Northam WWTP: Environmental Impact Assessment ● 43 4. ENVIRONMENTAL SURVEY RESULTS 4.1 SITE DESCRIPTIONS AND HABITAT ASSESSMENT Table 4-1 Summarised habitat descriptions for each site Site (representative image) Description Burlong Pool (control site upstream of WWTP) Burlong Pool is an analogue site located 9.5 km upstream of the WWTP discharge and is of similar size and condition to the potential impact site, Katrine Pool. It is one of the 16 priority rehabilitation pools identified by the DoW (2007). Situated between farmland with highly disturbed riparian vegetation consisting of fragments of native vegetation on right bank and predominantly exotic grasses, and good coverage on the left bank. Local grazing. Highly eroded banks in places as a result of vegetation clearing. Limited shading of the channel. Submerged and emergent macrophytes present (~30% of channel). Small amount of woody debris present. Deep channel in parts and heavily vegetated with macrophytes, although noticeably less after February 2017 floods. A small culvert at the road crossing/bridge allows pool formation as the river dries. Report to the Water CoRporation of Western Australia www.hydrobiology.biz Northam WWTP: Environmental Impact Assessment ● 44 Site (representative image) Description Mortlock (Mortlock River upstream WWTP) A control site situated at the edge of Northam township on the Mortlock River, just upstream from the confluence with the Avon River, and assessed for water quality only. The Mortlock River is known to be a significant contributor to nutrient and salt concentrations in the lower Avon River. The site is situated between grazing land and a public recreation/parking area (Enright Park Corroborree Site), with a small cement weir/river walkway presenting a physical barrier to fish passage in some flows. Extremely disturbed riparian area, dominated on the left bank by exotic grasses and providing minimal shading (<5% of channel). Severe bank erosion on the right bank with undercutting. No obvious channel modifications. Small amount of macrophytes present (5% cover). Moderate deposition including vegetated instream bars. US 1.8km (control site upstream WWTP 1.8km) The control site US 1.8km site represents similar habitat to the potential impact site DS 3.0km and contains inflow from the Mortlock River. This site is representative of conditions immediately prior to the WWTP discharge location. Site upstream of road crossing/bridge and culvert. Riparian zone cleared in places, dominated by exotic grasses (95%) and Sheoaks (25%), overall of a good width. Some grazing evident. Vegetation overall very highly disturbed including valley clearing. Vegetated mid-channel bars. Low macrophyte presence (5%). Report to the Water CoRporation of Western Australia www.hydrobiology.biz Northam WWTP: Environmental Impact Assessment ● 45 Site (representative image) Description WWTP Out Situated on a bend in the Avon River approximately 4.5km downstream of the Northam weir. Water quality only was measured at this site, at a point approximately 150m prior to release into the Avon River. DS 3.0 (downstream WWTP 3.0km) The potential impact site 3km downstream of the WWTP, and upstream of Katrine Pool, will provide information on impact gradients (if any) and replicate to assess variability within the downstream habitats. Situated on farmland with local impacts associated with grazing and direct access of stock to water way, and beyond riparian zone, cropping. Overall very high disturbance to vegetation including intrusion of exotic grasses and clearing to valley vegetation. Good riparian coverage of banks but providing limited shading of the channel. Emergent macrophytes present (~10% of reach). Small amount of woody debris present. Exotic grasses present on mid- channel bars. Report to the Water CoRporation of Western Australia www.hydrobiology.biz Northam WWTP: Environmental Impact Assessment ● 46 Site (representative image) Description Katrine Pool (downstream WWTP 10km) Katrine Pool, approximately 10 km downstream of the WWTP discharge, has been identified as a high value aquatic habitat, recreational area and local government reserve. This pool is also one of 16 in the Avon Catchment identified by the DoW as a priority for rehabilitation (DoW 2007). The Katrine Pool sampling site has been selected as the key downstream receptor site for this impact assessment. Local landuse includes recreational picnic areas and cropping. Vegetation highly disturbed with clearing to valley but with native species present and good to excellent coverage in riparian zones. Groundcover predominantly exotic grasses. High percentage cover of macrophytes (40%). Road access point was washed out during the February 2017 floods, though this is unlikely to have impacted greatly on the site. Table 4-2 Summarised USEPA Habitat characterisation for Low Gradient Streams with total low gradient habitat score (out of a possible 200) Site bank bank bank bank (N/200) Epifaunal score Pool variability Pool susbstrate characterization Channel sinuosity channel alteration stability right bank channel flow status sediment deposition Riparian score zone left Bank stability Left bank Bank Riparian score zone right Vegetative protection left substrate/available cover Total low habitat gradient vegetative protection right Burlong 14 11 6 5 20 15 6 6 3 6 6 7 1 106 Mortlock 6 13 N/A 10 18 15 9 3 1 8 6 3 2 94 US 1.8 6 12 12 5 19 12 7 6 6 6 6 7 8 112 DS 3.0 6 11 11 6 18 13 8 7 7 6 6 7 7 113 Katrine 10 12 14 3 19 13 10 5 7 6 6 5 9 119 4.2 WATER QUALITY 4.2.1 FIELD PARAMETERS The major physico-chemical difference between the TWW discharge water quality and the receiving waters of the Avon River across all sampling seasons is the level of salinity. The Avon River sites ranged from 4.90-18.76 ppt salinity, the Mortlock River was more saline ranging from 18.47-26.75 ppt, whereas the Report to the Water CoRporation of Western Australia www.hydrobiology.biz Northam WWTP: Environmental Impact Assessment ● 47 WWTP site was fresher than all other sites with salinity values ranging 1.11-1.46 ppt (Figure 4-1). The most saline values at all river sites were recorded in the recessional period, with the least saline values for each site being recorded in the high-flow sampling period. The influence of the WWTP discharge on salinity downstream was negligible with DS 3.0 recording similar salinity levels to US 1.8 across the sampling periods (DS 3.0 = 11.80, 18.52, 14.13 and 13.33; US 1.8 = 11.61, 17.68, 14.14 and 12.07). While the Avon River is considered mid-high saline (salinity levels recorded for the survey were orders of magnitude above the ANZECC/ARMCANZ (2000) guidance for south-west lowland rivers (120-300 µS/cm)), the water at the WWTP site was marginal-high brackish (DoW 2011a), above fresh water guidance for south-west lowland rivers though within ranges (for example) for moderately salt tolerant irrigation purposes and stock watering (ANZECC/ARMCANZ 2000). The Avon River is well above suitable salinity for irrigation of even very salt tolerant plant species or any stock watering. The pH of the TWW is typically at the lower end of the range within the Avon River though within the ANZECC/ARMCANZ (2000) guidance for south-west lowland rivers (pH 6.5-8). The lowest pH recorded for the survey was 6.07 at the upstream reference pool (Burlong Pool) during the high-flow period. This site also recorded the lowest pH during the recessional sampling (Figure 4-1). No influence of the TWW discharge on downstream Avon River pH was apparent. Dissolved oxygen was lower within the TWW discharge than the receiving waters, with elevated DO recorded at several sites during the high-flow and low-flow periods (Figure 4-1). There was no consistent trend with DO downstream of the TWW discharge with DO reducing (upstream to downstream) during the recessional period and increasing (upstream to downstream) during the low-flow period. It was not considered likely that there was a significant impact to DO from the TWW discharge. Report to the Water CoRporation of Western Australia www.hydrobiology.biz Northam WWTP: Environmental Impact Assessment ● 48 Figure 4-1 Salinity, pH and Dissolved Oxygen by site and season. Note: dissolved oxygen (% saturation) was recorded at Mortlock in the low-flow resample but measured far higher than all other sites at 567.9 so was excluded from the chart for clarity reasons. There was no indication of impacts to water temperature downstream of the TWW discharge (Figure 4-2) Report to the Water CoRporation of Western Australia www.hydrobiology.biz Northam WWTP: Environmental Impact Assessment ● 49 Figure 4-2 Water temperature by season and site There is no indication of an impact to dissolved oxygen levels in the Avon River from the Water Corporation long-term monitoring program (2013 to 2017; Figure 4-3). See Figure 3-2 in Section 3.1 for site locations. Figure 4-3 Dissolved oxygen from Water Corporation long-term monitoring (2013-2017) 4.2.2 LOGGER DATA Two water level, conductivity and water temperature loggers were installed for the study program at the 1.8 km upstream site and Katrine Pool respectively. Unfortunately, the data for these loggers was compromised by the large flood event in February 2017 in which one logger was buried in sediment though still recoverable (upstream 1.8 km) and the other (Katrine Pool) was buried too deeply to be recovered. A data download did occur mid-study in November 2016 which allowed comparison of the upstream and downstream sites for the high-flow to mid-recessional periods. The dataset for the upstream site is considered reasonable until the flood event and therefore provides a record to early February 2017 (Figure 4-4).