All local authorities must identify their significant infrastructure issues for the period covered by the strategy (at least 30 years). The document must identify the principal options for managing those issues and the implications of those options.
Here are some useful links. I found the first document (the fictional Matawhero District Council example) particularly useful for understanding what the strategy needs to achieve:
Relevant sections of the Local Government Act 2002
Part 1, clause 9 - Financial strategy and infrastructure strategy
A long-term plan must include a local authority's financial strategy described under section 101A and infrastructure strategy described under section 101B.
101B Infrastructure strategy
(1) A local authority must, as part of its long-term plan, prepare and adopt an infrastructure strategy for a period of at least 30 consecutive financial years.
(2) The purpose of the infrastructure strategy is to--
(a) identify significant infrastructure issues for the local authority over the period covered by the strategy; and
(b) identify the principal options for managing those issues and the implications of those options.
(3) The infrastructure strategy must outline how the local authority intends to manage its infrastructure assets, taking into account the need to--
(a) renew or replace existing assets; and
(b) respond to growth or decline in the demand for services reliant on those assets; and
(c) allow for planned increases or decreases in levels of service provided through those assets; and
(d) maintain or improve public health and environmental outcomes or mitigate adverse effects on them; and
(e) provide for the resilience of infrastructure assets by identifying and managing risks relating to natural hazards and by making appropriate financial provision for those risks.
(4)The infrastructure strategy must outline the most likely scenario for the management of the local authority’s infrastructure assets over the period of the strategy and, in that context, must--
(a) show indicative estimates of the projected capital and operating expenditure associated with the management of those assets--
(i) in each of the first 10 years covered by the strategy; and
(ii) in each subsequent period of 5 years covered by the strategy; and
(i) the significant decisions about capital expenditure the local authority expects it will be required to make; and
(ii) when the local authority expects those decisions will be required; and
(iii) for each decision, the principal options the local authority expects to have to consider; and
(iv) the approximate scale or extent of the costs associated with each decision; and
(c) include the following assumptions on which the scenario is based:
(i) the assumptions of the local authority about the life cycle of significant infrastructure assets:
(ii) the assumptions of the local authority about growth or decline in the demand for relevant services:
(iii) the assumptions of the local authority about increases or decreases in relevant levels of service; and
(d) if assumptions referred to in paragraph (c) involve a high level of uncertainty,--
(i) identify the nature of that uncertainty; and
(ii) include an outline of the potential effects of that uncertainty.
(5) A local authority may meet the requirements of section 101A and this section by adopting a single financial and infrastructure strategy document as part of its long-term plan.
(6) In this section, infrastructure assets includes--
(a) existing or proposed assets to be used to provide services by or on behalf of the local authority in relation to the following groups of activities:
(i) water supply:
(ii) sewerage and the treatment and disposal of sewage:
(iii) stormwater drainage:
(iv) flood protection and control works:
(v) the provision of roads and footpaths; and
(b) any other assets that the local authority, in its discretion, wishes to include in the strategy.