Operational and Water
Quality Summary Report
for Grand Lake and Shadow Mountain Reservoir
2010
Revision 1
Operational and Water Quality Summary Report for Grand Lake and Shadow Mountain Reservoir 2010
This report was prepared for:
Grand County Northern Water U.S. Bureau of Reclamation
by:
Jean Marie Boyer, PhD., PE, Hydros Consulting Inc. Christine Hawley, M.S., Hydros Consulting Inc.
We wish to thank members of the Three Lakes Nutrient Study Technical Committee and external reviewers for their thoughtful review of, and comments on, the draft of this report. Your comments led to valuable insights and helped to produce a more in-depth analysis. December 2, 2011
Revision 1: Replaced Figures 28 and 74 with corrected versions.
Issued March 16, 2012
December 2, 2011 Page i Operational and Water Quality Summary Report for Grand Lake and Shadow Mountain Reservoir 2010
Table of Contents
I. Introduction ...... 1 A. Statement of Problem and Background Information ...... 1 B. Purpose and Scope of Report ...... 4
II. Three Lakes System Operations ...... 5
III. Factors Impacting Water Clarity ...... 7
IV. Data and Analysis ...... 10 A. Data Sources ...... 10 B. Conditions in Previous Years (2007-2009) ...... 11 1. Hydrology and C-BT Operations ...... 11 2. Lake and Reservoir Water Clarity ...... 19 3. Water Clarity During „Stop-Pump‟ Periods ...... 23 4. Nutrient Loading (2007-2009) ...... 27 5. Meteorology...... 33 6. Grand Lake Clarity Standard Assessment (2007-2009)...... 44 C. Conditions in 2010 ...... 46 1. Hydrology and C-BT Operations ...... 46 2. Lake and Reservoir Water Clarity ...... 54 3. Conditions at Connecting Channel ...... 61 4. Nutrient Loading (2010) ...... 64 5. Meteorology...... 70 6. Grand Lake Clarity Standard Assessment (2010) ...... 75
V. Lessons Learned and Recommendations ...... 77
VI. References ...... 80
Appendix A: Three Lakes Clarity Monitoring Program…….…..……….A-1
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List of Figures
Figure 1. The Three Lakes System ...... 1 Figure 2. Major Watersheds that Contribute Water to the Three Lakes System ...... 2 Figure 3. Historical Secchi-Depth Measurements for Grand Lake (Data are from various locations in the lake and do not include measurements taken with the use of a view scope.) ...... 3 Figure 4. Breakdown of Light-Attenuating Constituents in Water ...... 8 Figure 5. Tributary and Pumped Inflows into the Three Lakes System (2007-2009) Tributary Inflows: North Inlet, East Inlet, North Fork of the Colorado River, Stillwater Creek, Columbine Creek, Roaring Fork, and Arapaho Creek. Pumped Inflows: Windy Gap Pipeline and Willow Creek Pump Canal Note: Stop-pump periods are shaded...... 12 Figure 6. Outflows from the Three Lakes System (2007-2009) Stop-pump periods are shaded. ... 13 Figure 7. Flow between the Three Water Bodies (2007-2009) (Stop-pump periods are shaded. When flow is negative, the direction of flow is reversed) ...... 13 Figure 8. Farr Pumping Plant Flows (Granby Pump Canal) –2007 ...... 14 Figure 9. Farr Pumping Plant Flows (Granby Pump Canal) –2008 (Shaded box denotes stop-pump period.) ...... 14 Figure 10. Farr Pumping Plant Flows (Granby Pump Canal) –2009 (Shaded box denotes stop-pump period.) ...... 15 Figure 11. Surface Water Elevation for Granby Reservoir (2007-2009) ...... 15 Figure 12. Inflows into Grand Lake by Source (2007-2009) Total Average Inflow 316,469 AF/yr.. 18 Figure 13. Inflows into Shadow Mountain Reservoir by Source (2007-2009) Total Average Inflow 332,464 AF/yr ...... 18 Figure 14. Inflows into Granby Reservoir by Source (2007-2009) Total Average Inflow 300,325 AF/yr ...... 19 Figure 15. Grand Lake Secchi-Depth Data (All Locations, View-Scope Data) – 2007-2009 ...... 21 Figure 16. Grand Lake Secchi-Depth Data (All Locations, Non- View-Scope Data) – 2007-2009 .... 21 Figure 17. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2007-2009 ...... 22 Figure 18. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, Non-View Scope Data) – 2007-2009 ...... 22 Figure 19. Grand Lake Secchi-Depth Data During 2008 Stop-Pump Period (All Locations, View- Scope Data) Stop-pump period is shaded. Inflow and Farr Pumping are also indicated...... 24 Figure 20. Shadow Mountain Reservoir Secchi-Depth Data During 2008 Stop-Pump Period (All Locations, View-Scope Data) Stop-pump period is shaded. Inflows are also indicated...... 24 Figure 21. Grand Lake Secchi-Depth Data During 2009 Stop-Pump Period (All Locations, View- Scope Data) Stop-pump period is shaded. Inflow and Farr Pumping are also indicated...... 26 Figure 22. Shadow Mountain Reservoir Secchi-Depth Data During 2009 Stop-Pump Period (All, Locations, View-Scope Data) Stop-pump period is shaded. Inflows are also indicated...... 26 Figure 23. Average Annual Total Phosphorus Load into Grand Lake (2007-2009 Average, Total = 5,844 kg/yr) ...... 29 Figure 24. Average Annual Total Phosphorus Load into Shadow Mountain Reservoir (2007-2009 Average, Total = 11,098 kg/yr) ...... 29
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Figure 25. Average Annual Total Phosphorus Load into Granby Reservoir (2007-2009 Average, Total = 16,035 kg/yr) ...... 30 Figure 26. Average Annual Total Nitrogen Load into Grand Lake (2007-2009 Average, Total = 123,435 kg/yr) ...... 32 Figure 27. Average Annual Total Nitrogen Load into Shadow Mountain Reservoir (2007-2009 Average, Total = 122,999 kg/yr) ...... 32 Figure 28. Average Annual Total Nitrogen Load into Granby Reservoir (2007-2009 Average, Total = 185,837 kg/yr) ...... 33 Figure 29. Locations of Weather Stations – (1) = „Grand Lake 6 SSW‟ (2) = „Native Grass Site at Windy Gap Reservoir‟ ...... 34 Figure 30. Daily Maximum Air Temperature at Weather Station „Grand Lake 6 SSW‟ (1-year Running Average) with Trend Line ...... 35 Figure 31. Daily Minimum Air Temperature at Weather Station „Grand Lake 6 SSW‟ (1-year Running Average) with Trend Line ...... 35 Figure 32. Average Monthly Air Temperature at Weather Station „Grand Lake 6 SSW‟ ...... 36 Figure 33. Boxplot of Average Monthly Air Temperature at Weather Station „Grand Lake 6 SSW‟ . 36 Figure 34. Annual Precipitation at Weather Station „Grand Lake 6 SSW‟ with Trend Line ...... 37 Figure 35. Average Monthly Precipitation at Weather Station „Grand Lake 6 SSW‟ (2007-2009) .. 38 Figure 36. Boxplot of Average Monthly Precipitation at Weather Station „Grand Lake 6 SSW‟ Thick black line: 50th percentile Upper and lower edges of the box: 25th and 75th percentiles Whiskers extend to the 5th and 95th percentiles Open circles are observations above or below the 95th or 5th percentiles, respectively ...... 38 Figure 37. Daily Solar Radiation at Weather Station „Windy Gap Reservoir‟ – 2007 ...... 39 Figure 38. Daily Solar Radiation at Weather Station „Windy Gap Reservoir‟ – 2008 ...... 39 Figure 39. Daily Solar Radiation at Weather Station „Windy Gap Reservoir‟ - 2009 ...... 39 Figure 40. Wind Speed at Weather Station „Windy Gap Reservoir‟‟ – 2007 ...... 40 Figure 41. Wind Speed at Weather Station „Windy Gap Reservoir‟‟ – 2008 ...... 40 Figure 42. Wind Speed at Weather Station „Windy Gap Reservoir‟‟ – 2009 ...... 41 Figure 43. Air Temperature and Secchi Depth (View-Scope Data) at SM-MID, Data from 2005-2010 ...... 43 Figure 44. Air Temperature and Secchi Depth (View-Scope Data) at GL-MID, Data from 2005-2010 ...... 43 Figure 45. Grand Lake Clarity Standards Assessment (View-Scope Data) “Standard” is the 4 m value described in Regulation 33...... 45 Figure 46. Grand Lake Clarity Standards Assessment (Non-View Scope Data) “Standard” is the 4 m value described in Regulation 33...... 45 Figure 47. Shadow Mountain Reservoir Residence Time (2010) ...... 46 Figure 48. Tributary and Pumped Inflows into the Three Lakes System (2007-2010) Tributary Inflows: North Inlet, East Inlet, North Fork of the Colorado River, Stillwater Creek, Columbine Creek, Roaring Fork, and Arapaho Creek. Pumped Inflows: Windy Gap Pipeline and Willow Creek Pump Canal Note: Stop-pump periods are shaded...... 48 Figure 49. Outflows from the Three Lakes System (2007-2010) Stop-pump periods are shaded. . 48 Figure 50. Flow between the Three Water Bodies (2007-2010) Stop-pump periods are shaded. ... 49 Figure 51. Farr Pumping Plant Flows (Granby Pump Canal) –2010 ...... 49 Figure 52. Surface Water Elevation for Granby Reservoir (2007-2010) ...... 50
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Figure 53. Inflows into Grand Lake by Source for 2010. Total Inflow 276,016 AF/yr ...... 53 Figure 54. Inflows into Shadow Mountain Reservoir by Source for 2010. Total Inflow 332,706 AF/yr ...... 53 Figure 55. Inflows into Granby Reservoir by Source for 2010. Total Inflow 301,706 AF/yr ...... 54 Figure 56. Grand Lake Secchi-Depth Data (All Locations, View-Scope Data) – 2007-2010 ...... 55 Figure 57. Grand Lake Secchi-Depth Data (All Locations, Non-View Scope Data) – 2007-2010 ...... 56 Figure 58. Grand Lake Secchi-Depth Data (All Locations, View-Scope Data) –2010 ...... 56 Figure 59. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2007- 2010 ...... 58 Figure 60. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, Non- View Scope Data) – 2007-2010 ...... 59 Figure 61. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2010 ...... 59 Figure 62. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2009 ...... 60 Figure 63. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2008 ...... 60 Figure 64. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2007 ...... 61 Figure 65. Flow and Water Quality at the Connecting Channel between Grand Lake and Shadow Mountain Reservoir (2010) (Shaded box indicates flow in the direction of Grand Lake to SMR.) .... 62 Figure 66. Chlorophyll a as a Function of Flow Rate at the Connecting Channel between Grand Lake and Shadow Mountain Reservoir (2010) ...... 63 Figure 67. Turbidity as a Function of Flow Rate at the Connecting Channel between Grand Lake and Shadow Mountain Reservoir (2010) ...... 63 Figure 68. Comparisons between Computed and Measured Flow and Direction in the Connecting Channel ...... 64 Figure 69. Total Phosphorus Load into Grand Lake (2010 Average = 4,582 kg/yr) ...... 66 Figure 70. Total Phosphorus Load into Shadow Mountain Reservoir (2010 Average = 10,196 kg/yr) ...... 66 Figure 71. Total Phosphorus Load into Granby Reservoir (2010 Average = 15,141 kg/yr) ...... 67 Figure 72. Total Nitrogen Load into Grand Lake (2010 Average = 108,959 kg/yr) ...... 69 Figure 73. Total Nitrogen Load into Shadow Mountain Reservoir (2010 Average = 126,486 kg/yr) ...... 69 Figure 74. Total Nitrogen Load into Granby Reservoir (2010 Average = 205,408 kg/yr) ...... 70 Figure 75. Average Monthly Air Temperature at Weather Station „Grand Lake 6 SSW‟ (2007-2010) ...... 71 Figure 76. Boxplot of Average Monthly Air Temperature at Weather Station „Grand Lake 6 SSW‟ (includes 2010) Thick black line: 50th percentile Upper and lower edges of the box: 25th and 75th percentiles Whiskers extend to the 5th and 95th percentiles Open circles are observations above or below the 95th or 5th percentiles, respectively ...... 71 Figure 77. 2010 Daily Maximum and Minimum Air Temperatures at Weather Station „Grand Lake 6 SSW‟ ...... 72 Figure 78. Average Monthly Precipitation at Weather Station „Grand Lake 6 SSW‟ (2007-2010) .. 72
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Figure 79. Boxplot of Average Monthly Precipitation at Weather Station „Grand Lake 6 SSW‟ (includes 2010) Thick black line: 50th percentile Upper and lower edges of the box: 25th and 75th percentiles Whiskers extend to the 5th and 95th percentiles Open circles are observations above or below the 95th or 5th percentiles, respectively ...... 73 Figure 80. Daily Precipitation at Weather Station „Grand Lake 6 SSW‟ (2010) ...... 73 Figure 81. Daily Solar Radiation at Weather Station „Native Grass Site at Windy Gap Reservoir‟ – 2010 ...... 74 Figure 82. Wind Speed at Weather Station „Native Grass Site at Windy Gap Reservoir‟‟ – 2010 .... 74 Figure 83. Grand Lake Clarity Standards Assessment (View-Scope Data) “Standard” is the 4 m value described in Regulation 33...... 75 Figure 84. Grand Lake Clarity Standards Assessment (Non-View Scope Data) “Standard” is the 4 m value described in Regulation 33...... 76
Figure A- 1. GCWIN Secchi Depth Sampling Sites ...... A-2
List of Tables Table 1. Sources of Data ...... 10 Table 2. Grand Lake Inflows, Outflows, and Residence Time (2007-2009) ...... 16 Table 3. Shadow Mountain Reservoir Inflows, Outflows, and Residence Time (2007-2009) ...... 16 Table 4. Granby Reservoir Inflows, Outflows, and Residence Time (2007-2009) ...... 17 Table 5. Minimum and Maximum Secchi-Depth Measurements for Grand Lake and Shadow Mountain Reservoir (All Locations, View-Scope Data) – 2007-2009 ...... 20 Table 6. Flow into Shadow Mountain Reservoir during the Stop-Pump Periods ...... 27 Table 7. Total Phosphorus Loads (kg/yr) by Water Body (2007-2009) ...... 28 Table 8. Annual Volume-Weighted Total Phosphorus Concentrations for Tributaries and Pumped Inflows (ug/L) (2007-2009)...... 30 Table 9. Total Nitrogen Loads (kg/yr) by Water Body (2007-2009) ...... 31 Table 10. Annual Volume-Weighted Total Nitrogen Concentrations for Tributaries and Pumped Inflows (ug/L) (2007-2009)...... 33 Table 11. Total Flow* (AF) in the Connecting Channel, July 1st – September 15th ...... 47 Table 12. Grand Lake Inflows, Outflows, and Residence Time (2007-2010) ...... 50 Table 13. Shadow Mountain Reservoir Inflows, Outflows, and Residence Time (2007-2010) ...... 51 Table 14. Granby Reservoir Inflows, Outflows, and Residence Time (2007-2010) ...... 52 Table 15. Minimum and Maximum Secchi-Depth Measurements for Grand Lake and Shadow Mountain Reservoir (All Locations, View-Scope Data) – 2007-2010 ...... 54 Table 16. Total Phosphorus Loads (kg/yr) by Water Body (2007-2010) ...... 65 Table 17. Annual Volume-Weighted Total Phosphorus Concentrations for Tributaries and Pumped Inflows (ug/L) (2007-2010)...... 67 Table 18. Total Nitrogen Loads (kg/yr) by Water Body (2007-2010) ...... 68 Table 19. Annual Volume-Weighted Total Nitrogen Concentrations for Tributaries and Pumped Inflows (ug/L) (2007-2010)...... 70
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I. Introduction
A. Statement of Problem and Background Information
Grand Lake is a large natural lake located in Grand County, Colorado adjacent to a small mountain community with the same name. It is the largest (by volume) and deepest (maximum depth = 265 feet) natural lake in Colorado. In addition to its use as a recreational amenity for local, state, national, and international visitors Grand Lake serves as part of the west slope water collection and conveyance system for the Colorado-Big Thompson (C-BT) Project. Shadow Mountain and Granby Reservoirs were constructed as part of the C-BT Project in the 1940s. These three water bodies, Grand Lake, Shadow Mountain Reservoir, and Granby Reservoir, are collectively referred to as the “Three Lakes System” (Figure 1). Shadow Mountain Reservoir has a relatively shallow maximum depth of only about 30 feet compared to Grand Lake and Granby Reservoir, which has a maximum depth of 221 feet. Shadow Mountain Reservoir and Grand Lake are used as conveyance facilities for water pumped from Granby Reservoir to the Adams Tunnel. Water level in both water bodies is maintained at a relatively constant level. The major watersheds that contribute water to the Three Lakes System are shown in Figure 2.
Figure 1. The Three Lakes System
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Shadow Mtn Res Direct Watershed
Willow Creek Watershed
Grand Lake Direct Watershed
Granby Res Direct Watershed
Windy-Gap Watershed
Figure 2. Major Watersheds that Contribute Water to the Three Lakes System
The C-BT Project had its beginnings in the late 1930‟s and became fully operational about 20 years later. Its main purpose is to collect water from the upper Colorado River Basin and transport it to the eastern slope of Colorado for supplemental agricultural, municipal and industrial use of the North Front Range. The C-BT Project is the largest trans-mountain water diversion project in Colorado which is operated in accordance with Senate Document No. 80, 75th Congress, 1st Session. The United States owns the C-BT Project and the Bureau of Reclamation (Reclamation)
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operates it jointly with Northern Water. The operation of the C-BT project, which began in the late 1940s / early 1950s, alters the natural sources of water and direction of flow in Grand Lake, as described in Section II.
For many of the residents that live near the Three Lakes, the decreased clarity in Grand Lake compared to pre C-BT Project conditions has been a major concern since the C-BT Project became operational. Historical Secchi-depth data1 reach back to 1941 but only one measurement is from the period when Grand Lake was simply a natural lake (Figure 3). A Secchi-depth value of 9.2 meters was recorded on September 6, 1941 (Pennak, 1955), but since the C-BT Project became operational, Secchi-depth readings have ranged from 1.2 to 5.7 meters. The lowest measurements were in 1953 and 2007 and the highest were in 2000 and 2010.
Figure 3. Historical Secchi-Depth Measurements for Grand Lake (Data are from various locations in the lake and do not include measurements taken with the use of a view scope.)
In 2006 Grand County, Northern Water, and a group of local residents jointly funded a preliminary reconnaissance-level study that conceptually identified several structural alternatives that could change circulation patterns in the Three Lakes System by avoiding use of Grand Lake as part of the C-BT conveyance system. One idea was the construction of a tunnel around Grand Lake. Another was the installation of a submerged flexible pipeline structure in Grand Lake itself. The effect of these proposals on the quality of water in Shadow Mountain Reservoir or Granby Reservoir was not considered.
In 2007, Grand County and Northwest Colorado Council of Governments requested that the Colorado Water Quality Control Commission adopt a water clarity standard for Grand Lake. The Commission adopted a 4-meter Secchi depth numerical clarity standard to be effective by 2015 if a
1 Secchi-depth measurements are an indication of water clarity. Measurements involve lowering a disk into the water until it is no longer visible. A larger value means greater clarity.
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more appropriate standard has not been determined (CDPHE, 2011). The narrative standard was set to “the highest level of clarity attainable, consistent with the exercise of established water rights and the protection of aquatic life” (CDPHE, 2011). Reclamation, Grand County, and Northern Water are cooperatively working together on a Grand Lake clarity study that will: 1) identify and evaluate factors that diminish Grand Lake clarity, 2) coordinate water quality monitoring that supports an appropriate clarity standard for Grand Lake as well as exploring options for meeting the clarity standard and, 3) identify and evaluate structural and nonstructural alternatives that could be implemented without adversely impacting C-BT Project yield. In addition, Reclamation, Grand County and Northern Water are also involved in an on-going, multi-year nutrient study to determine sources and quantities of nutrients contributing to water-quality changes in the Three Lakes System and in east slope C-BT facilities.
Among other things, operational modifications are being explored to improve clarity and water quality in Grand Lake. Reclamation, Grand County and Northern Water have been working since 2008 on alternative operations in order to improve water quality while meeting water delivery obligations.
B. Purpose and Scope of Report
The purpose of this report is fourfold. Based on an analysis of data for 2007-2010:
1. Provide a synopsis of operational changes and their effect on water quality and clarity in Grand Lake and Shadow Mountain Reservoir on an annual basis.
2. Provide an assessment of the effectiveness of operational modifications under meteorologic, hydrologic and environmental conditions.
3. Provide recommendations for consideration when examining future operational modifications.
4. Provide an assessment of non-operational factors that affect water quality and clarity and recommendations on how operational changes might complement and optimize these.
The following section contains a description of general C-BT Project operations. Factors impacting water clarity, in general, are described in Section III. Section IV includes a discussion of conditions for 2007 – 2009 followed by a summary for 2010. Recommendations and lessons learned are the focus areas of the final section.
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II. Three Lakes System Operations
Grand Lake is a natural lake with the majority of its pre-C-BT Project inflow provided by two tributaries emanating from the west side of Rocky Mountain National Park (North Inlet and East Inlet). Prior to construction of the C-BT Project, water from Grand Lake flowed westward through the Grand Lake outlet to its confluence with the North Fork of the Colorado River (now inundated by Shadow Mountain Reservoir). Construction of the west slope C-BT facilities, including the Adams Tunnel, Shadow Mountain Reservoir, Granby Reservoir, and the Farr Pumping Plant has significantly altered this hydrologic regime. The direction of flow though the connecting channel between Shadow Mountain Reservoir and Grand Lake (previously the Grand Lake outlet) is largely dependent upon the rate of diversion through the Adams Tunnel. During the spring runoff period, when the natural inflow to Grand Lake exceeds the Adams Tunnel diversion, the inflow in excess of the diversion flows westward from Grand Lake to Shadow Mountain Reservoir. However, when the Adams Tunnel diversions exceed the natural inflow to Grand Lake, water must be pumped at the Farr Pumping Plant from Granby Reservoir to Shadow Mountain Reservoir via the Granby Pump Canal. This operation causes water to flow eastward from Shadow Mountain Reservoir into Grand Lake through the connecting channel. This reverse flow condition generally occurs between late July and April of each year. Also note that the water flowing into Grand Lake from Shadow Mountain Reservoir is of poorer water quality (i.e., higher nutrient, chlorophyll a, and suspended solids concentrations) than flows from North Inlet and East Inlet.
In addition to tributary inflows, water can be pumped from two other drainage basins into the Three Lakes System. As part of the C-BT Project, water is pumped into Granby Reservoir from Willow Creek Reservoir, which is located to the west of the Three Lakes. Water is also pumped into Granby Reservoir from Windy Gap Reservoir, which is located to the southwest of the Three Lakes and is part of the Windy Gap Project as shown in Figure 1. The Windy Gap Project consists of a diversion dam on the Colorado River, a 445 acre-foot reservoir, a pumping plant, and a six-mile pipeline to Granby Reservoir. During spring runoff, water is pumped from Windy Gap Reservoir to Granby Reservoir, where it is stored for delivery through the C-BT Project facilities to water users on the North Front Range. Pumped flows from Willow Creek and Windy Gap typically occur during the April-July period. The volumes pumped from Willow Creek and Windy Gap to the Three Lakes vary from year to year, but average 48,000 AF and 29,000 AF, respectively, from 2005 through 2010. In 2010, 45,000 AF were pumped from Willow Creek and 6,800 AF were pumped from Windy Gap to Granby Reservoir.
Operations of the C-BT Project vary year-to-year and are based on several factors, including the requirements of Senate Document No. 80. Senate Document 80 lists 17 stipulations that are to be followed in operating the C-BT Project to meet the following five primary purposes for the project:
To preserve the vested and future rights in irrigation; To preserve the fishing and recreational facilities and the scenic attractions of Grand Lake, the Colorado River, and the Rocky Mountain National Park; To preserve the present surface elevations of the water in Grand Lake and to prevent a variation in these elevations greater than their normal fluctuation;
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To so conserve and make use of these waters for irrigation, power, industrial development, and other purposes, as to create the greatest benefits; and To maintain conditions of river flow for the benefit of domestic and sanitary uses of this water.
Factors that are considered when planning for Adams Tunnel diversions include the following:
East Slope Demands East Slope Storage Conditions Project Yield Power Generation Maintenance (Scheduled and Unscheduled) Water Quality/Clarity Recreation Flooding Potential Water Rights Protection of Project Facilities Shadow Mountain Reservoir Drawdown Potential
In the future, if the Windy Gap Firming Project is implemented, Windy Gap prepositioning will also become a factor. These individual factors become more or less important, depending on storage levels, water demands, infrastructure maintenance, and hydrologic conditions for a particular year.
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III. Factors Impacting Water Clarity
Visual water clarity, the distance at which objects can be seen through water, is typically described by Secchi-depth measurements. A Secchi disk is a circular plate divided into quarters painted alternately black and white. The disk is attached to a rope and lowered into the water until it is no longer visible.
Clarity is a function of the transmission of light through water and is thus dependent on the water‟s optical character. Optical character can be described by two properties:
Absorption; and Scattering.
These are the two processes by which light is attenuated after it enters the water.
Absorption represents the capture of photons by water, solutes, and particulate matter. The absorbed energy may be re-radiated as heat, used for plant photosynthesis, or emitted at a different wavelength (fluorescence). The net result is that fewer photons penetrate downward through the water column.
Scattering represents the deflection of photons from their original path, primarily by particles. Although scattering does not directly remove photons, it decreases light penetration in two ways: 1) by backscattering some of the light upward, and 2) by increasing the light‟s path length. The latter diminishes penetration by increasing the probability that the light will be absorbed. Turbidity is a measure of scattering.
Both absorption and scattering need to be considered to understand visual water clarity, in that one or both of these processes can dominate. In very clear lakes, large numbers of photons are transmitted unabsorbed and un-deviated by scattering.
Major light-attenuating constituents in water include the following:
Pure Water; Dissolved Matter; and Particulate Matter.
These categories can be broken down into sub-categories, as shown in Figure 4. Four of the boxes are outlined and represent key sub-categories. Inorganic dissolved matter is insignificant – ocean water has a high salt content but the dissolved inorganic matter does not significantly impact its clarity. In addition, the impact of pure water is constant for each water body. Thus, the components of interest are:
Algae; Non-Algal Organic Particulates (Detritus); Inorganic Particulates; and Dissolved Organic Matter.
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Figure 4. Breakdown of Light-Attenuating Constituents in Water
Each of these components has a different optical character (Davies-Colley, et al; 1993):
Algae: Algal biomass is typically described as chlorophyll a. Chlorophyll a absorbs strongly and usually scatters strongly. Often the scattering is higher than absorption and the scattering is dependent on cell size (small algae are much more efficient at scattering). Algae typically grows within the water body, depending on light, temperature, and nutrient concentrations although algae can also be transported from one water body to another via flow (e.g. through the connecting channel between Grand Lake and Shadow Mountain Reservoir).
Non-Algal Organic Particulates (Detritus): Detritus is non-living particulate matter and includes fragments of dead organisms. A potentially important source of detritus for the Three Lakes is dead and decomposing aquatic macrophytes from shallow Shadow Mountain Reservoir. Detritus typically absorbs strongly and scatters strongly.
Inorganic Particulates: Inorganic particulates (inorganic suspended solids) are of mineral origin and include sand-, silt – and clay-sized particles. Sources include inflowing water, shoreline erosion, and resuspension from the bottom of the lake/reservoir. Resuspension may be particularly important in Shadow Mountain Reservoir due to its shallow depth and often, large flow rates. Inorganic suspended solids absorb weakly and scatter intensely.
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Dissolved Organic Matter: Dissolved organic matter (DOM) is produced internally (e.g., algal excretion) and is received by inflowing water. DOM strongly absorbs and scattering is negligible.
Thus, water clarity is a function of the concentrations of these four components. It is important to identify the most important component (or components) and associated sources in order to plan how to best improve the clarity of a water body. Activities focused on the management of inorganic particles, for example, would be very different from activities focused on the control of algal growth.
In 2009, a focused data-collection effort and study was conducted to investigate the water clarity of Grand Lake (McCutchan, 2010). Based on an analysis of attenuation spectra, the study concluded that for most of the study period, 40-60% of the total attenuation in Grand Lake was due to non- algal particles (detritus + inorganic particulates)2. Fifty to sixty-five percent was attributed to non- algal particles for Shadow Mountain Reservoir. Algae were found to contribute 16-30% for Grand Lake and 16-27% to Shadow Mountain Reservoir.
The data collected for the 2009 study were also analyzed by Boyer (2011) based on mathematical relationships that consider absorption and scattering (Preisendorfer, 1986; Tyler 1968; Kirk 1981, 1994; Weidemann and Bannister 1986). Conclusions from this analysis indicated that for Grand Lake, 42-52% of light attenuation could be attributed to non-algal organic particulates and 23-39% could be attributed to algae. Inorganic suspended solids and dissolved organic matter were found to be less significant. Similar conclusions were made for Shadow Mountain Reservoir. These conclusions were in-line with the ones reported by McCutchan, 2010.
In addition to reporting and analyzing Secchi-depth data for Grand Lake and Shadow Mountain Reservoir, the evaluation of water clarity, herein, focuses on hydrology, water operations, meteorology, and nutrient loading. Each of these factors can play an important role in determining the concentrations of particulate matter and dissolved organic matter. It is recommended that future reports also include an annual in-depth look at the four specific light-attenuating constituents, listed above. Northern Water is currently in the process of preparing a monitoring plan to provide additional information to support differentiation of these constituents.
2 McCutchan, 2010, Table 4, page 38
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IV. Data and Analysis
A. Data Sources
Data were obtained from a variety of sources for this analysis (Table 1). Efforts were made to obtain all available data for the periods listed. Some sources of data contained redundant information. Data were resolved into a single complete dataset.
Table 1. Sources of Data
Type of Data Date Source Secchi-Depth Data (1941-2010) Grand County Watershed Information Network (GCWIN, 2011a; Northern Water, 2011b) Northern Water (Northern Water, 2011b) Reclamation (Northern Water, 2011b) USGS (Northern Water, 2011b; USGS, 2011a) University of Colorado (Pennak, 1955; McCutchan, 2010) EPA (EPA, 2011) Colorado Lake Volunteer Monitoring Program (CLVM Program, 2011) Grand County Volunteers (Northern Water, 2011b; GCWIN, 2011b)
Daily Hydrology and Operational Data Northern Water (Northern Water, 2011a) (2007-2010) Reclamation (USBR, 2011) USGS (USGS, 2011b)
Inflow Nutrient Data (2007-2010) Northern Water (Northern Water, 2011b) Reclamation (Northern Water, 2011b) USGS (USGS, 2011a, Northern Water, 2011b)
Connecting Channel Flow and Water USGS (USGS, 2011a) Quality (2010) Meteorology (1949-2010) NOAA (USBR, 2011) Northern Water (Northern Water, 2011c)
Precipitation Water Quality USGS (USGS, 2011a)
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B. Conditions in Previous Years (2007-2009)
1. Hydrology and C-BT Operations Daily hydrologic flows were obtained and estimated when missing (e.g. when gages were iced-up). The water balance includes all major tributary inflows, pumping operations, outflows, precipitation, evaporation, gains, and ungaged inflows for each water body. Gaged data are applied where available. Regressions and historical ratios were used to fill in missing information at gaged locations and to generate input for currently-ungaged tributaries. Ungaged gains are solved for by computing a water balance on Grand Lake and Shadow Mountain Reservoir, and apportioning the gains based on relative ungaged watershed area.
System-wide inflows and outflows for 2007 through 2009 are shown in the Figure 5 and Figure 6. Inflow from tributaries was lower in 2007. Outflows via the Adams Tunnel were highest in 2008 and lowest in 2009. Flow between the three water bodies is displayed in Figure 7. Flow at the connecting channel between Grand Lake and Shadow Mountain Reservoir was computed using a mass balance3. The year with the highest total flow from Shadow Mountain Reservoir to Grand Lake was 2007 (225,000 AF); the year with the lowest is 2009 (194,000 AF). The year 2009 thus had the highest volume of water moving from Grand Lake to Shadow Mountain Reservoir down to Granby Reservoir. „Stop-pump‟ periods (where the Farr Pumping Plant stopped pumping) occurred in August of 2008 and 2009 for 2-week periods (Figure 9 and Figure 10) and not in 2007 (Figure 8). More Farr pumping occurred in the months of May and June for 2008 than the other years.
Surface water elevations for Shadow Mountain Reservoir and Grand Lake are held relatively constant (operated within +/- 6 inches). An exception occurred just prior to 2007 when Shadow Mountain Reservoir was drawn-down approximately 10 feet from mid-October to mid-December, 2006 for aquatic weed management (Sisneros, 2010). The contents of Granby Reservoir can vary considerably, reaching peak storage in early July and the lowest storage in mid-April (Figure 11). Granby Reservoir‟s highest overall volume occurred in 2009.
Total annual flows and annual hydraulic residence times for each of the Three Lakes are listed in Table 2, Table 3, and Table 4. Note that the volume of each water body varies significantly (Grand Lake is 4 times larger than Shadow Mountain Reservoir; Granby Reservoir is over 5 times larger than Grand Lake). Although Shadow Mountain Reservoir is the smallest water body by volume, it receives the highest volume of inflow per year. Annual hydraulic residence times are computed based on the entire water body volume. Hydraulic residence times are also computed for the period July to September (the summer period when the Farr Pumping Plant typically operates) for Grand Lake and Shadow Mountain Reservoir. For Grand Lake, this summer computation is based on the volume of the epilimnion. The epilimnetic volume is used since much of the water flowing into Grand Lake from Shadow Mountain Reservoir moves across the top of Grand Lake from mid- summer when Farr pumping resumes after spring runoff and stratification is established, to just before fall turnover (Lieberman, 2008). In each case, the hydraulic residence time is computed as:
3 The displayed flow rates were computed taking precipitation and ungaged gains into account and are consistent with the values used in the Three Lakes Water-Quality Model. Mass balance computations made by Reclamation (Morris, 2011) do not account for precipitation and ungaged gains (R. Thomasson, USBR, personal communication, November 29, 2011).
December 2, 2011 Page 11 Operational and Water Quality Summary Report for Grand Lake and Shadow Mountain Reservoir 2010
( )
where:
Hydraulic residence time [days]
Average volume for the period of interest (total or epilimnetic) [AF]
Total Outflow over the period of interest [AF]
Number of days in the period of interest [days]
The distribution of inflows by water body can be found in Figure 12, Figure 13, and Figure 14. The majority of inflow into Shadow Mountain Reservoir and Grand Lake is due to pumping at the Farr Pumping Plant which is driven by the Adams Tunnel diversions.
Figure 5. Tributary and Pumped Inflows into the Three Lakes System (2007-2009) Tributary Inflows: North Inlet, East Inlet, North Fork of the Colorado River, Stillwater Creek, Columbine Creek, Roaring Fork, and Arapaho Creek. Pumped Inflows: Windy Gap Pipeline and Willow Creek Pump Canal Note: Stop-pump periods are shaded.
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Figure 6. Outflows from the Three Lakes System (2007-2009) Stop-pump periods are shaded.
Figure 7. Flow between the Three Water Bodies (2007-2009) (Stop-pump periods are shaded. When flow is negative, the direction of flow is reversed)
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Figure 8. Farr Pumping Plant Flows (Granby Pump Canal) –2007
Figure 9. Farr Pumping Plant Flows (Granby Pump Canal) –2008 (Shaded box denotes stop-pump period.)
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Figure 10. Farr Pumping Plant Flows (Granby Pump Canal) –2009 (Shaded box denotes stop-pump period.)
Figure 11. Surface Water Elevation for Granby Reservoir (2007-2009)
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Table 2. Grand Lake Inflows, Outflows, and Residence Time (2007-2009)
2007 2008 2009 Inflows (AF/yr) North Inlet 46,460 61,554 59,357 East Inlet 32,652 39,376 41,799 From SMR 224,626 206,064 193,605 Gains 12,289 9,740 20,200 Precipitation 579 592 515 Total 316,606 317,326 315,476 Outflows (AF/yr) To SMR 47,853 24,043 73,162 Adams Tunnel 262,643 285,822 236,628 Evap and Losses 6,124 7,471 5,655 Total 316,620 317,336 315,445 Hydraulic Average Annual Residence Time Based on Total 78 78 79 (days) Volume* Average July- September Based on 5 5 6 Epilimnetic Volume** *Average Total Volume for 2007-2009 = 67,897 AF **Average Epilimnetic Volume for 2007-2009 = 4,434 AF
Table 3. Shadow Mountain Reservoir Inflows, Outflows, and Residence Time (2007-2009)
2007 2008 2009 Inflows (AF/yr) North Fork 28,545 52,335 52,079 From Grand 47,853 24,043 73,162 From Granby 233,796 213,336 200,118 Gains 19,687 15,604 32,360 Precipitation 1,536 1,571 1,367 Total 331,417 306,889 359,086 Outflows (AF/yr) To Grand 224,626 206,064 193,605 To Granby 95,786 87,431 155,187 Evap and Losses 11,084 13,275 10,349 Total 331,496 306,770 359,141 Hydraulic Residence Average Annual Based 19 20 17 Time (days) on Total Volume* Average July-September 19 21 23 Based on Total Volume* *Average Total Volume for 2007-2009 = 16,925 AF
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Table 4. Granby Reservoir Inflows, Outflows, and Residence Time (2007-2009) 2007 2008 2009 Inflows (AF/yr) Arapaho 49,252 57,988 61,837 Stillwater 8,239 9,616 8,719 Roaring Fork 12,952 19,030 14,148 Columbine 8,808 13,282 9,888 Windy Gap 40,992 33,523 26,368 Willow Creek 39,348 57,709 57,078 Gains 2,689 3,994 2,971 From SMR 95,786 87,431 155,187 Precipitation 8,284 8,477 7,377 Total 266,350 291,050 343,573 Outflows (AF/yr) To SMR 233,796 213,336 200,118 To CO River 32,542 29,829 33,006 Evap and 30,677 23,115 39,007 Losses Total 297,015 266,280 272,131 Hydraulic Average Residence Time Annual (days) Based on 440 496 543 Total Volume* * Average Total Volume: 358,192 AF for 2007; 361,009 AF for 2008; 405,091 AF for 2009
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Figure 12. Inflows into Grand Lake by Source (2007-2009) Total Average Inflow 316,469 AF/yr
Figure 13. Inflows into Shadow Mountain Reservoir by Source (2007-2009) Total Average Inflow 332,464 AF/yr
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Figure 14. Inflows into Granby Reservoir by Source (2007-2009) Total Average Inflow 300,325 AF/yr
2. Lake and Reservoir Water Clarity Secchi-depth measurements for Grand Lake and Shadow Mountain Reservoir are described in this section. The current clarity monitoring program and sample sites are described in Appendix A.
All Secchi-depth data are included in the analysis and sampling location and frequency vary over time for both water bodies. Measurements taken with a view scope are shown separately from those taken without a view scope. The use of a view scope tends to minimize the effects of reflected light / wave action and surface particles and generally results in a greater and more reproducible value than without a view scope.
Minimum and maximum Secchi-depth measurements for Grand Lake and Shadow Mountain Reservoir by year can be found in Table 5. Grand Lake has slightly better water clarity than Shadow Mountain Reservoir. There is not much variation year-to-year, with the exception of Shadow Mountain Reservoir in 2009, where the maximum was higher by 1.5 meters over the 2007 maximum. Note that the frequency of data collection varies year-to-year; the fewest measurements were taken in 2007 and the highest number occurred in 2009. Due to differences in year-to-year sampling frequency and sampling locations, it is difficult to make direct comparisons between years using monthly averages and to draw meaningful conclusions. It is recommended that Secchi-depth measurements be taken consistently at the same sites on the same days in the future.
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Table 5. Minimum and Maximum Secchi-Depth Measurements for Grand Lake and Shadow Mountain Reservoir (All Locations, View-Scope Data) – 2007-2009 Grand Lake Shadow Mountain Reservoir Minimum Maximum Minimum Maximum 2007 1.4 4.9 1.2 3.1 2008 1.5 4.6 1.3 3.3 2009 2.0 4.9 1.5 4.6
a) Grand Lake
Secchi depths for Grand Lake are shown in Figure 15 and Figure 16. Measurements are categorized by month. A general improvement in clarity can be seen in the months of September and October. Patterns for July and August vary depending on the year. In general, clarity degrades between July and late August / early September.
The lake had the lowest reading in 2007 and the highest reading in 2009. The highest number of measurements with values less than 2 meters occurred in 2007. The year 2007 differed from the other years with respect to at least three factors. First of all, as mentioned in Section IV.B, Shadow Mountain Reservoir was drawn down in late 2006 for purposes of weed management. The low Secchi-depth readings in 2007 appear to be related to this event. Drawdowns can result in increases in non-algal organic particulate matter which subsequently decomposes into inorganic forms of phosphorus and nitrogen. Increases in both non-algal particulate matter and chlorophyll a (due to increases in inorganic nutrients) have a negative effect on water clarity. Although the drawdown occurred in Shadow Mountain Reservoir, Grand Lake is also impacted due to the large amount of flow from Shadow Mountain Reservoir to Grand Lake (Table 2).
Second, air temperatures during the summer of 2007 were high (described in a subsequent section, see Figure 32). Average monthly air temperatures in July and August were at or above the 95th percentile of the historical data. Temperatures for June and September were above the 75th percentile.
Third, Farr pumping patterns were different in 2007. There was essentially no pumping at the Farr Pumping Plant from the beginning of May through mid-July (Figure 8). Thus, flushing flows through Shadow Mountain were low during this period of unusually high air temperatures. When Farr pumping resumed in July, flows quickly reached >1,000 AF/day. In 2008 and 2009, Farr pumping resumed more gradually and at lower flow rates (Figure 9 and Figure 10). The total flow through the connecting channel from Shadow Mountain Reservoir to Grand Lake in the summer of 2007 was higher than other years (described in a subsequent section, see Table 11). Over the ten years (2001-2010), the highest August flow through the Farr Pumping Plant occurred in 2007. Each of these factors likely played a role in Grand Lake water clarity degradation during that year.
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Figure 15. Grand Lake Secchi-Depth Data (All Locations, View-Scope Data) – 2007-2009
Figure 16. Grand Lake Secchi-Depth Data (All Locations, Non- View-Scope Data) – 2007-2009
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b) Shadow Mountain
Secchi depths for Shadow Mountain Reservoir are shown in Figure 17 and Figure 18. Measurements are categorized by month. Similar to Grand Lake, the reservoir had the lowest reading in 2007 and the highest reading in 2009. Patterns for each month tend to vary year-to- year. In general, clarity degrades between July and late August / early September. Factors occurring in the summer of 2007 (as described in the above section on Grand Lake) also played a role in the degradation of Shadow Mountain Reservoir water clarity.
Figure 17. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2007-2009
Figure 18. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, Non-View Scope Data) – 2007-2009
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3. Water Clarity During „Stop-Pump‟ Periods In August of 2008 and 2009, the Farr Pumping Plant was stopped for a two-week period to observe the impact on Grand Lake water clarity. Although there was no water flowing from Shadow Mountain Reservoir to Grand Lake during these periods, some water continued to flow out the Adams Tunnel. Secchi depths during the stop-pump periods are described in this section. All clarity data displayed were taken with the use of view scope.
a) Stop-Pump Period 2008
The stop-pump period in 2008 was from August 1st through August 14th. Prior to August 1st, water clarity was declining in Grand Lake and Shadow Mountain Reservoir (Figure 19 and Figure 20). In Grand Lake, the lowest clarity was observed on July 28 (2.0 m average). During the stop-pump period, Grand Lake clarity improved from an average of 2.2 m to 3.5 m. Shadow Mountain Reservoir clarity also improved, although not as much (from an average of 1.8 m to 2.3 m). After the stop-pump period, the amount of pumping was gradually increased (Figure 9). Gradually is defined relative to the rate of increase in pumping that occurred in 2009; specifically, in 2008 pumping resumed with an increase in pumping of roughly 200 AF/d, taking about 5 days to reach the full rate. In contrast, pumping went from 0 to 827 AF/day in one day when pumping was resumed in 2009. In 2008, clarity continued to improve in Grand Lake after Farr Pumping resumed. Nine days after the pumps were turned on, the average Secchi-depth measurement in Grand Lake had continued to improve, reaching 3.75 m, and then began to decline, reaching 2.6 m on September 11th. Figure 19 shows distinct symbols for three frequently sampled locations across Grand Lake (GL-WES [closest to the connecting channel], GL-MID [central Grand Lake], and GL-ATW [closest to Adams Tunnel] to allow for a look at spatial patterns in the dataset. There are no strong spatial patterns in this 2008 Grand Lake dataset; however, measurements at GL-WES tend to show some of the shallowest Secchi results (lower clarity) when the pumping resumes, reflecting the proximity to the connecting channel and the source of water of lower clarity (Granby Reservoir).
For Shadow Mountain Reservoir, clarity also continued to improve after the stop-pump period and reached 3.0 m on August 26th. Clarity then declined to 1.6 m by September 9th. Note that the average clarity values described here were computed using all of the locations sampled on a particular day. This analysis would be improved if the same sites had been consistently sampled on the same days to eliminate any localized impacts on certain dates. Figure 20 shows distinct symbols for three sampled locations across Shadow Mountain Reservoir (SM-DAM [closest to the outlet of the Granby Pump Canal], SM-MID [central Shadow Mountain], and SM-NOR [closest to channel between Grand Lake and Shadow Mountain] to allow for a look at spatial patterns in the dataset. For 2008, there is a pattern of lesser clarity (shallower Secchi depths) at SM-NOR during pumping and non-pumping conditions. SM-DAM and SM-NOR show similar results, with the exception of a few cases during pumping of measurably greater clarity at SM-DAM.
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Figure 19. Grand Lake Secchi-Depth Data During 2008 Stop-Pump Period (All Locations, View- Scope Data) Stop-pump period is shaded. Inflow and Farr Pumping are also indicated.
Figure 20. Shadow Mountain Reservoir Secchi-Depth Data During 2008 Stop-Pump Period (All Locations, View-Scope Data) Stop-pump period is shaded. Inflows are also indicated.
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b) Stop-Pump Period 2009
The stop-pump period in 2009 was from August 13th through August 26th. Again, prior to the start of the stop-pump period, water clarity was declining in Grand Lake and Shadow Mountain Reservoir (Figure 21 and Figure 22). In Grand Lake, clarity readings declined to an average of 3.2 m on August 13th. During the stop-pump period, Grand Lake clarity improved and reached a value of 3.4 m at the end of the period (although an average of 3.9 m was observed in the middle of the period).
As opposed to 2008, Shadow Mountain Reservoir clarity declined from an average of 2.5 m to 1.9 m and the peak chlorophyll a concentration occurred. There was 30% more inflow into Shadow Mountain Reservoir during the stop-pump period in 2008 than there was in 2009 (Table 6). Note that less tributary flow would typically be expected later in the year and the stop-pump period occurred later in 2009 than in 2008. The increased flow in 2008 may have served to dilute and improve clarity conditions. After the 2009 stop-pump period, the amount of pumping was suddenly increased (Figure 10), as opposed to 2008, when operations resumed more gradually (Figure 9). Grand Lake responded (after a short clarity improvement of 3.6 m the day after the stop-pump period) and the Secchi-depth readings declined to 2.1 m by September 9th. Figure 21 shows distinct symbols for three frequently sampled locations across Grand Lake (GL-WES [closest to the connecting channel], GL-MID [central Grand Lake], and GL-ATW [closest to Adams Tunnel] to allow for a look at spatial patterns in the dataset. For 2009, GL-WES exhibits some of the worst clarity in Grand Lake prior to the stop-pump period then again for about a week immediately after pumping resumes.
Clarity in Shadow Mountain Reservoir improved after the stop-pump period from an average of 1.6 m to 4.0 m on September 14th. Again, note that the average values described here were computed using all of the locations sampled on a particular day. This analysis would be improved if the same sites had been consistently sampled on the same days to eliminate any localized impacts on certain dates. Figure 22 shows distinct symbols for three sampled locations across Shadow Mountain Reservoir (SM-DAM [closest to the outlet of the Granby Pump Canal], SM-MID [central Shadow Mountain], and SM-NOR [closest to channel between Grand Lake and Shadow Mountain] to allow for a look at spatial patterns in the dataset. For 2009, after pumping resumes, there is greater clarity at SM-DAM, with an apparent gradient of decreasing clarity to the channel connecting with Grand Lake. As McCutchan (2010) suggested, this may indicate that Granby is a source of clearer water. Further, this may suggest that the pumping operations cause resuspension of settled particulates across Shadow Mountain. Interestingly, this gradient across Shadow Mountain (particularly between SM-DAM and SM-MID) is more apparent in 2009 than in 2008, when pumping was resumed more gradually. This patterning could be an important key to operational optimization for water quality purposes, and needs additional study, including additional spatial and temporal sampling across Shadow Mountain.
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Figure 21. Grand Lake Secchi-Depth Data During 2009 Stop-Pump Period (All Locations, View- Scope Data) Stop-pump period is shaded. Inflow and Farr Pumping are also indicated.
Figure 22. Shadow Mountain Reservoir Secchi-Depth Data During 2009 Stop-Pump Period (All, Locations, View-Scope Data) Stop-pump period is shaded. Inflows are also indicated.
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Table 6. Flow into Shadow Mountain Reservoir during the Stop-Pump Periods Inflow into SMR (AF) 2008* 2009** From Grand 1,281 763 From Granby (Farr) 0 0 North Fork 1,400 1,193 Gains 601 504 Precipitation 73 59 Total 3,355 2,519 *8/1/08 – 8/14/08 **8/13/09 – 8/26/09
4. Nutrient Loading (2007-2009) Total phosphorus and total nitrogen loading into the Three Lakes System is described in this section. Sources are broken out by tributary, pumped source, internal loading, gains, precipitation, and stormwater contributions. Loadings were determined as part of the development of the Three Lakes Water-Quality model and were based on time series of flows (see Section IIV.B.1) and concentrations. Daily concentration time series for inflowing tributaries (North Inlet, East Inlet, Arapaho Creek, Stillwater Creek, North Fork, and Roaring Fork), pumped flows (Willow Creek and Windy Gap), and precipitation were developed based on observations (Table 1) and filled in where missing using methods described in Koltun, 2006. Precipitation concentrations were based on data from two USGS stations - East Inlet Near Grand Lake, CO, (9013500) and Green Ridge Precip Site Near Granby, CO, (401145105504700).
Nutrient concentrations for Columbine Creek and gains were assumed to be similar to nutrient concentrations of Arapaho Creek. Internal loading is based on nutrient release rates, hypolimnetic sediment area, and dissolved oxygen concentrations in the lowest model layer of each water body. Stormwater contributions are incorporated into the model as additional loads based on daily precipitation patterns.
a) Total Phosphorus
Total phosphorus loads by water body are listed in Table 7. In addition, the relative annual distributions of loads for 2007-2009 are reported in Figure 23, Figure 24, and Figure 25. Note that Shadow Mountain Reservoir, the smallest by volume, receives a disproportionate amount of total phosphorus loading. Total phosphorus loading into Grand Lake is higher than it would be under more natural conditions (receiving inflow from only North Inlet and East Inlet) by a factor of four to seven, depending on the year. Stormwater contributions are significant for Shadow Mountain Reservoir and for Granby Reservoir. Internal loads of total phosphorus are significant for Granby Reservoir due to low dissolved oxygen concentrations at the bottom of the reservoir and the large sediment area available for phosphorus release. Internal loads of total phosphorus in Shadow
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Mountain are highest in 2007 due to low dissolved oxygen concentrations in the reservoir, which developed as a result of high July air temperatures (Figure 33) and low Farr Pumping for May through mid-July. Inflow volume-weighted concentrations are listed in Table 8 by year. The highest concentrations occur at Stillwater Creek and the Windy Gap pipeline. The North Fork experienced significantly higher total phosphorus concentrations during the run-off period in 2008, resulting in increased loading for that year.
Table 7. Total Phosphorus Loads (kg/yr) by Water Body (2007-2009) Water Body Source 2007 2008 2009 Grand Lake North Inlet 510 1,141 831 East Inlet 266 496 451 From SMR 4,314 4,377 3,869 Gains 65 104 160 Precipitation 29 30 26 Stormwater 166 118 137 Internal Load 147 147 147 Total 5,497 6,413 5,621 Shadow Mtn Reservoir North Fork 778 4,792 1,294 From Grand 421 400 852 From Granby 4,966 6,055 5,982 Gains 104 167 256 Precipitation 78 79 69 Stormwater 1,659 1,175 1,521 Internal Load 1,328 661 656 Total 9,334 13,329 10,630 Granby Reservoir Arapaho 391 669 626 Stillwater 1,034 1,579 1,641 Roaring Fork 113 259 144 Columbine 77 190 103 Windy Gap 2,696 3,535 1,897 Willow Creek 1,168 2,934 2,699 Gains 16 45 23 From SMR 1,317 3,637 2,702 Precipitation 419 429 373 Stormwater 4,147 2,938 3,802 Internal Load 2,079 2,118 2,306 Total 13,457 18,333 16,316
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Figure 23. Average Annual Total Phosphorus Load into Grand Lake (2007-2009 Average, Total = 5,844 kg/yr)
Figure 24. Average Annual Total Phosphorus Load into Shadow Mountain Reservoir (2007-2009 Average, Total = 11,098 kg/yr)
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Figure 25. Average Annual Total Phosphorus Load into Granby Reservoir (2007-2009 Average, Total = 16,035 kg/yr)
Table 8. Annual Volume-Weighted Total Phosphorus Concentrations for Tributaries and Pumped Inflows (ug/L) (2007-2009)
Inflow 2007 2008 2009
North Inlet 9 15 11 East Inlet 7 10 9 North Fork 22 74 20 Arapaho 6 9 8 Stillwater 102 133 153 Roaring Fork 7 11 8 Columbine 7 12 8 Windy Gap 53 85 58 Willow Creek 21 41 38
b) Total Nitrogen
Total nitrogen4 loads by water body are listed in Table 9. In addition, the relative annual distributions of loads for 2007-2009 are reported in Figure 26, Figure 27, and Figure 28. Note that Shadow Mountain Reservoir, the smallest by volume, receives a disproportionate amount of total nitrogen loading. Total nitrogen loading into Grand Lake is higher than it would be under more
4 Total nitrogen is computed by summing total Kjeldahl nitrogen (TKN) and nitrate + nitrite.
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natural conditions (receiving inflow from only North Inlet and East Inlet) by a factor of four to six, depending on the year. Stormwater contributions are significant for all three water bodies. Total nitrogen loads for the North Fork in 2007 and for the contribution from Grand Lake into Shadow Mountain Reservoir are lower than other years, predominantly due to lower flows (Table 3). Inflow volume-weighted concentrations are listed in Table 10. The highest concentrations occur at Stillwater Creek and the Windy Gap pipeline.
Table 9. Total Nitrogen Loads (kg/yr) by Water Body (2007-2009) Water Body Source 2007 2008 2009 Grand Lake North Inlet 13,215 19,355 17,519 East Inlet 7,848 10,444 12,678 From SMR 83,713 76,060 66,355 Gains 2,752 2,401 3,746 Precipitation 523 535 466 Stormwater 12,960 9,180 11,465 Internal Load 6,624 6,234 6,233 Total 127,635 124,209 118,462 Shadow Mtn Reservoir North Fork 7,796 20,068 17,848 From Grand 14,025 8,108 25,276 From Granby 75,760 71,496 62,762 Gains 4,409 3,847 6,000 Precipitation 1,387 1,420 1,236 Stormwater 17,626 12,485 16,157 Internal Load 962 165 164 Total 121,965 117,589 129,443 Granby Reservoir Arapaho 11,359 13,274 11,886 Stillwater 4,449 6,566 5,799 Roaring Fork 2,986 5,585 3,035 Columbine 2,081 4,124 2,194 Windy Gap 18,917 29,172 14,789 Willow Creek 9,526 18,248 14,280 Gains 574 1,122 588 From SMR 31,085 36,813 58,390 Precipitation 7,485 7,660 6,665 Stormwater 61,690 43,697 56,549 Internal Load 27,611 18,879 20,435 Total 177,763 185,140 194,610
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Figure 26. Average Annual Total Nitrogen Load into Grand Lake (2007-2009 Average, Total = 123,435 kg/yr)
Figure 27. Average Annual Total Nitrogen Load into Shadow Mountain Reservoir (2007-2009 Average, Total = 122,999 kg/yr)
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Figure 28. Average Annual Total Nitrogen Load into Granby Reservoir (2007-2009 Average, Total = 185,837 kg/yr)
Table 10. Annual Volume-Weighted Total Nitrogen Concentrations for Tributaries and Pumped Inflows (ug/L) (2007-2009)
Inflow 2007 2008 2009 North Inlet 231 255 239 East Inlet 195 215 246 North Fork 221 311 278 Arapaho 187 186 156 Stillwater 438 554 539 Roaring Fork 187 238 174 Columbine 192 252 180 Windy Gap 374 705 455 Willow Creek 196 256 203
5. Meteorology Meteorological data were obtained from two weather stations (Figure 29). Air temperature and precipitation data were available at the „Grand Lake 6 SSW‟ weather station (NOAA Station ID CO053500, latitude 40◦ 10‟ 54” N, longitude 105◦ 54‟ 15” W). Since wind speed and solar radiation data were not available at this station, these data were obtained from a station operated and maintained by Northern Water upstream of the confluence of the Colorado and Fraser Rivers near the Fraser River near Windy Gap Reservoir (Northern Water Station „Native Grass Site at Windy Gap Reservoir‟ latitude 40◦ 5‟ 49” N, longitude 105◦ 58‟ 19” W).
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Figure 29. Locations of Weather Stations – (1) = „Grand Lake 6 SSW‟ (2) = „Native Grass Site at Windy Gap Reservoir‟
a) Air Temperature
Daily minimum and maximum air temperature data are shown in Figure 30 and Figure 31. Data are displayed as a 1-year running average to remove daily and seasonal fluctuations so that a long term pattern can be discerned. Evaluating the 1-yr running average results using a Pearson‟s correlation coefficient indicates a weak (Pearson‟s r values of 0.26, 0.46, and 0.47 for min, average, and max temperature running averages, respectively) but statistically significant positive trend exists for both the minimum and maximum air temperatures. The trend corresponds to an overall daily temperature range increase of 1.9 ◦F over the 60 year period. The linear regressions are shown on Figure 30 and Figure 31. Average monthly air temperatures are displayed in Figure 32 for the longer period of record (58 years) along with results from 2007 – 2009. Figure 33 presents the average monthly air temperatures as box plots, showing the range and spread of data
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with additional symbols indicating monthly results from 2007, 2008, and 2009. Figure 32 and Figure 33 show that the year 2007 was warmer than average and warmer than 2008 and 2009 throughout the summer and fall. Air temperatures in July and August of 2007 were at or above the 95th percentile of the historical data. June and September temperatures were above the 75th percentile. Algae concentrations in both Grand Lake and Shadow Mountain Reservoir were the highest in 2007. The year 2009 was cooler than average and for 2007 and 2008 in June through August.
Figure 30. Daily Maximum Air Temperature at Weather Station „Grand Lake 6 SSW‟ (1-year Running Average) with Trend Line
Figure 31. Daily Minimum Air Temperature at Weather Station „Grand Lake 6 SSW‟ (1-year Running Average) with Trend Line
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Figure 32. Average Monthly Air Temperature at Weather Station „Grand Lake 6 SSW‟
Figure 33. Boxplot of Average Monthly Air Temperature at Weather Station „Grand Lake 6 SSW‟
Thick black line: 50th percentile Upper and lower edges of the box: 25th and 75th percentiles Whiskers extend to the 5th and 95th percentiles Open circles are observations above or below the 95th or 5th percentiles, respectively
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b) Precipitation
Precipitation data are shown in Figure 34. A linear regression on the annual precipitation totals indicates no significant increasing or decreasing trend with time over the 61 year dataset (R2 = 0.002). Average monthly precipitation values are displayed in Figure 35 and Figure 36 for the longer period of record (58 years) along with results from 2007 – 2009. For each of the past three years, the average monthly precipitation during the summer far exceeded the long-term average. For 2007, precipitation was high in August and September. For 2008, precipitation was high in May, August, and September. For 2009, precipitation was high in June and July. 2007 was dry April – July, 2008 was dry June and July, and 2009 was dry August – September.
Figure 34. Annual Precipitation at Weather Station „Grand Lake 6 SSW‟ with Trend Line
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Figure 35. Average Monthly Precipitation at Weather Station „Grand Lake 6 SSW‟ (2007-2009)
Figure 36. Boxplot of Average Monthly Precipitation at Weather Station „Grand Lake 6 SSW‟ Thick black line: 50th percentile Upper and lower edges of the box: 25th and 75th percentiles Whiskers extend to the 5th and 95th percentiles Open circles are observations above or below the 95th or 5th percentiles, respectively
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c) Solar Radiation
Daily solar radiation data for 2007-2009 are shown in Figure 37, Figure 38, and Figure 39. Magnitudes are similar each year and the annual pattern is as expected. A noticeable decline occurs in late May / early June of 2009. Dips in daily solar radiation occur as a result of cloud cover and atmospheric constituents.
Figure 37. Daily Solar Radiation at Weather Station „Windy Gap Reservoir‟ – 2007
Figure 38. Daily Solar Radiation at Weather Station „Windy Gap Reservoir‟ – 2008
Figure 39. Daily Solar Radiation at Weather Station „Windy Gap Reservoir‟ - 2009
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d) Wind Speed
Wind speed data are displayed in Figure 40, Figure 41, and Figure 42 for May through September. Daily averages along with daily gusts are shown. Higher daily gusts tend to occur in May and June for all three years.
Figure 40. Wind Speed at Weather Station „Windy Gap Reservoir‟‟ – 2007
Figure 41. Wind Speed at Weather Station „Windy Gap Reservoir‟‟ – 2008
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Figure 42. Wind Speed at Weather Station „Windy Gap Reservoir‟‟ – 2009
e) Impacts of Meteorology on Water Clarity
Air temperature, precipitation, wind, and solar radiation can all play an important role in determining the clarity in Shadow Mountain Reservoir and Grand Lake. Examples of how clarity may be impacted include:
Air Temperature: Air temperature affects water temperature. Higher water temperatures can increase algal growth, leading to increased chlorophyll a concentrations. Increased water temperatures can also lead to increased growth of macrophytes in the system and subsequent non-algal particulate organic matter. Precipitation: Precipitation can increase nutrient loading to the water column through stormwater runoff contributions. This can lead to increases in chlorophyll a concentrations. Wind: Wind can affect stratification, which can in turn affect dissolved oxygen and internal nutrient loading, improving conditions for increased algal growth and correspondingly higher chlorophyll a concentrations. Wind can also increase suspended solids concentrations in the water column. Larger wind events can lead to uprooting of macrophytes as witnessed in 2010 (J. Metzger, personal communication, August 2, 2011). Solar Radiation: Solar radiation can directly increase both algal and macrophyte growth. Solar radiation can also affect water temperatures, further increasing algal and macrophyte growth.
In this system, the effects of these meteorological conditions on clarity are complex, interrelated, and dependent on operations and other dynamic water-quality variables such as nutrient concentrations and hydrodynamics. Clarity effects from meteorological conditions may also exhibit varying temporal delays. Each parameter also has different effects depending on the duration and
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intensity of the condition (e.g., several days of moderate-but-continuous winds can have a very different effect on clarity than an 8-hr high wind event, with a different duration of recovery). Effects can also be expected to vary by location on each lake. As such, simple regressions of chlorophyll a or Secchi depth with meteorological data are oversimplifications that do not take into account the other factors at work. As examples, Figure 43 and Figure 44 show Shadow Mountain Reservoir Secchi depth (SM-MID) and Grand Lake Secchi depth (GL-MID), respectively, plotted as a function of average daily air temperature. It appears that there may be a very slight decrease in clarity with an increase in air temperature for Grand Lake, although the correlation is very weak, with an R2 of 0.18. A relationship is not apparent for Shadow Mountain Reservoir (R2 = 0.016). The lack of a relationship appears because these figures do not account for the complexity of the system, nor the fact that clarity is a function of the concentrations of particulate matter and dissolved organic matter, some of which may have a seasonal pattern. Temperature only indirectly impacts water clarity, and cannot be expected to be a predictor of water clarity. In fact, some reservoirs experience the greatest clarity in mid-summer and the worst clarity in late fall / early winter.
Although air temperature can affect reservoir stratification, wind and flushing flows can also play an important role. The role that each of these variables plays in Shadow Mountain Reservoir stratification dynamics should be a topic of future study. More detailed temperature profile information would be required than is available now. Use of a continuous vertical profiling system (such as a YSI Vertical Profiler) would provide data to better tie stratification to factors such as flushing, wind, and air temperature. Activities to ensure that local weather data are available in the future are currently underway.
Nutrient contributions to Grand Lake and Shadow Mountain Reservoir via stormwater have been found to be important through the Three Lakes Water-Quality Modeling effort (Figure 23, Figure 24, Figure 26, and Figure 27). These contributions, triggered by the amount and timing of rainfall, were found to significantly improve the calibration of the model.
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Figure 43. Air Temperature and Secchi Depth (View-Scope Data) at SM-MID, Data from 2005-2010
Figure 44. Air Temperature and Secchi Depth (View-Scope Data) at GL-MID, Data from 2005-2010
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6. Grand Lake Clarity Standard Assessment (2007-2009) As noted in the Introduction, the Colorado Water Quality Control Commission adopted a 4-meter Secchi-depth numerical clarity standard for Grand Lake, with an effective date of 2015 if a more appropriate standard has not been adopted. According to Regulation 33 (CDPHE, 2011), the “intention [of the numerical clarity standard] is that for the majority of the summertime days, the water of Grand Lake shall be clearer than 4 meter Secchi Depth… Fifteen percent of the measurements may have Secchi depth shallower than 4 meters.” The standard is to be assessed by calculating the 15th percentile of available Secchi-depth data collected from July through September5. When two samples are collected in different locations or by different agencies on the same day, the Secchi-depth value is the average of those samples (CDPHE, 2011).
Based on this description, an assessment of the numerical standard has been conducted for 2007- 2009. There is no discussion in Regulation 33 regarding the type of Secchi-depth data to use in the assessment (view scope or non-view scope). Because of this, the assessments were done for each type of data. Note that use of a view scope generally results in a larger (higher clarity) number. The following steps were taken to generate values for comparison with the Grand Lake numerical standard:
All Grand Lake Secchi-depth data for July-September were included in the evaluation, including volunteer-collected data. These data are plotted in Figure 15 and Figure 16. Duplicate results at a single location on a given day were averaged. Data from separate stations collected on a given day were averaged to produce a single Grand Lake result for that day. The 15th percentile of the resulting dataset from July – September for each year was calculated. The calculated 15th percentile value for each year was compared against the 4-meter numerical standard.
The results are displayed in Figure 45 and Figure 46. The target of 4-meter+ was not obtained in any of the years but there was an improvement over the three year period. As expected, the values computed using the view scope data were larger (indicating higher clarity) than those using the non-view scope data.
5 Assessment of the standard is described in Regulation 33 as comparing the 85th percentile of the data to the 4-meter standard. However, to meet the intent of the standard, the 15th percentile of the data (and not the 85th percentile) should be compared to the 4-meter standard (S. Wheeler, WQCD, personal communication, November 21, 2011).
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“Standard”
Figure 45. Grand Lake Clarity Standards Assessment (View-Scope Data) “Standard” is the 4 m value described in Regulation 33.
“Standard”
Figure 46. Grand Lake Clarity Standards Assessment (Non-View Scope Data) “Standard” is the 4 m value described in Regulation 33.
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C. Conditions in 2010
1. Hydrology and C-BT Operations In 2010, operational objectives to improve water clarity in Grand Lake were developed. An analysis of data from several previous years (Boyer, 2010) indicated that, in general, keeping a residence time of less than 50 days in Shadow Mountain Reservoir and at the same time, minimizing the flow from Shadow Mountain Reservoir to Grand Lake, tended to result in lower algal blooms (and higher clarity) in Grand Lake. A certain amount of Shadow Mountain Reservoir flushing is required to prevent stratification, which can trigger low dissolved oxygen (DO) levels and nutrient releases in the reservoir during the hot summer months. It was also noted that air temperature and wind also play a role in stratification, but these factors were not controllable. Based on this information, an operational target was set of running 225 cfs through the Adams Tunnel until August 27th. The flow at the Adams Tunnel would then be ramped up over a three-day period to full capacity.
Note that maximizing the flow through the Adams Tunnel does not always result in pumping at the Farr Pumping Plant because natural inflows into Grand Lake and Shadow Mountain can meet C-BT Project demand at times. So, although the plan was to keep Shadow Mountain Reservoir flushed with a target residence time of 50 days (or just under), a period of greater than usual precipitation in early August resulted in no Farr pumping for a few days and an increase in residence time (Figure 47). Otherwise, the residence time was kept to below 50 days.
Figure 47. Shadow Mountain Reservoir Residence Time (2010)
Other aspects of operations and hydrology in 2010 are depicted in Figure 48 through Figure 55 and Table 12 through Table 14. Noteworthy items include:
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The connecting channel between Shadow Mountain Reservoir and Grand Lake was shut down for the month of October in 2010. This was done in order to complete maintenance on the control structure, including rehabilitation of deteriorated structural concrete, installation of a new aluminum check dam system that helps maintain water levels in Grand Lake, and replacement of the walkway and rail system with more durable composite materials;
There was no stop-pump period;
Peak tributary inflows were higher than in previous years, although there was less total flow than 2008 and 2009;
Granby Reservoir content was higher than in previous years; and
Adams Tunnel deliveries and Farr Pumping were lower than the previous years. Thus, the total flow from Shadow Mountain Reservoir to Grand Lake through the connecting channel was also the lowest in 2010 for the 2007-2010 period.
A comparison of flows in the connecting channel for the summer was made across the four years (Table 11). Although 2010 had the lowest total flow from Shadow Mountain Reservoir to Grand Lake, 2009 had the lowest flow during the critical time period from a clarity standpoint (July through September 15th). Using daily average flows, there was no flow from Grand Lake to Shadow Mountain Reservoir during this period in 2010.
Table 11. Total Flow* (AF) in the Connecting Channel, July 1st – September 15th Year Flow from Grand Lake to Flow from Shadow Mountain Shadow Mountain Reservoir Reservoir to Grand Lake 2007 1,673 56,584 2008 1,404 44,277 2009 7,790 28,400 2010 0 34,328 *Flow computed using the Three Lakes Model water mass balance approach
One of the intentions of the 2010 operational plan was to prevent stratification and resultant low DO at the bottom of Shadow Mountain Reservoir. Data measurements throughout the summer indicated that this effort was successful and low DO events (<2mg/L) were prevented. Chlorophyll a in Grand Lake remained low (<4 ug/L at the GL-MID station) through August 9th and chlorophyll a in Shadow Mountain Reservoir remained low (<5.4 ug/L at SMR-MID) until August 11th. On August 23rd, the chlorophyll a at GL-MID climbed to almost 12 ug/L and the measured chlorophyll a at SM- MID was close to 13 ug/L on August 24th. It appears that an algal bloom developed in Shadow Mountain Reservoir, in response to a large spike in total nitrogen concentration, which may have been a result of earlier precipitation events. There is no indication that the increase in total nitrogen is a result of water operations. There is some uncertainty about the actual impact of residence time on Shadow Mountain Reservoir stratification in 2010 since wind speeds throughout the spring, summer, and fall were much higher than in previous years (see Figure 40, Figure 41,
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Figure 42, and Figure 82). Strong winds could have prevented stratification even without the targeted amount of flushing flow in Shadow Mountain Reservoir.
Figure 48. Tributary and Pumped Inflows into the Three Lakes System (2007-2010) Tributary Inflows: North Inlet, East Inlet, North Fork of the Colorado River, Stillwater Creek, Columbine Creek, Roaring Fork, and Arapaho Creek. Pumped Inflows: Windy Gap Pipeline and Willow Creek Pump Canal Note: Stop-pump periods are shaded.
Figure 49. Outflows from the Three Lakes System (2007-2010) Stop-pump periods are shaded.
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Figure 50. Flow between the Three Water Bodies (2007-2010) Stop-pump periods are shaded.
Figure 51. Farr Pumping Plant Flows (Granby Pump Canal) –2010
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Figure 52. Surface Water Elevation for Granby Reservoir (2007-2010)
Table 12. Grand Lake Inflows, Outflows, and Residence Time (2007-2010) 2007 2008 2009 2010 Inflows North Inlet 46,460 61,554 59,357 51,490 (AF/yr) East Inlet 32,652 39,376 41,799 33,376 From SMR 224,626 206,064 193,605 171,838 Gains 12,289 9,740 20,200 18,701 Precipitation 579 592 515 611 Total 316,606 317,326 315,476 276,016 Outflows To SMR 47,853 24,043 73,162 68,430 (AF/yr) Adams Tunnel 262,643 285,822 236,628 202,320 Evap and Losses 6,124 7,471 5,655 5,292 Total 316,620 317,336 315,445 276,042 Hydraulic Average Annual Based 78 78 79 90 Residence on Total Volume* Time Average July- (days) September Based on 5 5 6 4 Epilimnetic Volume** *Average Total Volume for 2010 = 67,882 AF **Average Epilimnetic Volume for 2010 = 4,407 AF
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Table 13. Shadow Mountain Reservoir Inflows, Outflows, and Residence Time (2007-2010)
2007 2008 2009 2010 Inflows North Fork 28,545 52,335 52,079 50,954 (AF/yr) From Grand 47,853 24,043 73,162 68,430 From Granby 233,796 213,336 200,118 182,014 Gains 19,687 15,604 32,360 29,959 Precipitation 1,536 1,571 1,367 1,622 Total 331,417 306,889 359,086 332,979 Outflows To Grand 224,626 206,064 193,605 171,838 (AF/yr) To Granby 95,786 87,431 155,187 151,345 Evap and Losses 11,084 13,275 10,349 9,822 Total 331,496 306,770 359,141 333,005 Hydraulic Average Annual Based 19 20 17 18 Residence on Total Volume* Time Average July-September 19 21 23 16 (days) Based on Total Volume* *Average Total Volume for 2010 = 16,830 AF
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Table 14. Granby Reservoir Inflows, Outflows, and Residence Time (2007-2010) 2007 2008 2009 2010 Inflows (AF/yr) Arapaho 49,252 57,988 61,837 52,176 Stillwater 8,239 9,616 8,719 8,255 Roaring Fork 12,952 19,030 14,148 15,539 Columbine 8,808 13,282 9,888 10,468 Windy Gap 40,992 33,523 26,368 6,758 Willow Creek 39,348 57,709 57,078 45,201 Gains 2,689 3,994 2,971 3,214 From SMR 95,786 87,431 155,187 151,345 Precipitation 8,284 8,477 7,377 8,750 Total 266,350 291,050 343,573 301,706 Outflows To SMR 233,796 213,336 200,118 182,014 (AF/yr) To CO River 32,542 29,829 33,006 36,331 Evap and 30,677 23,115 39,007 34,996 Losses Total 297,015 266,280 272,131 253,341 Annual Hydraulic 440 496 543 650 Residence Time (yr) *Average Total Volume for 2010 = 451,082 AF
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Figure 53. Inflows into Grand Lake by Source for 2010. Total Inflow 276,016 AF/yr
Figure 54. Inflows into Shadow Mountain Reservoir by Source for 2010. Total Inflow 332,706 AF/yr
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Figure 55. Inflows into Granby Reservoir by Source for 2010. Total Inflow 301,706 AF/yr
2. Lake and Reservoir Water Clarity Secchi-depth measurements for Grand Lake and Shadow Mountain Reservoir in 2010 are described in this section. Minimum and maximum Secchi-depth measurements for Grand Lake and Shadow Mountain Reservoir by year can be found in Table 15. Grand Lake has slightly better water clarity than Shadow Mountain Reservoir. There is not much variation year-to-year, with the exception of maximum values in Shadow Mountain Reservoir. Note that the frequency of data collection varies year-to-year; the fewest measurements were taken in 2007 and the highest number occurred in 2009. In addition to the figures shown below, spatial representations of Secchi-depth data are displayed in Appendix A. The graphics in Appendix A were developed by GCWIN and approximate how clarity in both water bodies changes over time and space in 2010.
Table 15. Minimum and Maximum Secchi-Depth Measurements for Grand Lake and Shadow Mountain Reservoir (All Locations, View-Scope Data) – 2007-2010 Grand Lake Shadow Mountain Reservoir Minimum Maximum Minimum Maximum 2007 1.4 4.9 1.2 3.1 2008 1.5 4.6 1.3 3.3 2009 2.0 4.9 1.5 4.6 2010 1.6 4.8 1.4 4.4
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a) Grand Lake
Secchi depths for Grand Lake are shown in Figure 56, and Figure 57. Measurements are categorized by month. In 2010, high (more clear) Secchi depths were recorded in May and October although the summer months experienced Secchi-depth readings of less than 2 m. In general, clarity tended to degrade in July and August, similar to 2009. A more focused look at Grand Lake clarity in 2010 is shown in Figure 58. A degradation and then subsequent improvement in clarity is evident in August 2010. The degradation coincides with the increase in algae concentrations described earlier. Clarity in September was relatively constant and then an improvement was seen in October. Figure 58 shows distinct symbols for three frequently sampled locations across Grand Lake (GL-WES [closest to the connecting channel], GL-MID [central Grand Lake], and GL-ATW [closest to Adams Tunnel] to allow for a look at spatial patterns in the dataset. Figure 58 also shows flow rates from Shadow Mountain to Grand Lake to support the pattern review. For 2010, clear spatial patterns across Grand Lake are not apparent.
Figure 56. Grand Lake Secchi-Depth Data (All Locations, View-Scope Data) – 2007-2010
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Figure 57. Grand Lake Secchi-Depth Data (All Locations, Non-View Scope Data) – 2007-2010
Figure 58. Grand Lake Secchi-Depth Data (All Locations, View-Scope Data) –2010
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b) Shadow Mountain
Secchi-depth data for Shadow Mountain Reservoir in 2010 indicate very poor clarity in June (<1 m) and several higher (more clear) readings in September (Figure 59 and Figure 60). In August, a similar pattern occurs as in Grand Lake, corresponding to the algae bloom (Figure 61). Figure 61 shows distinct symbols for three sampled locations across Shadow Mountain Reservoir (SM-DAM [closest to the outlet of the Granby Pump Canal], SM-MID [central Shadow Mountain], and SM-NOR [closest to channel between Grand Lake and Shadow Mountain] to allow for a look at spatial patterns in the dataset. Figure 61 also shows flows between Shadow Mountain Reservoir and Grand Lake to support this analysis.
Interesting spatial patterns are apparent across Shadow Mountain Reservoir in the 2010 dataset. First, during the runoff period (May-June), when flow is coming from Grand Lake into Shadow Mountain, the greatest clarity in Shadow Mountain is apparent near the connecting channel to Grand Lake, with deteriorating clarity to SM-MID, then to SM-DAM. In July and August, when Farr is pumping at a rate of ~500 AF/day, conditions change to show more uniform clarity across Shadow Mountain. A decrease in clarity across from roughly mid-July through mid-August is apparent, and corresponds with the timing of an increase in chlorophyll a in the channel (Figure 65). The increase in clarity, starting in mid-August corresponds to a decrease in chlorophyll a (also seen in the channel data (Figure 65). Another change in spatial clarity patterns in Shadow Mountain is observed in the first week of September, when the Farr pumping rate is increased, and flow from Shadow Mountain Reservoir to Grand Lake increases from 500 AF/day to 1,000 AF/day. At this time, clarity at the SM-DAM location (closest to the Granby Pump Canal) increases by about a meter. The increased clarity effect is diminished across Shadow Mountain Reservoir, with the worst clarity (shallowest Secchi readings) observed at SM-NOR.
To take a closer look at this spatial patterning, data from 2009, 2008, and 2007 were plotted in the same format in Figure 62, Figure 63, and Figure 64, respectively. 2009 shows a similar pattern to 2010, but to a somewhat lesser extent. First, SM-NOR clarity is the best in Shadow Mountain Reservoir during the runoff season (presumably due to clear inflow from Grand Lake). Next, there is no pattern among the three sites, but clarity steadily and uniformly deteriorates from mid-July to late-August, while pumping is on the order of 500 AF/day or stopped (the stop-pump period occurred in the second half of August). Finally, when pumping jumps to 1,000 AF/day, a gradient seems to develop across Shadow Mountain Reservoir, with the greatest clarity at the SM-DAM location (closest to the Granby Pump Canal).
2007 and 2008 have less data (less frequent measurements in both years and no SM-NOR in 2007) but still show some interesting patterns. In 2008, the SM-NOR location has greater clarity during pumping (pumping was generally on the order of 1,000 ft/day, following the pattern seen in 2009 and 2010. Both 2007 and 2008, however, show less of a gradient between the SM-Dam and SM-MID location, as compared to 2009 and 2010. This may be due to lower flow rates from Grand Lake through Shadow Mountain Reservoir in the runoff, worse water quality in Granby Reservoir in those years, and/or operational pumping patterns.
The data from all four years suggest that (during the seasonal periods of observations) when Farr is pumping, the clarity in Shadow Mountain Reservoir is best at the southern end and worse at the
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northern end. The magnitude and pattern of this gradient may be a function of flow rates and/or Granby water quality, among other possible factors. When Shadow Mountain Reservoir is receiving flow from Grand Lake, the opposite spatial pattern occurs. This spatial patterning has also recently been noted by Stahl (2011), based on a review of 2011 data.
All of these data lead to some important observations and considerations. First, as McCutchan (2010) suggests, the clearer water at the south end of Shadow Mountain during pumping indicates that Granby Reservoir may be a source of clearer water to Shadow Mountain Reservoir in some years. Likewise, the effect of relatively clearer inflows from Grand Lake is often apparent in Shadow Mountain Reservoir in the runoff season. Second, the declining clarity during the summer in Shadow Mountain seems to occur regardless of pumping rates (high, moderate, or stopped), likely reflecting algal growth in the warm season which is then diminished later in the season. Third, there appears to be an energetic threshold of Farr pumping rates that generates a gradient of clarity across Shadow Mountain Reservoir. Somewhere between 500 AF/day and 1,000 AF/day, a stronger signal of clearer Granby Reservoir water is apparent but does not carry through all of Shadow Mountain. This may or may not indicate an energetic resuspension of materials in Shadow Mountain Reservoir, reducing clarity. Resuspension could involve one or both of the following: non- algal organic particulates (and associated absorbed nutrients), and non-algal inorganic particulates.
This patterning could be important to understanding the impacts of operations on water quality and needs additional study, including additional spatial and temporal sampling across Shadow Mountain Reservoir.
Figure 59. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2007- 2010
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Figure 60. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, Non- View Scope Data) – 2007-2010
Figure 61. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2010
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Figure 62. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2009
Figure 63. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2008
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Figure 64. Shadow Mountain Reservoir Secchi-Depth Data (All Locations, View-Scope Data) – 2007
3. Conditions at Connecting Channel Starting in 2010, the USGS collected continuous sampling records in the connecting channel between Grand Lake and Shadow Mountain Reservoir (USGS Site 09014050). Data include flow (flow rate and direction), turbidity, chlorophyll a fluorescence, and water temperature. These data are plotted in Figure 65. Measurements were not taken in October when channel maintenance activities occurred. In addition, flow measurements are not available in November. The dotted line in the figure indicates flows that were estimated using a water balance approach. Flow was generally in the direction of Shadow Mountain Reservoir to Grand Lake until May 17th. Flow direction then reversed in the direction of Shadow Mountain Reservoir until June 28th. For the rest of the data collection period, the flow was into Grand Lake. Water temperature begins to increase mid-June due to the decreasing flow rate of cooler water from Grand Lake and increasing air temperatures.
The effect of flow direction between Shadow Mountain Reservoir and Grand Lake on water quality conditions at the connecting channel is evident. Note the increase in chlorophyll a in August when water is flowing from Shadow Mountain Reservoir to Grand Lake. An algal bloom was occurring in Shadow Mountain Reservoir during this period and the channel data reflects this increase. This bloom appears to be related to a large increase in total nitrogen in Shadow Mountain Reservoir, which may be a result from earlier precipitation events and not due to any operational factors. Figure 66 shows the relationship between flow rate / direction and chlorophyll a in the channel. It is evident that the higher chlorophyll a values are associated with periods when the flow is from Shadow Mountain Reservoir to Grand Lake, although it should be noted that flow was always in the direction of Grand Lake during the warm months (July – August) when algae are most likely to grow. Elevated turbidity measurements at the beginning of November may be due to October construction activities although there may be some other explanation.
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Turbidity tends to increase with chlorophyll a concentrations in the channel although less so during some periods. Note that turbidity is a measure of light scattering and the amount of scattering due to algae (one cause of scattering) can vary considerably due to differences in cell size and intracellular pigment concentration. Thus, chlorophyll a concentrations can increase without a concurrent increase in turbidity, as seen in early July and in September. The relationship between flow direction and, to a lesser extent, flow rate and turbidity is shown in Figure 67 and follows a similar pattern as chlorophyll a.
Figure 65. Flow and Water Quality at the Connecting Channel between Grand Lake and Shadow Mountain Reservoir (2010) (Shaded box indicates flow in the direction of Grand Lake to SMR.)
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Flow from Flow from Grand Lake SMR to to SMR Grand Lake
Figure 66. Chlorophyll a as a Function of Flow Rate at the Connecting Channel between Grand Lake and Shadow Mountain Reservoir (2010)
Flow from Flow from Grand Lake SMR to to SMR Grand Lake
Figure 67. Turbidity as a Function of Flow Rate at the Connecting Channel between Grand Lake and Shadow Mountain Reservoir (2010)
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The year 2010 is the first year that flow rate and direction in the connecting channel between Grand Lake and Shadow Mountain Reservoir have been measured. As noted in IV.B.1, a water mass balance approach has been taken to quantify channel flow and direction for previous years. Now that data are available for 2010, comparisons between the computed values and the measured values can be made (Figure 68). Results are very similar for April through July. For August and September observed flow rates are lower than computed values. The reason for this difference is under investigation. The difference in the total volume of flow for December was less than 5%, although the timing of the flows is not the same. This may be due to having to estimate tributary inflows in the winter. Measured data are not available in October and November of 2010.
Figure 68. Comparisons between Computed and Measured Flow and Direction in the Connecting Channel
4. Nutrient Loading (2010) Total phosphorus and total nitrogen loading into the Three Lakes System for 2010 is described in this section and compared with previous years.
a) Total Phosphorus
Total phosphorus loads by water body are listed in Table 16. In addition, the relative annual distributions of loads for 2010 are reported in Figure 69, Figure 70, and Figure 71. Total phosphorus loadings for all three water bodies were lower in 2010 as compared to the average of the past three years. The distribution of phosphorus loadings in 2010 was similar to previous years (Figure 23, Figure 24, and Figure 25). Inflow volume-weighted concentrations are listed in Table 17. Values listed are similar to previous years with the exception of Windy Gap.
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Table 16. Total Phosphorus Loads (kg/yr) by Water Body (2007-2010)
Water Body Source 2007 2008 2009 2010
Grand Lake North Inlet 510 1,141 831 652 East Inlet 266 496 451 402 From SMR 4,314 4,377 3,869 3,148 Gains 65 104 160 145 Precipitation 29 30 26 31 Stormwater 166 118 137 58 Internal Load 147 147 147 147 Total 5,497 6,413 5,621 4,583 Shadow Mtn Reservoir North Fork 778 4,792 1,294 1,611 From Grand 421 400 852 795 From Granby 4,966 6,055 5,982 4,747 Gains 104 167 256 232 Precipitation 78 79 69 82 Stormwater 1,659 1,175 1,521 2,074 Internal Load 1,328 661 656 656 Total 9,334 13,329 10,630 10,197 Granby Reservoir Arapaho 391 669 626 505 Stillwater 1,034 1,579 1,641 1,065 Roaring Fork 113 259 144 167 Columbine 77 190 103 115 Windy Gap 2,696 3,535 1,897 150 Willow Creek 1,168 2,934 2,699 1,945 Gains 16 45 23 26 From SMR 1,317 3,637 2,702 2,954 Precipitation 419 429 373 442 Stormwater 4,147 2,938 3,802 5,184 Internal Load 2,079 2,118 2,306 2,589 Total 13,457 18,333 16,316 15,142
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Figure 69. Total Phosphorus Load into Grand Lake (2010 Average = 4,582 kg/yr)
Figure 70. Total Phosphorus Load into Shadow Mountain Reservoir (2010 Average = 10,196 kg/yr)
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Figure 71. Total Phosphorus Load into Granby Reservoir (2010 Average = 15,141 kg/yr)
Table 17. Annual Volume-Weighted Total Phosphorus Concentrations for Tributaries and Pumped Inflows (ug/L) (2007-2010)
Inflow 2007 2008 2009 2010 North Inlet 9 15 11 10 East Inlet 7 10 9 10 North Fork 22 74 20 26 Arapaho 6 9 8 8 Stillwater 102 133 153 105 Roaring Fork 7 11 8 9 Columbine 7 12 8 9 Windy Gap 53 85 58 18 Willow Creek 21 41 38 35
b) Total Nitrogen
Total nitrogen loads by water body are listed in Table 18. In addition, the relative annual distributions of loads for 2010 are reported in Figure 72, Figure 73, and Figure 74. Total nitrogen loadings for all three water bodies were lower in 2010 as compared to the average of the past three years. The distribution of loadings in 2010 was similar in previous years (Figure 26, Figure 27, and Figure 28).
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Inflow volume-weighted concentrations are listed in Table 19. Values reported for 2010 are similar to those reported in previous years.
Table 18. Total Nitrogen Loads (kg/yr) by Water Body (2007-2010) Water Body Source 2007 2008 2009 2010
Grand Lake North Inlet 13,215 19,355 17,519 14,695 East Inlet 7,848 10,444 12,678 10,612 From SMR 83,713 76,060 66,355 60,539 Gains 2,752 2,401 3,746 4,277 Precipitation 523 535 466 552 Stormwater 12,960 9,180 11,465 12,053 Internal Load 6,624 6,234 6,233 6,231 Total 127,635 124,209 118,462 108,959 Shadow Mtn Reservoir North Fork 7,796 20,068 17,848 16,018 From Grand 14,025 8,108 25,276 24,208 From Granby 75,760 71,496 62,762 55,748 Gains 4,409 3,847 6,000 6,851 Precipitation 1,387 1,420 1,236 1,465 Stormwater 17,626 12,485 16,157 22,032 Internal Load 962 165 164 164 Total 121,965 117,589 129,443 126,486 Granby Reservoir Arapaho 11,359 13,274 11,886 12,020 Stillwater 4,449 6,566 5,799 4,446 Roaring Fork 2,986 5,585 3,035 3,315 Columbine 2,081 4,124 2,194 2,290 Windy Gap 18,917 29,172 14,789 2,905 Willow Creek 9,526 18,248 14,280 12,318 Gains 574 1,122 588 630 From SMR 31,085 36,813 58,390 59,286 Precipitation 7,485 7,660 6,665 7,906 Stormwater 61,690 43,697 56,549 77,112 Internal Load 27,611 18,879 20,435 23,180 Total 177,763 185,140 194,610 205,408
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Figure 72. Total Nitrogen Load into Grand Lake (2010 Average = 108,959 kg/yr)
Figure 73. Total Nitrogen Load into Shadow Mountain Reservoir (2010 Average = 126,486 kg/yr)
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Figure 74. Total Nitrogen Load into Granby Reservoir (2010 Average = 205,408 kg/yr)
Table 19. Annual Volume-Weighted Total Nitrogen Concentrations for Tributaries and Pumped Inflows (ug/L) (2007-2010)
Inflow 2007 2008 2009 2010 North Inlet 231 255 239 231 East Inlet 195 215 246 258 North Fork 221 311 278 255 Arapaho 187 186 156 187 Stillwater 438 554 539 437 Roaring Fork 187 238 174 173 Columbine 192 252 180 177 Windy Gap 374 705 455 349 Willow Creek 196 256 203 221
5. Meteorology
a) Air Temperature
Average monthly air temperatures for 2010 are shown in Figure 75 along with data for previous years for comparison. January to June temperatures were generally on the cool side, especially June of 2010. Temperatures were warmer than average in the July to October period. Daily maximum and minimum air temperatures are found in Figure 77. Figure 76 presents the average monthly air temperatures as box plots, showing the range and spread of data with additional symbols indicating monthly results from 2007, 2008, 2009, and 2010.
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Figure 75. Average Monthly Air Temperature at Weather Station „Grand Lake 6 SSW‟ (2007-2010)
Figure 76. Boxplot of Average Monthly Air Temperature at Weather Station „Grand Lake 6 SSW‟ (includes 2010) Thick black line: 50th percentile Upper and lower edges of the box: 25th and 75th percentiles Whiskers extend to the 5th and 95th percentiles Open circles are observations above or below the 95th or 5th percentiles, respectively
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Figure 77. 2010 Daily Maximum and Minimum Air Temperatures at Weather Station „Grand Lake 6 SSW‟
b) Precipitation
Monthly precipitation data for 2010 are shown in Figure 78 and Figure 79 along with data from previous years. In 2010, there were months which were unusually dry and wet – most notably April and October (wet) and January and March (dry). During the summer, some months were above average and others were below average. Daily precipitation in 2010 is displayed in Figure 80.
Figure 78. Average Monthly Precipitation at Weather Station „Grand Lake 6 SSW‟ (2007-2010)
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Figure 79. Boxplot of Average Monthly Precipitation at Weather Station „Grand Lake 6 SSW‟ (includes 2010) Thick black line: 50th percentile Upper and lower edges of the box: 25th and 75th percentiles Whiskers extend to the 5th and 95th percentiles Open circles are observations above or below the 95th or 5th percentiles, respectively
Figure 80. Daily Precipitation at Weather Station „Grand Lake 6 SSW‟ (2010)
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c) Solar Radiation
Daily solar radiation data for 2010 are displayed in Figure 81. Patterns and magnitudes are similar to those observed in 2007-2009.
Figure 81. Daily Solar Radiation at Weather Station „Native Grass Site at Windy Gap Reservoir‟ – 2010
d) Wind Speed
Wind speed data for 2010 are shown in Figure 82. Compared to the previous three years, conditions were much windier during the entire period of May – September in 2010 – especially in May. Note that y-axis scale for Figure 82 has been increased from those for previous years (Figure 40, Figure 41, and Figure 42) to accommodate higher wind gusts. There have been reports of rooted aquatic weeds becoming uprooted in Shadow Mountain Reservoir due to the very windy conditions and blowing over to the north-east portion of the reservoir.
Figure 82. Wind Speed at Weather Station „Native Grass Site at Windy Gap Reservoir‟‟ – 2010
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6. Grand Lake Clarity Standard Assessment (2010) Assessment of the Grand Lake numeric clarity standard, as described in Section IIV.B.6 was conducted for 2010. All available July through September 2010 data were used in the analysis and are plotted in Figure 56 and Figure 57. The results of this assessment against the numerical standard are displayed in Figure 83 (using view scope data) and Figure 84 (using non- view scope data) along with results for 2007-2009 for comparison. Although there was an improvement over the previous three year period, results for 2010 show a slight setback. Clarity in July and August of 2010 was generally lower than in 2009, particularly during the last half of July.
“Standard”
Figure 83. Grand Lake Clarity Standards Assessment (View-Scope Data) “Standard” is the 4 m value described in Regulation 33.
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“Standard”
Figure 84. Grand Lake Clarity Standards Assessment (Non-View Scope Data) “Standard” is the 4 m value described in Regulation 33.
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V. Lessons Learned and Recommendations
Water clarity is predominantly a function of algae, non-algal organic particulate matter, inorganic suspended solids, and dissolved organic matter. Factors that can influence the concentrations of these constituents include:
Hydrology; Operations; Weather; and Concentrations of light-attenuating constituents in inflowing water.
The Three Lakes System is very complicated and these factors play very different roles at different times of the year. Review of the information presented in this report indicates the following:
The variety of operational, hydrologic, and environmental conditions that occurred 2007- 2010 did not result in meeting or coming close to the Grand Lake clarity standard, described in Regulation 33. Improvements in Grand Lake water clarity occurred during the two-week stop-pump periods (from 2.2 m to 3.5 m in 2008 and from 3.2 m to 3.4 m in 2009). Shadow Mountain water clarity improved during one stop-pump period (from 1.8 m to 2.3 m in 2008) and declined during the other (from 2.5 m to 1.9 m in 2009). It appears that the amount and quality of inflow into Shadow Mountain Reservoir during the stop-pump period may impact Shadow Mountain Reservoir water clarity. There are some interesting spatial patterns in the Secchi dataset that may relate to flow direction between Grand Lake and Shadow Mountain, flow rates, and the water quality in Granby of the particular year. Specifically, data suggest development of a gradient of increasing clarity at whichever end of Shadow Mountain Reservoir is experiencing inflow. This is likely a clarity dilution effect of clearer water flowing in; however, there may also be an indication of the resuspension of materials from the sediment bed of Shadow Mountain Reservoir. The effect appears to possibly be magnified with increased flow rates (pumping or runoff). The magnitude of the effect for pumping from Granby Reservoir may also relate to the water quality of Granby in the given year. There may be an energetic threshold between Farr pumping rates of 500 AF/yr and 1,000 AF/yr causing stronger clarity gradients across Shadow Mountain. There is still significant uncertainty about the mechanisms causing the observed gradient across Shadow Mountain Reservoir, but this patterning could be important and warrants additional study. Corresponding recommendations for additional data collection are provided under “Other recommendations” below. The declining clarity during the summer in Shadow Mountain seems to occur regardless of pumping rates (high, moderate, or stopped), likely reflecting algal growth in the warm season which is then diminished later in the season. Weather can play a role in Grand Lake / Shadow Mountain Reservoir water-quality dynamics. High algal concentrations (and poor water clarity) occurred during the hot summer of 2007. Precipitation events increase the amount of stormwater-related nutrients
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delivered to the water bodies. Wind conditions and air temperatures can impact the amount of stratification in Shadow Mountain Reservoir and associated internal nutrient loading, although the effects have not been quantified. Because of the complicated and difficult-to-anticipate future conditions (e.g., air temperatures, east slope demands, hydrology, and precipitation events), it is hard to rely on a single operational strategy to achieve water clarity improvements. Other management decisions (such as the drawdown of Shadow Mountain in late 2006) can also impact subsequent water-quality conditions (as experienced in 2007).
In order to improve water clarity in Grand Lake between July and September, it will be important to minimize the inflow of water with poor water quality into the lake. Management strategies include decreasing the amount of water pumped at the Farr Pumping Plant, improving the water quality of Shadow Mountain Reservoir, and bypassing the flow from Shadow Mountain Reservoir around Grand Lake. It is anticipated that it will be difficult to significantly improve the water quality and clarity characteristics of Shadow Mountain Reservoir due to shallow conditions, sources of nutrients, and weather conditions, although using the Three Lakes Water-Quality Model to answer this question is recommended. Large changes from current conditions are probably required to shift Grand Lake clarity to the point of consistently meeting (across a range of hydrologic conditions and demands) the 4-meter standard, listed in Regulation 33.
Recommendations for future operations include:
Run longer-term stop-pump periods to determine the impact on Grand Lake and Shadow Mountain Reservoir water clarity. These tests would provide more data and information to confirm or disprove the hypothesis that additional clarity gains would occur with longer stop-pump periods. Continuing the test into Labor Day could improve conditions on Grand Lake from a tourism standpoint but conditions on Shadow Mountain are more uncertain. It is important to monitor water clarity in Shadow Mountain Reservoir during these tests. During previous stop-pump periods, Shadow Mountain Reservoir was monitored less often than Grand Lake. After a stop-pump period (or any period with low Farr pumping in the summer), resume pumping gradually. In 2008, pumping was increased approximately 200 AF/day over 5 days versus a sudden increase in 2009 (0 to 827 AF in one day), resulting less degradation in Grand Lake water quality. Use the Three Lakes Water-Quality Model to determine the limits or bounds of water-quality conditions for Shadow Mountain Reservoir and Grand Lake, under a variety of operational scenarios.
Other recommendations include:
Ensure that Secchi-depth measurements are taken at the same sites on the same days to eliminate any localized impacts on certain dates. This should be done each year into the future. A systematic analysis of appropriate sampling sites for both Grand Lake and Shadow Mountain Reservoir should be made. It is suggested that additional sites be added for Shadow Mountain Reservoir and that less sites be included for Grand Lake. Currently, there
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are three sites on Shadow Mountain Reservoir and 14 sites on Grand Lake (Appendix A). Additional Shadow Mountain Reservoir sites should be placed to provide greater resolution of the clarity gradients observed in runoff season and during Farr pumping. To better understand the factors impacting stratification in Shadow Mountain Reservoir, one, or ideally more than one, continuous vertical profiling system (such as YSI Vertical Profilers) would be installed to continuously measure temperature with depth. Monitoring for other variables such as DO, pH, chlorophyll a, conductivity, and turbidity can also be made using this type of device and these data could provide important insights regarding the hydrodynamics and water-quality dynamics of the reservoir, including the observed clarity gradients. Continuous chlorophyll a and turbidity measurements would be especially important for future water-clarity analyses. Coordinate water-quality monitoring and water operations efforts to better understand the clarity gradient associated with sudden changes in pumping at the Farr Pumping Plant. It is recommended to collect data immediately before and after significant increases in pumped flows.
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VI. References
Boyer, J.M. 2010. Analysis Regarding Possible Impacts of Residence Time on Shadow Mountain Reservoir Dissolved Oxygen. Technical Memorandum. Hydros Consulting Inc.
Boyer, J.M. 2011. Optical Water Quality Modeling for the Three Lakes System. In Preparation. Hydros Consulting Inc.
Colorado Department of Public Health and Environment (CDPHE). 2011. Classifications and Numeric Standards for Upper Colorado River Basin and North Platte River (Planning Region 12). 5 CCR 1002-33 (Regulation 33). Water Quality Control Commission. Amended June 13, 2011; Effective January 12, 2012.
Colorado Lake Volunteer Monitoring Program (CLVM Program). 2011. Secchi-Depth Data. Email communication from K. Morris, Grand County, to J.M. Boyer, Hydros Consulting. July 7, 2011.
Davis-Colley, R.J., W.N. Vant, and D.G. Smith. 1993. Colour and Clarity of Natural Waters. Ellis Horwood Limited. West Sussex.
Grand County Watershed Information Network (GCWIN). 2011a. Secchi-Depth Data. Accessed at http://wilbur.gcwin.org/.
Grand County Watershed Information Network (GCWIN). 2011b. Historical Volunteer Secchi Data. Email communication from K. Morris, Grand County, to J.M. Boyer, Hydros Consulting. July 12, 2011.
Kirk, J.T.O. 1981. Estimation of the scattering coefficient of natural waters using underwater irradiance measurements. . Aust. J. Mar.Freshwater Res., 32:533-539.
Kirk, J.T.O. 1994. Light and Photosynthesis in Aquatic Ecosystems. Second Edition. Cambridge University Press.
Koltun, G.F., M. Eberle, J.R. Gray, and J.D. Glysson. 2006. User‟s Manual for the Graphical Constituent Loading Analysis System (GCLAS). Techniques and Methods 4-C1. U.S. Geological Survey.
Lieberman, D.M. 2008. Physical, Chemical, and Biological Attributes of Western and Eastern Slope Reservoir, Lake, and Flowing Water Sites on the C-BT Project, 2005 - 2007: Lake Granby, Grand Lake, Shadow Mountain Reservoir, Horsetooth Reservoir, Carter Lake. U.S. Bureau of Reclamation. Prepared for Northern Colorado Water Conservancy District.
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McCutchan, J.H. 2010. Factors Controlling Transparency in Grand Lake, Colorado. Rpt 299. July 2, 2010.
Morris, K. 2011. Email communication from K. Morris (Grand County) to J.M. Boyer (Hydros Consulting) on August 19, 2011.
Northern Water. 2011a. Daily Flow Data. Accessed at http://www.ncwcd.org/datareports/westflow.asp.
Northern Water. 2011b. West Slope Water Quality Database. Provided by J. Stephenson (Northern Water) to J.M. Boyer (Hydros Consulting) via ftp. June 6, 2011.
Northern Water. 2011c. Weather Files. Email communication from K. Rademacher (Northern Water) to J.M. Boyer (Hydros Consulting) on April 4, 2011.
Pennak, R.W. 1955. Comparative Limnology of Eight Colorado Mountain Lakes. University of Colorado Studies. Series in Biology. No. 2. University of Colorado Press. Boulder, Colorado. July, 1955.
Preisendorfer, R.W. 1986. Secchi disc science: visual optics of natural waters. Limnology and Oceanography. 31:909-926.
Sisneros, D. 2010. 2010 Status of Aquatic Macrophytes in Shadow Mountain Reservoir. Prepared for the Northern Colorado Water Conservancy District. November 2010.
Stahl, J. 2011. Email communication from J. Stahl to J.M. Boyer (Hydros Consulting) on December 1, 2011.
Tyler, J.E. 1968. The Secchi Disc. Limnology and Oceanography, 13(1):1-6.
Weidemann, A.D and T.T. Bannister. 1986. Absorption and scattering coefficients in Irondequoit Bay. Limnol. Oceanogr. 31(3):567-583.
U.S. Bureau of Reclamation (USBR). 2011. Data Report – Eastern Colorado Projects. Monthly Reports (January 2007 – December 2010) provided by K. Bricker (USBR) to J.M. Boyer (Hydros Consulting).
U.S. Environmental Protection Agency (EPA). 2011. Legacy STORET Database. http://www.epa.gov/storet/
U.S. Geological Survey (USGS). 2011a. National Water Information System data available on the World Wide Web (Water Data for the Nation), at http://waterdata.usgs.gov/nwis/qw.
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U.S. Geological Survey (USGS). 2011b. National Water Information System data available on the World Wide Web (Water Data for the Nation), at http://waterdata.usgs.gov/nwis/sw.
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APPENDIX A
Three Lakes Clarity Monitoring Program
The Three Lakes clarity monitoring program is an ongoing effort, started in 2008, that supports weekly clarity measurements using a Secchi Disk from May to October in Grand Lake and Shadow Mountain Reservoir (sampling was increased in frequency to three times a week in July and August during 2010). Secchi depths are taken both with and without a view scope. These measurements are often taken at the same time and location, but not always. The program includes 14 sampling sites in Grand Lake, three in Shadow Mountain Reservoir, and one reference site at Columbine Lake (Figure A- 1). The reference site serves to measure clarity at a natural body of water not connected to the C-BT Project. Weather data, water surface temperature, water color, and visual observations on algal conditions and recreation potential are also taken at each sampling site.
Secchi-depth measurements are not taken in the winter, primarily because there are no aesthetic issues during this time. In addition, power boats used for sampling are winterized and unavailable from November through April. Also, due to the size of the water bodies, it is impractical to row out to the sampling sites and it is unsafe to walk on the ice while ice is forming (J. Tollett, GCWIN, personal communication, November 28, 2011).
Grand County Water Information Network (GCWIN), manages the sampling and uses both field technicians and volunteers to collect the data which undergoes a QA/QC process to ensure accuracy of the Secchi-depth readings. The 2008-2010 data is available for viewing and download via an online database that GCWIN maintains.
Project Partners:
Grand County Northern Water USDA Forest Service Greater Grand Lake Shoreline Association Three Lakes Watershed Association Shadowcliff Lodge Colorado Lake and Reservoir Management Association Grand Lake Fire Department LightHawk
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Figure A- 1. GCWIN Secchi-Depth Sampling Sites
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Spatial and Temporal Changes in Water Clarity – 2010
The following graphics were developed by GCWIN. Secchi depths using a view scope were used as the basis for the graphics. Note that the following representations of Shadow Mountain Reservoir and Grand Lake are to be used for comparison only. They are not to scale, do not reflect correct areal extent of each water body, and are not accurate reflections of lake position in relation to one another (see Figure 1).
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** Based on Secchi depths measured using a view scope
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** Based on Secchi depths measured using a view scope
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