Lignite/Marine Terraces Technical Information
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SOUTHLAND PHYSIOGRAPHIC ZONES LIGNITE/MARINE TERRACES Technical information Physiographic zones are part of the Water and Land 2020 & Beyond project that aims to maintain and improve water quality in the Southland region, and to help us as a community achieve our goals for water. Understanding our Physiographic zones water and water quality The Physiographics of Southland Physiographic zones represent areas What’s inside project was developed to better of the landscape that have a common understand the evolution of water influence over water quality. The Overview and map of the across Southland. By understanding proposed Southland Water and Land Lignite/Marine Terraces where water comes from and the Plan identifies nine physiographic zones zone and variants processes it undergoes as it moves in Southland that can be used to manage through drainage networks, we can land use effects on water quality. Variants and associations better understand the reasons for different water quality outcomes across Landscape characteristics the region. Physiographic zone technical information Surface zone The findings of the Physiographics of characteristics Southland project have been published The purpose of this booklet is to in two reports, which identify the key describe generalised water quality Soil zone characteristics drivers of hydrochemistry and water risks associated with individual quality variability in Southland (Rissmann physiographic zones. A companion Saturated zone et al., 2016), and describe a classification booklet titled Guide for using the characterisitcs system for managing land use effects on Southland physiographic zones water quality (Hughes et al., 2016). technical information explains the terms Water quality implications and source data used in this booklet. LIGNITE/MARINE TERRACES physiographic zone Lignite/Marine Terraces zone VARIANTS Artificial Drainage Overland flow Lignite/Marine Terraces Physiographic Zone APPROXIMATE AREA 100,710 hectares GEOGRAPHIC DISTRIBUTION Along the south coast between Bluecliffs and Awarau Bay, Fortrose and the Haldane Estuary. Inland areas of Eastern Southland where lignite measure sediments occur near the land surface. Go to our online BEACON mapping service to view MAIN SURFACE WATERWAYS the physiographic zones of Te Tipua Stream, Hedgehope Southland in more detail. Stream 2 Overview The Lignite/Marine Terraces physiographic zone occurs along the south coast and in areas of eastern and western Southland where organic-rich sediments occur at or near the land surface. Key features Water quality • Located where the underlying implications geology is highly to moderately • When soils are wet, episodic reducing. contaminant loss occurs via • Mostly flat to gently undulating overland flow or artificial drainage terrain. in response to precipitation. • Soils are fine-textured with slow • The potential for elevated nitrate subsoil permeability. concentrations in groundwater can • The redox state of groundwater be limited by high denitrification varies according to the thickness potential. of alluvium overlying organic-rich sediments. • Surface water quality is influenced by groundwater quality (baseflow), overland flow and artificial drainage. WATER QUALITY RISK LIGNITE/MARINE LIGNITE/MARINE LIGNITE/MARINE TERRACES TERRACES(a) TERRACES(o) Contaminant pathways Deep drainage Artificial drainage Overland flow Dilution and attenuation Reducing aquifers Reducing aquifers Reducing aquifers processes Primary receiving Aquifers Surface waterways Surface waterways environments Water quality risk Low Nitrogen, phosphorus, Nitrogen, phosphorus, sediment, microbes sediment, microbes 3 Variants and associations Variants Associations Gleyed The Lignite/Marine Terraces zone Variants identify areas within The Lignite/Marine Terraces occurs adjacent to the Gleyed zone in physiographic zones where there is physiographic zone is commonly the Hedgehope and Waimumu areas increased water quality risk when soils associated with three physiographic where Quaternary alluvium thins and are wet. Contaminant losses from zones in Southland (Figure 1). lignite sediments occur at or near the variants occur along alternate drainage land surface. pathways that have lower attenuation Bedrock/Hill Country potential. Streams originating from the Bedrock/ In the lower Aparima catchment, the Hill Country zone provide headwater Lignite/Marine Terraces zone occurs The Lignite/Marine Terraces discharge to surface waterways on remnant marine terraces, which physiographic zone has two identified draining the Lignite/Marine Terraces are located within the more extensive variants. zone along the south coast, east of alluvial deposits of the Gleyed zone. Riverton. Drainage from the Lignite/Marine Peat Wetlands Terraces zone contributes to baseflow Lignite/Marine of small streams that also drain the Terraces(a) – Artificial Along the south coast, east of Gleyed zone. Drainage variant Invercargill, the Lignite/Marine Terraces zone occurs on near-surface lignite Areas of undulating land that measure sediments adjacent to the have slow subsoil permeability Peat Wetlands zone. Discharge from the and may be seasonally wet. Lignite/Marine Terraces zone provides This results in an increased flow to wetland areas. potential for artificial drainage to maintain agricultural production. Approximate area: 37,000 ha Lignite/Marine Terraces(o) – Overland Flow variant Areas of gently undulating to rolling land that have elevated potential for overland flow, due to a combination of steeper slopes and/or less well drained soils. Approximate area: 58,730 ha Figure 1: Landscape context image illustrating the relationship between the Lignite/Marine Terraces zone and neighbouring physiographic zones. The Lignite/Marine Terraces zone occurs in two physical settings: elevated terraces on the Southland Plains which are underlain at shallow depths by Tertiary (lignite measure) sediments and low-lying marine terraces along the south coast, which are often associated with the Peat Wetlands zone. The Lignite/Marine Terraces zone receives recharge from rainfall and often discharges to streams draining the Gleyed zone inland of the coastal margin, or to the coast. 4 Dominant characteristics that affect water quality 1 2 3 5 4 Landscape characteristics Surface zone characteristics Soil zone characteristics Saturated zone characteristics Water quality implications 5 L1 andscape characteristics The Lignite/Marine Terraces physiographic zone 1 occupies marine terraces along the south coast between Bluecliffs and Awarua Bay, and between Fortrose and the Haldane Estuary. It also extends across a large area between Grove Bush and Upper Charlton where Gore Lignite Measure sediments occur near the land surface. In the Ohai area, this zone occurs where Beaumont Coal Measure sediments are similarly exposed. Topography Geology Climate Elevation This zone is associated with two distinct Average annual rainfall in this zone geological environments: varies spatially between 773 and 6,553 Most of this zone occurs at elevations less mm, with higher rainfall occurring on than 220 metres relative to sea level (m Marine terraces of late Quaternary age isolated marine terraces along the RSL). This reflects the spatial distribution (Q5 to Q7) Fiordland coast. of this zone across downlands in the lower Mataura catchment and alluvial • Located along the south coast terraces around the coastal margin. • Comprised of a mix of reworked alluvium and variable amounts of Slope fine-grained sediment and organic Most of this zone occurs on flat to materials undulating land (≤7o slope). Organic-rich Tertiary sediments of the East Southland Group, with surface or Steeper areas generally occur in the near surface exposure (<15 m below Overland Flow variant, which occupies ground level) predominately flat to rolling land (≤15o slope). • Located across a broad area extending along the southern Flatter areas with less well drained soils margin of the Hokonui Hills (from typically occur in the Artificial Drainage Grove Bush to Upper Charlton) and o variant (≤3 slope). in the vicinity of Ohai • The main sub-rock types are lignite and coal 6 Lignite/Marine Lignite/Marine Lignite/Marine Terraces LANDSCAPE Terraces(a) LANDSCAPE Terraces(o) LANDSCAPE zone characteristics zone characteristics zone characteristics ELEVATION ELEVATION ELEVATION 0 – 220 m RSL 0 – 140 m RSL 0 – 320 m RSL SLOPE SLOPE SLOPE Flat to undulating Flat to gently undulating Flat to rolling GEOLOGY GEOLOGY GEOLOGY Hard rock and Quaternary Quaternary sediments Hard rock sediments LANDFORM AGE LANDFORM AGE LANDFORM AGE Q2-Q4 and Pre-Quaternary Pre-Quaternary Pre-Quaternary AvERAGE ANNUAL RAINFALL AvERAGE ANNUAL RAINFALL AvERAGE ANNUAL RAINFALL 1,102 mm per year 1,506 mm per year 1,346 mm per year 7 2 Surface zone characteristics Recharge to the Lignite/Marine Terraces zone predominantly occurs from local precipitation infiltrating through the soil matrix. Runoff from 2 adjacent higher elevation land provides minor recharge in some areas. short, higher order streams (3rd order Dilution and above). These drain either to the Overland flow This zone is predominately recharged coast or to adjacent physiographic In steeper areas, or on rolling via land surface recharge (matrix flow). zones. topography where subsoil permeability There is less potential for dilution of is low, overland flow can be generated Temporal discharge is characterised contaminant concentrations with this during sustained wet periods. by frequent