2 Methodology
This project presents an overview of current and potential demands for water from the Waitaki Catchment excluding the water used for hydro-electricity, irrigation and stock. The report includes consumptive water demands in the following use type categories:
- community and domestic water supplies
- private potable water abstractions (whether existing or permitted under present planning rules)
- commercial and industrial (other than those arising within municipal supply areas)
- recreation and tourism.
The project requires an assessment of the demands arising from local in-catchment activities and also from out-of-catchment activities. By far, the majority of data available has been for demands arising from within the catchment and therefore we believe estimates of demand from outside the catchment will be less certain.
The data sources used for identifying the location, scale and nature of current demands were current consent database information, water supply records from district councils, Statistics New Zealand population data and land parcel information from the Land Information New Zealand Digital Cadastral Database (LINZ DCDB).
Where possible, demands have been assessed as:
- peak day demand flow rate [Where peak daily demand flow rates have been calculated, derived or inferred they are assumed to be a flow taken at constant rate over a 24-hour period. The instantaneous rate of take may be greater than the peak daily rate, but we have assumed consumers have on-site storage available to meet instantaneous peaks in demand.] measured in litres/second (l/s)
- average annual demand volume measured in cubic metres per annum (m3/year).
Our original proposal was to evaluate the current water takes from the Waitaki Catchment based on consents information, supported by an assessment of other unregistered water users. This method is referred to as Method 1: Assessment of resource consent data, in the flow chart presented as Figure 2.1.
However the original approach presented a number of problems and an alternative method was sought to act as a double check for peak flows and annual volumes and to fill in the gaps where consent information was not available. This method is based on recorded flow data and population and is referred to as Method 2: Assessment of population and recorded flow data, in the flow chart presented as Figure 2.1.
These two methods will be discussed in greater detail in sections 2.2.2.1 and 2.2.2.2.
The larger Waitaki Catchment has been divided into 16 smaller catchments. These 16 catchments represent clusters of sub-catchments defined in the ECan GIS database. These catchment boundaries have been based on criteria provided by the consultants completing the regional economic analysis.
Figure 2.1 below presents the catchments of the significant catchment analysis.
Interviews and discussions with local and regional authorities formed a significant part of this project and are outlined in Section 3.0.
Results summary tables and a brief discussion are included in Section 5.0, while detailed spreadsheets of results are included in Appendices A and B.
2.1 Methodology for demand modelling
The flow chart below outlines the overall approach to quantifying current and future demands included in the models. Two alternate methods were required to complete the demand assessment.
2.2 Assessment of current water demands
2.2.1 Current consumptive demands
As a brief introduction to the scale of water demands being considered in this project a number of charts are presented below. Data was sourced from Environment Canterbury consents using primary use codes.
When water take consents are issued they may contain allocations to a number of different uses. For example, a consent may be issued primarily for irrigation; however a smaller part may also be designated for rural farm supply (stock water) and an even smaller part may be designated for industrial cooling water. Hence this consent would have primary, secondary and tertiary allocations ranked in order of magnitude. The primary use will dominate the overall water use but the secondary use may be significant.
Figure 2.2.1a: Summary of consumptive demands from Waitaki Catchment for stock water, irrigation, community/domestic, industrial/commercial and recreation/tourism
Figure 2.2.1b: Proportion of surface water takes vs groundwater takes in Waitaki Catchment - community/domestic, industrial/commercial and recreation/tourism
Figure 2.2.1c: Proportion of project use types (community/domestic, industrial/ commercial and recreation/tourism) by resource consent primary use codes
Note that the figures presented above have used resource consent data sorted by the consents primary use code (Use_1) with the exception of the estimated demand for the freezing works at Pukeuri.
Figure 2.2.1a illustrates the majority of consumptive water demands in existing resource consents are for irrigation and stock water, approximately 99.9 percent by daily flows. Thus our project is concerned with a relatively small proportion of the total water consented from the Waitaki Catchment.
As shown in Figures 2.2.1b and 2.2.1c, when considering consumptive water demands for the uses of water covered by this project they are primarily taken from surface water (87 percent) and primarily used for community and domestic water supply (75 percent). Industrial/ commercial and tourism/recreation have lesser proportions of 20 percent and 5 percent respectively. Although industrial uses appear to be significant, this is skewed somewhat by the presence of one major industry (the freezing works at Pukeuri) that accounts for approximately 75 percent of the consented industrial demand.
2.2.2 Current demand identification
The data sources used for identifying the location, scale and nature of current demands were current consent database information, water supply records from district councils, Statistics New Zealand population data and land parcel information from the Land Information New Zealand Digital Cadastral Database (LINZ DCDB).
Where possible, demands have been assessed as:
- peak day demand flow rate [Where peak day demand flow rates have been calculated, derived or inferred they are assumed to be a flow taken at constant rate over a 24-hour period. White the instantaneous peak take can be higher, this approach assumes consumers have on-site storage available to meet the instantaneous peak in demand.] measured in litres/second (l/s)
- average annual demand volume measured in cubic metres per annum (m3/year).
Our original proposal was to evaluate the current water takes from the Waitaki Catchment based on consents information, supported by an assessment of other unregistered water users. However, this presented a number of problems and an alternative method was sought to act as a double check for peak flows and annual volumes and to fill in the gaps where consent information was not available. These two methods will be discussed in greater detail later in this section.
Figure 2.2.2 on the following page presents:
- catchments defined for the project
- location and type (surface or ground water) of consents used in Method 1: Assessment of resource consent data
- communities and other consented water takes used in Method 2: Assessment of population and recorded flow data
As community consents make up the bulk of consent flow information we have included individual consent references on the figure that can be linked to the spreadsheets in Appendix A.
2.2.2.1 Method 1: Assessment of resource consent data
Establishing consents to be included
Consents are issued for one or more uses, many of which are not water consuming. For the purpose of this project we have included only the consent codes that are specific to the use type categories in this project. A list of ECan GIS consent codes can be found in Appendix E.
For assessing demands from current consents we originally assumed the primary use code (Use_1) from the consent database was adequate to classify the water use in to the project use type categories (community/domestic, industrial/commercial and recreation/tourism). However the secondary use codes (Use_2) of resource consents may also contain significant allocations.
Issues with using only the primary use codes were noticeable in rural water supply schemes which are primarily for stock water but also secondly for domestic consumption. Similarly, schemes that are primarily allocated for irrigation may also have components for community and other uses. An example of this is the Lower Waitaki Irrigation Company scheme supplying the community of Oamaru and the freezing works at Pukeuri.
As a result we endeavoured to incorporate the community and domestic water supply secondary use types from irrigation and stock water consents. However, this was not a simple process because the flows for secondary uses are only components of the total consent value and are not explicitly stated. Peak flows and daily maximum demands have therefore been estimated based on available information.
Other use types such as industry/commercial and tourism/recreation are also likely to be included as secondary uses in consents. However, they are assumed to be minor quantities in relation to community water supply.
The summary of current demands based on an assessment of consented takes and additional demands from unconsented takes via an assessment of land parcels is presented as summary tables in Appendix A.
Limitations of consent data
The consent data presented maximum allocations in terms of peak flows (l/s) and maximum daily volume (m3/d).
Peak flows are assumed to be in terms of instantaneous flow rates and will account for the maximum pumping capacity of specific equipment at a site. Some systems may operate on demand at very high flow rates during the day. Other systems may pump to storage over a 24-hour period at moderate flow rates and some systems may operate only at night. Because it is unlikely that all consumers will be demanding water at the same time the sum of the peak flows on a catchment basis is likely to overestimate the potential peak flow.
Maximum daily volume is assumed to be the volume taken on a peak demand day over 24 hours. These figures have been adjusted to an average day demand for calculating annual volumes. These annual adjustments have been calculated by project use type using a brief analysis of typical seasonal variation patterns. Charts of these patterns and annual adjustment figures used for this project are included in Appendix D.
A limitation in using consented maximum volumes for estimating current demands is that the consent may not be currently exercised to the full value. Rather the consent value will only be reached towards the end of the consent period. In the case of community supplies, this may be up to 35 years in the future. Because it would be difficult to accurately determine the proportion of the consent value currently being exercised it is likely that this method will overestimate the potential annual demand.
A limitation of using consents data for total water demand estimation is not all water users hold a current consent. There was a significant difference between the number of consents and the number of farms and land parcels (excluding residential) in the Waitaki Catchment. A way of accounting for this difference is described in Section 2.2.2.3.
2.2.2.2 Method 2: Assessment of demand population and recorded flow data
Because of issues with consent information the community demand calculated from consents is likely to be overstated. We have found an alternative method using recorded flow figures and resident population data. This is also the only method used to estimate out-of-catchment demands. A variation of this method (not population-based) was used to estimate demand for industrial/commercial and recreation/tourism uses.
Methodology
Mackenzie, Waimate, Waitaki, Timaru and Dunedin district/city councils provided recorded flow data for communities they considered likely to require additional water from a Waitaki source. Coupling this information with resident population data provided by Statistics New Zealand we were able to determine an average daily flow on a per person basis. Peak day factors for each community were derived from records of peak day flows.
This information enables us to calculate both peak day flows and a probable annual demand. This method is likely to yield a good approximation of the current demands, as they are specific for communities based on recorded flow data. Where recorded flow data were not available we have inferred that per person flows and peak day factors will be similar to those of nearby communities.
To account for demands arising outside of community schemes we have used a method described in Section 2.2.2.3.
Derived average daily flows (ADF) and peak day factors (PDF)
Average daily flow is calculated from the total water volume used in a year divided by an appropriate timescale (ie, litres used per year/seconds in a year = l/s). To estimate the water used on the peak day of the year a multiplier must be calculated. This is called a peak day factor.
The recorded flows method assumes that peak day demands are taken at a constant rate over a 24-hour period. This assumes consumers, in order to meet the peak instantaneous demand, have on-site storage. For most community supplies and large industries this will be true however it is likely that this will have an averaging effect and tend to understate the actual instantaneous peak flows from the catchment.
The accuracy of community demand estimates will be affected by the assumed demand per person. The main factors influencing the demand per person figures are likely to be:
- the resident population figures from Statistics New Zealand
- the amount of leakage and losses within the reticulated network
- local climate and desire for garden watering during dry/hot periods.
These three points are briefly discussed below.
Resident population figures have a significant impact on the daily flow figure. The communities of Tekapo and Twizel have significant holiday and visitor populations and the water demand from these uses is significant. Hence the total demand distributed over the resident population becomes inflated. This is not a problem for assessing future growth provided that the relative proportions of resident to holiday and visitor populations do not vary significantly in the future.
Leakage and losses in the reticulation of small townships are likely to be significant and may vary in the range of 20 to 50 percent of total water taken for supply. This may explain why water use in these community systems is so high.
The local climate is likely to have a substantial effect on the total water used by a community. Inland the predominantly dry and hot summer climate is likely to result in increased garden watering. This is a significant demand and a large contributor to the summer peak day demand factor (estimated between 2.0 and 2.7 for Waitaki communities).
Average daily flows (ADF) per resident population ranged from 0.0364 l/s in Tekapo to 0.010 l/s in the coastal downland communities of the Timaru and Dunedin districts. These figures appear to be conservative and there was a consistent trend of increasing water use with distance inland.
The following peak day factors were calculated for the communities and detailed tables are shown in Appendix B:
- inland resorts (Tekapo and Mt Cook), peak day factor = 2.0
- inland Mackenzie Basin (Twizel, Lake Ohau, Omarama to Kurow), peak day factor = 2.7
- Waitaki mid-catchment (Duntroon to Glenavy), peak day factor = 2.5
- other coastal north and south of the Waitaki, peak day factor = 2.0.
An indicative example of how demand may be apportioned for a typical community is shown below in Table 2.2. An average daily flow (ADF) of 0.01 l/s/resident equates to 864 litres per average day per person. A typical breakdown of daily demand may be as follows:
Table 2.2: Typical breakdown of demand for a community with ADF= 0.01 l/s/resident
|
Demand description |
Typical percentage of total |
Demand proportion |
|---|---|---|
|
Resident domestic |
35% |
295 |
|
Industrial/commercial |
25% |
219 |
|
Tourism/recreational |
15% |
130 |
|
Losses and leakage |
20% |
175 |
|
Other public uses |
5% |
45 |
|
100 |
864 |
The typical demand proportions presented above are for an indicative community only. Actual demand proportions will vary significantly between communities.
Assumptions were made about the industrial/commercial and tourism/recreation activities identified by the consents assessment to derive appropriate peak day factors and probable annual demands. These activities were then assessed by average daily flows and a summary of these figures is presented in Appendix B.
Assumed out-of-catchment demand
Waimate, Timaru, Waitaki and Dunedin district/city councils indicated that some communities that are not presently supplied from the Waitaki Catchment may require water from this source to supply a portion of their current water needs. To represent this demand we have included a portion of these communities estimated current water demand as the initial base demand for future projections. These demands are summarised in spreadsheet form in Appendix B.
Brief details are also included in the notes column of the spreadsheets. These notes relate to the assumed proportion of a community's total demand that will be provided from the Waitaki. We have not rigorously investigated whether these communities will have no other choice but to use water from the Waitaki.
2.2.2.3 Private potable takes
Although the majority of water for domestic supply is likely to occur in the various communities this will not account for all the demand. A number of consumers will rely on water from private bores or surface water that may not hold a current consent.
For consistency we have adopted the same method for including private potable takes in the consent demand data and the recorded flows data to assign additional demand.
For adding the private potable demands we have summarised the land parcels within the catchment from the Land Information New Zealand (LINZ) DCDB and the Ministry of Agriculture and Forestry's Agribase. All farms and rural residential sized properties (parcels greater than 1 ha) were assumed to require a supply independent of community reticulation. Table 2.2.2.3 below summarises the flows and demands assumed for each private take.
Table 2.2.2.3: Estimated demand from a rural residential or farm private take
|
Details |
Estimated flow |
Assumptions |
|---|---|---|
|
Demand per person |
0.022 (l/s/p) |
Median per person demand estimated for the catchment |
|
People per farm (or lot) |
2.4 |
Statistics New Zealand average number per household |
|
Average daily flow |
0.0528 (l/s) or 4,562 (l/day) |
|
|
Peak day factor |
2.5 |
Median peak day factor estimated for the catchment |
|
Peak day flow |
0.132 (l/s) or 11,405 (l/day) |
Note: These figures are deemed to be a conservative estimate for the Waitaki Catchment.
Figure 2.2.2.3 presented on the following page shows the land parcel data that was included in the Land Information New Zealand Digital Cadastral Database (LINZ DCDB) assessment of private potable demands (only rural residential and farm-sized parcels were included in demand estimations).
These demands are assumed to be additional to the figures estimated by either calculation Methods 1 or 2 (consents or population and recorded flows). A description of the land parcels identified using this method is included in Appendix F.
2.2.2.4 Issues to consider under the Resource Management Act
The Transitional Regional Plan for Canterbury and the proposed Canterbury Natural Resources Regional Plan (NRRP) Chapter 5 - Water Quantity contain rules that allow a limited amount of water to be taken without resource consent as a permitted activity. Under both plans, diverting and using water from surface water is permitted on a per property basis. Peak flows up to 5 l/s and 10 m3/day are permitted under the rules subject to conditions.
Assuming that the conditions were satisfied for all properties outside a reticulated supply (excluding residential size lots from the LINZ DCDB), this means there is a potential for landholders to take, as of right, up to 10 m3/day.
Section 2.2.2.3 suggests that on a peak demand day the rural household water consumption could be approximately 11,405 litres, which is approximately 10 m3/day. This observation is important because it suggests that the household would use all water available as a permitted take with no allowance remaining for stock water on peak days. Therefore we have not added this demand into the current demand estimates as it is already counted.
2.2.3 Annual demand adjustment factors
Annual demand adjustment factors for assessment of consent volumes
For Methods 1 and 2, annual demand adjustment factors were required to convert from maximum daily flows to average daily flows. These figures were determined from recorded flows or provided by industry representatives as a description of seasonal variation patterns.
The following adjustment factors were calculated. More detailed information is shown in the charts in Appendix D.
- industrial/commercial, a factor of 0.56
- tourism/recreation, a factor of 0.38
- community and domestic supply, a factor of 0.50.
The average annual adjustment factors for industry and commercial have been derived from seasonal patterns for the largest industries in or near the Waitaki Catchment. As other industries are unlikely to have average annual water use higher than these industries we believe that 0.56 is a conservative estimate.
In the Waitaki Catchment, tourism and recreation demands are primarily snow making. For this reason we have adopted the snow making average annual adjustment factor of 0.38 to represent this activity group. Many tourism specific demands such as visitor accommodation will be incorporated in the community and domestic demands.
Community average annual demand will vary with peak day factor. Peak day factors of 2.0 were towards the lower end of the range for Waitaki communities and this assumes reasonably constant water use throughout the year. This means that for consent data an annual factor of 0.5 should be adopted. Since small communities generally have peak day factors greater than 2.0 using this figure will tend to overstate the annual volumes required and is a conservative approximation.
2.3 Demand growth projections
Statistics New Zealand population growth projections for the Waitaki Catchment are likely to be similar to those for South Canterbury. A figure of the projections for the Timaru district is shown below as Figure 2.3a.
Current trends assume the population will either:
- continue the present slow steady decline (low projection)
- flatten off to no growth (static) and then resume declining from 2006 (medium)
- slow growth that will plateau around 2009 (high).
These projections imply that water demand from population will remain more or less static in the medium term. However the growth potential of the region due to the flow-on effects of irrigation, industry and the development of tourism and recreation sectors cannot be discounted. For these reasons we believe that using national population growth figures will yield a more appropriate estimate of growth in the region for use in this project.
Population data was obtained from Statistics New Zealand. The base for future population projections is the estimated resident population of New Zealand on census night, 30 June 2001. Alternative projection series have been produced incorporating different assumptions on the future fertility, mortality and migration of the population. We have assumed three of these projection series (series 1, 4 and 6) will estimate the low, medium and high population growth ranges.
Charts of the growth scenarios produced by Statistics New Zealand are shown below in Figure 2.3b.
Charts of the growth scenarios and the assumptions used by Statistics New Zealand are contained in Appendix C.
2.3.1 Generation of demand growth scenarios
Growth scenarios for community and domestic use types
The growth scenarios used for community and domestic are the low (series 1), medium (series 4) and high (series 6) growth series projections to generate normalised growth curves.
Figure 2.3.1a: Normalised growth projections for the period 2001 to 2051, community and domestic use types
Growth scenarios for industry/commercial and tourism/recreation use types
The growth scenarios used for industrial and tourism are a combination of the Statistics New Zealand growth curves and independent data on economic growth. The economic growth data may be more representative of the way in which industry and tourism activities will grow differently from domestic population. Economic growth data was assessed from the "high production" growth scenario of the agriculture production input-output analysis supplied in the regional economic analysis of use of water from the Waitaki Catchment (Harris Consulting et al, 2004). We have assumed that demand for water is proportional to economic growth.
Figure 2.3.1b: Normalised growth projections for the period 2001 to 2051, industrial and tourism use types
The low projection was assumed to be the Statistics New Zealand projection based on low fertility, high mortality and low immigration estimates (series 1). The medium projection was a curve developed from the economic development data. The high growth projection was assumed to be a composite curve of the maximum values for the economic development data and the Statistics New Zealand population projections based on medium fertility, mortality and immigration (series 6).
2.4 Summary of demand inputs and outputs
Summary of demands calculated by Method 1: Assessment of Resource Consent Data plus Private Potable Takes can be found in:
- Appendix A. Potential water demands from significant catchments - consents data.
Summary of demands calculated by Method 2: Assessment of Recorded Flow and Population Data plus Private Potable Takes can be found in:
- Appendix B. Potential water demands including out-of-catchment - recorded flow and population data.
