FORESTS AND WATER. effects of forest management on floods, sedimentation, and water supply HENRY W. ANDERSON, MARVIN 0. HOOVER, KENNETH G. REINHART PACIFIC SOUTHWEST Forest and Range Experiment Station FOREST SERVICE. U. S.DEPARTMENT OF AGRICULTURE P. 0. BOX 245, BERKELEY, CALIFORNIA 94701 USDA FOREST SERVICE GENERAL TECHNICAL REPORT PSW- 18I1976 CONTENTS Page Introduction.............................................. 1 I-Hydrologic Processes ................................... 3 Hydrology in the Forest ................................ 6 Water Inputs ......................................... 6 Precipitation Measurement ........................... 6 Snowfall ........................................... 7 Interception Processes ................................. 7 Snow Interception ................................... 8 Interception and Floods .............................. 8 Variability of Interception ............................ 9 Surface Storage .......................................10 Infiltration Processes .................................. 11 Watershed Storage ..................................12 Subsurface Flow ....................................15 Peak Flows .........................................15 Evapotranspiration ....................................17 Transpiration.......................................17 Evaporation ........................................20 Water Yield ..........................................20 Groundwater .......................................20 Streamflow.........................................20 Modifiers of the Forest Influence ........................23 Storm Size .........................................23 Watershed Size .....................................23 Physiography.......................................23 Geology ........................................... 24 Forest and Frost .................................... 24 Forestry, Erosion. and Water Quality ....................25 Erosion and Sedimentation ........................... 25 Water Temperature ..................................27 Water Chemistry ....................................27 Integrating Hydrologic Processes ........................28 11-Forest Treatment and Water ............................. 30 Timber Harvesting ....................................30 Interception ........................................30 Snow Accumulation .................................30 Surface Detention ................................... 32 Infiltration. Overland Flow. Erosion. and Sedimentation . 32 Evapotranspiration..................................37 Soil-Water Storage .................................. 37 Quantity of Streamflow .............................. 38 Peak Flows and Stormflow Volumes ................... 42 Water Temperature.................................. 44 Water Chemistry .................................... 45 Summary .......................................... 45 Regeneration and Tree Planting ......................... 46 Interception ........................................ 46 Infiltration. Overland Flow. Erosion. and Sedimentation ..... 47 Soil-Water Storage .................................. 47 Evapotranspiration and Streamflow .................... 48 Peak Flows ......................................... 48 Summary .......................................... 49 Type Conversions ..................................... 49 Fertilizers. Herbicides. and Insecticides ................... 52 Fertilizers .......................................... 52 Herbicides ......................................... 52 Insecticides......................................... 52 Fire ................................................. 53 Interception ........................................ 53 Infiltration. Overland Flow. Erosion. and Sedimentation . 53 Soil-Water Storage ..................................55 Evapotranspiration..................................56 Quantity of Streamflow ...............................56 Peak Flows .........................................56 Summary ..........................................57 Grazing..............................................57 Interception and Evapotranspiration ................... 57 Infiltration. Overland Flow. Erosion. Sedimentation. and Peak Flow .................................... 57 Summary .......................................... 58 Forest-Land Disposal of Wastes .......................... 58 Insects. Diseases. and Weather ..........................59 Minimum-Treatment Management .......................60 111-Special Problems .....................................61 Southern California and Arizona Chaparral ...............61 Fire-Flood Erosion ..................................61 Erosion Without Fire ................................62 Erosion After Fire ...................................63 Control and Rehabilitation ........................... 63 Arizona Chaparral .................................. 64 Wetland Forests .......................................65 Wetflats ...........................................65 Bays ..............................................65 Swamps and Upland Ponds ...........................65 Bottomlands .......................................66 Phreatophytes ........................................66 Surface Mining .......................................67 IV-Potentials for Management ............................. 68 Conflicting Objectives ................................. 68 Management for Water Yield ........................... 68 Management for Maximum Water Yield ................ 69 Water-Yield Increase Resulting from Multiple Use ........ 69 Cost of Increasing Water Yield ........................ 70 Management for Flood Reduction ....................... 71 Forest Management and Rainfall Floods ................71 Conversion of Open Land to Forest .................... 72 Snow Management .................................. 72 Management for Maintaining Water Quality ................ 72 Erosion and Sedimentation ........................... 73 Erosion Control-Logging ........................... 74 Microbiological..................................... 75 Erosion Control-Fire ............................... 75 Regional Characteristicsand Possibilities: The East ......... 76 Water Chemistry and Temperature..................... 77 Northeastern Conifers and Hardwoods .................78 Central-Southeastern Hardwoods ...................... 80 Southeastern Pines .................................. 81 Regional Characteristics and Possibilities: The West ........82 West Coast Forests .................................. 83 Rocky Mountain Forests ............................. 87 Southwestern Brushlands ............................. 89 V-Tomorrow's Forestry and Water ......................... 91 Water Yield ..........................................91 Selection of Areas for Cutting .........................91 Antitransoirants andAntievaporants ...................91 Recreation Use and Environmental Quality ............... 92 Comparison with Alternatives ......:..................92 Potential Role of the Forest ...........................93 Flood Prevention...................................... 93 Forest Role ......................................... 93 Protection and Reforestation.......................... 93 Research ...........................................94 Erosion-Sedimentation-Water Quality .................94 VI- Literature Cited ...................................... 96 Anderson, Henry W., Marvin D. Hoover, and Kenneth G. Reinhart. 1976. Forests and water: effects of forest management on floods, sedimentation, and water supply. USDA Forest Sew. Gen. Tech. Rep. PSW-18, 115 p., illus. Pacific Southwest Forest and Range Exp. Stn., Berkeley, Calif. From the background of more than 100 years' collective experience in watershed research and from comprehensive review of the literature of forest hydrology, the authors summarize what is known about the forest's influence on the water resource, particularly the effects of current forestry practices. They first examine the fundamental hydrologic processes in the forest. They then discuss how water supply, floods, erosion, and water quality are affected by timber harvesting, regeneration, tree planting, type conversion, fire, grazing, and the application of fertilizers and pesticides. They consider and present the special problems of fire-prone chaparral, phreatophytes, wetland forests, and surface-mined sites. Finally, they assess potential increases in water yield that might be achieved by forest management in each of six major forest regions in the United States and venture some predictions about future management of watersheds. Nearly 600 references provide a fairly comprehensive overview of the literature. Oxford; 116.1 907.3 :(73) Retrieval Terms: forest influences, water yield, flood control, erosion, sedimentation, water quality, multiple-use, watershed management, forest fire, logging, forest grazing, wetlands, phreatophytes, surface mining. The Authors were, until their retirement, research hydrologists with various Experiment Stations of the Forest Service, U.S. Department of Agriculture. HENRY W. ANDERSON served at the Pacific Southwest Forest and Range Experiment Station, headquartered in Berkeley, California, from 1946 to 1976. He was formerly in charge of the Station's research on hydrologic processes in mountain watersheds. He earned bachelor's (1943) and master's (1947) degrees in forestry at the University of California, Berkeley. MARVIN D. HOOVER served on the research staff on the Southeastern Forest Experiment