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| Massachusetts and Rhode Island Water Science Center |
U.S. Geological Survey, Scientific Investigations Report 2005-5256
By Mark T. Nimiroski and Emily C. Wild
In cooperation with the Rhode Island Water Resources Board
This report is available as a pdf
During the 1999 drought in Rhode Island, below-average precipitation caused a drop in ground-water levels and streamflow was below long-term averages. The low water levels prompted the U. S. Geological Survey and the Rhode Island Water Resources Board to conduct a series of cooperative water-use studies. The purpose of these studies is to collect and analyze water-use and water-availability data in each drainage area in the State of Rhode Island. The West Narragansett Bay study area, which covers 118 square miles in part or all of 14 towns in coastal Rhode Island, is one of nine areas investigated as part of this effort. The study area includes the western part of Narragansett Bay and Conanicut Island, which is the town of Jamestown. The area was divided into six subbasins for the assessment of water-use data. In the calculation of hydrologic budget and water availability, the Hunt, Annaquatucket, and Pettaquamscutt River Basins were combined into one subbasin because they are hydraulically connected.
Eleven major water suppliers served customers in the study area, and they supplied an average of 19.301 million gallons per day during 1995?99. The withdrawals from the only minor supplier, which was in the town of East Greenwich in the Hunt River Basin, averaged 0.002 million gallons per day. The remaining withdrawals were estimated as 1.186 million gallons per day from self-supplied domestic, commercial, industrial, and agricultural users. Return flows from self-disposed water (individual sewage-disposal systems) and permitted discharges accounted for 5.623 million gallons per day. Most publicly disposed water (13.711 million gallons per day) was collected by the Rhode Island Economic Development Corporation, and by the East Greenwich, Fields Point, Jamestown, Narragansett, and Scarborough wastewater-treatment facilities. This wastewater was disposed in Narragansett Bay outside of the study area.
The PART program, a computerized hydrograph-separation application, was used to determine water availability in the study area on the basis of low flows measured at a nearby index station, the Pawcatuck River at Wood River Junction, Rhode Island. Water availability was defined as the 75th, 50th, and 25th percentiles of the total base flow; the base flow minus the 7-day, 10-year flow; and the base flow minus the Aquatic Base Flow at the index station. The base-flow contributions per unit area of sand and gravel deposits and of till were computed for June, July, August, and September for the index station and multiplied by the areas of sand and gravel and till in the subbasins. The calculated base flows at the index station were lowest in August at the 75th, 50th, and 25th percentiles for total base flow and for two additional low-flow scenarios.
Because water withdrawals and use are greater during June, July, August, and September than at other times of the year, water availability was compared to water withdrawals in the subbasins for these summer months. Ratios were calculated by dividing the summer withdrawals by the water availability at the 75th, 50th, and 25th percentiles, and these percentiles of the base flow minus the two low flows for each subbasin. The closer this ratio is to one, the closer the withdrawals are to the estimated water available. These ratios allow comparisons of the use of water to the available water from one subbasin to another. The ratios were highest in July for the 50th percentile of the estimated gross yield minus the Aquatic Base Flow. The ratios ranged from 0.01 in the Providence and Seekonk subbasin to 0.38 in the Hunt-Annaquatucket-Pettaquamscutt subbasin for the 50th percentile of the gross yield minus the 7Q10 for August.
A long-term (1941-2000) water budget was calculated for the study area to assess the basin inflows and outflows. The water withdrawals and return flows used in the budget were from 1995 through 1999. Inflow was assumed to equal outflow. The total water budget was 146.29 million gallons per day for the combined Hunt-Annaquatucket-Pettaquamscutt subbasin, 48.71 million gallons per day for the Greenwich Bay subbasin, 238.98 million gallons per day for the Providence and Seekonk Rivers subbasin, and 21.32 million gallons per day for the Conanicut Island subbasin. The estimated inflows from precipitation, streamflow from upstream basins, and wastewater return flow for the entire study area were 59.3, 38.5, and 2.2 percent, respectively. The estimated outflows for the study area from evapotranspiration, streamflow, and water withdrawals were 24.9, 73.9, and 1.2 percent, respectively.
Abstract 1
Introduction 2
Purpose and Scope 2
Previous Investigations 2
Description of the Study Area 4
Population 4
Sand and Gravel Aquifers and Ground-Water Reservoirs 4
Climate 8
Land Use 9
Surface Water 9
Minor Civil Divisions 13
Subbasins 13
Annaquatucket River Subbasin 13
Greenwich Bay Subbasin 15
Hunt River Subbasin 16
Pettaquamscutt River Subbasin 16
Providence and Seekonk Rivers Subbasin 16
Conanicut Island Subbasin 17
Water Use 17
New England Water-Use Data System 17
Public Water Supply and Interbasin Transfers 17
Domestic Water Use 19
Public-Supply Use 19
Self-Supply Use 21
Commercial and Industrial Water Use 21
Public-Supply Use 21
Self-Supply Use 25
Agricultural Water Use 25
Return Flow and Interbasin Transfers 33
Site-Specific Return Flow 33
Aggregate Return Flow 33
Interbasin Transfers 33
Water Availability 37
Summer Water Availability By Subbasin 38
Water Budget 40
Summary and Conclusions 41
Selected References 46
Glossary 53
1–3. Maps showing:
1. Streamflow-gaging stations, USGS wells, and climatological stations in the West Narragansett Bay area 3
2. Towns, counties, subbasins, hydrography, and sand and gravel deposits in the West Narragansett Bay area, coastal Rhode Island 5
3. Water-supply districts, RIPDES sites, and wastewater-treatment plants in the West Narragansett Bay area 14
4–13. Diagrams showing:
4. Jamestown Water Division withdrawals, distribution, and estimated use, West Narragansett Bay area 18
5. Kent County Water Authority withdrawals, distribution, and estimated use, West Narragansett Bay area 20
6. Narragansett Water Department distribution and estimated use, West Narragansett Bay area 21
7. North Kingstown Water Department withdrawals, distribution, and estimated use, West Narragansett Bay area 22
8. Providence Water Supply Board distribution and estimated use, West Narragansett Bay area 23
9. Pawtucket Water Supply Board distribution and estimated use, West Narragansett Bay area 24
10. Rhode Island Economic Development Corporation withdrawals, distribution, and estimated use, West Narragansett Bay area 25
11. South Kingstown Water Department withdrawals, distribution, and estimated use, West Narragansett Bay area 30
12. United Water of Rhode Island distribution and estimated use, West Narragansett Bay area 31
13. Warwick Water Authority distribution and estimated use, West Narragansett Bay area 32
14. Map showing ratio of withdrawals (1995–99) to estimated availability (1957–99) during August and graphs showing availability for June, July, August, and September for the West Narragansett Bay area 39
1. Total town population by subbasins for 1990, estimated populations, and estimated populations on public and self-supply and on public and self-disposal of water in the West Narragansett Bay area, coastal Rhode Island, 1995–99 6
2. Land use and sand and gravel areas in the West Narragansett Bay area 7
3. Summary of climatological data for the West Narragansett Bay area 8
4. Land-use areas served by major public-water suppliers in the West Narragansett Bay area 10
5. Estimated water use by category, town, and subbasin in the West Narragansett Bay area, 1995–99 11
6. Defined subbasins in the West Narragansett Bay study area in comparison to the 10-digit and 12-digit HUC areas in the National Hydrography Dataset 12
7. Summary of total land area, land area in the study area, total 1990 populations, estimated 1995–99 populations, and land-use area by category in the West Narragansett Bay area 15
8. Minor suppliers by subbasin in the West Narragansett Bay area 15
9. Estimated consumptive water use by town and subbasin in the West Narragansett Bay area, 1995–99 26
10. Estimated water use for each 2-digit Standard Industrial Classification code by town in the West Narragansett Bay area, 1995–99 27
11. Estimated domestic, commercial, industrial, and metered return flow in the West Narragansett Bay area, 1995–99 34
12. RIPDES sites by town and subbasin in the West Narragansett Bay area, 1995–99 35
13. Return flow from wastewater-treatment facilities within and outside of the West Narragansett Bay area, 1995–99 36
14. Summary of estimated water withdrawals, imports, exports, use, nonaccount water use, consumptive use, and return flow in the West Narragansett Bay area, 1995–99 36
15. U.S. Geological Survey streamflow-gaging stations and minimum streamflows pertinent to the West Narragansett Bay area 37
16. Average water withdrawals for June, July, August, and September in the subbasins of the West Narragansett Bay area, 1995–99 38
17. Summary of water availability from sand and gravel deposits and from till for June, July, August, and September in the West Narragansett Bay area, 1995–99 42
18. Summary of total water availability for June, July, August, and September in the West Narragansett Bay area, 1995–99 44
19. Summary of ratios of water withdrawals to availability for June, July, August, and September in the West Narragansett Bay area, 1995–99 45
20. Average water budget by subbasin for the West Narragansett Bay area 46
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Suggested Citation:
Nimiroski, M.T., and Wild, E.C. Water use and availability in the West Narragansett Bay Area, coastal Rhode Island 1995-99: Scientific Investigations Report 2005-5256, 54 p.
For more information about USGS activities in Massachusetts, visit the USGS Massachusetts-Rhode Island Water Science Center home page.
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