Glendhu, New Zealand 1980-

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Location of the Glendhu catchments, New Zealand
Tussock catchment, looking north, 1992
Plantation catchment weir, 2011
Tussock catchment weir, 2011

Location and Scale[edit]

Southern flank of the Waipori River, East Otago, South Island. New Zealand

• Tussock catchment (GH1): 216 ha

• Planted catchment (GH2): 310 ha

Dates[edit]

1980 to present

Climate[edit]

Cool temperate climate, with an average annual rainfall of 1300 mm.

Geology[edit]

The catchments are located on the eastern edge of an extensive plateau comprising remnants of a Cretaceous erosion surface that experienced uplift in the late Tertiary. The moderately weathered schist bedrock is overlain by a blanket of loess 1-5 m thick.

Topography[edit]

The catchments range in elevation from 460 to 680 mm a.s.l. The easy rolling interfluves have been dissected by moderately steep to very steep valley sides. Wetlands commonly occupy the headwaters of many of the larger sub-catchments. Well-drained soils are found on the interfluves and accompanying slopes, poorly-drained soils on the toe slopes, and peaty soils in the valley bottoms. Typical profiles on the interfluves and most slopes exhibit a highly permeable moss layer and A-horizon overlying a massive, relatively impermeable B-horizon.

== Vegetation / Land Use GH2 was planted over two-thirds of its area in Pinus radiata in the latter half of 1982. Both catchments were subject to grazing with sheep until planting. GH1 continued to be grazed at approximately one sheep per hectare until 2002. Harvesting commenced in GH2 in March 2014, and is expected to be completed in late 2018.

History[edit]

The study was established by the former New Zealand Forest Service in response to concerns expressed over the possible effects on water yield of converting native tussock grasslands to pine plantation. This was of special significance here because of the presence of hydro-electric generating plants in the lower Waipori basin, and the potential for the loss of generating capacity. Following the demise of the Forest Service in 1992, the operation of the catchments was taken over by the newly-established Crown Research Institute, Landcare Research.

The initial hydrological consequences of the effects of afforestation on tussock grasslands were discussed by Fahey and Watson (1991) and Fahey and Jackson (1997). Fahey and Payne (2017) present the results of the study covering a complete forest rotation from planting to harvesting. Early effects of afforestation on soil properties, sediment yields, soil and water chemistry, and aquatic ecology are summarised by Fahey and Payne (2015).

The Glendhu catchments have served as a natural laboratory for the investigation of evapotranspiration processes in tussock grasslands (e.g., Campbell 1989; Campbell & Murray 1990), and have been the focus for numerous student dissertations and theses (e.g., Campbell 1987; Lewis 1999; McLean 2001; Miller 1994; Milner 1995; Smith 1996). In addition, a number of studies have sought to identify the mechanisms responsible for both stormflow and baseflow in the tussock catchment at Glendhu. For example, Bonell et al. (1990) concluded that most moderate to small storms were dominated by old (pre-event) water (derived from shallow unconfined groundwater), especially early in the storm. It was only in the larger storms that new (event) water, thought to be derived from saturated overland flow, was present in the storm hydrograph. Bowden et al. (2001) found that stormflow occurs primarily in response to interflow, and confirmed that baseflow can be sustained for long periods from water stored in the thick loess horizons that blanket the surrounding hillslopes, but only for a few days from the wetland itself. Stewart and Fahey (2010) observed that, while most of the water comprising runoff from the two catchments is quite young (c. 1 month), minor but substantial amounts of old water from slow flow through bedrock (mean transit time, 25–26 years) also contribute to baseflow.

The Glendhu catchments have also been an important source of rainfall and runoff data for calibrating and validating a water balance-based hydrological model (WATYIELD) which has been used to help resolve regional water resource management issues (Fahey et al. 2010; Fahey et al. 2011). The planned continuation of the current hydrological monitoring programme offers a unique opportunity to assess not only the extent to which the progressive removal of the tree crop affects water yields, low flows and stormflows, but also the sediment response to harvesting.


Reference Material[edit]

Campbell, D.I., 1987. Evaporation, energy, and water balance studies of narrow-leaved snow tussock in Otago, New Zealand. Unpublished PhD Thesis, University of Otago, New Zealand.

Campbell, D.I., 1989. Energy balance and transpiration from tussock grassland in New Zealand. Boundary Layer Meteorology 46, pp. 133-152.

Bonell, M., Pearce, A.J. and Stewart, M.K., 1990. The identification of runoff production mechanisms using environmental isotopes in a tussock grassland catchment, eastern Otago, New Zealand. Hydrological Processes 4, pp.15–34.

Campbell, D.I. and Murray, D.L., 1990. Water balance of snow tussock grassland in New Zealand. Journal of Hydrology 118, pp. 229-245.

Fahey, B.D. and Watson, A.J., 1991. Hydrological impacts of converting tussock grassland to pine plantation, Otago, New Zealand. Journal of Hydrology (NZ) 30, pp.1-15. Miller, B.J., 1994. Soil water regimes of the Glendhu experimental catchments BSc Hons Dissertation, University of Otago, New Zealand. Smith, J., 1996. Runoff at Glendhu. BSc Hons Dissertation, University of Otago, New Zealand

Fahey, B.D. and Jackson, R.J., 1997. Hydrological impacts of converting native forests and grasslands to pine plantations, South Island, New Zealand. Agricultural and Forest Meteorology 84, pp. 69-82. Lewis, M., 1999. Modelling hillslope runoff in the Glendhu experimental catchments, eastern Otago, New Zealand. MSc thesis, University of Otago, New Zealand.

Bowden, W.B., Fahey, B.D., Ekanayake, J. and Murray, D.L., 2001. Hillslope and wetland hydrodynamics in a tussock grassland, South Island, New Zealand. Hydrological Processes 15. pp.1707-1730. McLean, S., 2001. Baseflow response to vegetation change, Glendhu State Forest, Otago, New Zealand. MSc Thesis, University of Otago, New Zealand.

Fahey, B.D., Ekanayake, J., Jackson, R.J., Fenemor, A., Davie, T.J.A. and Rowe, L.J., 2010. Using the WATYIELD water balance model to predict catchment water yields and low flows. Journal of Hydrology (NZ) 45, pp 39-48.

Stewart, M.K. and Fahey, B.D., 2010. Runoff generating processes in adjacent tussock grassland and pine plantation catchments as indicated by mean transit time estimation using tritium. Hydrology and Earth System Sciences 14: 1021-1032.

Fahey, B.D., Davie, T.J.A. and Stewart, M., 2011. The application of a water balance model to assess the role of fog in water yields from catchments in the east Otago uplands, South Island, New Zealand. Journal of Hydrology (NZ) 50, pp. 279-292.

Fahey, B.D. and Payne, J., 2015. Report on the Glendhu experimental catchments: 1980-2013. Landcare Research Internal Report.

Fahey, B.D. and Payne, J., 2017. The Glendhu experimental catchment study, upland east Otago, New Zealand: 34 years of hydrological observations on the afforestation of tussock grasslands. Hydrological Processes 31: 2921-2934.


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