Assessing the spatial, temporal and depth variation using electrical conductivity in Cape Flats Aquifer, Western Cape, South Africa By Danica Carnow 3244225@myuwc.ac.za Supervisors: Dr. T.O.B Kanyerere and Prof. Y. Xu UNESCO Chair on Groundwater Wednesday, 11t h November 2015
PRESENTATION OUTLINE Study Area Map with Sampling Sites Conceptual Model Of Groundwater System For Cape Flats Focus Of The Study Data Collection and Analysis Methods Key Results Discussion Of Results Conclusion UNESCO Chair on Groundwater 2 Wednesday, 11 November 2015
Study Area Map with Sampling Sites Figure 1. Location of sampling sites in Cape Flats study area UNESCO Chair on Groundwater 3 Tuesday, 15 th September 2015
Hydrogeological Conceptual Model of Groundwater Salinity System for Cape Aquifer Figure 2. Conceptual model of the groundwater salinity system of the Cape Flats aquifer unit (based on information retrieved from literature and field observation) UNESCO Chair on Groundwater Wednesday, 11 th November 2015 4
Focus of the Study Main Aim: The aim of this study is to provide spatial status of electrical conductivity profiling as an indicator of salinity levels in the Cape Flats aquifer which will improve knowledge and provide understanding of salinity variation in the Cape Flats aquifer. Objectives: Describe the groundwater quality system using an initial hydrogeological conceptual model which will be refined during my MSc studies Determine salinity levels of groundwater in Cape Flats aquifer by using specific depth sampling technique Assess the suitability of groundwater quality in the Cape Flats aquifer for irrigation use using a hydrogeochemical analysis method with focus on SAR UNESCO Chair on Groundwater 5 Wednesday, 11 th November 2015
Research Problem The extent to which groundwater salinity levels vary spatially, temporally and with depth in the Cape Flats aquifer is little understood. The main concern regarding high salinity in groundwater is the degradation and impairment of water quality for irrigation use. Research Question To what extent does salinity levels vary in groundwater of Cape Flat Aquifer with respect to space, time and depth? UNESCO Chair on Groundwater 6 Wednesday, 11 th November 2015
Data Collection and Analysis Methods Data collection entailed depth- specific depth sampling and Low-Flow Purging in five sampling sites in Cape Flats Graphical methods were used to display data and descriptive statistics were used to describe trends UNESCO Chair on Groundwater Wednesday, 11 th November 2015 7
Key Results 2500 2000 Electrical Conductivity (µS/cm) 1500 1000 500 0 0 5 10 15 20 25 30 Distance away from coast (Km) Figure 3. Spatial variation of electrical Figure 4. Electrical conductivity (µS/cm) versus distance conductivity (µS/cm) for study sites in away from False Coastline (Km) the Cape Flats aquifer UNESCO Chair on Groundwater 8 Wednesday, 11 th November 2015
Key Results Electrical Conductivity (µS/cm) Sampling Standard points August September October Average Deviation Lentegeur 1665 2353 2350 2122,67 ± 396,35 Westridge 694 873 789 785,33 ± 89,56 Philippi 1207 1130 1257 1198 ± 63,98 University of the 325 345 356 342 ± 15,72 Western Cape Bellville 892 1 690 1082 1221,33 ± 416,85 Average for all 956.6 1278.2 1166.8 1133.86 ± 163,31 sampling points Table 1. Temporal variation of electrical Figure 4. Boxplots of temporal variation of electrical conductivity (µS/cm) for August, September and conductivity (µS/cm) for the Cape Flats aquifer during October sampling period August, September and October sampling UNESCO Chair on Groundwater 9 Wednesday, 11 th November 2015
Key Results Figure 5: Schematic diagram of borehole depth variation at study sites and electrical conductivity (µS/cm) in the Cape Flats aquifer UNESCO Chair on Groundwater 10 Wednesday, 11 th November 2015
Key Results 45 Depth- Sampling Average EC Study site specific 40 point (µS/cm) sample (m) G46051 35 Lentegeur BG00139 9 2122.67 30 Depth ( m) 25 Westridge G32691 15 785.33 20 Philippi BG00153 16 1198.00 UWC 4 15 G32691 BG00153 University 10 of the UWC 4 19 342.00 BG00139 5 Western Cape 0 0 500 1000 1500 2000 2500 Bellville G46051 39 1221.33 Electrical Conductivity (µS/cm) Figure 6. Electrical conductivity (µS/cm) variation Table 1. Average electrical conductivity ( µS/cm) with depth for sampling sites in the Cape Flats aquifer of depth-specific sample for study sites in Cape Flats aquifer UNESCO Chair on Groundwater Wednesday, 11 th November 2015 11
Discussion of results Main findings suggest that: - salinity decreases with increasing distance from the shoreline/ coast agreeing with theory -temporal variation displays a general trend in which salinity increases with time which agrees with theory -depth variation of salinity has revealed a trend whereby salinity increases with decreasing depth disagreeing with theory Relation with previous studies - spatial and temporal variation agrees with studies conducted by Kortasi and Jorgensen (2001) and Aza-Gnandji et al (2013) (high salinity levels maybe be attributed to seawater mixing and residence time causing mineralisation) -Depth Variation agrees with a study conducted by Mitra et al (2007) as increasing salinity was attributed to anthropogenic activities 12 UNESCO Chair on Groundwater Wednesday, 11 th November 2015
Discussion of results Strengths – ability to constrain salinity level stratification as the aquifer is heterogeneous (geology varies with respect to depth and space) - little is known about the variation of quality with depth in the Cape Flats aquifer thus the study is able to provide - insight into this Weaknesses - sampling time and sample size - require multiple boreholes, screened at multiple depths - the study could not constrain the source causing the variation Implications - High salinity levels may have negative implications for irrigation activities and agricultural practices as -Negative implications for serving as a supplementary resource for drinking water supply - 13 UNESCO Chair on Groundwater Wednesday, 11 th November 2015
Conclusion It may be deduced that salinity levels in groundwater of the Cape Flats aquifer varies with respect space, time and depth which concomitantly influences quality. This means groundwater quality (in terms of salinity) deteriorates with decreasing depth (anthropogony), with decreasing distance from the shore (seawater intrusion) and with time (mineral dissolution). 14 UNESCO Chair on Groundwater Wednesday, 11 th November 2015
THANK YOU UNESCO Chair on Groundwater 15 Wednesday, 11 th November 2015
Recommend
More recommend
