Island of Maui Hydrologic Unit 6008 Kahoma September 2018 PR-2018-09
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Instream Flow Standard Assessment Report Island of Maui Hydrologic Unit 6008 Kahoma September 2018 PR-2018-09 State of Hawaii Department of Land and Natural Resources Commission on Water Resource Management COVER Satallite image of Kahoma Gulch with the Kahoma Stream flowing into the Pacific Ocean, West Maui [Google Earth, 2008]. Note: This report is intended for both print and electronic dissemination and does not include diacritical marks in spelling of Hawaiian words, names, and place names due to problems associated with its use electronically. However, Commission staff has made attempts to include diacritical marks in direct quotations to preserve accuracy. Table of Contents 1.0 Introduction ......................................................................................................... 1 General Overview ................................................................................................................................... 1 Current Instream Flow Standard ........................................................................................................... 1 Instream Flow Standards ....................................................................................................................... 2 Interim Instream Flow Standard Process ............................................................................................. 3 Instream Flow Standard Assessment Report ...................................................................................... 4 Surface Water Hydrologic Units ............................................................................................................ 4 Surface Water Definitions ...................................................................................................................... 5 2.0 Unit Characteristics ............................................................................................ 5 Geology .................................................................................................................................................... 5 Soils ......................................................................................................................................................... 5 Rainfall ..................................................................................................................................................... 6 Solar Radiation........................................................................................................................................ 8 Evaporation ............................................................................................................................................. 8 Land Use .................................................................................................................................................. 9 Land Cover ............................................................................................................................................ 10 Flood ...................................................................................................................................................... 11 Drought .................................................................................................................................................. 12 3.0 Hydrology .......................................................................................................... 23 Streams in Hawaii ................................................................................................................................. 23 Ground Water ........................................................................................................................................ 25 Wells in the Kahoma Hydrologic Unit ................................................................................................. 26 Groundwater Pumping and Salinity Levels ....................................................................................... 26 Kahoma and Kanaha Streamflow Characteristics............................................................................. 29 Long-term trends in flow ...................................................................................................................... 32 4.0 Maintenance of Fish and Wildlife Habitat ....................................................... 36 Hawaii Stream Assessment ................................................................................................................. 37 5.0 Outdoor Recreational Opportunities .............................................................. 40 6.0 Maintenance of Ecosystems............................................................................ 42 7.0 Aesthetic Values ............................................................................................... 50 8.0 Navigation ......................................................................................................... 51 9.0 Instream Hydropower Generation ................................................................... 51 10.0 Maintenance of Water Quality ......................................................................... 52 11.0 Conveyance of Irrigation and Domestic Water Supplies .............................. 57 12.0 Protection of Traditional and Customary Hawaiian Rights ........................... 58 Taro Production .................................................................................................................................... 66 Fishponds .............................................................................................................................................. 71 13.0 Public Trust Uses of Water .............................................................................. 74 Hawaiian Home Lands .......................................................................................................................... 74 Domestic Water Supply ........................................................................................................................ 75 i 14.0 Noninstream Uses ............................................................................................ 77 Water Leaving the Kahoma Hydrologic Unit in Ditch Systems ....................................................... 77 Modifications of Ditch Systems and Groundwater Recharge .......................................................... 84 Utilization of Important Agricultural Lands ........................................................................................ 85 Irrigation Needs of the Kahoma Hydrologic Unit .............................................................................. 86 15.0 Bibliography ...................................................................................................... 90 16.0 Appendices ....................................................................................................... 99 ii List of Figures Figure 1-1. Information to consider in setting measurable instream flow standards. ..................................................... 2 Figure 1-2. Simplified representation of the interim instream flow standard and permanent instream flow standard processes. Keys steps of the adopted interim IFS process are depicted in the left column by the boxes drawn with dotted lines. ...................................................................................... 3 Figure 1-3. Quickbird satellite imagery of the Kahoma hydrologic unit and streams in West Maui, Hawaii. (Source: State of Hawaii, Planning Department, 2004; State of Hawaii, Commission on Water Resource Management, 2015c; State of Hawaii, Division of Aquatic Resources, 2005) ............................................................................................................................................ 7 Figure 1-4. Elevation range of the Kahoma hydrologic unit, Maui, Hawaii. (Source: State of Hawaii, Office of Planning, 2004e; U.S. Geological Survey, 2001) .................................................................. 7 Figure 1-5. USGS topographic map of Kahoma hydrologic unit, Maui, Hawaii. (Source: U.S. Geological Survey, 1996) ................................................................................................................................. 3 Figure 1-6. Major and minor roads in the Kahoma hydrologic unit. (Source: State of Hawaii, Office of Planning 2018) ............................................................................................................................................. 4 Figure 2-1. Orographic precipitation in the presence of mountains higher than 6,000 feet. .......................................... 7 Figure 2-2. Generalized geology of the Kahoma hydrologic unit, Maui, Hawaii. (Source: Sherrod et al., 2007) ........................................................................................................................................................ 14 Figure 2-3. Soil classification of the Kahoma hydrologic unit, Maui, Hawaii. (Source: State of Hawaii, Office of Planning, 2015m) ................................................................................................................ 15 Figure 2-4. Mean annual rainfall of the Kahoma hydrologic unit, Maui, Hawaii. (Source: Giambelluca et al., 2013) ............................................................................................................................... 15 Figure 2-5. Mean annual solar radiation of the Kahoma hydrologic unit, Maui,