Working with the Water Balance Forest Hydrology and Land Use Change Paul K. Barten, Ph.D. Professor of Forestry and Hydrology Department of Environmental Conservation www.forest-to-faucet.org The Living Filter Hillsborough 1
www.epa.gov Flow chart of the hydrologic cycle Reprinted from: Satterlund, D.R. and P.W. Adams. 1992. Wildland Watershed Management. 2nd edition. John Wiley & Sons, New York, 448 pp. Hillsborough 2
The Water Balance P -ET -Q ± S = P - (E + T + I) -(Q OF + Q SSF + Q GW ) ± (S SNOW + S SOIL + S WETLANDS +S LAKES + S STREAMS + S BIOMASS ) = where: f (Energy Balance, time, terrain, land use, climate, etc.) P = precipitation ET = evapotranspiration Q = streamflow + groundwater recharge S = water storage (in soils, wetlands, lakes and ponds) deceptively simple and remarkably powerful tool Law of Conservation of Mass and Energy Focus on compensatory changes (use deductive reasoning) ET is the biological variable (positive or negative) S and Q are the physical variables water quality follows (+ or -) When we try to pick out anything by itself, we find it hitched to everything else in the Universe. John Muir, 1911 Hillsborough 3
Calendar Year Water Year P ET Q ± S = IF S THEN P ET Q or P Q ET Dormant Season Growing Season Dormant Season Fall recharge snow accumulation Snowmelt (!) leaf-out Growing season leaf fall and dormancy Fall recharge 6 5 Precip. (mm/day) 4 3 2 1 OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP 1 31 61 91 121 151 181 211 241 271 31 331 361 3 25 mean air temp. (deg C) 2 15 1 5-5 1 31 61 91 121 151 181 211 241 271 31 331 361-1 -15 DORMANT SEASON 22 25 DAYS 1/2 YEAR mean daily streamflow (mm/day) 16 14 OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP 12 1 8 6 4 2 1 31 61 91 121 151 181 211 241 271 31 331 361 Hillsborough 4
6 5 Precip. (mm/day) 4 3 2 1 OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP 1 31 61 91 121 151 181 211 241 271 31 331 361 PET (mm/day) 6 5 4 3 2 1 GROWING SEASON 115 145 DAYS 1/2 YEAR 1 31 61 91 121 151 181 211 241 271 31 331 361 mean daily streamflow (mm/day) 16 14 OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP 12 1 8 6 4 2 1 31 61 91 121 151 181 211 241 271 31 331 361 Effects on development on stormflow volume, peak, and timing 2 18 16 Urban Mean daily discharge (CSM) 14 12 1 8 6 4 Suburban Forest (reference) 2 1-Mar-91 15-Mar-91 29-Mar-91 12-Apr-91 26-Apr-91 Figure 8.7 Normalized mean daily discharge ([ft 3 /sec]/mi 2 ) for three gaging stations in the Chickahominy River watershed, Virginia, used by Focazio and Cooper (1995). Solid line = Upham Brook (urbanized, 38 mi 2 ); Dashed line = Chickahominy River at Atlee (residential, 62 mi 2 ); Dotted line = Chickahominy River at Providence Forge (rural, but includes Upham and Atlee subwatersheds, 252 mi 2 ). The period from 29 March to 12 April 1991 corresponds to "Storm 4" in Figure 8.6. Data source: http://waterdata.usgs.gov/va/nwis/discharge? (de la Cretaz and Barten, 27) Hillsborough 5
17 185 192 (Greeley 1925) (Foster and O Keefe 2) Soil surface characteristics influence the pathway, volume, and rate of water movement. Measurable changes in water yield occur when 2 to 3% (area or biomass) of a fully forested watershed is harvested or cleared. Changes in streamflow persist until forest regeneration is 3 to 5 years old in the northeastern United States. Deep-rooted woody vegetation uses more water than shallow-rooted annual plants (crops). Evergreens intercept more precipitation than deciduous trees (2-3% of annual precipitation). Hillsborough 6
17 173 Hillsborough 7
183 Reference Treatment (6-9% agriculture) Treatment relative to Reference P ET Q (Water Year) Forest vegetation Notes Area (% of landscape) Biomass Interception Precipitation (net) Transpiration Evaporation (from bare soil, etc.) Actual Evapotranspiration (E + T + I) Snowmelt Timing (earlier, same, later) Peak flow (lower, same, higher) Annual Water Yield (Q) Overland flow volume Soil erosion rate Riparian forest continuity Sediment delivery to watershed outlet Nutrient loading (NPK) to streams Stream temperature Pathogen loading (wildlife + livestock + humans) Overall Water Quality!!!!!! Hillsborough 8
183 191 Hillsborough 9
Reference Treatment (6 years old, pre-harvest) Treatment relative to Reference P ET Q (Water Year) Forest vegetation Area (% of landscape) Biomass Interception Precipitation (net) Transpiration Evaporation (from bare soil, etc.) Actual Evapotranspiration (E + T + I) Snowmelt Timing (earlier, same, later) Peak flow (lower, same, higher) Annual Water Yield (Q) Overland flow volume Soil erosion rate Riparian forest continuity Sediment delivery to watershed outlet Nutrient loading (NPK) to streams Stream temperature Pathogen loading (wildlife + livestock + humans) Overall Water Quality? Notes 191 Hillsborough 1
193 Reference (evergreen) Treatment (deciduous) Treatment relative to Reference P ET Q (Water Year) Forest vegetation Notes Area (% of landscape) Biomass Interception Precipitation (net) Transpiration Evaporation (from bare soil, etc.) Actual Evapotranspiration (E + T + I) Snowmelt Timing (earlier, same, later) Peak flow (lower, same, higher) Annual Water Yield (Q) Overland flow volume Soil erosion rate Riparian forest continuity Sediment delivery to watershed outlet Nutrient loading (NPK) to streams Stream temperature Pathogen loading (wildlife + livestock + humans) Overall Water Quality?? Hillsborough 11
Changing one part of a forest ecosystem leads to changes in other parts, processes, and patterns (spatial and temporal). Figure 1 Changes in forest cover (%, solid line and circles) on the Prospect Hill Tract of the Harvard Forest, Petersham, Massachusetts and estimated annual water yield (cm, dashed line and diamonds) (Watson and Barten, 1997) 1 % FOREST?? TIME Hillsborough 12
Hillsborough 13
2 23 25 15 1 5 1 31 61 OCT NOV Month October November Rain 65 68 Snowmelt 1 - Evapotranspiration 39 17 Total Storage 9 21 Streamflow 19 32 Hillsborough 14
2 43 26 24 15 1 5 1 DEC 31 JAN 61 FEB 91 MAR 121 APR 151 Month December January February March April Rain 51 15 84 41 Snowmelt 16 12 44 13 ET 1 1 3 29 Total Storage 36 1 32 75-152 Streamflow 54 31 34 61 169 2 26 24 53 27 27 3 15 1 5 1 31 61 91 12 151 MAY JUN JUL AUG SEP Month May June July August September Rain 64 139 95 44 14 Snowmelt - - - - - ET 62 91 89 14 7 Total Storage -19 4-27 -44 25 Streamflow 25 47 9 5 1 Hillsborough 15