Providing enforceable conditions to ensure consented water quality outcomes are achieved during earthworks has received increasing attention over recent years. There has been a move by some regulators towards imposing rigid water discharge limits for sediment control measures, often based on total suspended solids (TSS) and sometimes including turbidity and / or clarity. These are consistently imposed alongside conditions that require the adoption of erosion and sediment control measures and plans that are consistent with the local best-practice erosion and sediment control guidelines. But here's the catch. Best practice sediment retention devices (e.g. ponds and decanting earth bunds) cannot comply with rigid standards across all rain events. Device performance on which consent assessments are based are average efficiencies across a rainfall event and across a range of rain events. So the conditions imposing limits are self-defeating and are unlikely to the meet the Newbury test (can it be reasonably complied with?).
The legislated move towards standards and limits through the National Policy Statement for Freshwater Management (NPS:FM) and the Natural and Built Environment Bill (NBE) has added further challenge to earthworks and associated temporary discharges of sediment to receiving environments.
This paper describes in detail how sediment retention devices operate, the most effective means of ensuring the effects remain within the consented envelopes, and how performance can be conditioned through response triggers rather than hard limits. It also offers ideas on how regional plan provisions can be promulgated in the new legislative regime to accommodate the realities of earthworks.
Thursday 2 November
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Director, SouthernSkies Environmental
Michael has 25 years experience in resource management and planning, with technical expertise in erosion and sediment control and resource use. Michael is an independent hearing commission; sitting on many council hearings, two boards of inquiry, and three fast-track consent applications. His experience encompasses council regulatory roles and private sector, including technical design, consenting, policy, guideline development and training.