Long-term land treatment constraints for hyporheic zone management

Author: Alana Bowmar, Katy Grant, and Azam Khan

Source: Pattle Delamore Partners Ltd

Year: 2019

Abstract

The introduction of the National Policy Statement for Freshwater Management (NPSFM) is requiring regional councils to start developing the framework for addressing the implementation of freshwater management units for all catchments under their control (Ministry for the Environment [MfE], 2017). This in turn is creating additional elevated regulatory pressure to improve water quality, especially for catchments that drain agricultural farmland.

When wastewater is applied on the same land, as part of a land treatment system, the controls required are increased to ensure the outcomes sought for the NPSFM are maintained at all times.

As land treatment systems have been progressively established, there has undoubtedly been some examples of poor land treatment practices that have the potential to quickly result in negative environmental impacts. Particularly, if the shallow groundwater below the land treatment is in close proximity and/or directly connected to hyporheic zone where the groundwater and surface waters interact.

Surface water quality in the vicinity of an existing long-term land treatment system showed direct connection between shallow groundwater and surface water, resulting in a comprehensive review of current practices and significant tightening of nitrogen loading onto land. There has been a re-think of the likely sustainable level of nitrogen application despite nutrient modelling supporting a continued moderate to higher nitrogen application.

This paper discusses the importance of hyporheic zone management. It also assesses and discusses how an existing land treatment system receiving treated wastewater and other nitrogenous product inputs has quickly become a considerable water quality issue in the hyporheic zone and downstream surface water receiving environment.