However, Xu et al. Wide variations in estimates ranged between and mm per annum from these methods however, it has been accepted that the scale of the recharge study often dictates the most appropriate methods to be used to determine aquifer recharge. Concerns were raised for review of recharge estimates in the Kammanassie area due to the continual decline of groundwater levels in the Vermaaks River Wellfield from Temperature increases are worldwide however; precipitation decreases or increases are highly variable in time and space.
The Mann-Kendall Trend test was applied on historical temperature and rainfall data records over several years. The Trend tests in the study area did show gradual increases in temperature over recent years while generally no significant trends have been observed with precipitation amounts in the TMG area generally. Using the Standard Precipitation Index SPI analysis variations in precipitation patterns were observed such as the intensity, duration and shifts in seasons.
A particularly significant drought period was observed between and for three stations whiles in the fourth, Purification Works East, the drought is reflected between and period figure 2. The low rainfall coupled with abstractions has greatly influenced the continual decline in water levels in the well fields in the KKRWSS area. The results of the SPI analysis in this study have shown that there are wide variations in rainfall records in most of the stations which could be attributed to climate variability.
It is still not very clear if the variations are increasing with time. With the results of the autocorrelation analysis the present trend cannot be used to predict the future trend of rainfall in the region. Higher temperatures would however, increase evapotranspiration which would in turn reduce direct recharge. In the catchment area there have been more drought effects in recent years resulting in reduced recharge which together with groundwater abstraction have resulted in massive groundwater level declines the area.
The major concern in the area has been the decline of water levels. It has been reported that groundwater levels of the production boreholes have been falling since in the Vermaaks catchment. Even though the Vermaaks River wellfield had a fairly good recharge, by the water level decline was approximately 20 m.
By the decline had reached about 30 m and again approximately 40 m by Abstraction rates in the production boreholes have been reset a number of times since the scheme began its operations as the scheme managers battled the high demand for water and low recharge. Costly, high-yielding pumps were installed in the production boreholes to meet this expected yield. Kotze in conducted such recharge and water-balance studies using 74 months of hydrological monitoring data, as well as a re-evaluation of the and aquifer-test data. Kotze estimated that the long-term supply potential of the wellfield is in the order of 8.
Figure 3 is a plot of water levels in the Vermaaks wellfield. VG16 is the only observation borehole which reflects the decline of the production boreholes. With the continued adjustment in abstraction rates the decline of the production boreholes slowed down considerably from about except for the seasonal increases in abstraction rates at high demand periods summer as can be seen from figure 6. The wells are currently being pumped on the average at 5.
Even though some of these springs are ephemeral their existences however have been affected by groundwater abstractions in the catchment. In a report to the Department of Water Affairs, Xu et al. A spring G, 2 km downstream of borehole VG16 and located near the Cedarberg shale outcrop in the Vermaaks valley dried up after the construction of borehole GA in the vicinity in September Further downstream the spring G was affected when a borehole G was drilled through the Cedarberg shale into the Peninsula formation nearby in November The initial high pressure in the borehole was lost eventually.
It has also been reported by Xu et al. The hot spring was located at the intersection of two faults between the TMG and the Bokkeveld group. The drying up of the hot spring has been attributed to earthquakes Tulbagh in , magnitude 6. There were reported losses of many springs in and a few before, in and as a result of low rainfall and borehole constructions. Investigations by Xu et al. The most comprehensive study on the impact of abstractions on spring flow in the Kammanassie area was done by Cleaver et al.
The study grouped 53 springs in the area into 3 categories, 9 were considered most vulnerable to abstractions from the wellfield; 10 were considered as intermediate to vulnerability while the remaining 34 were considered least vulnerable. On the impact of abstraction on vegetation, the study concluded that groundwater abstraction has a significant negative impact on plant water stress at the experimental sites in the Vermaaks River valley and recommended that changes in the water abstraction management could improve the situation.
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Spring losses caused localized impact on spring vegetation and ecosystems. Spring losses were also linked directly and indirectly to the death of four Cape Mountain Zebra on the Kammanassie Mountain between November and August as a result of inaccessibility to natural flowing water sources.
Two artificial watering points were installed to protect the endangered species from extinction Cleaver et al. The problems associated with the sustainable management of the KKRWSS are common to most abstraction schemes of such nature. There are a lot of positive impacts that such schemes bring to the beneficiaries and the general economy of the municipality and the nation as a whole. It is a laudable project that has brought a lot of improvements in the life of several communities, the right to access safe drinking water.
Another positive indication from the project is the fact that the TMG has proven to be a good source of bulk water supply for many purposes. However, the challenges faced by the scheme need to be addressed not only to curb the negative impacts on the environment but also to ensure the long term survival of the scheme itself. In order to deal with the challenges facing the scheme there is a need to categorize them into what can be referred to as reversible and irreversible problems.
Groundwater resources and climate change
The reversible problems are those that can be rectified or reversed because no permanent damage has been caused. On the other hand, an irreversible problem is that which causes permanent damage that cannot be reversed, life of species may be lost. Sometimes the full impact of a problem may not be immediately known until a thorough investigation has been done. There have been suggestions and remedies provided in the past to arrest the critical problems of the scheme but they have been on ad-hoc basis and it is important that a comprehensive approach is taken to maintain a sustainable project that will continue to improve the quality of life to humans and other forms of life.
Some key goals related to groundwater sustainability in the United Kingdom are listed in figure 6. The most important attribute of the concept of groundwater sustainability is that it fosters a long-term perspective to management of groundwater resources. Several factors reinforce the need for a long-term perspective. First, groundwater is not a non-renewable resource, such as a mineral or petroleum deposit, nor is it completely renewable in the same manner and timeframe as solar energy. Recharge to groundwater from precipitation continually replenishes the groundwater resource but may do so at much smaller rates than the rates of groundwater withdrawals.
Second, groundwater development may take place over many years; thus, the effects of both current and future development must be considered in any water management strategy. Third, the effects of groundwater pumping tend to manifest themselves slowly over time. For example, the full effects of pumping on surface water resources may not be evident for many years after pumping begins.
Finally, losses from groundwater storage must be placed in the context of the period over which sustainability needs to be achieved. Groundwater withdrawals and replenishment by recharge usually are variable both seasonally and from year to year.
Linking Climate Change and Groundwater
Viewing the groundwater system through time, a long-term approach to sustainability may involve frequent temporary withdrawals from groundwater storage that are balanced by intervening additions to groundwater storage. The consequence of pumping should be assessed for each level of development; developments such as water-level declines, reduced streamflow, degradation of water quality and loss of dependent ecosystems through vegetation loss or spring loss.
A sustainable groundwater yield which will lead to a sustainable utilization should be expressed in the form of an extraction regime, not just an extraction volume. A regime in this context means a set of management practices that are defined within a specified time and place. In exceptional cases where draw beyond the rate of recharge may be acceptable, it may be only for a specified period, after which time the rate may be less than the rate of recharge to compensate for the loss.
Also under specified circumstances for example, high or low rainfall years the amount of water that may be abstracted may be greater or less than the longer-term value. It has already been stated above that records from the KKRWSS site indicate less than average rainfall for the past few years and one would have expected that abstraction levels would be much less than normal. From figure 3 , it appears that the Vermaaks wellfield is still experiencing water level decline.
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The four production boreholes in the Vermaaks wellfield are functioning well and appear to be producing the bulk of the water supply to the scheme. The following analysis is centered on the Vermaaks wellfield as the main area of concern. As has been stated elsewhere human activities such as groundwater withdrawals change the natural flow patterns and these changes must be accounted for in the calculation of the water budget. Because any water that is withdrawn must come from somewhere, human activities affect the amount and rate of movement of water in the system, entering the system, and leaving the system.
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For a sustainable utilization to occur, a sustainable pumping rate is defined by Eqn. Unless the borehole is drilled close to a reservoir, the induced recharge usually does not occur and reduced discharge dominates. Hence a sustainable pumping rate is given by:. In the case of over-pumping the residual discharge could be reduced to nothing and pumping will be drawing on storage setting up a long-term decline in groundwater level.
The yield of the groundwater system is at the expense of the groundwater discharge and storage components. This is the situation in the Vermaaks River wellfield where borehole levels have seen a long-term decline as shown above. The long-term decline of local groundwater level is an indication of unsustainable groundwater resource depletion.
Table 1 is the results of groundwater budget analysis in the Vermaaks wellfield. The average rainfall records for three stations Parshall, Wildebeesvlakte and V-notch from to were computed for the Vermaaks wellfield. The Peninsula formation window at the Vermaaks wellfield was used as the area of recharge given as 48 km 2. The legal provision of 25 litres per person per day is the basic human need requirement. The same quota was assumed for stock watering.
Related Climate Change Effects on Groundwater Resources
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