CLUES: Modelling the impacts of mitigation on sediment and nutrient loads to the Kaipara Harbour Annette Semadeni Davies Kelly May National Institute of Water and Atmospheric Research

Presentation order What is CLUES?Kaipara Harbour modellingMitigation scenariosResultsWhere to from here?

Introduction to CLUES Modelling system for assessing effects of land use and farm practices at catchment scale Semi-distributed (river reach) Developed for NZ government by NIWA and partners Links existing models within a GIS framework

CLUES Framework Land use change scenarios Choice of result display Choice of river reaches CLUES user interface Farm practice scenarios Stream accumulation and losses Contaminant yields, loads and concs. CLUES freshwater quality model suite - pasture TN and TP OVERSEER 6 ® - horticulture and crops TN SPASMO - microbes, sediment, TN and TP from other sources - contaminant transport SPARROW Contributing freshwater models CLUES geo-database Soil type and drainage class Catchment and drainage network Default land use Climate rainfall River environment classification (REC) Land Resources Inventory (LRI) Land Cover Database (LCDB) Agribase Spatial data sources Nutrient concentrations CLUES estuaries Estuarine hydraulics modelling systems NIWA estuary physiographic data Ocean salt and nitrate concentrations (CSIRO / CARS) Estuarine model and data

Water quality outputs from CLUES For each river reach: Nutrients (TN and TP) Load Concentration Generated yield Cumulative yield Sediment Load Generated yield Cumulative yield E. coli load

Kaipara Harbour Degradation of harbour Sediment accumulation Nutrients Loss of shellfish beds Decline in fisheries Spread in mangroves Stream network 5575 km 2 13,000 river reaches 24 catchments representing 7 river systems and numerous coastal streams

Study purpose Demonstrate use of CLUES in public sphere (Te Uri o Hau) Provide information to support catchment management: Identify contaminant sources Identify areas most suited to mitigation Estimate the reduction of contaminant loads Provide input data for harbour circulation modelling

CLUES default land use scenario CLUES land use 19 land cover classes represented by… % area in each reach sub-catchment Kaipara land use summary Sheep and beef 40% Native and exotic forest 29% Dairy 23% Scrub, urban and other 8%

Mitigation Scenarios 12 Scenarios developed for 3 mitigation strategies Conservation planting Stock exclusion Stock management to limit treading damage Combinations

Conservation planting Retire pasture by planting native vegetation based on land use capability (LUC) classes 6-8 Capacity for long-term sustained LUC classes 7-8 largely forested LUC 6-8 covers 55% of area Current forestPlanting scenario

Stock Exclusion Two scenarios: Fencing along all streams accessible to livestock Fencing of all accessible streams except head-water streams (Dairy Accord) - around 80% compliance in Northland and Auckland Stock type Mitigation reduction factor (% contaminant yield decrease) TNTPSediment Dairy Dry stock232460

Results 3 ways TablesChartsMaps

Results - Default Total loads – TN 5488 t/year – TP 804 t/year – Sediment 3913 kt/year Wairoa River has highest loads High TN yields associated with dairy High TP yields associated with sheep and beef No apparent relationship between sediment and pastoral land use

Scenario result tables Scenario TNTPSediment Load (t/yr) % difference Load (t/yr) % difference Load (kt/yr) % difference Default Conservation Planting LUC Stock excl. - all streams Stock excl. – non-headwater

Scenario results by catchment

Mitigation result summary Sediment reduction Stock exclusion of all streams – 38% Stock exclusion for non-headwater streams – 12% Conservation planting on LUC 6-8 – 36% TN reduction Stock exclusion of all streams – 17% Stock exclusion for non-headwater streams – 8% Conservation planting on LUC 6-8 – 17% TP reduction Stock exclusion of all streams – 27% Stock exclusion for non-headwater streams – 10% Conservation planting on LUC 6-8 – 37%

Where to from here? Presented to stakeholdersNeed to refine scenarios What is current level of fencing? How effective are mitigations locally? Bank erosion and riparian planting (SEDNET?) Restoration, reconstruction of wetlands

Final word CLUES is available free for non- commercial use from NIWA Visit the NIWA display stand – demos – brochures Hoteo River tidal inlet (NIWA image library, Davies-Colley)