Strategic Planning Workshop Rhode Island Water Resources Board
Strategic Planning Workshop Rhode Island Water Resources Board Water Availability An Overview of Water Supply and Water Resources May 5, 2011
Strategic Planning • • • Introduction Organizational Mission Plan Mission Past Studies and Investigations Workshops
Water Resources Major Public Water Supplies Study Areas 47 Existing Interconnections
Current Capacity Water Supply Area (Supplemental Water Studies) Total Capacity (Sources + Purchased Water) (MGD) Providence Northern Rhode Island 83 42. 5 East Bay Area 28. 87 West Bay, Central and Southern 63. 88 Richmond Water Supply System 0. 87 Westerly Water Division 7. 16 Block Island Water Company 0. 29 TOTAL 226. 57
Groundwater and Surface Water Resources
WRB Inventory of Water Resources • 7 basin studies • Watersheds (HUC 10 and 12) • Resource Inventory • Hydrology • Water budget • Summer Baseflow – Subbasin level – By study area (basin) Study Areas 10 Digit HUC
Watersheds • Boundaries define surface water drainage to a point. • Follow the highest ridgeline around the stream channels and meet at the lowest point, outflow. • Vary in size • Watershed and basins are interchangeable terms
Resource Inventory What the Glaciers Left Behind • How do hydrology and geology impact our options? • Interpreting and applying the studies
Water Budget Total Precipitation Basin Study Total Precipitation (MGD) Blackstone 452. 17 Woonasquatucket/Moshassuck 171. 26 Pawtuxet/Quinebaug 692. 20 East Narragansett Bay 289. 50 West Narragansett Bay 270. 04 Pawcatuck 715. 20 South Coastal 135. 20 Total Statewide 2, 725. 57
Water Budget Total Water Resources Basin Study Total Inflow/ Outflow (MGD) Blackstone 815. 83 Woonasquatucket/Moshassuck 175. 29 Pawtuxet/Quinebaug 723. 10 East Narragansett Bay 292. 10 West Narragansett Bay 455. 30 Pawcatuck 723. 10 South Coastal 136. 40 Total Statewide 3, 321. 12
Safe Yield • RIGL 46 -15. 7 -2 defines safe yield as a sustainable withdrawal that can be continuously supplied from a water source without adverse effects throughout a critical dry period with a one percent (1%) chance of occurrence, or one that is equivalent to the drought of record, whichever is worse.
Safe Yield Water Use and Availability Studies • Safe yield information for surface water reservoirs –Based on drought of record • Developing a methodology to determine groundwater safe yield –Based on baseflow
What is Baseflow ? • The flow in a channel sustained from groundwater discharge in the absence of direct runoff. • During most of the year, streamflow is composed of both groundwater discharge and runoff. • When groundwater provides the entire flow of a stream, baseflow conditions exist. • Only that portion of flow attributable to baseflow was considered available for use. • In some areas baseflow can be negative (losing streams).
Baseflow Water Use and Availability Reports • Estimate baseflow, gross yield, at the 25 th, 50 th, and 75 th percentiles of baseflow – June, July, August, and September • These estimates were made at the subbasin level but can be summarized by study area • How much of baseflow is available for use?
Why is Baseflow Important? • Sustainable flow in the channel • Temperature • Biological considerations • Water quality considerations
Time of year and variations among years affect water availability 600, 0 Monthly Mean Streamflow, and Baseflow Estimates from PART, at the Branch River at Forestdale gage (1111500), 1957 -99 500, 0 300, 0 Streamflow Mgal/d Baseflow Mgal/d 200, 0 100, 0 99 ян в- 97 в- ян 95 в- ян 93 в- ян 91 ян в- 89 в- ян 87 в- ян 85 в- ян 83 ян в- 81 в- ян 79 в- ян 77 в- ян 75 в- ян 73 ян в- 71 в- ян 69 в- ян 67 в- ян 65 в- ян 63 в- ян 61 в- ян 59 в- ян в- 57 0, 0 ян Flow in Mgal/d 400, 0
Flow Standards • Fixed flow standards – Aquatic Baseflow (ABF) – 7 Q 10 – Natural 7 Q 10 • Variable flow standards and depletions – RI Aquatic Baseflow (RI-ABF) – RI Stream Depletion Methodology (RI-SDM)
Aquatic Baseflow (ABF) • Aquatic Base Flow, U. S. Fish and Wildlife Service • Need at least 25 years of unregulated flow • DA at least 50 sq. mi. – ABF is often lower than streamflow during August and September • Example Forestdale gage – ABF = 38. 8 ft 3/s (25. 1 Mgal/d) – 83. 6 -percent flow duration
7 Q 10 • Definition • The 7 -day low flow • Commonly used to assess the capacity of a river to carry pollutants. • Example Forestdale gage – 7 Q 10 = 11. 9 ft 3/s (7. 9 Mgal/d) – 99. 5 percent flow duration (flow is lower 0. 5%)
Natural 7 Q 10 • Theoretical 7 -day low flow assuming little to no human effect on flows. – Forestdale, little difference between the 7 Q 10 and the Natural 7 Q 10 • Flows downstream of an impoundments (reservoir) – the natural 7 Q 10 may < measured 7 Q 10 • Basin with heavy pumping and no impoundments – the natural 7 Q 10 > measured 7 Q 10
600, 0 Monthly Mean Streamflow, Baseflow Estimates from PART, 7 Q 10, and Aquatic Baseflow at the Branch River at Forestdale gage (1111500), 1957 -99 500, 0 Streamflow Mgal/d 300, 0 Baseflow Mgal/d 7 Q 10 ABF 200, 0 100, 0 99 в- 97 ян вян 95 в- 93 ян в- 91 ян вян 89 в- 87 ян в- 85 ян вян 83 в- 81 ян в- 79 ян вян 77 в- 75 ян в- 73 ян ян в- 71 в- 69 ян в- 67 ян вян 65 в- 63 ян в- 61 ян в- 59 ян в- 57 0, 0 ян Flow in Mgal/d 400, 0
Rhode Island- Aquatic Baseflow (RIABF) RI specific modifications to the US Fish and Wildlife Aquatic Base Flow (ABF) methodology to better represent the climate and streamflow conditions found in RI.
How is RI-ABF Calculated? • Forestdale in the Eastern Highlands data set • DA for the Forestdale gage is 91. 2 sq. mi. • To calculate the RI-ABF – multiply DA by the RI-ABF flow values (table 5. 1) • Example Forestdale gage – June RI-ABF = 74. 8 ft 3/s (48. 4 Mgal/d) – 65. 6 -percent flow duration
DRAFT Stream Depletion Methodology (RIDEM, 2010) 1. Classification based on watershed and other characteristics 2. Links seasonal flow variations and ecology needs 3. Quantifies allowable stream flow depletions as a percentage of the natural 7 Q 10
Monthly Mean Streamflow, Baseflow Estimates from PART, 7 Q 10, Aquatic Baseflow, RI Aquatic Baseflow, and SDM Net Flow, at the Branch River at Forestdale gage (1111500), 1995 -99 400, 0 350, 0 Flow in Mgal/d 300, 0 Streamflow Mgal/d Baseflow Mgal/d 250, 0 7 Q 10 200, 0 ABF RI-ABF 150, 0 SDM Net Flow 100, 0 50, 0 янв-95 янв-96 янв-97 янв-98 янв-99
400, 0 350, 0 Monthly Mean Streamflow, Baseflow Estimates from PART, 7 Q 10, Aquatic Baseflow, RI Aquatic Baseflow, and SDM Net Flow, plus Five Percentiles of Baseflow at the Branch River at Forestdale gage (1111500), 1995 -99 300, 0 Streamflow Mgal/d Baseflow Mgal/d 250, 0 7 Q 10 ABF RI-ABF SDM Net Flow 150, 0 10 th 25 th 50 th 100, 0 75 th 90 th 50, 0 в 9 ма 5 р9 ма 5 й 9 ию 5 л 9 се 5 н 9 но 5 я 9 ян 5 в 9 ма 6 р9 ма 6 й 9 ию 6 л 9 се 6 н 9 но 6 я 9 ян 6 в 9 ма 7 р9 ма 7 й 9 ию 7 л 9 се 7 н 9 но 7 я 9 ян 7 в 9 ма 8 р9 ма 8 й 9 ию 8 л 9 се 8 н 9 но 8 я 9 ян 8 в 9 ма 9 р9 ма 9 й 9 ию 9 л 9 се 9 но 9 я 99 0, 0 ян Flow in Mgal/d 200, 0
Percent of flow remaining in Natural System After Allowable Depletion Example Forestdale gage Date Jan-97 Feb-97 Mar-97 Apr-97 May-97 Jun-97 Jul-97 Aug-97 Sep-97 Oct-97 Nov-97 Dec-97 ------Percent Remaining----- Streamflow Mgal/d Baseflow Mgal/d 92. 4 90. 3 91. 9 91. 1 90. 9 89. 3 95. 2 92. 9 92. 3 91. 0 86. 8 86. 6 81. 0 79. 5 83. 2 79. 5 82. 5 77. 0 79. 1 73. 5 87. 7 82. 5 84. 6 81. 9
Conclusions • Several Flow Standards have been considered in the past – * ABF, 7 Q 10 and Natural 7 Q 10 • More recent standards have evolved to mimic the natural hydrograph – *RI-ABF, DRAFT SDM methodology • What standard will support future water supply, economic development and population needs? – * Alternate SDM, % of baseflow
Policy Considerations • Any use of ground water changes the subsurface and surface environment (that is, the water must come from somewhere). • Public policy issue is to understand the tradeoffs between ground-water use and changes to the environment and set a threshold for what level of change becomes undesirable.
Scituate Reservoir
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