Plymouth Carver Aquifer Area Water Budgets

1. Plymouth Carver Aquifer Area Water Budgets Nigel Pickering Senior Engineer and Modeler Charles River Watershed Association www.charlesriver.org

2. PCAA Water BudgetsProject Structure • Funding & Project Management • EOEEA • Data Collection & Processing • Fuss & O’Niell • MassGIS • Analysis & Reports • CRWA • Collaborators • Communities • MassDEP • EPA • USGS

3. PCAA Project Location

4. Why Water Budgets? • Assess human impacts on streamflow • Need a balanced, standardized approach • Results should help prioritize remediation • Educate & promote sustainable water use

5. Water Budget Inputs and Outputs

6. Water Budget Components(units are mgd) Impact = SD – SW + (WS – WW – IRR – RIA + GD – GW) * SFAC Impact = total subbasin gain or loss SD = wastewater discharge to surface water SW = withdrawal from surface water WS = water supply gain WW = wastewater loss including infiltration from groundwater IRR = evaporation loss from irrigation RIA = recharge loss from impervious area GD = wastewater discharge to ground water GW = withdrawal from ground water SFAC = storage factor (0.9 – 1.1)

7. Water Budget Examples • PWS, septic, no IA • water in - no water out = net gain • PWS, sewer, no IA • water in - more water out (incl. I/I) = net loss • Water withdrawal, no PWS, no WW, no IA • no water in - water out = net loss • Wastewater discharge, no PWS, no WW, no IA • water in – no water out = net gain • No PWS, no WW, large IA • no water in - water out = net loss

8. Withdrawals and Discharges • Monthly flows for 2000-2004 • filled-in if necessary • Average monthly flow computed • River withdrawals & discharges directly from sub-basin • Well withdrawals converted to stream depletion using StrmDepl (USGS) • Well withdrawals distributed over subbasins with zone of contribution

9. Cranberry Bog Impacts • Reported system areas for 2000-2004 • filled-in if necessary • System area distributed over number of number of withdrawal points • Monthly sub-model developed for 1-ac of cranberry • monthly inputs/outputs in ac-ft of water • Converted to monthly point volumes (mgd) using annual area and monthly factors

10. Cranberry Sub-Model • Water balance of typical cranberry farm • Assumed calendar and amounts for water-related events • Water moved in and out for harvesting, frost-damage control, and weed control • Water used for irrigation in the growing season--small for “average” year • Net water use expressed relative to natural landscape i.e. wetland

11. Cranberry Sub-Model • Calendar • May to Sep-growing season • crop ET coefficient = 0.66 • irrigation at 1”/wk when dry • Oct-harvest • field flooded (1.5 ft) and drained (1.5 ft) • Nov & Dec-freeze protection • Add water (1.0 ft then further 0.7 ft) • Mar-drain and flood • Release (2.0 ft) and add water (2.0 ft) • early May-drain field • Release water (2.0 ft)

12. Cranberry Sub-Model

13. Cranberry Sub-Model

14. Cranberry Sub-Model

15. Water Transfers and Irrigation • Subbasin transfers computed using system unit flows with people and areas • People and areas from distribution system maps and new MassGIS population density map • Monthly irrigation loss computed as: • 75% of (monthly use - winter use) • Applied to both public/private irrigation areas

16. Piped Distribution Systems • Water supply only • Sewer only • Water & sewer

17. Effective Impervious Area (EIA) • Loss assumed proportional to EIA • 10% EIA  10% reduction in streamflow • Subbasin TIA from new MassGIS IA grid • Subbasin EIA computed from TIA as: Effectiveness (%) = -0.214+1.429*TIA (0 to 100) EIA (%) = Effectiveness (%) * TIA (%) / 100

18. Effective Impervious Area (EIA)

19. Natural Streamflow Estimation QNm = (Int + AreaAC * S&GSGC * PrecPC * ElevEC * SlopeSC) / Area m= month (1=Jan, 2=Feb, etc.) QNm = natural flow in month m (cfsm) Int = Intercept coefficient (-) Area = subbasin area (mi2), AC = Area coefficient S&G = percent sand and gravel (%), SGC = S&G coefficient Prec = annual precip. (in/yr) from 30-s PRIZM grids (1970-2000), PC = Prec coefficient Elev = avg. subbasin elevation (ft) from 30-m DEMs, EC = Elev coefficient Slope = average subbasin slope (%), SG = Slope coefficient • Based on 23 USGS index flow gages (Armstrong et al., 2003) • No flow gages in PCAA or Cape Cod • For PCAA, the range of values is: • QN4 = 3.0-3.7 cfsm • QN9 = 0.1-0.7 cfsm

20. PCAA Natural Streamflows

21. Water Budget Calculations Impact (mgd) = SD – SW + (WS–WW–IRR–RIA+GD–GW)*SFAC Impact (cfsm) = Impact (mgd) * 1.547 cfs/mgd / Area (mi2) Impact (%) = Impact (cfsm) / QN (cfsm) * 100

22. PCAA Water Budgets Report • Summarizes subbasin results within the aquifer boundary • Outlines general mitigation measures

23. Impact Maps April September

24. Impact Table for September

25. Remediation Options • Water Conservation • Withdrawal Optimization • Stormwater Recharge • Wastewater Recharge and Reuse • Water Transfers and Trading

26. Water Budgets ─ Implications for PCAA • Identifies impacts by subbasin • Roadmap for protection and/or remediation • Sets up framework for flow trading