Goulburn Broken Water Quality Strategy Issues Paper 2A (IP2A)
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Goulburn Broken Water Quality Strategy Issues Paper 2A (IP2A) Nutrients from Dryland Diffuse Sources (Addendum) May 1996 Goulburn Broken Water Quality Working Group Issues Paper 2A - Nutrients From Dryland Diffuse Sources (Addendum) 1. SUMMARY ............................................................................................ Error! Bookmark not defined. 2. INTRODUCTION .............................................................................................................................. 2 3. CATCHMENT NUTRIENT GENERATION RATES .................................................................... 2 3.1 ESTIMATING CATCHMENT NUTRIENT LOADS ....................................................................................... 2 3.2 DRYLAND CATCHMENT AREA. ............................................................................................................ 2 3.3 CATCHMENT LAND USE ...................................................................................................................... 3 3.4 NUTRIENT AND FLOW DATA AVAILABILITY ......................................................................................... 4 3.4.1 Nutrients in Streams.................................................................................................................... 4 3.4.2 Flow ............................................................................................................................................ 5 3.5 REVISED GAUGED CATCHMENT NUTRIENT GENERATION RATES. .......................................................... 6 3.5.1 Annual Variation in Generation Rates ....................................................................................... 9 3.6 ESTIMATING TOTAL DRYLAND CATCHMENT NUTRIENT LOADS ........................................................ 11 3.6.1 Assigning Ungauged Areas to Gauged Catchments ................................................................. 11 3.6.2 Land Use Generation Rates ...................................................................................................... 14 4. IMPORTANCE OF IN STREAM SEDIMENT ............................................................................ 18 4.1 BACKGROUND ................................................................................................................................... 18 4.2 REVIEW OF IMPORTANCE OF SEDIMENT IN STREAMS ......................................................................... 18 4.3 CONCLUSION ..................................................................................................................................... 20 5. NUTRIENT CONTROL OPTIONS IN THE DRYLAND ............................................................ 22 5.1 STREAM LENGTH IN THE CATCHMENT. ............................................................................................... 22 6. ECONOMIC ASPECTS .................................................................................................................. 25 6.1 BASIC COSTS ...................................................................................................................................... 25 6.1.1 Filter Strip costs: ...................................................................................................................... 25 6.1.2 Forested filter strips .................................................................................................................. 27 6.1.3 Summary of costs to Install Filter Strip .................................................................................... 28 6.1.4 Total Cost of installing these filter strips. ................................................................................. 28 6.2 HOW MUCH NUTRIENT DO FILTER STRIPS HAVE TO DEAL WITH? ......................................................... 29 6.2.1 Cost Effectiveness of Filter Strips ............................................................................................. 29 6.3 RIVER MANAGEMENT WORKS ........................................................................................................... 29 6.3.1 How much P reduction could be attributed to river management works?................................ 30 6.3.2 Cost Effectiveness of River Management Works. ...................................................................... 30 6.4 SUMMARY. ........................................................................................................................................ 30 7. CONCLUSIONS ............................................................................................................................... 31 8. BIBLIOGRAPHY ............................................................................................................................. 31 9. APPENDIX 1- SUMMARY OF AVAILABILITY OF WATER QUALITY DATA .................. 33 10. APPENDIX 2 NUTRIENT GENERATION RATES................................................................... 35 Page 1 Goulburn Broken Water Quality Working Group Issues Paper 2A - Nutrients From Dryland Diffuse Sources (Addendum) 1. Introduction Since the publication of Issues Paper No 2 (IP2), which investigated nutrients from dryland diffuse sources, work has been done to more accurately calculate catchment nutrient generation rates. The revised rates are in some cases substantially different from those presented in the original issues paper. This has significant implications for the conclusions originally drawn. The WQWG has decided to prepare this addendum (IP2A) to Issues Paper 2 to canvass these revised conclusions. In addition, the preparation of this addendum allows the opportunity to address some corrections to various parts of the original issues paper and to include some further information, which has since become available. This paper reviews Sections 4.3, 4.6, 5 and 9 of Issues Paper 2. The work of Kelly O’Shannassy (Water Ecoscience), Peter Hopmans (Centre for Forest Tree Technology), and Michael Papworth (CNR) is providing information and comment on sections of this paper is acknowledged. 2. Catchment Nutrient Generation Rates 2.1 Estimating Catchment Nutrient Loads Methods of estimating catchment nutrient generation rates include: determining land use generation rates from a combination of gauged catchment data and literature values and assigning these rates to the estimated area of land use in the catchment assigning ungauged catchments to similar gauged catchments and estimating loads. Both approaches have their problems. The first requires good land use information as well as reliable land use nutrient generation rates. A problem with the second approach is that large areas of the catchment are ungauged (eg northern section of Shires of Yea and Alexandra) - what values do we assign them? There may also be errors associated with scaling up factors. This paper attempts to estimate catchment nutrient loads using both methods. The estimates presented are just that - estimates. They will be updated as more information becomes available. 2.2 Dryland Catchment Area. The total area of the catchment is approximately 2.4 million ha. Of this, approximately 570 000 ha is identified as the “irrigation region” of the catchment (although even this includes substantial dryland areas (71 500 ha (SIRLWSMP 1995)). Page 2 Goulburn Broken Water Quality Working Group Issues Paper 2A - Nutrients From Dryland Diffuse Sources (Addendum) The remaining 1 830 000 ha is identified as the “dryland” part of the catchment. Table 1 shows the dryland part of the catchment split into “old” municipal boundaries. (MAP) Table 1 also estimates areas in the Upper-Mid and Mid-Lower catchment. Table 1 - Dryland Area by “Old” Municipal Boundaries. Municipality Total Estimated Estimated Area (est) Area in Area in Area of area % in % of GB in Dryland Mid-Upper Mid-Lower Farmland km2 catchment catchment km2 catchment catchment (km2) from proportion ABS (Table in dryland 4 in IP2) Alexandra 1905 100 100 1905 1905 470 Benalla (City) 16 100 100 16 16 16 Benalla 2320 100 100 2320 2320 1230 (Shire) Broadford 576 100 100 576 576 138 Euroa 1412 100 100 1412 1412 961 Goulburn 1031 100 95 1031 1031 718 Kilmore 508 50 100 254 254 235 Mansfield 3919 100 100 3919 3919 765 McIvor 1295 50 100 650 650 Pyalong 577 100 100 577 577 Seymour 945 100 100 945 945 623 Shepparton 917 100 30 275 275 Tungamah 1128 100 66 745 745 897 Violet Town 935 100 100 935 935 585 Waranga 1644 66 50 540 540 Yarrawonga 627 100 80 500 500 Yea 1391 100 100 1391 1391 639 TOTAL 21146 17991 8045 9946 Note small areas in the former municipalities of Whittlesea, Eltham, Healesville, Upper Yarra are ignored, as is the portion of Mansfield in Gippsland. Source of areas - Victorian Municipal Directory. The estimated area in Table 1 is in reasonable agreement with the figure of 1 830 000 ha above. 2.3 Catchment Land Use Determining dryland catchment land use is a frustrating exercise. The many different published catchment based land use figures conflict, do not agree and land use classifications vary. As well, the boundary of the “dryland” does not coincide with shire, parish or other reporting boundaries. The land use figures reported in Issues Paper 2 are based on, amongst other things, ABS statistics. For the year data was selected, ABS surveyed only those properties with an “estimated agricultural value of output” greater than $25000. Many farms were excluded. Therefore the total farm area reported using the ABS cannot be relied upon to provide a reasonable guide to catchment land use. (see Table