$420. Seven nodes were deployed across an elevation gradient on the of Laidley Creek, Queensland, Australia, and two of these nodes successfully characterised the near-bed suspended sediment dynamics across a major flood event. Near-bed TSS concentrations were closely related to stream flow, with the contribution of suspended bed material dominating the total during peak flows. Observed TSS concentrations were orders of magnitude higher than historical monitoring data for this site collected using the State government event station. This difference was attributed to the event station pump inlet screening the suspended bed material prior to sample collection. The ‘first flush’ phenomenon was detected and attributed to a local resuspension of muddy crusts immediately upstream of the study site. This low-cost approach will provide an important addition to the existing monitoring of fluvial sediment discharge during flood events.

Keywords: low-cost monitoring; instrumentation; suspended sediment dynamics; downstream and upstream effects

1. Introduction Quantifying fluvial suspended sediment discharge is critical to understanding the sustainability of agricultural practice, the of downstream systems, and carbon export from terrestrial systems [1,2]. Total suspended sediment loads carried during high flow events are a combination of washload and suspended bed material. Washload is usually dominated by silt and clay particles (<63 µm) and its vertical concentration profile is relatively constant. In contrast, suspended bed material is enriched in coarser sand particles and its vertical profiles are characterised by greatly increased concentrations near the sediment bed. To quantify downstream sediment loading rates, it is important to characterise both components of total suspended loads [3]. of channels during major flow events represents the dominant erosion process in the cleared catchments of South East Queensland, Australia [4,5]. As a result of wide-scale clearing of upper catchments for agricultural land use, increases in fluvial sediment loading are evident in

Water 2018, 10, 34; doi:10.3390/w10020034 www.mdpi.com/journal/water Water 2018, 10, 34 2 of 17 Water 2018, 10, x FOR PEER REVIEW 2 of 17 catchmentsreceiving water for agricultural bodies [6]. land This use, is exemplified increases in thefluvial receiving sediment coastal loading water are body evident of Moreton in receiving Bay, waterQueensland, bodies [6]. where This areal is exemplified coverage byin the terrestrial receiving muds coastal has increasedwater body by of more Moreton than Bay, 50% Queensland, in less than where45 years areal [7]. coverage Quantifying by terrestrial sediment dischargemuds has from increa thesesed catchments by more than is challenging 50% in less due than to the45 irregularyears [7]. Quantifyingnature of rainfall sediment patterns discharge and resultant from these flashy, catchments high flow is events challenging as well due as theto largethe irregular spatial coveragenature of 2 rainfallrequired patterns to effectively and resultant monitor flashy, the 21,000 high kmflow Moretonevents as Bay well catchment. as the large spatial coverage required to effectivelyExisting monitor event the monitoring 21,000 km approaches2 Moreton Bay focus catchment. on capturing samples across the and on the post-processingExisting event monitoring of samples approaches after collection. focus There on capturing is little consideration samples across given the to hydrograph the sampling and inlet on thedesign post-processing and placement, of samples which isafter a critical collection. consideration There is little given consideration the high gradients given to in the total sampling suspended inlet designsediment and (TSS) placement, concentrations which is that a critical occur inconsideration the near-bed given zone. Therethe high is a gradients need to develop in total monitoring suspended sedimentsystems to(TSS) capture concentrations the near-bed that gradients occur in in the TSS near-bed concentrations zone. There in order is a to need better to understanddevelop monitoring rates of systemssediment to transportcapture the in fluvialnear-bed systems. gradients One in major TSS conc limitationentrations of in order event to monitoringbetter understand stations rates is the of sedimenthigh costs transport associated in fluvial with the systems. installation One major and maintenance limitation of ofcurrent systems: event the monitoring capital costs stations associated is the highwith costs establishing associated a new with station the installation are in excess and of mainte US$75,000.nance Thisof systems: is primarily the capital due to costs the needassociated to ensure with establishingthat sample a collectionnew station occurs are in across excess major of US$75,000. flood events This and, is primaril therefore,y due monitoring to the need stations to ensure require that samplelarge investment collection inoccurs infrastructure across major to house flood the events pump and, inlet therefore, and sample monitoring collection stations and storage require facilities large investment(Figure1). in infrastructure to house the pump inlet and sample collection and storage facilities (Figure 1).

FigureFigure 1. 1. TypicalTypical arrangement arrangement for for current event monitoringmonitoring stationsstations inin thethe SouthSouth EastEast Queensland Queensland network:network: ( A) MonitoringMonitoring equipment equipment housed housed in a largein a infrastructure large infrastructure facility located facility above located a streambank; above a streambank;(B) Inset showing (B) Inset the showing location the of alocation pump inletof a forpump water inlet collection; for water ( Ccollection;) Inset showing (C) Inset the showing protective the protectivecover of thecover pump of the inlet pump relative inlet to relative the stream to the bed. stream The pumpbed. The inlet pump has an inle additionalt has an additional screen (500 screenµm) (500within µm) this within cover. this cover.

ThisThis study study monitored monitored the the near-bed near-bed suspended suspended sedi sedimentment concentrations concentrations during during a major a major flood flood event inevent a in a channel erosion erosion hotspot. hotspot. This Thisaddresses addresses a gap a gap in inthe the knowledge knowledge of of existing event-monitoringevent-monitoring programs,programs, where where it it is is unclear unclear where where the the primary area of uncertainty lieslies inin estimatingestimatingsediment sediment loading loading duringduring flood flood events. events. Does Does it it lie lie in in capturing capturing changes changes in sediment concentration atat aa singlesingle pointpoint across across thethe hydrograph, hydrograph, or or does does it itlie lie in incharacterising characterising the the near-bed near-bed concentration concentration gradient? gradient? To provide To provide for a balancefor a balance between between temporal temporal and spatial and spatialsampling, sampling, we utilized we utilized commercially commercially available available washing washing machine turbiditymachine sensors turbidity as sensorsthis allows as this for allowsa truly forlow-cost a truly approach. low-cost approach.

Water 2018, 10, 34 3 of 17

2. Materials and Methods

Water 2018, 10, x FOR PEER REVIEW 3 of 17 2.1. Study Site Description Laidley2. Materials Creek and is Methods located in South East Queensland, Australia (Figure2A), a sub-tropical region 2 prone2.1. to large,Study Site irregular Description rainfall events [8]. The creek has a catchment surface area of 462 km and runs for approximately 60 km, with much of the course through highly erodible alluvium plains. Laidley Creek is located in South East Queensland, Australia (Figure 2A), a sub-tropical region The original vegetation cover was dominated by dry sclerophyll forest and the riparian vegetation prone to large, irregular rainfall events [8]. The creek has a catchment surface area of 462 km2 and runs coverfor is typically approximately mixed 60 eucalypt, km, with casuarina,much of the and course wattle through forest highly [9]. However,erodible alluvium the catchment plains. The is highly modified,original with vegetation a large-scale cover was clearing dominated of forest by dry trees sclero inphyll the lateforest 1800s and the resulting riparian invegetation present cover day landuseis dominatedtypically by mixed grazing eucalypt, and high casuarina, intensity and wattle agriculture forest [9]. [4 ].However, It is a sub-catchment the catchment is ofhighly the largermodified, Lockyer catchment,with a andlarge-scale previous clearing studies of forest of both trees thein the Laidley late 1800s Creek resulting and Lockyerin present Creekday landuse systems dominated have clearly demonstratedby grazing that and the high erosion intensity processes agriculture are [4]. dominated It is a sub-catchment by gulley of and the channellarger Lockyer erosion catchment, [10,11]. and The creek previous studies of both the Laidley Creek and Lockyer Creek systems have clearly demonstrated that banks are highly degraded, with limited riparian vegetation remaining and very steep channel profiles. the erosion processes are dominated by gulley and channel erosion [10,11]. The creek banks are highly Duringdegraded, flood events, with limited large sectionsriparian ofvegetation the channel remaining are eroded, and very resulting steep channel in the profiles. loss of hugeDuring quantities flood of sedimentevents, from large the sections upper catchments.of the channel Theare eroded, finer sediment resulting fractionsin the loss (silts of huge and quantities clays) of of this sediment material are transportedfrom the several upper catchments. hundred kilometersThe finer sediment downstream fractions to(silts Moreton and clays) Bay of this [4]. material The Lockyer are transported catchment is part ofseveral the Brisbane hundred River kilometers system, downstream which drains to Moreton over 13,000 Bay [4]. km The2 into Lockyer the coastal catchment embayment, is part of the Moreton Bay (FigureBrisbane2B). River The system, gulley whic andh channel drains over erosion 13,000 of km the2 into upper the coastal catchments embayment, has resulted Moreton inBay rapid (Figure infilling 2B). The gulley and channel erosion of the upper catchments has resulted in rapid infilling of the of the Moreton Bay with terrestrial silts and clays [6,7]. Moreton Bay with terrestrial silts and clays [6,7].

FigureFigure 2. Study 2. Study site site location location relative relative to to (A (A) Queensland,) Queensland, Australia; Australia; (B) Brisbane (B) Brisbane River catchment River in catchment South in East Queensland (sub-catchments indicated in red outlines) and (C) long-term State Government South East Queensland (sub-catchments indicated in red outlines) and (C) long-term State Government monitoring station: Laidley Creek at Mulgowie gauging station (No. 143209B). Elevation referenced to monitoring station: Laidley Creek at Mulgowie gauging station (No. 143209B). Elevation referenced to Australian Height Datum (AHD). Australian Height Datum (AHD). The deployment of a low-cost monitoring network was undertaken upstream of the Beckman Rd TheBridge deployment across Laidley of a Creek low-cost at Mulgowie, monitoring Queensland, network Australia was undertaken (Figure 2C). upstream Initial aerial of the surveys Beckman of Rd the study sites were undertaken in July 2016, shortly after extensive streambank works were Bridge across Laidley Creek at Mulgowie, Queensland, Australia (Figure2C). Initial aerial surveys undertaken to rehabilitate the western bank (Figure S1). The long-term streamflow monitoring at of theMulgowie study sites gauging were station undertaken (1967–present) in July recorded 2016, a shortly median afterof 0.08 extensive m3/s, a mean streambank of 0.83 m3/s, works and a were undertaken to rehabilitate the western bank (Figure S1). The long-term streamflow monitoring at Mulgowie gauging station (1967–present) recorded a median of 0.08 m3/s, a mean of 0.83 m3/s, and a maximum of 349 m3/s. These highly variable flow rates indicate that the system is event-driven, Water 2018, 10, 34 4 of 17 with 90% of the annual flow occurring during the summer rainfall period [12]. The low-cost monitoring network was deployed between 29 March 2017 and 1 April 2017 to capture a major flood event Water 2018, 10, x FOR PEER REVIEW 4 of 17 resulting from the passage of Ex-Tropical Cyclone Debbie across the study region. On 30 March 2017, overmaximum 170 mm of of rainfall349 m3/s. was These recorded highly variable in 24 hflow at Laidleyrates indica Creekte that at the the system Stony is Creekevent-driven, Rd monitoring with station90% located of the annual 16 km flow upstream occurring of theduring study the sitesumme [13r], rainfall and the period peak [12]. water The levellow-cost of 9.35monitoring m was the second-highestnetwork was on deployed record, between just below 29 March the maximum 2017 and 1 April of 9.37 2017 m to in capture January a major 2013 flood [12]. event resulting from the passage of Ex-Tropical Cyclone Debbie across the study region. On 30 March 2017, over 170 2.2. Fieldmm of Monitoring rainfall was recorded in 24 h at Laidley Creek at the Stony Creek Rd monitoring station located 16 km upstream of the study site [13], and the peak water level of 9.35 m was the second-highest on The low-cost monitoring of TSS concentration was undertaken using custom-built sensors as record, just below the maximum of 9.37 m in January 2013 [12]. described in AppendixA, and each sensor has a total parts cost under US$150 (Table A1, AppendixA). Raw2.2. sensor Field Monitoring output was converted directly to TSS concentration following the methodology in (Figure A5The)[14 low-cost]. In addition monitoring to the of low-costTSS concentration sensors, singlewas undertaken stage samplers using werecustom-built deployed sensors in parallel as to collectdescribed discrete in samples Appendix for A, analysis and each of sensor suspended has a to sedimenttal parts cost particle under US$150 size distribution (Table A1, Appendix and total nutrientA). concentrations.Raw sensor output Time-lapse was converted cameras di (Pandarectly to UV535 TSS concentration trail camera, foll UOVisionowing the methodol Australia,ogy Oakleigh in (Figure South, VIC,A5) Australia) [14]. In addition were utilized to the low-cost to record sensors, changes single in waterstage samplers level and were colour deployed at 5-min in parallel intervals. to collect The total cost ofdiscrete a single samples monitoring for analysis node, of consistingsuspended sediment of one 1.8 particle m star size picket distribution (US$9), and one total low-cost nutrient sensor (US$148),concentrations. one single Time-lapse stage sample cameras (US$35), (Panda and UV535 one trail time-lapse camera, cameraUOVision (US$190), Australia, was Oakleigh less than South, US$400. MonitoringVIC, Australia) nodes were utilized were deployed to record changes along an in water elevation level gradientand colour up at 5-min the streambank intervals. The to total capture cost of a single monitoring node, consisting of one 1.8 m star picket (US$9), one low-cost sensor changes in sediment loading across different stages of the hydrograph (Figure3). The deployment (US$148), one single stage sample (US$35), and one time-lapse camera (US$190), was less than US$400. configurationsMonitoring were nodes mounted were ondeployed star pickets along drivenan elevation into thegradient bank up and the followed streambank the to methodology capture outlinedchanges in [in3]. sediment A total loading of seven across monitoring different stages nodes of the were hydrograph deployed (Figure across 3). theThe sitedeployment with sensor heightsconfigurations ranging from were 0.2mounted m to 9.5on star mabove pickets local driven water into the level, bank which and followed were then the referencedmethodology to the Stateoutlined Government in [3]. A gauging total of seven station monitoring (Figure2 nodesC). Local were streamdeployed height across changes the site with were sensor recorded heights using a non-ventedranging from underwater 0.2 m to pressure9.5 m above transducer local water (Level level, TROLL which 400were Data then Logger, referenced In-situ, to the Fort State Collins, CO, USA),Government which gauging was deployed station (Figure immediately 2C). Local adjacent stream toheight the lowestchangesmonitoring were recorded node. using The a non- pressure vented underwater pressure transducer (Level TROLL 400 Data Logger, In-situ, Fort Collins, CO, USA), transducer was anchored in a 0.3 m water depth using a star picket and the water level was logged which was deployed immediately adjacent to the lowest monitoring node. The pressure transducer was at 1-minanchored intervals in a 0.3 for m thewater duration depth using of thea star deployment. picket and the During water level zero was flow logged conditions, at 1-min intervals surface and sub-surfacefor the duration (10 cm depth)of the deployment. sediment samples During zero were flow collected conditions, within surface the and creek sub-surface bed for analysis (10 cm depth) of particle size distribution.sediment samples The surfacewere collected extent within of bed the material creek bed deposits for analysis was estimated of particle immediatelysize distribution. upstream The of the studysurface site extent by visualof bed material inspection depo ofsits a serieswas estimated of holes immediately dug across upstream the deposit of the at study 5-m intervals.site by visual inspection of a series of holes dug across the deposit at 5-m intervals.

(A) (B)

Figure 3. Field installation of low-cost total suspended sediment (TSS) sensors and single stage samplers Figure 3. Field installation of low-cost total suspended sediment (TSS) sensors and single stage on star pickets. (A) Installation directly adjacent to stream. (B) Upslope installation on a rehabilitated bank samplers7 m above on star the stream pickets. bed; (A note) Installation that this installation directly has adjacent a time-lapse to stream. camera on (B )top Upslope of the star installation picket. on a rehabilitated bank 7 m above the ; note that this installation has a time-lapse camera on top of the star picket.

Water 2018, 10, 34 5 of 17

2.3. Laboratory Analysis Water samples from single stage samplers were retrieved within 24 h of peak flows. A total nitrogen and total phosphorus analysis was undertaken on these samples using standard methods [15] by the National Association of Testing Authorities, Australia (NATA)-accredited laboratory Environmental Analysis Laboratory at the Southern Cross University. To better understand the relative contribution of washload to downstream nutrient loading, subsamples from two single stage samplers were sieved through a 63 µm sieve to remove the sand fraction and the filtrate was analysed for total phosphorus and total nitrogen. Samples of suspended and bed material for analysis of particle size distribution were sonicated for one minute prior to measurement to separate aggregated particles, allowing the true particle size to be calculated [16]. Particle sizing was undertaken using laser diffraction (Malvern Mastersizer 2000E, Malvern Instruments Ltd., Malvern, UK), and five measurement cycles were performed for each sample. were classified according to the Wentworth scale, with mud fractions defined as sediment particles with a diameter of <63 µm [17]. Given the extreme TSS concentrations as well as the obvious sand fractions in the single stage samples collected during high flows, a whole-water test was undertaken to determine how representative the TSS particle size distribution estimated by laser diffraction was. The issue of obtaining representative sub-samples for particle size distribution or TSS concentration from samples with significant sand fractions has been well-established [18]. The whole-water test followed the methodology outlined in [19], where a 12:10 p.m. single stage sample was wet sieved through a 63 µm micron sieve and the sand and mud fractions were dried at 105 ◦C. The relative sand and mud fractions were determined gravimetrically and expressed as a percentage. TSS concentrations were determined gravimetrically, where samples were filtered using a dried pre-weighed 0.7 µm filter (Whatman glass microfiber filter GF/F grade) and then dried at 105 ◦C to a constant weight. Filters were reweighed and the TSS concentration (mg/L) was then calculated from the filter weight difference and normalized to the sample volume.

2.4. Imagery Analysis To obtain high-resolution imagery of the study site before and after a flood event, a series of drone flights were undertaken in July 2016, one day before the flood event (29 March 2017) and one day after the flood event (31 March 2017). The DJI Phantom 3 Pro platform was utilized with the camera (DJI FC300X with a 12 megapixel RGB sensor) in a nadiral orientation for mapping flights. Georeferenced imagery was downloaded from the drone and images selected for photogrammetric data processing. Data processing was undertaken using dedicated processing software (Pix4D Promapper, Pix4D SA, Lausanne, Switzerland), and the resulting mosaics were visualized using the geographical information system ArcGIS (Version 10.3, ESRI Inc., Redlands, CA, USA).

3. Results

3.1. Time-Lapse and Drone Imagery High-resolution drone mosaics before and after the event provided a detailed picture of the impact of this flood event, with clear signs of erosion on the natural eastern bank as well as the breach on the rehabilitated western bank (Figure4A,B; Video S1; Video S2). Erosion of the natural bank occurred along at least 250 m of the creek channel upstream from the study site, with slope failures resulting in up to 3 m (horizontal) and 4 m (vertical) of bank loss (Figure4B; Video S3). The levee breach on the rehabilitated bank highlighted the extreme nature of the flood event, as this was designed to withstand major floods (Figure4B; Video S4). Water 2018, 10, x FOR PEER REVIEW 6 of 17 Water 2018, 10, 34 6 of 17 Water 2018, 10, x FOR PEER REVIEW 6 of 17

FigureFigure 4. High-resolution 4. High-resolution mosaic mosaic imagery imagery (pixel (pixel resolution resolution <2<2 cm) of of the the study study area area collected collected (A ()A prior) prior Figureto 4.the High-resolution major flood event mosaic on 16 Julyimagery 2016 (pixeland (B )resolution immediately <2 aftercm) ofthe the event, study 31 Marcharea collected 2017, showing (A) prior to the major flood event on 16 July 2016 and (B) immediately after the event, 31 March 2017, showing to thethe major widespread flood event channel on erosion16 July on 2016 the andnatural (B )bank immediately and the levee after breach the event, on the 31rehabilitated March 2017, bank. showing the widespread channel erosion on the natural bank and the levee breach on the rehabilitated bank. the widespread channel erosion on the natural bank and the levee breach on the rehabilitated bank. Oblique imagery from the site highlighted the contrast between the natural bank and the ObliquerehabilitatedOblique imagery imagery bank from(Figure from the the5). site siteDespite highlighted being on theththee contrastcontrastinside bend, betweenbetween the natural thethe naturalnatural bank bankexperiencedbank andand the the substantial erosion, whilst the rehabilitated bank on the outside of the bend was largely stable (Figure rehabilitatedrehabilitated bank bank (Figure (Figure 55).). Despite beingbeing onon thethe insideinside bend,bend, the the natural natural bank bank experienced experienced 5). This further highlights the potential for streambank rehabilitation to reduce sediment loading from substantialsubstantial erosion, erosion, whilst the rehabilitatedrehabilitated bank bank on on the the outside outside of of the the bend bend was was largely largely stable stable (Figure (Figure5). channel erosion, a critical sediment loading source to Moreton Bay [6,11]. 5).This This further further highlights highlights the the potential potential for for streambank streambank rehabilitation rehabilitation to to reduce reduce sediment sediment loading loading from from channelchannel erosion, erosion, a a critical critical sediment sediment loading loading source source to to Moreton Moreton Bay Bay [6,11]. [6,11].

Figure 5. Drone image facing upstream from the study site clearly showing channel degradation along the far (natural) bank and the relatively intact nature of the near (rehabilitated) bank after the major flood event.

FigureFigure 5. 5. DroneDrone image image facing facing upstream upstream from from the study site clearly showingshowing channelchanneldegradation degradation along along the the far far (natural) (natural) bank bank and and the the relatively intact nature ofof thethe nearnear (rehabilitated)(rehabilitated) bankbank after after the the major major floodflood event. event.

Water 2018, 10, 34 7 of 17

3.2. Suspended Sediment Dynamics Water 2018, 10, x FOR PEER REVIEW 7 of 17 The stream flow across this major flood event consisted of a relatively small initial peak of 86 m3.2.3/s Suspended occurring Sediment at 1:00 Dynamics p.m. followed by the far larger peak of over 320 m3/s occurring after 8:00 p.m.The on 30stream March flow 2017 across (Figure this 6majorA). Due flood to event the extremity consisted of a the relatively flood event, small initial only two peak of of the 86 sevenm3/s sensorsoccurring deployed at 1:00 were p.m. recovered followed by (Figure the far S2). larger Logged peak of TSS over concentrations 320 m3/s occurring were after strongly 8:00 p.m. correlated on 30 to streamflowMarch 2017 across (Figure the 6A). event; Due to however,the extremity the of timing the flood of event, peaks only in thetwo TSSof the and seven streamflow sensors deployed differed slightly.were The recovered initial flows (Figure were S2). characterisedLogged TSS concentrations by a peak in thewere TSS strongly that preceded correlated the to peakstreamflow flow; thisacross was followedthe event; by a laghowever, in the the TSS timing peak of with peaks the in much the TSS higher and streamflow secondary differed peak in slightly. streamflow The initial (Figure flows6A). Changeswere incharacterised TSS concentrations by a peak werein the mirroredTSS that preced by bothed the loggers peak flow; recovered, this was although followed loggerby a lag 2 in lost the its TSS peak with the much higher secondary peak in streamflow (Figure 6A). Changes in TSS sensor just prior to the major peak flow. The majority of suspended occurred at concentrations were mirrored by both loggers recovered, although logger 2 lost its sensor just prior to high flow rates, with TSS concentrations recorded above 80 g/L by both TSS loggers as well as by the major peak flow. The majority of suspended sediment transport occurred at high flow rates, with a singleTSS stage concentrations sampler. recorded A large discrepancy above 80 g/L wasby both observed TSS loggers between as well the as TSS by concentration a single stage sampler. of the 7 p.m.A singlelarge stage discrepancy sample (384 was mg/L) observed and between that of the the TSS logged concen valuestration (57 of and the 7 59 p.m. mg/L) single recorded stage sample at this (384 time (Figuremg/L)6A). and Overall, that of these the logged data arevalues in contrast(57 and 59 to mg/L) the long-term recorded at event this time monitoring (Figure 6A). undertaken Overall, these by the Statedata Government, are in contrast where to the event long-term mean concentrationsevent monitoring from undertaken 203 samples by the collected State Government, between 2002 where and 2015event averaged mean 0.272 concentrations g/L and rangedfrom 203 between samples 0.094collected and between 0.762 g/L 2002 [ 20and,21 2015]. Whilst averaged these 0.272 data g/L include and a numberranged of between small flow 0.094 events, and 0.762 there g/L were [20,21]. at least Whilst two these major data floods include (in a 2011 number and 2013)of small that flow occurred events, in this timethere period were at and least that two recorded major similar (in peaks 2011 and to this 2013) 2017 that event. occurred in this time period and that recorded similar peaks to this 2017 event.

Figure 6. (A) TSS measurements recorded from two low-cost sensors and stream flow during the high Figure 6. (A) TSS measurements recorded from two low-cost sensors and stream flow during the high flow event proceeding the passage of Ex-Tropical Cyclone Debbie. Discrete single stage sample timing flowand event concentrations proceeding theare passageindicated of with Ex-Tropical arrows. Cyclone(B) Particle Debbie. size distribution Discrete single for samples stage sample collected timing by and concentrationssingle stage samplers are indicated on 30 March with 2017 arrows. during ( Bthe)Particle initial phases size distributionof the flood event. for samples collected by single stage samplers on 30 March 2017 during the initial phases of the flood event. The suspended sediment particle size distribution across the event clearly showed an increasing Thecontribution suspended from sediment sand particles particle during size distributionhigher flows across(Figure the6B). event Relatively clearly low showed flows were an increasing almost exclusively composed of fine silt and clay sediment particles (D10% 2.3 µm; D50% 14.8 µm; D90% 50.4 contribution from sand particles during higher flows (Figure6B). Relatively low flows were almost µm). The increasing contribution from sandy particles is observed in the D90% particle diameter, which exclusively composed of fine silt and clay sediment particles (D10% 2.3 µm; D50% 14.8 µm; increased from 50.4 µm (coarse silt) at 11:25 a.m. to 92.5 µm (very fine sand) at 12:10 p.m. and 448 µm µ D90%at 50.47:00 p.m.m). (medium The increasing sand). Particle contribution sizing using from laser sandy diffraction particles heavily is observed favoured in the fine D90% particles. particle diameter, which increased from 50.4 µm (coarse silt) at 11:25 a.m. to 92.5 µm (very fine sand) at 12:10 p.m. and 448 µm at 7:00 p.m. (medium sand). Particle sizing using laser diffraction heavily

Water 2018, 10, 34 8 of 17 favoured the fine particles. At 12:10 p.m., the mud fraction was estimated to be 80%; however, theWater sieve 2018 analysis, 10, x FOR of PEER the REVIEW whole sample estimated the mud fraction to be 40%. This is likely8 of due 17 to the difficulty associated with taking a truly representative sample for laser diffraction with slurries At 12:10 p.m., the mud fraction was estimated to be 80%; however, the sieve analysis of the whole containing such a high sand fraction. The issue of obtaining representative sub-samples applied to sample estimated the mud fraction to be 40%. This is likely due to the difficulty associated with taking quantifying TSS concentrations in the single stage as well, with sub-samples approximately 10% lower a truly representative sample for laser diffraction with slurries containing such a high sand fraction. thanThe whole-sample issue of obtaining estimates. representative sub-samples applied to quantifying TSS concentrations in the single stage as well, with sub-samples approximately 10% lower than whole-sample estimates. 3.3. First Flush Phenomenon 3.3.The First first Flush flush Phenomenon is often defined as the disproportionate increase in concentration of soluble and particulateThe materialsfirst flush duringis often thedefined rising as stagethe disproport of a flowionate event increase [21]. The in concentration initial flows of observed soluble and in this studyparticulate underwent materials a first during flush phenomenon, the rising stage as of watera flow colourevent [21]. rapidly The initial changed flows from observed transparent in this study to highly colouredunderwent with aa veryfirst flush small phenomenon, rise (approximately as water 20 colo cm)ur in rapidly water levelchanged (Figure from7; transparent Video S4). Theto highly cause of thiscoloured rapid colour with changea very small was arise large (approximately increase in suspended20 cm) in water clay level and silt(Figure particles 7; Video (Figure S4). The6B). cause The water of discolorationthis rapid colour persisted change with was the a large subsequent increase in flows suspended across clay the and whole silt eventparticles (Video (Figure S5). 6B). Together The water with discoloration persisted with the subsequent flows across the whole event (Video S5). Together with the the rapid increase in TSS preceding the initial peak (Figure6A), these data suggest the importance of rapid increase in TSS preceding the initial peak (Figure 6A), these data suggest the importance of this this ‘first flush’ phenomenon and that even low streamflow events may be important contributors to ‘first flush’ phenomenon and that even low streamflow events may be important contributors to downstreamdownstream sediment sediment loading. loading.

Figure 7. Selected time-lapse images recorded during the initial phase of the flood event showing rapid Figurediscoloration 7. Selected associated time-lapse with images a 20 cm recorded rise in stream during height. the initial phase of the flood event showing rapid discoloration associated with a 20 cm rise in stream height. A large sandy deposit was observed within the creek channel immediately upstream of the study siteA largewith a sandy surface deposit area of was approximately observedwithin 174 m2 theand creek a minimum channel deposit immediately depth of upstream 70 cm (Figure of the 8A). study siteThe with entire a surface surface area of ofthis approximately deposit was covered 174 m 2inand a thin a minimum crust between deposit 1 and depth 3 cm of deep, 70 cm which (Figure was8 A). greatly enriched in silt and clay fractions (50% mud) relative to the underlying sandy bed material (10% The entire surface of this deposit was covered in a thin crust between 1 and 3 cm deep, which was mud) (Figure 8B). greatly enriched in silt and clay fractions (50% mud) relative to the underlying sandy bed material Total nutrient concentrations were highly elevated in both the single stage samples collected at (10%relatively mud) (Figure low flows8B). and relatively high flows (Table 1). In addition, there was relatively little change betweenTotal nutrient total nutrient concentrations concentrations were of highlytotal and elevated sieved samples, in both thewhich single suggests stage that samples much collectedof the at relativelynitrogen and low phosphorus flows and relativelyspecies was high associated flows (Tablewith the1). washload In addition, (Table there 1). The was association relatively littleof changephosphorus between with total fine nutrient sediment concentrations particles in washload of total and has sieved been observed samples, during which high suggests flow thatevents much in of thethis nitrogen region and [22]. phosphorus Total nitrogen species concentrations was associated during with the the high washload flows (Tableat 7:001 ).p.m. The were association lower of phosphorusconcentrations with fineafter sediment sieving (Table particles 1). inIn washloadthis region, has total been nitrogen observed is dominated during high by flowthe particulate events in this regionorganic [22]. nitrogen Total nitrogen fractions concentrations during high flows during [23], the and high larger flows fragments at 7:00 may p.m. have were been lower trapped concentrations by the aftersample sieving sieving, (Table reducing1). In this the region, concentration total nitrogen of total nitrogen. is dominated Long-term by the event particulate monitoring organic total nutrient nitrogen concentrations from the State Government event station were approximately one order of magnitude fractions during high flows [23], and larger fragments may have been trapped by the sample sieving, lower than those found in the single stage samples (Table 1). reducing the concentration of total nitrogen. Long-term event monitoring total nutrient concentrations from the State Government event station were approximately one order of magnitude lower than those found in the single stage samples (Table1).

Water 2018, 10, 34 9 of 17 Water 2018, 10, x FOR PEER REVIEW 9 of 17

Figure 8. (A) Image of creek bed facing upstream of the study site showing muddy crust overlying the Figure 8. (A) Image of creek bed facing upstream of the study site showing muddy crust overlying the large sandy bed deposit. (B) Particle size distribution of the muddy crust as well as the underlying sandy large sandy bed deposit. (B) Particle size distribution of the muddy crust as well as the underlying bed. sandy bed.

Table 1. Total nutrient concentrations from two single stage samplers during the flow event collected Table 1. Total nutrient concentrations from two single stage samplers during the flow event collected at 12:10 p.m. and 7:00 p.m. on 30 March 2017. The washload refers to samples that passed through a 63- at 12:10 p.m. and 7:00 p.m. on 30 March 2017. The washload refers to samples that passed through micron sieve. Total phosphorus (TP) and total nitrogen (TN) concentration units in mg/L. a 63-micron sieve. Total phosphorus (TP) and total nitrogen (TN) concentration units in mg/L. Study Sample TP TN Study12:10 p.m. Sample 8.83 TP TN 18.71 12:10 p.m. washload 8.32 19.24 Present study 12:10 p.m. 8.83 18.71 12:107:00 p.m. p.m. washload 8.04 8.32 19.24 19.34 Present study 7:00 p.m. washload7:00 p.m. 8.03 8.04 19.34 16.47 7:00 p.m. washload0.82 8.03 16.47 1.72 Long-term monitoring 1 2002–2015 (0.48–1.95)0.82 1.72(1.04–3.29) Long-term monitoring 1 2002–2015 Note: 1 Ref. [19] data summary from the State water quality monitoring(0.48–1.95) program.(1.04–3.29) Data is from 194 samplesNote: 1 Ref. collected [19] data during summary events from theat the State Mulgowie water quality event monitoring monitoring program. station Data isfrom from 2002 194 samples to 2015. collected Values referduring to eventsthe 50th at the percentile Mulgowie with event the monitoring 20th to 80th station in brackets. from 2002 to 2015. Values refer to the 50th percentile with the 20th to 80th in brackets. 4. Discussion 4. Discussion This study successfully captured changes in near-bed TSS concentrations across a major flood This study successfully captured changes in near-bed TSS concentrations across a major event using a low-cost approach. Changes in suspended sediment particle size distribution clearly flood event using a low-cost approach. Changes in suspended sediment particle size distribution showed the increasing contribution of sandy fractions to TSS as the flood event developed. Total clearly showed the increasing contribution of sandy fractions to TSS as the flood event developed. nitrogen and phosphorus fractions were closely associated with washload, suggesting that the majority Total nitrogen and phosphorus fractions were closely associated with washload, suggesting that of nutrient load was exported from this system to downstream receiving water bodies. The near-bed the majority of nutrient load was exported from this system to downstream receiving water bodies. TSS concentrations were in excess of that required to hinder settling (5 to 10 g/L) of suspended sand

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The near-bed TSS concentrations were in excess of that required to hinder settling (5 to 10 g/L) of suspended sand particles [24]; this would reduce the settling rates of these particles and, therefore, increase their time in suspension and subsequent transport distances downstream [25]. We suggest that the first flush phenomenon observed in this study is a result of local resuspension of muddy crusts immediately upstream of the monitoring site. Whilst this resulted in relatively high TSS concentrations in the near-bed, the higher flows experienced subsequently entrained the underlying sandy bed, which resulted in the extreme TSS concentrations during peak flows. The widespread channel erosion occurring throughout the creek system would likely result in a continuous sediment supply across the event. The finer mud fractions would settle more slowly than the sandy particles as the flood event recedes, reforming the muddy crusts observed in the stream bed. This behavior has been clearly demonstrated in laboratory experiments examining sand-mud suspensions [26]. The discrepancy in TSS concentration between the 7 p.m. single stage sample and the logged values was likely due to the shroud structure surrounding the low-cost sensors (Figure A1). This shroud would shield the sensor face from direct water flows, slowing the near-field water velocities and allowing larger sand particles to rapidly settle in this zone [27]. The net effect would reduce the concentration of sand particles passing the sensor face and greatly reduce the observed TSS concentrations [28]. The lower flows during the initial stage of the flood event were dominated by silt and clay fractions which would not settle as quickly and showed good agreement between single stage measurements and logged values. In addition, the extremely high TSS concentrations during peak flows resulted in the sensors approaching their upper detection limits (Figure A5)[14]. These limitations will form the basis of future research to improve the shroud design and sensor signal-to-noise ratio at extreme TSS concentrations. The TSS and total nutrient concentrations observed in this study were greatly elevated compared to the long-term monitoring data from the State Government event station located approximately 250 m downstream. The pump inlet for the event station was located on the stream bed and would have been exposed to similarly high concentrations of suspended bed material and washload as the low-cost sensors. One explanation for this discrepancy lies in the protective cover surrounding the pump inlet (Figure1C) as well as the 500- µm screen on the inlet . This would greatly reduce water flow in the immediate vicinity of the inlet as well as physically filter out much of the coarser fraction of the suspended bed material prior to collection. Sediment particle fractions that were able to pass through these would likely be limited to very fine particles, which would lead to significant undersampling of the actual sediment load [27]. This highlights an area of uncertainty in current event-monitoring practices; standardisation of the inlet structure and its elevation above the bed should be considered in standard operating procedures in order to ensure comparable results are obtained. For instance, sample collection systems that integrate over the entire water column as described in [29] should be considered. These findings have direct relevance to understanding and analysing sediment budgets, e.g., the contribution of catchment-wide sediment yield, erosion from upstream channel regions or floodplain sources, and changes to the volume and residence time within the system [30]. Particularly in larger catchment areas, the quantification of these processes is complex [31]. Careful and extensive monitoring is required [32,33], which poses a logistical and financial challenge in many river systems from mountainous to the ocean. In addition, the variation of suspended sediment concentration during flood events as reported here and in numerous other studies [34–39] adds to the difficulty and uncertainty of an efficient and robust monitoring strategy. The development of a truly low-cost approach to monitoring sediment dynamics during flood events will provide an opportunity for spatially intense regional monitoring programs as well as a cost-effective method to quantify vertical TSS gradients at single sites. This is of particular importance to guide catchment rehabilitation management actions where it will be critical to separate the effects of regional landuse changes from local stream bed effects. In addition, as climate-induced changes Water 2018, 10, 34 11 of 17 Water 2018, 10, x FOR PEER REVIEW 11 of 17 willin also rainfall provide patterns opportunities increase theglobally likelihood to deploy of extreme these sensors flood events in areas [40 currently], this low-cost lacking approach any formal will monitoringprovide system. an important addition to the existing monitoring of these events. The simplicity of the approach will also provide opportunities globally to deploy these sensors in areas currently lacking Supplementaryany formal monitoringMaterials: The system. following are available online at www.mdpi.com/link, Figure S1: Drone images facing upstream from study site showing: (A) Recently completed earth works on rehabilitated left hand bank in JulySupplementary 2016; and (B) successful Materials: revegetationThe following of rehabilitated are available bank online one at dayhttp://www.mdpi.com/2073-4441/10/2/34/s1 prior to flood event in March 2017. Figure , S2. (A)Figure High S1: resolution Drone images drone facingmosaic upstream of study site from imme studydiately site showing:after the major (A) Recently flood event, completed showing earth the recovery works on statusrehabilitated of deployed left nodes hand at bank the study in July site 2016; and andthe upst (B) successfulream site. Image revegetation collected of rehabilitatedon 31 March 2017. bank (B) one Creek day priorcross- to sectionflood transect event in prior March to 2017.flow event Figure from S2. (A) study High site resolution and the dronerelative mosaic position of study of depl siteoyed immediately nodes. Note after that the majortwo flood event, showing the recovery status of deployed nodes at the study site and the upstream site. Image collected nodes were placed at the lowest position. (C) Zoomed image of a tree trunk deposited during peak flows; the trunk on 31 March 2017. (B) Creek cross-section transect prior to flow event from study site and the relative position wasof 9 deployedm long and nodes. 1.3 m Note in diameter. that two Video nodes S1: were One_Day_Before_Flood, placed at the lowest position. Video S2: (C) One_Day_After_Flood, Zoomed image of a tree Video trunk S3: depositedChannel_Erosion, during peakVideo flows; S4: Mulgowie_High_Came the trunk was 9 m longra_9_m, and 1.3 Video m in diameter. S5: Mulgowie_Low_2_m, Video S1: One_Day_Before_Flood, Computer code folderVideo 1: S1_Sensor_Code, S2: One_Day_After_Flood, Computer Videocode folder S3: Channel_Erosion, 2: S2_Sensor_Code. Video S4: Mulgowie_High_Camera_9_m, Video S5: Mulgowie_Low_2_m, Computer code folder 1: S1_Sensor_Code, Computer code folder 2: S2_Sensor_Code. Acknowledgments: We acknowledge The University of Queensland and Port of Brisbane Pty Ltd. Research Acknowledgments: We acknowledge The University of Queensland and Port of Brisbane Pty Ltd. Research Partnership for providing financial support to this study. Graham Lancaster from the EAL, Southern Cross Partnership for providing financial support to this study. Graham Lancaster from the EAL, Southern Cross UniversityUniversity is gratefully is gratefully ackn acknowledgedowledged for foradvice advice on appr on appropriateopriate analysis analysis techniques. techniques. AuthorAuthor Contributions: Contributions: P.F.,P.F., A.G., A.G., and and N.D. N.D. conceived conceived and and designed designed the the low-cost low-cost sensors; sensors; all all authors authors contributed contributed to studyto study design design and and data data analysis; analysis; S.A., S.A., N.D., N.D., and and A.G. A.G. undertook undertook field field deployments; deployments; M.L. M.L. contributed contributed background background informationinformation and and facilitated facilitated access; access; A.G., A.G., N.D., N.D., S.A., S.A., and and R.C. R.C. wrote wrote the thepaper. paper. Conflicts of Interest: The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest. Appendix A Appendix A To develop a regional monitoring network of fluvial suspended sediment discharge during high To develop a regional monitoring network of fluvial suspended sediment discharge during high flow events, a low-cost sensing solution was required. The low-cost system is manufactured from flow events, a low-cost sensing solution was required. The low-cost system is manufactured from a a commercial washing machine turbidity sensor (TSD-10 Turbidity Sensor, Amphenol Advanced commercial washing machine turbidity sensor (TSD-10 Turbidity Sensor, Amphenol Advanced Sensors, Wallingford, CT, USA) calibrated to total suspended sediment concentration. The sensor Sensors, Wallingford, CT, USA) calibrated to total suspended sediment concentration. The sensor system is assembled in three parts: the electronics board, the housing and battery assembly, and the system is assembled in three parts: the electronics board, the housing and battery assembly, and the sensor assembly (Figure A1). The total cost of the parts, outlined in Table A1, is US$147.66. sensor assembly (Figure A1). The total cost of the parts, outlined in Table A1, is US$147.66.

FigureFigure A1. A1. ExampleExample of a of completed a completed low-cost low-cost sensor sensor and and housing housing layout. layout.

Appendix A.1. Sensor Assembly Appendix A.1. Sensor Assembly 1. Drill a 21 mm hole in the top of two 50 mm PVC caps (Figure A2C) corresponding to the diameter 1. Drill a 21 mm hole in the top of two 50 mm PVC caps (Figure A2C) corresponding to the diameter of the lower section of the Amphenol Sensor (Figure A2A). Then, drill eight (10 mm) holes evenly of the lower section of the Amphenol Sensor (Figure A2A). Then, drill eight (10 mm) holes evenly spaced around the cap flange and four holes (3.5 mm) in the inner edges of one cap, cleaning all spaced around the cap flange and four holes (3.5 mm) in the inner edges of one cap, cleaning all burrs. Ensure both caps are clean and glue the two caps back to back with PVC cement/glue. burrs. Ensure both caps are clean and glue the two caps back to back with PVC cement/glue.

WaterWater 20182018, 10, ,10 x ,FOR 34 PEER REVIEW 12 of 17

Water 2018, 10, x FOR PEER REVIEW 12 of 17

(A) (B) (C)

Figure A2. (A) Amphenol sensor. (B) Third PVC cap and cable gland. (C) Two caps produced in step 1 Figure A2. (A) Amphenol sensor. (B) Third PVC cap and cable gland. (C) Two caps produced in step 1 for forming the(A bottom) of the sensor assembly.(B ) (C) for forming the bottom of the sensor assembly. Figure A2. (A) Amphenol sensor. (B) Third PVC cap and cable gland. (C) Two caps produced in step 1 2. Measure the diameter of the waterproof cable glands threaded section (≈19 mm) and drill the for forming the bottom of the sensor assembly. 2. correspondingMeasure the size diameter hole in of the the centre waterproof of the third cable 50 glands mm PVC threaded Cap. sectionClean the (≈ 19edges mm) of andthe hole, drill 2. Measureensuringthe correspondingthe there diameter is no ofburr size the or holewaterproof raised in the markings. centrecable ofglands Secure the thirdthreaded the 50cable mm section gland PVC in( Cap.≈ 19the mm) drilled Clean and thehole drill edges (Figure the of correspondingA2B).the Hot hole, glue ensuringsize can hole be thereusedin the on is centre nothe burrnut of ofthe or the raisedthird glan 50d markings. tomm provide PVC Secure Cap.additional Clean the cablesupport the edges gland when of in thetightening. the hole, drilled 3. ensuringCuthole a 75 there (Figure mm islength A2no B).burr of Hot 50 or mm glueraised diameter can markings. be used PVCon Securepipe, the nutclean the of cable the the edges glandgland of to in the provide the cut. drilled additional hole (Figure support 4. A2B).Cutwhen Hot the glueappropriate tightening. can be used length on of the cable nut forof the the glan proposd toed provide deployment, additional noting support that the when length tightening. should be 3. 3.Cut 500 aCut 75 mm mm a 75greater length mm lengththan of 50 required. ofmm 50 diameter mm diameter PVC PVCpipe, pipe,clean clean the edges the edges of the of cut. the cut. 4. 5. 4.CutStrip theCut appropriate50 the mm appropriate of outer length black length of cablecoating of cablefor from the for propos both the proposedendsed deployment, of the deployment, sensor noting cable. noting thatThen, the that strip length the a lengthsmall should amount should be 500( ≈mm10be mm) 500greater mmfrom than greater the required.red, than yellow, required. and internal black wire covers. Cut the green cable off to the same 5. 5.Striplevel Strip50 atmm 50the of mm outer outer of outerblack black blackcoating coating coating (Figure from from both A3A). both ends ends of the of thesensor sensor cable. cable. Then, Then, strip strip a small a small amount amount 6. (≈10Twist mm)(≈10 the from mm) ends the from of red, the the yellow,exposed red, yellow, and wires internal and separately internal black andwire black apply covers. wire lead-free covers.Cut the solder. Cutgreen the cable green off cable to the off same to the 7. levelRemove sameat the leveltheouter black at black the cap outer coating from black the (Figure Amphenol coating A3A). (Figure Sensor A3 anA).d then remove the sensor board from the clear 6. 6.Twist housing.Twist the ends the Cut endsof the the white of exposed the plastic exposed wires plug wires se offparately separatelythe sensor and apply andboard, apply lead-free and lead-free then solder. solder solder. the sensor cable wires to 7. 7.RemovetheRemove uncovered the black the pinsblackcap from(Figure cap the from A3A), Amphenol the covering Amphenol Sensor connectio Sensor and thenns and removein then heat-shrink remove the sensor or the electrical board sensor from board tape. the Place from clear the housing.sensorclear Cutboard housing. the back white Cut into plastic the the white housing plug plastic off and the plug reattachsensor off board, the the sensor black and cap,board,then ensuring solder and then th thate sensor solder the sensor cable the sensor wirescable cabletoexits thethrough uncoveredwires tothe the pinshole. uncovered (Figure Seal the A3A), pinscable (Figure coveringgap with A3 connectioA),hot coveringglue. ns in connections heat-shrink in or heat-shrink electrical tape. or electrical Place the tape. sensorPlace board the back sensor into board the housing back into and the reattach housing th ande black reattach cap, theensuring black cap,that ensuringthe sensor that cable the exits sensor throughcable the exits hole. through Seal the the cable hole. gap Seal with the hot cable glue. gap with hot glue.

(A) (B) (C) (D) Figure A3. (A) Illustrating the cable soldered on the sensor board, ensuring the solder does not bridge between(A the) sensors. The wires connected(B) as; Red to A/C, Black (toC )K, and Yellow to E. (B) Epoxy-filled(D) Figuresensor A3. housing. (A) Illustrating The harder the cableepoxy soldered is first to on provide the sensor a dense board, base, ensuring and hold the the solder cable does firmly not in bridge place to Figure A3. (A) Illustrating the cable soldered on the sensor board, ensuring the solder does not bridge betweenprevent the movement sensors. The of thewires soldered connected joint. as; (C Red) Silicon to A/C, filling Black is usedto K, inand the Yellow top to toprovide E. (B) Epoxy-filleda more flexible between the sensors. The wires connected as; Red to A/C, Black to K, and Yellow to E. (B) Epoxy-filled sensorhousing housing. fill so The the harder cable can epoxy be positioned is first to provide for the topa dense cap. base,(D) Completed and hold thesensor cable assembly. firmly in place to sensor housing. The harder epoxy is first to provide a dense base, and hold the cable firmly in place to prevent movement of the soldered joint. (C) Silicon filling is used in the top to provide a more flexible 8. Placeprevent the movementsensor into of the solderedglued caps joint. assembled (C) Silicon fillingin Step is used1, ensuring in the top that to provide the lower a more section flexible of the housing fill so the cable can be positioned for the top cap. (D) Completed sensor assembly. sensorhousing is the fill soon the the cable side can of beshroud. positioned Hot forglue the the top sensor cap. (D in) Completed this position, sensor and assembly. slide the pipe down 8. Placethe thecable. sensor Glue into the lowerthe glued caps caps and assembledthe pipe together in Step with 1, ensuring PVC cement/glue that the lower (Figure section A3D). of the sensor is the on the side of shroud. Hot glue the sensor in this position, and slide the pipe down the cable. Glue the lower caps and the pipe together with PVC cement/glue (Figure A3D).

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8. Place the sensor into the glued caps assembled in Step 1, ensuring that the lower section of the sensor is the on the side of shroud. Hot glue the sensor in this position, and slide the pipe down the cable. Glue the lower caps and the pipe together with PVC cement/glue (Figure A3D). 9. Position so the opening in the pipe is facing up, and prepare the Araldite epoxy as per the manufacturer’s instructions. Pour epoxy into the pipe until 10–20 mm above the black cap, Water 2018, 10, x FOR PEER REVIEW 13 of 17 and agitate to remove the air voids while topping up with epoxy as required. Sit for 24–48 h until epoxy9. Position is fully so set the (Figure opening A3 B).in the pipe is facing up, and prepare the Araldite epoxy as per the 10. Fill themanufacturer’s remaining void instructions. area with Pour waterproof epoxy into silicon the pipe (Figure until A3 10–20C), and mm then above pull the the black sensor cap, cableand throughagitate the to cable remove gland. the air Use voids PVC while cement/glue topping up to with affix epoxy the top as required. cap to the Sit pipe,for 24–48 and h then until tightenepoxy the glandis fully around set (Figure the cable A3B). to seal the assembly. 10. Fill the remaining void area with waterproof silicon (Figure A3C), and then pull the sensor cable Appendix A.2.through Case the and cable Power gland. Supply Use Assembly PVC cement/glue to affix the top cap to the pipe, and then tighten the gland around the cable to seal the assembly. 11. Drill a hole corresponding to the diameter of the cable gland threaded section in the acrylonitrile butadieneAppendix A.2. styrene Case and (ABS) Power case Supply on Assembly the opposite side to the attachment strap. Clean burrs and remove the inner foam lining around the hole. Affix the second cable gland in the hole using hot 11. Drill a hole corresponding to the diameter of the cable gland threaded section in the acrylonitrile glue to prevent excessive spinning of the nut. butadiene styrene (ABS) case on the opposite side to the attachment strap. Clean burrs and remove 12. Collectthe the inner battery foam lining holder around and solder the hole. the Affix red the jumper second wire cable to gland the red in the battery hole using holder hot wire glue and to the blackprevent jumper excessive wire spinning to the of black the nut. battery holder wire. Cover the joints in heat-shrink or electrical12. Collect tape. the battery holder and solder the red jumper wire to the red battery holder wire and the 13. Placeblack batteries jumper in thewire holder to the and black test battery the voltage holder (7.2wire V).. Cover the joints in heat-shrink or electrical tape. Appendix13. A.3.Place Electronics batteries in Board the holder Assembly and test the voltage (7.2 V).

14. SolderAppendix the A.3. stacking Electronics header Board to Assembly the outer holes in the prototyping board, and ensure that this can bridge to a DRFudino board (Figure A4B). 14. Solder the stacking header to the outer holes in the prototyping board, and ensure that this can 15. Oncebridge the stacking to a DRFudino headers board are in (Figure place, A4B). the inner headers are soldered in an upright orientation; this15. allowsOnce the for stacking easy wiring headers of theare circuit.in place, the inner headers are soldered in an upright orientation; 16. Finally,this the allows electronic for easy components wiring of the are circuit. added following the wiring pattern in Figure A4A. 16. Finally, the electronic components are added following the wiring pattern in Figure A4A.

(A)(B)

Figure A4. (A) Electronics wiring schematic for the electronics board applicable for the code provided. Figure A4. (A) Electronics wiring schematic for the electronics board applicable for the code For the Amphenol TSD-10 sensor used, the R1 resistor is 4700 Ohms and R2 is 470 Ohms. (B) provided.Preassembled For the Amphenol board and recommended TSD-10 sensor configuration. used, the R1 resistor is 4700 Ohms and R2 is 470 Ohms. (B) Preassembled board and recommended configuration. Appendix A.4. Final Assembly 17. Place components in the ABS housing case (Figure A1).

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Appendix A.4. Final Assembly 17. Place components in the ABS housing case (Figure A1). 18. Connect the battery to the electronics board by plugging the red wire from the battery pack to Vin and the black wire to ground pin (GND). Ensure the red light on the electronics board lights up, then remove the battery wires until deployment. 19. Run the sensor cable through the cable gland in the housing and connect the wires as shown (Figure A4A). Before tightening the gland around the cable, ensure that there is extra cable length for board movement within the case. Water 2018, 10, x FOR PEER REVIEW 14 of 17 Appendix A.5. Programing 18. Connect the battery to the electronics board by plugging the red wire from the battery pack to Vin 20. Downloadand thethe black Arduino wire to program ground pin from (GND). the Ensure Arduino the red website. light on the electronics board lights up, 21. Install thethen relevant remove the libraries, battery wires outlined until deployment. in Code S1. 19. Run the sensor cable through the cable gland in the housing and connect the wires as shown 22. Connect(Figure the electronics A4A). Before board tightening to the the computer.gland around the cable, ensure that there is extra cable length 23. Set the real-timefor board movement clocks using within the the correspondingcase. code (Code S2). 24. Upload the sensor code to the board (Code S1). Note that the monitoring frequency can be Appendix A.5. Programing adjusted within the code, the default is 10 s of monitoring. 20. Download the Arduino program from the Arduino website. 25. Check21. thatInstall the the code relevant is running, libraries, outlined the time in isCode correct, S1. and the sensor functions correctly (bits reduce when22. the Connect sensor the is electronics blocked) board by opening to the computer. the serial monitoring portal. 23. Set the real-time clocks using the corresponding code (Code S2). Appendix24. A.6. Upload Deployment the sensor code to the board (Code S1). Note that the monitoring frequency can be adjusted within the code, the default is 10 s of monitoring. 26. Connect25. Check the battery that the code pack is torunning, the electronics the time is corre boardct, and (Red: the Vin,sensor Black: function Ground)s correctly (bits reduce 27. To checkwhen that the the sensor sensor is blocked) is functioning by opening correctly,the serial monitoring log 3–5 portal. monitoring intervals. Disconnect the

battery,Appendix remove A.6. Deployment the storage device (SD) card, and check readings. If functioning correctly, reinsert the SD card and then reattach the battery. 26. Connect the battery pack to the electronics board (Red: Vin, Black: Ground) 27. To check that the sensor is functioning correctly, log 3–5 monitoring intervals. Disconnect the Appendix A.7. Calibration battery, remove the storage device (SD) card, and check readings. If functioning correctly, reinsert Low-costthe sensor SD card laboratory and then reattach calibration the battery. was undertaken using a silica-based slurry at increasing concentrationAppendix across A.7. Calibration the sensor measurement range (200 mg/L to 120 g/L). After each increase in TSS concentration, the sensor signal was monitored until this stabilised, usually after a period of one Low-cost sensor laboratory calibration was undertaken using a silica-based slurry at increasing minute, untilconcentration no further across change the sensor in signal measurement was detected. range (200 The mg/L concentrations to 120 g/L). After observed each increase during in TSS the higher flow stagesconcentration, mean that the the sensor sensor signal itself was wasmonitored likely unt toil bethis atstabilised, or above usually its detection after a period limit. of one The sensor appears tominute, have until a reasonable no further change signal-to-noise in signal was ratio detect ated. concentrations The concentrations below observed 30 g/L;during however, the higher the peak flow stages mean that the sensor itself was likely to be at or above its detection limit. The sensor appears concentrations recorded were well above this threshold (Figure A5). The single stage TSS estimates to have a reasonable signal-to-noise ratio at concentrations below 30 g/L; however, the peak at lower flowconcentrations rates agreed recorded well were with well above the logged this thresh data;old (Figure however, A5). The at highsingle stage flows TSS the estimates single at stage TSS concentrationlower wasflow almostrates agreed 5 times well higherwith the compared logged data; with however, the logged at highvalues. flows the Future single researchstage TSS will trial higher-rangeconcentration sensors was to betteralmost quantify5 times higher the compared loads during with the high logged flows. values. Future research will trial higher-range sensors to better quantify the loads during high flows.

Figure A5.FigureSensor A5. Sensor signal-to-noise signal-to-noise ratio ratio from from increasing increasing suspended suspended sediment sediment concentrations concentrations under under controlled laboratory conditions [14]. controlled laboratory conditions [14].

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Appendix A.8. Required Parts

Table A1. A complete list of required parts, consumables, and tools required for the assembly of a low-cost sensor, prices as of November 2017.

Qty Supplier Part # Cost (US$) Electronics Board DFRduino UNO R3—Arduino Compatible 1 DFRobot DFR0216 $15.19 MicroSD card module for Arduino 1 DFRobot DFR0229 $3.97 Real Time Clock Module (DS1307) V1.1 1 DFRobot DFR0151 $3.36 10 Pcs 40 pin Headers Straight 1 DFRobot FIT0084 $2.37 4.7 k Ohm 0.5 Watt Metal Film Resistor 1 Jaycar RR0588 $0.42 470 Ohm 0.5 Watt Metal Film Resistor 1 Jaycar RR0564 $0.42 2 GB Class 4 microSD Card 1 Jaycar XC4998 $7.60 3 Way PCB Mount Screw Terminal—5 mm Pitch 1 Jaycar HM3173 $1.18 ProtoShield Basic for Arduino 1 Freetronics PSB $2.29 Shield stacking headers for arduino (R3 compatible) 1 Adafruit 85 $1.49 Sub-total $38.28 Sensor Assembly Amphenol Advanced Sensors TSD-10 1 Mouser Electronics TSD-10 $8.24 50 mm PVC DWV Pipe 1 m Bunnings 4770087 $5.40 50 mm PVC Caps 3 Bunnings 4750164 $6.30 Multipurpose Water Proof Silicon 1 Bunnings 1232705 $4.08 5–10 mm DIA IP68 Waterproof Cable Glands—Pk.2 1 Jaycar HP0727 $4.54 Sealer Araldite Epoxy K106 1 Blackwoods 00405455 $22.14 14/0.20 Black 4 Core Security Cable 5 m Altronics W2355 $8.40 Sub-total $59.11 Housing and Power Supply Case Abs Blk IPX8 210 × 120 × 90 mm 1 Jaycar HB6425 $26.68 4 × D CELL 2 Rows of 2 battery holder 1 Jaycar PH9222 $2.25 D cell Alkaline Batteries 4 $6.07 Sub-total $35.00 Consumables Hot glue Lead free solder PVC cement for pressurised pipes Jumper shunts (links) 2 Jaycar HM3240 Premium Female/Male ‘Extension’ Jumper Wires—40 × 300 (75 mm) 1 Adafruit 825 Premium Female/Female Jumper Wires—40 × 300 (75 mm) 1 Adafruit 794 Heat-shrink or electrical tape Sub-total $15.27 Total $147.66 Required Tools Soldering iron Hack saw Drill Drill bit (3.5 mm, 10 mm, 19 mm, and 21 mm) Wire strippers and cutters Phillips head screw driver #1, 2.5 mm shaft Snap-off or retracting knife (9 or 18 mm) Measurement tools (Ruler, Calipers) Multimeter Water 2018, 10, 34 16 of 17

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