5 Results and Recommendations
The tables below show the results from the demand modelling for the various growth scenarios. The tables have been arranged to accommodate data calculated by both estimation Methods 2 and 1 (population/recorded flows and consents). This is indicated where a cell contains a range of values. Where a cell contains a single value, this has been calculated by Method 2 only.
The row designated 'current total' sums the demands within the Waitaki Catchment and the three out of catchment demands that are currently served (Waikakahi and lower Waihao rural schemes and Oamaru).
The row designated 'future out of catchment' incorporates the Timaru and Waitaki districts. While the row designated 'future out of catchment including DCC' represents Dunedin City district.
Because the consents method (Method 1) does not include future out-of-catchment demands, the last 'total' row is a composite total. The 'future out-of-catchment' and 'future out-of-catchment including Dunedin City Council' rows are added to the previous consents total to get the final result.
Table 5.1: Summary of current and projected demands from the Waitaki Catchment (low growth scenarios)
Table 5.2: Summary by current and projected demands from the Waitaki Catchment (medium growth scenarios)
Table 5.3: Summary of current and projected demands from the Waitaki Catchment (high growth scenarios)
Table 5.4: Summary of peak flows from the Waitaki Catchment (high growth scenarios)
View summary of peak flows from the Waitaki Catchment (high growth scenarios) (large table)
Table 5.5: Summary by use type within Waitaki Catchment (high growth scenarios - consents data only)
|
Location of demand |
Current peak flow range |
Current annual range |
Projected 2051 peak flow range |
Projected 2051 annual range |
|---|---|---|---|---|
|
Industrial/commercial |
212.6 |
3589 |
317.0 |
5,352 |
|
Tourism |
64.0 |
352 |
95.4 |
524 |
|
Community |
810.0 |
9930 |
1208.0 |
14,808 |
|
Private potable |
86.0 |
1081 |
128.0 |
1611 |
|
Total |
1172.6 |
14952 |
1748.4 |
22,295 |
5.1 Discussion of the results
Given the scale of the assessment and diverse nature of potential demands it is difficult to estimate the level of accuracy that has been obtained. Because this project has been undertaken to establish the order of magnitude of demands using available information, we suggest that a relatively wide confidence interval is allowed when interpreting the results. As such an interval of -25% to +50% may be appropriate.
5.1.1 Agreement of estimation methods
The current annual volumes obtained by two methods (consents and recorded flows/population) were 12,738,000 m3/year and 13,856,000 m3/year respectively, and these agree to within 8%.
Peak flows by the consents method were approximately 1.4 times higher than by the recorded flow/population method as expected. As discussed in Section 2, this is due to the recorded flow/population method approximation of taking peak day demand to storage over a 24-hour period in contrast to the instantaneous peak demand calculated by summing consent data.
Because we are considering demands from the catchment as a whole, the recorded flow/population method is valid because there will be some averaging that occurs. As a result it is likely that the actual peak flow from the Waitaki Catchment will lie somewhere between the two figures calculated. Hence we have included a range of peak flows in the tables above.
5.1.2 Future Waitaki Catchment demand results
As estimated by this project, the low and high growth scenarios for all areas serviced with water from the Waitaki Catchment may require between 26 million and 36 million cubic metres of water annually for the use types included in the project.
Considering the existing trends of population decline in the Waitaki and adjacent districts these figures rely on a significant change in terms of attracting more people and industries to the region. In the event that this trend does not change, then it may be possible that the future water demand could remain at levels similar to what they are today, around 12 million to 14 million cubic metres annually.
5.1.3 Future out-of-catchment demand results
As stated in Section 3, future out-of-catchment demands were estimated using Method 2: Assessment of recorded flows and population data. Represented by rows four and five in the summary tables 5.1 to 5.3 as 'future out-of-catchment' and 'future out-of-catchment (including DCC)', these demands represent communities and industries that may require water from the Waitaki catchment in the future as expressed by the territorial local authorities.
Considering the low and high growth scenarios, these areas may require between 11.7 million and 15.4 million cubic metres of water annually for the use types included in the project. These estimates are the least certain because of the assumptions that underpin them and these are discussed below.
Future out-of-catchment demands are estimates of the water that could be used if new takes were established from the Waitaki. These takes would service communities within the Mackenzie, Timaru, Waimate and Waitaki districts and Dunedin city that presently do not have access to water from the Waitaki. Examples of the possible nature of supply are:
- supply to the Mackenzie and Timaru districts from Fairlie to Timaru, possibly from a source below Lake Tekapo
- supply to the Waitaki district from Oamaru to Palmerston in the south, possibly from a piped extension of the current Lower Waitaki Irrigation Company scheme
- supply to Dunedin from a similar piped extension of the Lower Waitaki Irrigation Company scheme. It may be more likely that this demand would be supplied from an extension of the Dunedin City Council water supply scheme if it is required.
We have assumed that supplying districts from the Waitaki by some method will be feasible and in the general proportions indicated. Notes regarding how demand was estimated are included in the summary spreadsheets of Appendix B.
5.1.4 Relevant additional research
There are two projects in progress that may provide further information supporting the conclusions and recommendations made in this report. The two projects are:
- Water and Sanitary Services Assessment of Council Water and Wastewater Assets, required under the Local Government Act 2002
- Effect of Irrigation on Economic Development in South Canterbury - Post Construction of Opuha Dam, to be commissioned by Aoraki Development Trust.
