Geospatial Analysis of the Tarawera River Catchment

Dietrich HoefnerUniversity of Auckland School of Geology, Geography and Environmental Science

Auckland, New Zealand

Lafayette College, Easton, Pennsylvania

June 26, 2009

Abstract

The Tarawera River watershed is an important source of economic, cultural andenvironmental values in the Bay of Plenty Region, New Zealand. Understandingthe structure and function of the watershed, in terms of landcover and hydrology, isan important step in establishing natural influences on water quality. Establishingthis natural range of conditions can help to provide a ”baseline” in order to assessanthropomorphic influence on the area. This study uses a GIS based analysis, whichincludes analysis of spatial distribution of landcover in the watershed, as well asanalysis of results from the event-based kineros2 runo! and erosion model. Areasof potentially high runo! and erosion are identified, and limitations of the modelwithin this context are discussed.

1 Introduction

Water quality is the result of many natural and anthropogenic influences within a givenwatershed (Maybeck et al. 1989). These influences include land use and land cover withinthe boundaries of a watershed, which are known to have direct and indirect e!ects on thewater quality within that watershed (Omernik 1977; Hunsaker and Levine 1995; Allanand Johnson. 1997). Landcover, especially vegetation, acts as a strong control on wayruno! interacts with the landscape, as it has direct e!ects on the amount and timing ofruno! flows. These flows in turn act as controls on erosional and hydrologic processeswithin the catchment (Sparks 1995). The nonpoint-source contribution of land cover towater quality is one of the background considerations that must be taken into accountwhen assessing other impacts on a watershed.

This study aims to catalogue the variety, relative percentages and potential influenceof landcover types within the Tarawara River watershed in the Bay of Plenty Region,New Zealand. The purpose of such an inventory is to provide insight into some of thepotential di!use pollution sources a!ecting the watershed (with a focus on runo! sourcedpollutants and contributions of erosion to sediment loading), and to provide a basis for

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establishing background conditions for the area. These conditions can then be usedto support analysis of water quality, and the factors influencing water quality, withinthe Tarawera watershed. More specifically, this study will attempt to contextualizeinvestigation into pollution loads from a large pulp and paper mill in the town of Kawearuthat contributes to the water quality of the Tarawera River. Additionally, this studywill provide a comparison to similar work published by the regional agency, EnvironmentBay of Plenty (EBOP), in 2004 .

A Geographic Information System (gis) will be deployed in this study as the platformto do the assessment of the watershed. This system, in combination with previouslygathered spatial data, provides a powerful tool for investigating a large area such as theTarawera River watershed. gis is a popular tool for performing this type of analysis, as itprovides automated tools to delineate watersheds and estimate hydrologic regimes withinthem based on elevation data (Baker et al. 2006). A diversity of gis techniques can beused to conduct this type of study. Most techniques rely on the same general processes todelineate the watershed and the flows within it, using a method based on flow directionand accumulation(Baker et al. 2006). Many studies go beyond this to incorporate moreadvanced modeling to predict discrete pollution contributions to the watershed (Kinget al. 2005). In this study, watershed delineation will be carried out using the standardtechnique discussed by Band and Moore (1995), and erosion and runo! responses willbe estimated using the Kinematic Runo! and Erosion Model (kineros2) developed bythe United States Department of Agriculture (Woolhiser et al. 1990).

This type of analysis is important in that it can serve as a means of identifying areas ofinfluence and concern within the watershed, thereby acting as a guide for managementfunctions for the area. In context of the pulp and paper mill, establishing environmentalcontributions of erosion and runo! can contribute to establishing “baseline” conditionsfor water quality above the mill, thereby guiding analysis of contributions of plant e"uentto overall water quality. Areas that experience high runo! flows or high sediment fluxescan be identified through the model and compared with other geospatial informationto improve information quality for the area. This analysis is especially important withrespect to analysis of suspended and dissolved solids, which are identified as characteristicforms of pulp and paper pollution (Chandra et al. 2005).

It is important to note that although most of the literature supports the idea thatwatershed landcover has a strong relationship to the characteristics of runo! enteringflow channels (Weller et al. 2003; Reed and Carpenter 2002; Gri#th et al. 2002), there issome debate as to whether it is su#cient to analyze only riparian landcover, or whetherit is necessary to include the whole catchment area. Omernik et al. (1981) discuss thisand find that although for some (generally smaller) catchments, land use adjacent tostreams is most important, for large watersheds encompassing a diversity of conditions,considering the whole catchment area is useful . This focus on the whole catchmentarea guides this study, as it incorporates all the land that eventually drains to theTarawera river outlet. However, as this project uses a spatially distributed model toestimate landscape runo! response, it does, in a limited way, account for the importance

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of the spatial context of landcover (although not specifically with respect to riparianzones).

2 Area Background

The Tarawera River watershed is located in the Bay of Plenty Region, New Zealand(Figure 1). The catchment area for the river is about 980 square kilometers, with theriver itself running a length of about 65 kilometers from its source in Lake Tarawera tothe outlet in the Bay of Plenty. The catchment area is in a mild climate zone with averagesummer and winter temperatures recorded in nearby Edgecumbe of 19 and 10 degreesCelsius, respectively (Ellery 2007). Average rainfall for the region is 1236 millimetersper year, with fairly even distribution through the seasons. This rainfall translates intoan average recorded discharge of 30,364 liters per second at the Awakaponga recordernear the mouth of the Tarawera River, and a bed load sediment discharge of between200 and 400 tonnes daily (Ellery 2007).

The Tarawera River is fed primarily by Lake Tarawera in the upper catchment. LakeTarawera is in turn fed by overland streams flowing from Lake Rotokakahi, Lake Tiki-tapu, and Lake Okareka. Lakes Okaro, Okataina, and Rotomahana are likely connectedto Lake Tarawera via subsurface flow networks (Frye 2008).

Volcanism and Geothermal Activity The Tarawera Basin lies within the OkatainaVolcanic Center of the North Island’s Taupo Volcanic Zone. Volcanic and geothermalactivity act as major controls on the landscape in the catchment. Within the catchmentare the rhyolite domes of Mount Tarawera and Mount Edgecumbe, as well as the nu-merous caldera lakes in the upper catchment (Hodgson and Nairn 2004). Much of thesurface geology is a result of deposits from the 1886 eruption of Mount Tarawera andthe majority of other soils are related to ash deposits from other eruptions in the area.These soils and other associated volcanic sediments are the primary load transported bythe Tarawera river (EBOP 2004).

In the contemporary catchment, volcanic activity is expressed through hydrothermalactivity, with several smaller active areas in the upper catchment, and a larger activearea near Kawerau (Mroczek 2005). The area near Kawerau contributes marginally toriver flow (0.193 meters per second on average), and also contributes to concentrationlevels of arsenic and mercury in the river.

Tasman Pulp and Paper Mill The Norske Skog/Carter Holt Harvey combined pulpand paper mill is located just outside of the town of Kawerau in the middle section ofthe catchment. In addition to being a major economic contributer to the region, and toNew Zealand at large, the mill has been the source of ongoing environmental concernfor the area (Tull 2008). Although there are numerous contaminants that are of concern

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Figure 1: Location of the Tarawera River Catchment

in relation to pulp and paper milling (many of which are discussed in Tull (2008)), thecontaminant of importance to this paper is the discharge of suspended solids, as thepurpose of the modeling done here is in part to estimate a background level of suchsuspended loads and thereby contextualize any additions from the mill.

Land Cover The Tarawera watershed is home to a diversity of land cover and land useactivities. This includes large areas of pasture land, other agricultural land, productionpine forests and native forests, as well as residential areas and commercial and industrialactivity. (EBOP 2004). The main population center in the catchment area is the townof Kawerau (population about 6900), which is the location of the Norske Skog/Tasmanpulp and paper mill (Census 2006). In general, the watershed above Kawerau is muchless modified than the environment below Kawerau, with land use being dominatedby production and native forests and some pasture land. At Kawerau and below, thewatershed is in a more modified environment, with pasture and other agricultural landas the primary land use types. A more detailed discussion of land use will follow in theresults section.

3 Methods

This analysis was carried out using a combination of software tools (Figure 2), in con-junction with previously created spatially referenced data from several sources.1

1Thanks to Environment Bay of Plenty for elevation and landcover datasets

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Figure 2: Software Tools Used in Analysis

Software The gis package used to support this analysis is ArcGIS 9.3 developed bythe Environmental Systems Research Institute (ESRI). ArcGIS was used to performthe initial manipulation and merging of source data, and as a platform for runningthe kineros2 model. kineros2 is a distributed runo! model developed by The UnitedStates Department of Agriculture Agricultural Research Service (USDA ARS), that usesa network of planes and channel structures to represent a watershed as represented inFigure 5. The kineros2 model was run using the Automated Geospatial WatershedAssesment interface (AGWA), also created by USDA ARS (Miller et al. 2002).

Input Data The spatial data required for this analysis can be generalized into threecategories: a digital elevation model (DEM), land cover data, and soil coverage. Thedigital elevation model provides the basis for determining flow direction and accumu-lation for the watershed (and thus the basis for the watershed boundary) as well ascontributing to the evaluation of the runo! and erosion characteristics of the landscape.The land cover data provides the basis for determining coverage and area of di!erentland cover classes within the watershed, and also acts as an input to determining runo!and erosion characteristics (Woolhiser et al. 1990).

Creating the DEM required merging two di!erent elevation data sets for the region.High resolution Light Detection and Ranging (LiDAR) raster data was used for the low-lying, low relief Rangitaiki costal plain. For the rest of the area, the standard 1:50,000New Zealand topographic vector contour data was used, as it was the highest resolutionavailable. The two datasets were merged into a ”terrain” feature in Arcmap, which usesa triangular integrated network to represent elevation (ESRI 2009). This dataset wasthen sampled to create a composite raster DEM for the area (Figure 3). Although itwould have been possible to exclusively use the 1:50,000 data to represent elevation, theLiDAR data was used in order to capture the low-relief features of the Rangitaki plainsin order to generate more accurate output.

The land cover data used was from the New Zealand Land Cover Database (LCDB),

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Figure 3: Digital Elevation Model of the Catchment

developed by Land Information New Zealand (NZMFE 2000). This data provided 30categories of land cover for the watershed area, labelled by type. The AGWA modelingenvironment uses lookup tables based on US land cover classes. Therfore in order to usethe landcover data, it had to be reclassified according the the landcover types describedin the 1992 US National Land Cover Database (NLCD) project to achieve compatibil-ity(Vogelmann et al. 1998; Burns et al. 2007). This required grouping some of the classesdefined in the LCDB to match to categories in the NLCD (Table 1).

Soils data were sourced from the United Nations Food and Agriculture Organization’s(FAO) Digital Soil Map of the World (DSMW) (UNFAO 2003). Although the NewZealand specific soil data available for the watershed area is higher in detail and res-olution, the conversions that would be required to enter the higher detail data intokineros2 are beyond the scope of this project. The soil types included in the FAO soilmap are eutric fluvosoils, eutric regosols and vitric andosols. UNFAO (2003) discussesthe details of these soil types in-depth.

In addition to the spatial data, precipitation event data is required for the kineros2model. For this study a simulated 12 hour rainfall event was generated using a precipita-tion depth of 105mm. This precipitation depth is based on a five year return period rainevent for the Tarawera at Awakaponga rainfall gauge maintained by Environment Bayof Plenty (Ellery 2007). The rainfall hydrograph was generated within AGWA using

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Figure 4: Distribution of Soil Types (UNFAO 2003)

the type II methodology developed by the US Soil Conservation Service (USDA-SCS1973).

Delineation and Stream Network Creation The Tarawera River Watershed wasdelineated through computer analysis of the composite DEM. The delineation processidentifies all of the DEM cells that eventually drain to the specified outlet location (inthis case the mouth of the Tarawera River), and the stream network creation determineslikely flow channels for the catchment. The execution of this process relies on the creationof a flow direction grid, which determines the slope ( and thus flow direction) of each cell.This grid is used to generate the watershed outline, as well as a flow accumulation gridthat is used to determine the stream network (Burns et al. 2007). The flow accumulationgrid is created in a process that aggregates the contributing upslope area for each cell andassigns a ”flow accumulation” value. To create the stream network, a threshold is appliedto the accumulation grid, thereby ”pruning” the accumulation tree and leaving only thelarger streams (Miller et al. 2002). In this case, the threshold value of contributingsource area (CSA) for flow channelization was set at 2439 hectares, or about two and ahalf percent of the total watershed area. It is important to note that although there aresuspected subsurface flow features connecting lakes in the upper watershed, for modelingpurposes, links between the lakes are created as surface flow features.

KINEROS2 kineros2 is a “distributed, event-oriented, physically based model” thatis designed to describe runo! and erosion characteristics for small watersheds (Woolhiseret al. 1990). It is distributed in that it accounts for watershed characteristics using a

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Figure 5: Schematic Representation of the kineros2 Model. Adapted from Woolhiseret al. (1990)

series of discrete elements. It is event-oriented in that it is designed to simulate asingle rain event, and thus does not include provisions for enviro-transporation or soilwater movement, finally, it is physical because it uses a set of mechanistic mathematicalequations to simulate the environment (Woolhiser et al. 1990).

Implementing the kineros2 model requires that the greater watershed be discretizedinto smaller model elements containing channels and planes. These elements are auto-matically generated based on the threshold value for CSA’s discussed previously andthe location of lakes in the watershed (Burns et al. 2007). In this instance, 149 discreteplane elements and 89 channel elements were created. These discrete elements werethen intersected with the soil and landcover data for the simulation, and a number ofparameters for the plane and channel elements were calculated. Each model element isin e!ect a homogeneous collection of parameters including:

• Plane geometry (length, width, and slope), Mannings number

• Plane canopy cover, interception depth, average micro topographic relief, averagemicro topographic spacing

• Plane infiltration-related parameters including saturated hydraulic conductivity(Ks), initial degree of soil saturation, coe#cient of variation of Ks, mean capillarydrive, porosity

• Plane rain splash coe#cient, soil cohesion coe#cient, and particle class fractions

• Channel geometry (length, width, bed slope, and bank slopes), Mannings number

• Channel infiltration-related parameters (same as specified in plane element)

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• Cohesion coe#cient of bed material.

List adapted from USDA-ARS (2000) and Shoemaker et al. (2005).

The model rainfall hydrograph was then applied to the collection of model elements,and according to the governing set of kinematic wave equations in kineros2, outputis generated that describes infiltration, runo! and sediment balances for each modelelement.

4 Results

This project resulted in creation of a number of data sets. For each of the planes in themodel, data were created describing infiltration, runo! and sediment yield. Additionally,data were created describing activity over the course of the event at the catchment outlet.The data sets created include general data sets that establish topography, land cover,and soil information within the watershed area. The percentage breakdown of landcover is seen in Figure 1, the spatial distribution of of landcover in Figure 6, and spatialrepresentations of model runo! and erosion outputs are in Figures 8 and 7.

Area Distribution of Landcover Land cover (using New Zealand LCDB2 classes)in the watershed is dominated by indigenous forests, with 21.98% cover. This is followedby a similar amount of grassland at 21.51%, most of which is likely used for pasture andgrazing (EBOP 2004). Other major classes are water features, pine forests (productionforests) and other types of forest (Manuka, Kanuka, or other Indigenous Hardwoods).Harvested forest and a!orested land are also a significant landcover type, making up8.57% of the total cover. The percentage breakdown of landcover is seen in Table 1.

Spatial Distribution of Landcover Landcover in the upper catchment above theLake Tarawera outlet is composed mainly of grassland and forest, with some small areasof deforestation and built up features. The mid-catchment area has a much greater per-centage of harvested forest, as well as large areas of intact production and native forest.This area has the largest section of built-up area in the catchment around Kawearu.The lower catchment is dominated by grasslands, with some forest and agriculture. Thespatial distribution is illustrated in Figure 6.

Runo! The runo! component of the model yielded the output illustrated in figure8. This shows the total runo! volume for the watershed distributed by model plane forthe modeled rain event. This total runo! amounts to 4,992,909 cubic meters for theevent. Additionally, outflow was computed for the catchment outlet over the course of

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NZ LCDB Classification % NLCD1992 Classification %

River 0.66 Open Water 8.08Lake and Pond 7.99Estuarine Open Water 0.02Urban Parkland/Open Space 0.17 Low Intensity Residential 0.17Built Up Area 0.60 Commercial/Industrial/Transportation 0.73Transport Infrastructure 0.11Dump 0.02Forest Harvested 8.26 Transitional 8.57A!orestation (Imaged, post LCDB1) 0.30A!orestation(Not Imaged) 0.005River and Lakeshore Gravel and Rock 0.006 Bare Rock/Sand/Clay 0.17Alpine Gravel and Rock 0.16Landslide 0.005Surface Mine 0.06 Quarries/Strip Mines/Gravel Pits 0.06Broadleaved Indigenous Hardwoods 3.51 Deciduous Forest 4.04Deciduous Hardwoods 0.54Pine Forest Open Canopy 5.99 Evergreen Forest 24.10Pine Forest Closed Canopy 18.06Major Shelterbelts 0.05Manuka and or Kanuka 6.34 Mixed Forest 30.41Indigenous Forest 21.98Other Exotic Forest 2.09Mixed Exotic Shrubland 0.13 Shrubland 0.21Subalpine Shrubland 0.09Orchards and Other Perennial Crops .015 Orchards/Vineyards/Other 0.16High Producing Exotic Grassland 21.51 Grassland/Herbacious 22.44Low Producing Grassland 0.08Gorse and Broom 0.25Tall Tussock Grassland 0.57Alpine Grass/Herb Field 0.03Short-Rotation Cropland 0.74 Row Crops 0.74Herbaceous Freshwater Vegetation 0.09 Emergent Herbaceous Wetlands 0.09

Table 1: Land Cover Reclassification Scheme and Percent Cover

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Figure 6: Land Cover Classification with Computer Generated Stream Network

the rain event. This flow reached a maximum of 50,048 liters per second during thesimulation.

Erosion The erosion component of the model is illustrated in Figure 7. The figureshows total sediment mobilization from each model plane for the modeled rain event.The total sediment mobilization estimated for the catchment is 8.23x107 kilograms. Thiscorresponded to a maximum sediment flux of 286 kilograms per second at the catchmentoutlet. at the Tarawera River outlet.

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Figure 7: Erosion on Model Source Planes for Five Year Return, 12 Hour Rainfall

5 Discussion

Areas of Interest From the analysis, several areas can be identified as areas of interestfor further investigation. The modeling plane outside Kawearu on the west side of theriver was identified as a high-erosion and high runo! area for the modeled rainfall event(dark red in Figure 9). The factor that likely contributes to the characteristics of thismodeling plane is landcover that has high proportions of pastoral and developed landover an area with some high local slope features. This modeling plane, being relativelyclose to, and upstream from the Tasman pulp and paper mill, is an area that may beimportant in future analyses. High rates of soil erosion could be a significant contributorto suspended sediment loads, and high surface runo! could also be a mechanism for hightransfer rates of other pollutants into the channel.

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Figure 8: Runo! by Model Source Planes for Five Year Return, 12 Hour Rainfall

This plane is important in context of the pulp and paper mill, as understanding poten-tial nonpoint source pollution loads from the surrounding area is part of establishing”background” conditions for the area. Knowing that this potential pollution source isclose to the points of discharge for the mill can perhaps guide future sampling programsto ensure that high sampling densities are established in the area proximal to the millitself.

Other areas of interest were identified as those areas with high rates of runo! and erosionas illustrated in Figures 7 and 8. These areas do not follow an easily identifiable patternwhen viewed in context of the input data. The only characteristic that does seem tounify these units is that they each include some areas of high local slope, which likely isa key factor in determining erosive and runo! potential.

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Figure 9: Modeled Erosion Near Kawerau Pulp and Paper Mill

Somewhat surprisingly, areas of deforestation from lumbering did not register as areas ofhigh erosion or runo! potential. This is perhaps attributable to the fact that most of thedeforested areas do not lie in areas of high relief, and thus do not generate the high energyruno! needed to transport sediment. More explanation may lie in the NLCD ”transi-tional” landcover class assigned to areas of deforestation through commercial forestry, asit is not specific to this type of area, but includes other ”bare” areas (Vogelmann et al.1998).

Comparison with EBOP Work In comparing the results of this project with thework done in by Environment Bay of Plenty, there is general agreement although thereare some noteable discrepancies.

One major discrepancy between EBOP (2004) and this study is the delineation of thecatchment area. The delineation in this study accounts for 975 square kilometers ofcatchment, while EBOP accounts for 984 square kilometers. This di!erence is chieflybecause EBOP extends the Tarawera watershed all the way to the bank of the neigh-

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boring Rangitaki River in the lower watershed, whereas the delineation here is moreconservative, not extending the watershed much past the Eastern bank of the Tarawera.This di!erence is likely the result of the low relief of the lower catchment making itquite di#cult to realistically determine the catchment boundary. The purpose of us-ing high resolution LiDAR data (which was not yet gathered at the time of the EBOPstudy) for the lower catchment in this study was in part to attempt a better definitionof the watershed boundary in this area. However, even using the high-resolution data,the placement of the actual boundary is questionable, and likely amorphous in nature.Examining the LiDAR data, it is possible to identify abandoned and cut-o! channelstructures left by the river as it has shifted across the plain in the past. This shiftingwould almost certainly result in changes to the boundary of the watershed. Additionally,channel shifting likely accounts for some of the deviation between the location of com-puter generated channel placement in this study, and the location of the contemporarychannel as observed in aerial photographs.

The landcover classes used in EBOP (2004) are not the same as those used in eitherof the two classifications (LCDB2 or NLCD) used in this project. This, in conjunctionwith the di!erent watershed boundaries, makes a direct comparison di#cult. That said,the general proportions of major landcover groups (forest, pasture, water) are reasonablysimilar. The EBOP study used data based on 1992 aerial photography, while the LCDB2data used in this project is based on more recent (1997-2002) Landsat imagery (NZMFE2000). This suggests that no wholesale change has taken place in the watershed betweenthe date of the EBOP study and the creation of LCDB2, but due to the mismatch ofdata categories and resolutions, it is di#cult to quantify the magnitude of change.

The cumulative peak flow rate estimated in the model for a five year return rain eventcompares favorably with the flow data published in Ellery (2007). kineros2 estimated acumulative peak flow of 50,048 liters per second at the catchment outlet, as compared toa recorded five year return peak flow of 64,000 liters per second in Ellery (2007).

The erosion and sediment loads modeled here do not seem realistic in the context ofEBOP (2004) and Ellery (2007). The maximum outlet sediment flux calculated herewould correspond to a maximum sediment concentration of over 5,000 milligrams perliter. Even when accounting for the 400 tonnes of daily bedload transfer described inEllery (2007) that rate is likely much to high to be realistic.

Spatial Scale Roth et al. (1996) and Weller et al. (1996) suggest that scale is veryimportant when considering the e!ects of landscape features on water quality. Depend-ing on the size of a watershed, the elements within it may play a di!erent role. Forsmall watersheds (less than 100 square kilometers), surface runo! characteristics play amajor role in determining the response of the watershed to rain events, while in large(greater than 1000 square kilometers), channel storage is a much more important factorin determining hydrologic response (Burns et al. 2007). Mismatch of scale is likely one ofthe factors that contributed to model inaccuracy in this project. The kineros2 model

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is optimized for smaller watersheds, and probably does not account enough for channelstorage in the Tarawera watershed to be numerically accurate. However, it is still usefulin identifying areas of interest within the watershed, as the basic mechanistic underpin-nings of the model (i.e. relationship of landcover and slope to erosion potential) likelyhold true for most situations.

Future Work This study is perhaps best understood as a preliminary analysis. Fu-ture work in this area could improve a great deal on the modeling techniques used in thisproject. Improvements could be made in model selection, input data, and model calibra-tion. kineros2 was used in this project because the data input requirements could beeasily satisfied with the data on hand. It is likely that the catchment studied here is justtoo big to achieve high modeling accuracy in kineros2. Perhaps a better model for theTarawera River Watershed would be the Soil and Water Assessment Tool (SWAT) de-veloped by USDA ARS for larger watersheds. Whereas kineros2 is designed to supportanalysis of single rain events for small watersheds, SWAT is designed to support largewatersheds, and to do analyses in the long term (greater than one year)(Arnold et al.1994). With the proper data inputs, using SWAT would likely yield useful results.

Generalized landcover and soil data were used in this study, even though higher detaildata were available. This was done in order to more easily integrate New Zealand specificinformation with a simulation designed for United States specific datasets. Future workcould be done to establish conversion tables to better integrate the higher detail, NewZealand specific data into modeling environments. Also, using recorded rainfall data,rather than the simulated event used in this project, would also likely increase modelingaccuracy.

Additionally, this work could be continued in a variety of directions through adjustmentswithin the kineros2 model. The model established in this project could be calibrated toactual hydrological responses recorded in the watershed by Environment Bay of Plentyrecording stations (EBOP 2004). This would likely improve the accuracy of the model,and make it more useful as a numerical predictor of hydrological response. Better modelcalibration would also allow for more in-depth simulation of catchment processes suchas sensitivity analysis or ”what-if” scenario modeling (Al-Qurashi et al. 2008).

6 Conclusions

This project yielded interesting insights into some of the factors that play a role in thewater quality of the Tarawera River Catchment. The watershed boundary was mapped,and the spatial distribution of land use and soil coverage was established within thoseboundaries. A semi-distributed runo! and erosion model, kineros2, was implementedto estimate runo! and erosion response to a 5 year return, 12 hour rainfall event. Thelandcover established in this study serves as an update to the cover established in EBOP

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(2004). This is in addition to establishing a di!erent line of boundary for the water-shed that may be more accurate for hydrological purposes than the current boundarydescribed in EBOP (2004). The modeling results created in the project may be usefulindicators as to potential areas of erosion concern for the area. However, the resultsdo not seem to be of a high enough quality to be used for any quantitative purposes.Working with these data sets and perhaps other modeling tools, future studies couldexpand a great deal on the quality and quantity of information presented here.

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