5. Description of the Onshore Terrestrial Environment
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Sunbird Energy: Proposed development of the Ibhubesi Gas Project 5. DESCRIPTION OF THE ONSHORE TERRESTRIAL ENVIRONMENT This section provides a general overview of the biophysical and socio-economic aspects of the environment associated with the proposed onshore pipeline routes. Where applicable, detailed descriptions are provided of the environment that may be directly affected by the proposed project components. The target study area is essentially made up of two sections, referred to as the southern shore-crossing route between Grotto Bay and Duynefontein (see Section 5.2), and the northern shore-crossing route on the Saldanha Peninsula (see Section 5.3). 5.1 CLIMATE 5.1.1 RAINFALL 5.1.1.1 Southern study area Rainfall data collected by the South African Weather Service (SAWS) at Atlantis from 2008 to 2012 indicates an annual rainfall of between 370 mm and 550 mm. On average the area receives 452 mm of rain per year. A summary of monthly rainfall recorded at Atlantis is provided in Figure 5.1. Most rain is received in the winter months (June to August). Summer months are the driest. Figure 5.1: Monthly rainfall at Atlantis between 2008 and 2012 (SAWS data). 5.1.1.2 Northern study area Saldanha Bay falls within a winter rainfall region and receives most of its rain during June, July and August (see Table 5.1). The region, as observed at Langebaanweg, is relatively dry with an average annual rainfall of 278 mm. The annual average relative humidity is 50% and 76% for day and night, respectively, with ±10% variance over the yearly average. The annual average cloud cover is 35% and 29% for day and night, respectively. CCA Environmental (Pty) Ltd 5-1 Final EIR Sunbird Energy: Proposed development of the Ibhubesi Gas Project Table 5.1: Long-term rainfall at Langebaanweg. Average Average Number of Highest 24-hr Month monthly (mm) days with >= 1mm rainfall (mm) January 8 1.9 14 February 4 1.2 10 March 11 2.2 21 April 24 3.9 30 May 40 6.3 30 June 41 6.4 27 July 47 7.1 35 August 45 6.8 57 September 24 4.9 29 October 12 2.8 40 November 12 2.4 23 December 10 2.4 14 Year 278 48 57 5.1.2 TEMPERATURE 5.1.2.1 Southern study area Diurnal and average monthly temperature trends are presented in Figure 5.2. Monthly mean and hourly maximum and minimum temperatures are given in Table 5.2. Temperatures generally range between -1.8ºC and 40ºC. The highest temperatures occur in January, February and March. The lowest occur between June and September. During the day, temperatures increase to reach maximum at around 13h00. Ambient air temperature decreases to reach a minimum at around 07h00. Figure 5.2: Diurnal temperature profile at Atlantis between 2006 and 2010. CCA Environmental (Pty) Ltd 5-2 Final EIR Sunbird Energy: Proposed development of the Ibhubesi Gas Project Table 5.2: Monthly temperature summary for Atlantis between 2006 and 2010. Hourly Minimum, Hourly Maximum and Monthly Average Temperatures (°C) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 11.4 12.6 9.4 9.4 7.3 5.8 4.5 3.5 6.1 6.1 7.6 8.9 Maximum 40.0 40.9 37.7 36.6 32.5 30.0 28.0 29.9 38.6 37.5 37.5 39.9 Average 21.7 22.0 20.2 18.4 15.8 13.9 13.6 13.0 15.4 16.6 18.6 20.1 5.1.2.2 Northern study area The Saldanha Peninsula experiences a temperate climate with temperatures reaching a maximum during the months of January and February. July and August are generally the coldest months. Monthly mean and hourly maximum and minimum temperatures are presented in Table 5.3. From observations made by SAWS in Vredenburg, hourly averaged temperatures generally ranged between a minimum of 6ºC - 7ºC during the winter months (May to August) to a maximum of 36.8ºC during February. February is also the month with the highest monthly average temperature of 20.4ºC, with the lowest monthly average occurring in August (12.9ºC). The observations along the coast at Cape Columbine show lower temperatures with hourly averaged temperatures generally ranging between a minimum of 6.8ºC during August to a maximum of 33.7ºC during February. As with Vredenburg, February is also the month with the highest monthly average temperature of 18.4ºC, with the lowest monthly average occurring in August (13.9ºC). Table 5.3: Monthly temperature summary for Atlantis between 2006 and 2010. Hourly Minimum, Hourly Maximum and Monthly Average Temperatures (°C) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Cape Columbine Minimum 12.2 12.2 11.0 11.0 10.9 8.8 6.8 8.9 8.7 9.9 11.6 12.4 Maximum 23.5 33.7 32.7 34.0 29.1 24.7 24.7 26.5 21.1 27.2 29.1 26.1 Average 17.7 18.4 17.1 16.3 15.5 15.1 14.9 13.9 14.4 16.3 17.7 18.0 Vredenburg Minimum 12.0 12.0 11.0 10.0 7.0 6.0 7.0 7.0 8.0 7.0 10.0 12.0 Maximum 36.0 36.8 40.0 37.0 30.0 27.0 24.0 26.0 24.0 31.0 34.0 36.0 Average 18.5 20.4 19.9 17.1 14.8 13.7 14.1 12.9 13.5 15.9 17.0 18.4 5.1.3 WIND 5.1.3.1 Southern study area Predominant winds in the study area between 2006 and 2010 were from the north-west and east-south-east with an average wind speed of 4 m/s (see Figure 5.3). The strongest winds (> 10 m/s) were from the north and north-north-west. During this period calm conditions occurred 7.9% of the time. There is a distinct difference between the day and night-time wind field. The day-time wind field is dominated by winds from the west-north-west, an average wind speed of 4.1 m/s and 6.6% calm conditions. During the night the wind field is dominated by winds from the east-south-east, an average wind speed of 3.9 m/s and 9.2% calm conditions. Predominant winds in summer are from the south, with intermittent south-easterly and south- westerly winds. North-westerly winds dominate during winter months. CCA Environmental (Pty) Ltd 5-3 Final EIR Sunbird Energy: Proposed development of the Ibhubesi Gas Project Period Wind Rose Day-time Wind Rose Night-time Wind Rose Figure 5.3: Period, day- and night-time wind roses for the onshore study area (2006-2010). 5.1.3.2 Northern study area The northern study area is dominated by the southern wind sector at both Cape Columbine and Vredenburg) (see Figure 5.4). Cape Columbine has more frequent south-south-easterly winds than Vredenburg, where the south-south-westerly winds are more prevalent. Both the southerly (summer) and northerly (winter season) wind components are associated with frequent, strong wind speeds above 10 m/s. Whilst this is evident at both sites, the south-south-westerly winds at Vredenburg are not as strong as the south-south- easterly winds at Cape Columbine. There are also more calm wind conditions at Cape Columbine (9.9%) than at Vredenburg (3.5%). The land-sea breeze condition is clearly illustrated at Cape Columbine, where the frequency of westerly winds is high during the day, but nearly non-existent at night-time. Cape Columbine Vredenburg Figure 5.4: Wind roses for Case Columbine and Vredenburg. CCA Environmental (Pty) Ltd 5-4 Final EIR Sunbird Energy: Proposed development of the Ibhubesi Gas Project 5.2 SOUTHERN SHORE-CROSSING ROUTE (GROTTO BAY TO DUYNEFONTEIN) 5.2.1 TOPOGRAPHY The general topography of the area is fairly flat, but more undulating towards the east and with dunes near the coast. The northern parts of the pipeline routes reaches ±100 metres above mean sea level (mamsl) and the southern part varies between 50 and 70 mamsl. 5.2.2 GEOLOGY, SOILS AND GROUNDWATER Shales and greywacke of the Tygerberg Formation and Malmesbury Group are the older rocks that underlie the area. These rocks often weather to produce a substantial thickness of clay. The Tygerberg Formation outcrops in the eastern portion. The younger rocks of the Springfontein Formation, which is the main water- bearing formation, are predominant on the western side of the study area. The overlying unconsolidated sand layer increases in thickness to the north and west across the area. The most dominant soil types for the study area tend to be imperfectly drained grey sandy soils. The soils tend to be highly calcareous at the coast, often underlain by calcrete and susceptible to wind erosion. The study area falls within several protection zones of the Atlantis Aquifer (see Figure 5.5). This aquifer forms an important component of the water supply system for the City of Cape Town. Groundwater levels are between 2 - 12 m below natural ground level, although there are significant seasonal fluctuations. Groundwater flow is in a south-westerly direction. 5.2.3 FLORA 5.2.3.1 General description The southern area lies at the boundary of the Swartland and Sandveld bioregions. Five vegetation types occur along the proposed pipeline route and at the onshore facility sites (see Figure 5.6), including: Cape Seashore Vegetation (Least Threatened): This vegetation type is an azonal vegetation type associated with the mobile or semi-mobile dunes in a saline environment.