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"January 1996".Project Number: Quantity and quality of catchment water yield in response to drainage of non-irrigated land - SB/1/28, M/03/5112; LWRRDC Project LWMD6.MDFRC item.Associated Projects see Natural Resource Management Strategy Project M202.Two issues pertaining to the management of pollution from diffuse run-off were investigated in this project: the possibility that the use of mole drains to alleviate waterlogging in non-irrigated pastures could increase water yield and nutrient load from catchments; the potential for wetlands to ameliorate the quality of run-off water flowing through them. The research showed that the capacity for wetlands to retain nutrients was variable and affected by season, residence time of water in the wetland, and especially by groundwater influences in particular wetlands. Comparisons of mole drainage and surface run-off showed that the former generally had proportionately higher levels of nutrients than the latter, although there was an indication that phosphorus was being removed from water percolating through the soil. Annual water and nutrient yields from Crooke's Farm experimental site in the Kiewa valley for the drought year of 1994/95 were calculated. For surface run-off and mole drainage, respectively, these amounted to 36 and 8 ML water, 67 and 252 kg ha-l yr-l total dissolved salts, 645 and 6452 g ha-l yr-l total nitrogen, and 65 and 264 g ha-l yr-l total phosphorus. However, the area being subject to mole drainage was intensively managed to improve pasture productivity and therefore was not strictly comparable with most of the rest of the catchment. Moreover, the areas subjected to mole drainage within a catchment are likely to be relatively small because of the high cost of installation. Finally, it was unfortunately not possible to make direct comparisons of mole drainage and surface run-off from the same area during these studies. For all these reasons, caution must be exercised in the extrapolation of these results to the installation of mole drains in general, until further research is carried out. Economic evaluation of the benefit of installing mole drainage to improve dairy production showed a pay-back period between 1.4 and 2.4 years, depending on the nature of the mole drains used in the installation. |
