Hydrology and Water-Quality Characteristics 

of Muddy Creek and Wolford Mountain 

Reservoir near Kremmling, Colorado, 

1990 through 2001

By Michael R. Stevens and Lori A. Sprague

Water-Resources Investigations Report 03–4073

U.S. Department of the Interior

U.S. Geological Survey
Any use of trade, product, or firm names in this publication

is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director
Contents iii

Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Previous Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Description and Background Information of Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Methods of Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Field Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Data-Analysis Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Data-Set Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Hydrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Water Quality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Streamwater Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Field Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Major Ions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Trace Elements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Biological Indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Suspended Sediment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Reservoir Water Quality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Field Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Major Ions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Trace Elements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Biological Indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Trophic Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Water-Quality Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

References Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Hydrologic and Water-Quality Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Figures

1. Map showing location of study area and sampling sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2–5. Graphs showing:

2. Water-surface elevation and contents of Wolford Mountain Reservoir, water years April 1995 

through September 2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

3. Wolford Mountain Reservoir elevation-capacity relation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4. Comparison of observed monthly concentration and a flow-weighted monthly concentration 

of total nitrogen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5. Daily mean discharge at stream gages along Muddy Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6–8. Hydrographs showing:

6. Daily streamflow statistics for period of record at Muddy Creek at Kremmling 

water years 1982–96. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

7. Daily streamflow statistics for period of record at Muddy Creek above 

Antelope Creek water years 1990–2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

8. Daily streamflow statistics for period of record at Muddy Creek below Wolford 

Mountain Reservoir water years 1995–2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
iv

9. Instantaneous discharge hydrographs for two Muddy Creek gaging stations during a 

localized storm with maximum rainfall in the range of 3 inches total over a 1- to 2-square-mile 

area in a tributary of Muddy Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

10. Graph showing flow-duration curves for streamflow upstream and downstream from 

Wolford Mountain Reservoir, 1996 through 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

11. Boxplots of selected water-quality constituents.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

12. Time-series plots of field properties at Muddy Creek above Antelope Creek and Muddy Creek 

below Wolford Mountain Reservoir, and Muddy Creek at Kremmling (site located approximately 

7 miles downstream from reservoir.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

13–15. Graphs showing:

13. Daily mean specific conductance upstream and downstream from Wolford Mountain 

Reservoir. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

14. Daily mean water temperature upstream and downstream from Wolford Mountain Reservoir . . . . 27

15. Daily minimum, mean, and maximum dissolved-oxygen concentrations at Muddy Creek 

below Wolford Mountain Reservoir. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

16. Time-series plots of selected major-ion constituents at Muddy Creek above Antelope Creek 

and Muddy Creek below Wolford Mountain Reservoir , and Muddy Creek at Kremmling. . . . . . . . . . 32

17. Piper diagram showing major-ion composition of samples at selected sites. . . . . . . . . . . . . . . . . . . . . . . 33

18. Time-series plots of selected nutrient and organic carbon constituents at Muddy Creek above 

Antelope Creek and Muddy Creek below Wolford Mountain Reservoir, and Muddy Creek at 

Kremmling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

19–21. Graphs showing:

19. Nitrogen and phosphorus loads in Muddy Creek inflow and outflow to Wolford Mountain 

Reservoir. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

20. Monthly inflow and outflow mass of total nitrogen and total phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . 42

21. Total nitrogen and phosphorus load gained or lost in the reservoir mass balance . . . . . . . . . . . . . . . . . 42

22–26. Times-series plots showing:

22. Selected trace-element constituents at Muddy Creek above Antelope 

Creek and Muddy Creek below Wolford Mountain Reservoir , and Muddy Creek at Kremmling. . . 49

23. Bacteria data at Muddy Creek above Antelope Creek and Muddy Creek 

below Wolford Mountain Reservoir, and Muddy Creek at Kremmling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

24. Suspended-sediment concentration at Muddy Creek upstream from 

Antelope Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

25. Suspended-sediment transport curve for Muddy Creek upstream from Antelope Creek . . . . . . . . . . .53

26. Selected field properties from Wolford Mountain Reservoir, sampled 

near the dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

27–30. Graphs showing:

27. Specific-conductance profiles measured at Wolford Mountain Reservoir near the dam in 1999. . . 56

28. Water-temperature profiles measured at Wolford Mountain Reservoir near the dam in 1999 . . . . . 57

29. pH profiles measured at Wolford Mountain Reservoir near the dam in 1999. . . . . . . . . . . . . . . . . . . . . . 58

30. Dissolved-oxygen profiles measured at Wolford Mountain Reservoir near the dam in 1999 . . . . . . . 59

31–35. Time-series plots showing:

31. Selected major-ions from Wolford Mountain Reservoir, sampled near the dam . . . . . . . . . . . . . . . . . . . .60

32. Selected nutrients from Wolford Mountain Reservoir, sampled near the dam . . . . . . . . . . . . . . . . . . . . . .62

33. Selected trace elements from Wolford Mountain Reservoir, sampled near the dam. . . . . . . . . . . . . . .64

34. Selected chlorophyll and bacteria data from Wolford Mountain Reservoir, 

sampled near the dam 1995 through 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

35. Annual trophic status index computations for Secchi depth, total phosphorus, and 

chlorophyll-a by the Carlson method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
v

Tables

1. Water-quality sampling sites.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

2. Laboratory methods and minimum reporting limits for samples collected during the study . . . . . . . . . .8

3. Comparison of samples taken concurrently at the two downstream sites —Muddy Creek at 

Kremmling and Muddy Creek below Wolford Mountain Reservoir near Kremmling—between 

August and September 1995. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4. Comparison of concurrent total and dissolved analyses and results of Wilcoxon 

signed-rank test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5. Statistical summary of field-property data at S1 and S2/S3 from April 1990 through March 1995

before storage began in the reservoir, S1 and S2/S3 combined from April 1990 through 

October 2001, and S1 and S2/S3 from April 1995 to September 2001 after storage began in the 

reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

6. Summary of field-property temporal variation upstream from reservoir by seasonal 

Kendall test for Muddy Creek above Antelope Creek (S1) and downstream combined 

data from Muddy Creek at Kremmling and Muddy Creek below Wolford Mountain 

Reservoir 1990 through 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

7. Summary of prereservoir and postconstruction upstream/downstream field-property 

differences at Muddy Creek above Antelope (S1) and Muddy Creek at Kremmling (S2), 

1990 through 1995, and differences at Muddy Creek above Antelope (S1) and Muddy Creek 

below Wolford Mountain Reservoir (S3), 1995 through 2001 by Wilcoxon signed-rank test. . . . . . . . . 26

8. Statistical summary of major-ion data at S1 and S2/S3 from April 1990 through March 1995,

before storage began in the reservoir, S1 and S2/S3 combined from April 1990 through 

October 2001, and S1 and S2/S3 from April 1995 to September 2001 after storage began in 

the reservoir. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

9. Summary of major-ion temporal variation upstream from reservoir by seasonal Kendall test for 

Muddy Creek above Antelope Creek (S1), and downstream combined data from Muddy 

Creek at Kremmling (S2) and Muddy Creek below Wolford Mountain Reservoir (S3), 1990 

through 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

10. Summary of upstream/downstream major-ion differences at Muddy Creek above Antelope and 

Muddy Creek at Kremmling, 1990 through 1995, and differences at Muddy Creek above 

Antelope and Muddy Creek below Wolford Mountain Reservoir (S3), 1995 through 2001 

by Wilcoxon signed-rank test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

11. Statistical summary of nutrient and carbon data at S1 and S2/S3 from April 1990 through 

March 1995 before storage began in the reservoir, S1 and S2/S3 combined from April 1990 

through October 2001, and S1 and S2/S3 from April 1995 to September 2001 after storage 

began in the reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

12. Summary of nutrient temporal variation upstream from reservoir by seasonal Kendall test for 

Muddy Creek above Antelope Creek (S1), and downstream combined data from Muddy 

Creek at Kremmling (S2) and Muddy Creek below Wolford Mountain Reservoir (S3), 1990 

through 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

13. Summary of upstream/downstream differences in nitrogen Muddy Creek above Antelope and 

Muddy Creek at Kremmling (S2), 1990 through 1995, and differences at Muddy Creek above 

Antelope (S1) and Muddy Creek below Wolford Mountain Reservoir (S3), 1995 through 2001, 

by Wilcoxon signed-rank test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

14. Mass-balance calculations for total nitrogen and total phosphorus in Wolford Mountain 

Reservoir, 1996 to 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

15. Nitrogen mass balance detailed computations (in Hydrologic and Water-Quality Data section). . . 77

16. Phosphorus mass balance detailed computations (in Hydrologic and Water-Quality 

Data section. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
vi

17. Statistical summary of trace-element data at S1 and S2/S3 from April 1990 through March 1995 

before storage began in the reservoir, S1 and S2/S3 combined from April 1990 through 

October 2001, and S1 and S2/S3 from April 1995 to September 2001 after storage began in the 

reservoir. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

18. Summary of trace-element temporal variation upstream from reservoir by seasonal 

Kendall test for Muddy Creek above Antelope Creek, and downstream combined data 

from Muddy Creek at Kremmling, and Muddy Creek below Wolford Mountain Reservoir, 1990 

through 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

19. Summary of upstream/downstream trace-element differences at Muddy Creek above 

Antelope (S1) and Muddy Creek at Kremmling, 1990 through 1995, and differences at Muddy 

Creek above Antelope and Muddy Creek below Wolford Mountain Reservoir (S3), 1995 

through 2001 by Wilcoxon signed-rank test.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

20. Statistical summary of bacteria data at S1 and S3 from December 1999 through 

September 2001, after storage began in the reservoir.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

21. Statistical summary of suspended-sediment data at S1 and S2 from April 1990 through 

March 1995, before storage began in the reservoir, S1 from April 1990 through October 2001, 

and S1 from April 1995 to September 2001 after storage began in the reservoir. . . . . . . . . . . . . . . . . . . . 52

22. A comparison of spatial differences in field-measurement data from Wolford Mountain 

Reservoir, July 1995 to September 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

23. A comparison of spatial differences in major-ion data from Wolford Mountain Reservoir, 

July 1995 through September 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

24. A comparison of spatial differences in nutrient data from Wolford Mountain Reservoir, 

July 1995 through September 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

25. A comparison of spatial differences in trace-element data from Wolford Mountain Reservoir, 

July 1995 through September 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

26. A comparison of spatial differences in biological data from Wolford Mountain Reservoir, 

July 1995 through September 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

27. Summary of exceedances of Colorado aquatic water-quality standards, 1990 to 2001. . . . . . . . . . . . . 71

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

Temperature in degrees Celsius (°×C) may be converted to degrees Fahrenheit (°F) as follows:

°F=1.8°C+32

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 

(NGVD of 1929)—a geodetic datum derived from a general adjustment of the first-order level nets 

of both the United States and Canada, formerly called Sea Level Datum of 1929.

Water year: A continuous 12-month period selected to present data relative to hydrologic or 

meteorological phenomena during which a complete annual hydrologic cycle normally occurs. 

The water year used by the U.S. Geological Survey runs from October 1 through 

September 30, and is designated by the year in which it ends.

Multiply By To obtain

acre 0.00156 square mile

acre-foot (acre-ft) 1,233 cubic meter

cubic foot per second (ft3/s) 0.02832 cubic meter per second

foot (ft) 0.3048 meter

yard (yd) 0.9144 meter

inch 2.54 centimeter

mile (mi) 1.609 kilometer

meter 39.37 inch

millimeter (mm) 0.03937 inch

square centimeter (cm2) 0.1550 square inch (in2

)

square foot (ft2) 0.0929 square meter

square mile (mi2

) 2.590 square kilometer (km2)
vii

ADDITIONAL ABBREVIATIONS

MRL Minimum Reporting Level

mg milligrams

mg/L milligrams per liter

mm millimeters

NTU nephelometric turbidity units

μg/L micrograms per liter

μS/cm microsiemens per centimeter at 25 degrees Celsius
Hydrology and Water-Quality Characteristics of Muddy 

Creek and Wolford Mountain Reservoir near Kremmling, 

Colorado, 1990 through 2001

By Michael R. Stevens and Lori A. Sprague

Abstract

A water-quality monitoring program was begun in March 

1985 on Muddy Creek in anticipation of the construction of a 

reservoir water-storage project. Wolford Mountain Reservoir 

was constructed by the Colorado River Water Conservation 

District during 1992–94. The reservoir began to be filled in 

1995.

Water quality generally was good in Muddy Creek and 

Wolford Mountain Reservoir throughout the period of record 

(collectively, 1990 through 2001), with low concentrations of 

nutrients (median total nitrogen less than 0.6 and median total 

phosphorus less than 0.05 milligrams per liter) and trace elements (median dissolved copper less than 2, median dissolved 

lead less than 1, and median dissolved zinc less than 20 micrograms per liter). Specific conductance ranged from 99 to 

1,720 microsiemens per centimeter. Cation compositions at 

Muddy Creek sites were mixed calcium-magnesium-sodium. 

Anion compositions were primarily bicarbonate and sulfate. 

Suspended-sediment concentrations ranged from less than 

50 milligrams per liter during low-flow periods to hundreds of 

milligrams per liter during snowmelt. Turbidity in prereservoir 

Muddy Creek generally was measured at less than 10 nephelometric turbidity units during low-flow periods and ranged to 

more than 360 nephelometric turbidity units during snowmelt. 

Compared to prereservoir conditions, turbidity in Muddy Creek 

downstream from the reservoir was substantially reduced 

because the reservoir acted as a sediment trap. 

During most years, peak flows were slightly reduced by 

the reservoir or similar to peaks upstream from the reservoir. 

The upper first to fifteenth percentiles of flows were decreased 

by operation of the reservoir compared to prereservoir flows. 

Generally, the fifteenth to one-hundredth percentiles of flow 

were increased by operation of the reservoir outflow compared 

to prereservoir flows.

Nutrient transport in the inflow is proportional to the 

amount of inflow-water discharge in a given year. Some nitrogen was stored in the water column and gain/loss patterns for 

total nitrogen were somewhat related to reservoir storage. 

Nitrogen tended to move through the reservoir, whereas phosphorus was mostly trapped within the reservoir in bottom sediments. The reservoir gained phosphorus every year (1996–

2001) and, as a percentage, more phosphorus was retained than 

nitrogen in years when both were retained in the reservoir due 

to stronger phosphorus tendencies for adsorption, coprecipitation, and settling. Only small amounts of phosphorus were 

available in the water column at the outflow, and reservoir 

water-column storage did not influence phosphorus outflowloading patterns as much as settling further upstream in the 

reservoir.

From 1990 to 2001, upstream from the reservoir, concentrations and values of dissolved solids, turbidity, some major 

ions, and dissolved iron increased (p-value less than 0.10), and 

acid-neutralizing capacity decreased. From 1990 to 2001, there 

were no significant (p-value less than 0.10) trends in nutrient 

concentrations upstream from the reservoir. From 1990 to 2001, 

downstream from the reservoir, trends in concentrations and 

values of dissolved solids, turbidity, major ions, total ammonia 

plus organic nitrogen, dissolved and total-recoverable iron, and 

total-recoverable manganese were downward.

Upstream and downstream water-quality constituents for 

the prereservoir (1990 to 1995) period were compared. Concentrations and values of dissolved solids, major ions, turbidity, 

and manganese were greater (p-value less than 0.10) at the 

downstream site.

From 1995 to 2001 (postconstruction), upstream and 

downstream water-quality constituents also were compared. 

Concentrations of specific conductance and major ions 

increased at the downstream site when compared to the 

upstream site (p-value less than 0.10), except for acid-neutralizing capacity and silica, which decreased. Turbidity, concentrations of total-recoverable and dissolved manganese, and 

total-recoverable iron also were smaller downstream from the 

reservoir. 

Results indicate that concentrations of dissolved solids 

increased downstream in Muddy Creek before the reservoir was 

constructed. This trend continued after construction, but the difference between upstream and downstream median concentrations of dissolved solids and major ion concentrations was less 

than in the prereservoir period. 

Spring runoff temperatures and fall temperatures in 

Muddy Creek were lower than in the reservoir. Thus, inflows to 
2 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

the reservoir tended to settle near the thermocline. In summer, 

inflow-water temperature was similar to the surface layer, and 

flows were routed through the reservoir near the surface.

In winter, Muddy Creek stream temperatures were near 

0°C, and surface water at the ice cover interface was 0°C, but 

the temperature in the reservoir subsurface probably increased 

with depth to 4°C in the bottom waters (water is most dense at 

about 4°C). Although no winter stratification measurements 

were made under the ice, the reservoir was assumed to be similar to other dimictic, montane reservoirs. Thus, inflow will tend 

to be routed just under the ice. Flow patterns within the reservoir could be important because residence time varies from season to season, and in the event of a chemical spill upstream, 

knowledge of timing and probable vertical location of the 

plume would be important for outflow gate configurations to 

manage the spill.

Near-bottom samples of ammonia and nitrite plus nitrate 

generally had larger concentrations than concurrent surface 

samples. Surface-sample concentrations of nitrite plus nitrate 

were substantially depleted throughout the growing season. 

Temporally, surface and bottom concentrations tended to 

decrease and stabilize for ammonia plus organic nitrogen and 

ammonia throughout the period of record. Nitrite plus nitrate 

seemed to increase in bottom samples with time. Spatial variation in nutrient concentrations from inflow to dam tended to 

decrease for total ammonia plus organic nitrogen and total 

phosphorus in surface samples, whereas bottom-sample 

concentrations of nitrite plus nitrate tended to increase from 

inflow to dam.

Spatially, total recoverable and dissolved iron and manganese and total recoverable aluminum show decreasing median 

concentrations from inflow to dam in surface samples. Bottomsample median concentrations of total recoverable iron and aluminum decreased from inflow to dam. The spatial increases in 

manganese along the reservoir axis probably are related to 

redox reactions in the hypolimnion, which release manganese 

during periods of hypoxia.

Bacteria counts were low to not detected in the reservoir 

samples. Bacteria in Muddy Creek may be associated with suspended material that rapidly settles out in the reservoir.

Trophic conditions generally were upper oligotrophic to 

mesotrophic from 1995 to 2001 in Wolford Mountain Reservoir 

based on available Secchi depth, total phosphorus concentrations, and chlorophyll-a concentrations. Dissolved-oxygen 

concentrations generally were in the range of 3 to 7 milligrams 

per liter except in late summer when oxygen concentrations 

approached 1 milligram per liter or less in the hypolimnion.

Constituent concentrations generally were acceptable and 

met Colorado water-quality standards. Selenium concentrations 

exceeded chronic aquatic standards twice in Muddy Creek at 

the Kremmling site (prereservoir, 1982–95). Six selenium concentrations in near-bottom samples collected from the reservoir 

near the dam during 1995–97 exceeded chronic aquatic standards. Aquatic standards for iron and manganese were occasionally exceeded in Muddy Creek and in near-bottom samples 

from Wolford Mountain Reservoir.

Introduction

Wolford Mountain Reservoir was constructed during 

1992–94, and filling of the reservoir began in 1995. When water 

storage is created on a stream, changes can occur in downstream 

discharge patterns and water quality, and a new hydrologic 

environment is created in the resulting reservoir. Water-quality 

concerns such as changes to streamflow patterns, salinity, nutrient enrichment, oxygen depletion, and documentation of these 

changes prompted the Colorado River Water Conservation 

District (CRWCD) to initiate monitoring efforts both before 

construction of Wolford Mountain Reservoir and after construction. The U.S. Geological Survey (USGS), in cooperation 

with the CRWCD, began a monitoring program on Muddy 

Creek in March 1985 in anticipation of the construction of the 

Wolford Mountain Reservoir water-storage project (fig. 1).

Purpose and Scope

The purpose of this report is to describe water quality of 

the inflow, reservoir, and outflow and to assess the effects of 

Wolford Mountain Reservoir on streamflow and downstream 

water quality from 1990 to 2001. Specific objectives include the 

following:

1. To characterize and compare the upstream/downstream 

and prereservoir (before construction of the reservoir) 

and postconstruction (after construction of the reservoir) 

streamflow, water-quality characteristics, and temporal 

and spatial trends of water-quality properties and 

constituents in Muddy Creek;

2. To describe limnology and water-quality characteristics 

of Wolford Mountain Reservoir (1995–2001); and

3. To compare water-quality data to Colorado water-quality 

standards and guidelines. 

Previous Studies

Two studies of the potential effects of the proposed Wolford Mountain Reservoir were done before construction of the 

reservoir. Ruddy (1987) analyzed sediment discharge in Muddy 

Creek and predicted the effect of sedimentation rate on the proposed Wolford Mountain Reservoir near Kremmling, Colo. 

Ruddy determined that at the rate of mean annual total-sediment 

discharge for water years 1983 to 1985 (years data were collected), water-storage capacity of the proposed Wolford Mountain Reservoir would decrease 10 percent after 100 years. Butler 

(1990) estimated water-quality conditions and potential downstream channel effects of Wolford Mountain Reservoir. Butler 

used a one-dimensional temperature model with a conservative 

constituent routine (for specific conductance) that predicted 

changes in thermal structure with outlet elevation and predicted 

that the reservoir would have a dampening effect on water temperature and specific conductance. Empirical models were used 
Introduction 3

Grand Junction

SOUTH

PLATTE RIVER

DENVER

Study area

COLORADO 

GUNNISON RIVER

COLORADO R

Pueblo

40

40

134

9 0 1 MILE

0 1 KILOMETER

Base from U.S. Geological Survey

Gunsight Pass 1:24,000, 1980

Hinman Reservoir 1:24,000, 1980

Junction Butte 1:24,000, 1980

Kremmling 1:24,000, 1981

Reservoirs as of 1999

106°25' 106°22'30"

40°12'30"

40°07'30"

40°10'

40°05'

Hay Gulch

Wolford Mountain

Reservoir

Wolford

Mountain

Pass Creek

Slough

Alkali

Creek

Pinto

Antelope

Creek

Muddy

Creek

Kremmling

Cow Gulch

S2

S3

S1

L3

L2

S4

L1

Figure 1. Location of study area and sampling sites. 
4 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

to estimate total phosphorus, total nitrogen, and chlorophyll-a. 

Sedimentation rates and channel degradation downstream from 

the dam were estimated using sediment discharge, particle-size, 

and streamflow data. 

Description and Background Information of Study 

Area

Muddy Creek and Wolford Mountain Reservoir are 

located in the mountains of north-central Colorado near Kremmling (fig. 1). The reservoir collects water from Muddy Creek, 

a watershed that encompasses about 270 mi2

. Muddy Creek 

originates in the mountainous, forested terrain to the west and 

the northeast that sustain forestry activities and recreational 

land uses. These areas receive most of their annual precipitation 

(25 to 50 inches per year) as snowfall (Colorado Climate 

Center, 1984). Geology of the headwater area consists mostly of 

crystalline rocks in the Gore Range and volcanic rocks in the 

Rabbit Ears Range. The lower-elevation areas in the watershed 

are more arid (12 to 25 inches per year of precipitation) 

(Colorado Climate Center, 1984), sparsely vegetated rangeland 

underlain by marine shale (Tweto, 1979). Agricultural practices, such as irrigated hay and grass production and rangeland 

for livestock, occur in the lower elevation terrain. Domestic and 

livestock waste are factors with potential for affecting water 

quality in the Muddy Creek watershed. 

Wolford Mountain Reservoir was constructed by the 

CRWCD and benefits people living on the eastern and western 

slopes of Colorado. The western slope receives water for development, compensatory storage for the Windy Gap Diversion (a 

pump-back facility operated by the Northern Colorado Water 

Conservancy District on the upper Colorado River), and greater 

instream flows on the Colorado River system for current users, 

for recreation, and for protection of endangered fish. The Denver Water Board releases water from Wolford Mountain Reservoir to satisfy senior downstream users during drought, thereby 

avoiding the release of water from further upstream during dry 

years (Colorado River Water Conservation District, 2000).

Wolford Mountain Reservoir was constructed during 

1992–94. Filling of the reservoir began in 1995. The Ritschard 

Dam that retains Wolford Mountain Reservoir is about 7 miles 

upstream from the mouth of the Colorado River and 5 miles 

upstream from Kremmling. The dam is a zoned earth-filled type 

and is 120 ft high. The reservoir can store 68,000 acre-ft of 

water with an annual reliable yield of 28,000 acre-ft, and the 

reservoir covers approximately 1,550 surface acres at full storage (Colorado River Water Conservation District, 2000). There 

is no dead storage. The reservoir is about 4.5 miles in length and 

about one-quarter to one-half mile in width at full storage. The 

reservoir is long and narrow with an irregular shoreline and several shallow embayments on the western shore where larger 

tributaries enter the reservoir. Depths range from less than 10 ft 

in the inflow area to more than 100 ft near the dam, depending 

on water level. The major inflow to the reservoir is Muddy 

Creek. Pinto Creek, Pass Creek, Red Dirt Creek, and Alkali 

Slough are all intermittent tributaries to the reservoir. 

Reservoir operations affect seasonal streamflow downstream from the storage reservoir. Release and storage patterns 

were similar over the period of record on a year-to-year basis 

(fig. 2). Generally, reservoir storage reaches maximum elevation in April through June of each year and decreases steadily 

through summer and winter until April of the following year 

when storage of new snowmelt begins. Elevation capacity (a 

plot that relates water-surface elevation to water volume in the 

reservoir) for Wolford Mountain Reservoir is shown in figure 3. 

Release operations for the reservoir generally are similar from 

year to year (1995–2001). Four gates are available for releasing 

water from the reservoir: the main (bottom), 7,420 ft, 7,440 ft, 

and 7,460 ft gates. Fall and winter releases (September to April) 

are usually made from the upper two gates. In late spring and 

summer (May to August), releases are made from the main and 

uppermost gates (Jack Osburn, Colorado River Water Conservation District, written commun., 2002). 

Acknowledgments

The authors thank Jack Osburn at the Colorado River 

Water Conservation District for providing reservoir operations 

data. Thanks also to the Lakewood Field Office of the U.S. 

Geological Survey Colorado District for data collection activities over many years and the Colorado District Publishing 

Section—Mary Kidd for editorial review, Sharon Powers for 

illustrations, and Alene Brogan for manuscript preparation.

Methods of Investigation

Two types of methods are described in this section. The 

first, field methods, describes how data and samples were 

collected in streams and the reservoir, the processing of the 

samples, and the laboratory methods used. The second, data 

analysis methods, describes the statistical and analytical 

treatment of the data. 

Field Methods

Continuous-streamflow data were collected at three sites: 

Muddy Creek above Antelope Creek near Kremmling (S1) 

from April 1990 through September 2001, Muddy Creek at 

Kremmling (S2) from March 1985 through September 1995, 

and Muddy Creek below Wolford Mountain Reservoir near 

Kremmling (S3) from July 1995 through September 2001 

(Table 1). Continuous water-quality monitors were operated at 

Muddy Creek above Antelope Creek (S1) from April 1990 

through September 2001, Muddy Creek at Kremmling (S2) 

from April 1986 through September 1995, and Muddy Creek 

below Wolford Mountain Reservoir (S3) from October 1995 

through September 2001. Continuous water temperature and 

specific conductance data were collected at the three sites (S1, 

S2, and S3), but dissolved oxygen was collected only at S3 

below the reservoir. 
Methods of Investigation 5

1996 1997 1998 1999 2000

7,450

7,500

7,460

7,470

7,480

7,490

END OF MONTH RESERVOIR 

ELEVATION, IN FEET ABOVE SEA LEVEL

1996 1997 1998 1999 2000

20,000

70,000

30,000

40,000

50,000

60,000

END OF MONTH RESERVOIR 

CONTENTS, IN ACRE-FEET

Figure 2. Water-surface elevation and contents of Wolford Mountain Reservoir, water years April 

1995 through September 2000.

 Table 1. Water-quality sampling sites.

Station number Site 

code Station name Location description

09041090 S1 Muddy Creek above Antelope Creek near 

Kremmling

Approximately 1 mile upstream from reservoir 

10.9 miles upstream from Kremmling.

400812106254800 S4 Alkali Slough #2 at Wolford Mountain Reservoir near 

Kremmling

Approximately 300 feet upstream from mouth at 

reservoir.

09041400 S3 Muddy Creek below Wolford Mountain Reservoir 

near Kremmling

About 200 yards downstream from reservoir, about 

4 miles upstream from Kremmling.

09041500 S2 Muddy Creek at Kremmling On northern edge of Kremmling about 3 miles upstream 

from confluence with Colorado River.

09041395 L1 Wolford Mountain Reservoir near Kremmling Near the deepest part of the reservoir near the dam.

400841106240600 L2 Wolford Mountain Reservoir at midlake near 

Kremmling

At approximately midlake.

401110106244800 L3 Wolford Mountain Reservoir at inflow near 

Kremmling

Near the inflow of Muddy Creek to Wolford 

Mountain Reservoir.
6 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

20,000 30,000 40,000 50,000 60,000 70,000

7,440

7,500

7,450

7,460

7,470

7,480

7,490

WATER-LEVEL ELEVATION, IN FEET 

RESERVOIR CAPACITY, IN ACRE-FEET

Continuous data from the monitoring stations (S1, S2, and 

S3) were supported by monthly site visits during the open-water 

season (generally from April to October) and bimonthly visits 

when ice cover was present. Measurements of streamflow were 

made using a current meter by procedures given in Buchanan 

and Somers (1969). The calibration of water temperature, specific conductance, and dissolved oxygen for the water-quality 

monitors were checked using an ASTM thermometer, field 

meters, and standard solutions, and adjusted, if needed, according to procedures given in Wagner and others (2000). Data from 

these visits were used to analyze and compute the continuous 

data from the monitoring stations according to procedures given 

in Rantz and others (1982), Kennedy (1983), and Wagner and 

others (2000).

Water-quality samples were collected at four stream sites 

near the Wolford Mountain Reservoir area. Three sites were 

located on Muddy Creek, the primary inflow to and outflow 

from the reservoir: Muddy Creek above Antelope Creek (S1) 

from April 1990 through September 2001, Muddy Creek below 

Wolford Mountain Reservoir (S3) from July 1995 through September 2001, and Muddy Creek at Kremmling (S2) from March 

1985 through September 1995. Data and samples were collected approximately monthly in the streams and included field 

properties, major ions, nutrients, chlorophyll-a, fecal coliform, 

transparency, organic carbon, and suspended sediment. Traceelement samples were collected approximately twice per year 

during runoff and summer low flow. An intermittent stream, 

Alkali Slough #2 (site S4), was sampled from July 1996 through 

September 2001 twice per year in July and October.

In streams, field properties of specific conductance, water 

temperature, dissolved oxygen, and barometric pressure were 

made at streamside (U.S. Geological Survey, 1998). Turbidity 

and pH were measured from samples composited in a USGS 

churn splitter. Samples for inorganic analysis (major ions, nutrients, and trace elements) were collected by equal-width-increment (EWI) methods using a DH–81 polyethylene sampler and 

bottle, and composited in a USGS churn splitter, from which 

separate aliquots were withdrawn for each required analytical 

bottle (U.S. Geological Survey, 1998). 

 Turbidity and pH were measured from samples composited in a USGS churn splitter. Samples for inorganic analysis 

(major ions, nutrients, and trace elements) were collected by 

EWI methods using a DH–81 polyethylene sampler and bottle, 

and composited in a USGS churn splitter, from which separate 

aliquots were withdrawn for each required analytical bottle 

(U.S. Geological Survey, 1998). The sample collection and processing equipment were cleaned to trace-element standards 

according to procedures in USGS (1998). Samples for dissolved 

constituents were filtered through a disposable 0.45-μm capsule 

filter in an enclosed filter chamber using a peristaltic pump. 

Samples for trace-element analysis were preserved with traceelement grade nitric acid. Nutrient samples were chilled to 

approximately 4°C (U.S. Geological Survey, 1998). 

Samples for organic analysis were collected in a baked 

glass bottle by dip methods at the centroid of flow. The total 

organic carbon samples were not filtered. Dissolved organic 

carbon samples were filtered through a 0.45-μm filter. Carbon 

samples were chilled to less than 4°C until analyzed (U.S. Geological Survey, 1998).

Suspended-sediment samples were collected by EWI or 

equal-discharge-increment methods with a DH–48 hand sampler or DH–59 cable sampler (Guy and Norman, 1970) at sites 

S1 and S2, for analyses of concentration and particle-size percentage finer than 0.062 mm.

Water-quality samples were collected at three sites on 

Wolford Mountain Reservoir (fig. 1), at the dam (L1) from July 

Figure 3. Wolford Mountain Reservoir elevation-capacity relation.
Methods of Investigation 7

1995 through September 2001, at midlake (L2) from July 1995 

through September 2001, and at the Muddy Creek inflow (L3) 

from July 1995 through September 2001. Data and samples collected in the reservoir included field properties (water temperature, specific conductance, pH, and dissolved oxygen), major 

ions, nutrients, chlorophyll-a, fecal coliform, transparency, 

organic carbon, and trace elements. Samples were collected 

from just below the surface and near the bottom of the reservoir 

at L1 and L2, but only at mid-depth at L3. Depth profiles of 

water temperature, specific conductance, pH, and dissolved 

oxygen were measured every 5 ft up to 30 ft of depth and every 

10 ft for depths greater than 30 ft at every water-quality sampling visit. Samples and profile data were collected in June, 

July, August, and October each year.

Water-column samples and field-property profiles were 

collected in Wolford Mountain Reservoir (sites L1, L2, and L3). 

Water depth was determined by using a depth-finder in a boat. 

A multiparameter water-quality instrument was used to measure water temperature, specific conductance, pH, and dissolved oxygen. The transparency of the water was determined 

with a Secchi disk and measured in inches with a cloth tape or 

folding rule.

Samples for major ion, nutrient, and trace-element analyses were collected at the surface and just above the bottom by 

using a Van Dorn point sampler, a horizontal PVC cylinder with 

end seals that are triggered by a surface messenger, lowered on 

a cable (U.S. Geological Survey, 1998). Field properties were 

determined from measurements taken in the lake or reservoir. 

Sample water for inorganic analyses was transferred to clean, 

acid-rinsed, deionized-water rinsed, and native-water rinsed 

polyethylene containers. Sample water was transferred to a 

clean, acid-rinsed, deionized-water rinsed, and native-water 

rinsed USGS churn splitter and then processed and preserved as 

described in the streamwater-quality section of this report 

(U.S. Geological Survey, 1998). Chlorophyll-a samples were 

collected and processed according to methods described in 

Britton and Greeson (1987).

Laboratory analysis of all samples collected for major ion, 

nutrient, and trace-element analysis were analyzed at the USGS 

National Water Quality Laboratory in Lakewood, Colo., using 

standard analytical techniques described in Fishman and Friedman (1989), Fishman (1993), and Fishman and others (1994). 

Samples collected for concentrations of organic constituents 

were analyzed at the same laboratory using standard analytical 

techniques described in Wershaw and others (1987) and Fishman (1993). Suspended-sediment and bed-material samples 

were analyzed according to methods described in Guy (1969) at 

the USGS Iowa Sediment Laboratory in Iowa City, Iowa. Laboratory methods and minimum reporting limits for samples collected during the study are listed in table 2. All data are published in the USGS annual data report for Colorado and are 

stored in the USGS National Water Quality Information System 

(NWIS).

Data-Analysis Methods

For purposes of comparison, data sets were considered 

from 1990 to 2001 even though data were collected at S2 since 

March 1985. Data were collected at S1 from 1990 to 2001. 

Because data collection at the S2 site ended in 1995 and began 

at the S3 site in 1995, the two sites were combined for the purposes of time-series trend analysis to provide a complete 1990 

to 2001 record. Reservoir sampling for the entire period of 

record (1995 to 2001) at sites L1, L2, and L3 were used in data 

analysis.

Hydrologic data were analyzed by using time-series plots, 

plots of daily mean statistics, and flow-duration curves. The 

purpose was to characterize seasonal and long-term flow 

patterns and compare flows upstream and downstream from 

Wolford Mountain Reservoir.

Streamwater-quality data for field properties, nutrients, 

major ions, trace elements, suspended sediment, and biological 

indicators were analyzed by discussions of general characteristics, upstream to downstream prereservoir/postconstruction 

comparisons, seasonality, and temporal trends through the use 

of time-series plots, statistics, boxplots, seasonal Kendall test 

results, and spatial differences by Wilcoxon signed rank test 

results.

To estimate the nutrient mass entering and leaving the reservoir in surface-water inflows and outflows each year, and to 

determine how the reservoir may have influenced downstream 

nutrient concentrations, total nitrogen and total phosphorus 

mass balances were calculated for each year from 1996 through 

2001. Data were collected in 1996 only from April through 

December, and January through October in 2001. The general 

mass-balance equation used is:

(1)

where 

IMS is the mass in the surface-water inflow, in 

kilograms;

OMS is the mass in the surface-water outflow, in 

kilograms; and

UMS is the portion of the total mass that is unaccounted 

for (gained or lost), in kilograms.

Inflows as reported here are those measured in Muddy 

Creek above the reservoir, and outflows are those measured in 

Muddy Creek below the reservoir. Sources that are unaccounted 

for include inflow from intermittent and ephemeral streams, 

release from reservoir bottom sediment, runoff from surrounding land area, atmospheric deposition to the reservoir surface, 

changes in reservoir storage, and ground-water inflow, which 

could contribute to a positive unaccounted-for term. Sinks that 

are unaccounted for might include ground-water outflow, sedimentation, changes in reservoir storage, and biological uptake, 

which could contribute to a negative unaccounted-for term.

Inflow mass and outflow mass were calculated as the product of the concentration in a sample collected in a given month 

±UMS IMS OMS = –
8 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Table 2. Laboratory methods and minimum reporting limits for samples collected during the study.

[ICP, inductively coupled plasma; ICPMS, inductively coupled plasma mass spectrometry; IC, ion chromatography; AA, atomic absorption; GFAA, 

graphite furnace atomic absorption; HPLC, high-performance liquid chromatography; MF, membrane filtration; CVAF, cold vapor atomic fluorescence; 

EWI, equal-width increment; mg/L, milligrams per liter; μg/L, micrograms per liter; °C, degrees Celsius; ft3

/s, cubic feet per second; μS/cm, 

microsiemens per centimeter at 25°C; NTU, nephelometric turbidity units; T/d, tons per day]

Property or constituent Units Field method Analytical method

Minimum 

reporting 

limit

Field properties

Discharge ft3/s current meter mid-interval variable

Specific conductance μS/cm point electrode 1

pH units EWI electrode 0.1

Turbidity NTU EWI nephelometry .1

Dissolved oxygen mg/L point electrode .1

Secchi depth inches disk observation 1

Major ions

Hardness as CaCO3 mg/L EWI calculated 1

Calcium, dissolved mg/L EWI ICP .1

Magnesium, dissolved mg/L EWI ICP .1

Sodium, dissolved mg/L EWI ICP .1

Potassium, dissolved mg/L EWI ICP .1

Acid-neutralizing capacity, lab as CaCO3 mg/L EWI titration 1

Sulfate, dissolved mg/L EWI IC .1

Chloride, dissolved mg/L EWI IC .1

Fluoride, dissolved mg/L EWI ion selective electrode .1

Silica, dissolved mg/L EWI ICP .1

Dissolved solids, residue at 180°C mg/L EWI residue on evaporation at 180°C 1

Dissolved solids, sum of constituents mg/L EWI calculated 1

Nutrients

Nitrite, dissolved as N mg/L EWI colorimetry .001

Nitrite plus nitrate, dissolved as N mg/L EWI colorimetry .005

Nitrogen, ammonia, dissolved as N mg/L EWI colorimetry .002

Nitrogen, ammonia plus organic, dissolved as N mg/L EWI colorimetry .2

Nitrogen, ammonia plus organic, total as N mg/L EWI colorimetry .2

Phosphorus, total as P mg/L EWI colorimetry .001, .05

Phosphorus, dissolved as P mg/L EWI colorimetry .001

Phosphorus, dissolved orthophosphate as P mg/L EWI colorimetry .001

Biological

Chlorophyll-a and -b μg/L point HPLC .1

Fecal coliform col/100ml EWI, point MF 1

Trace Elements

Aluminum, dissolved as Al μg/L EWI ICPMS 1

Antimony, dissolved as Sb μg/L EWI ICPMS 1

Arsenic, dissolved as As μg/L EWI ICPMS, GFAA 1, 4

Barium, dissolved as Ba μg/L EWI ICPMS 1

Beryllium, dissolved as Be μg/L EWI ICPMS 1

Cadmium, total as Cd μg/L EWI GFAA 1

Cadmium, dissolved as Cd μg/L EWI ICPMS, GFAA 1
Methods of Investigation 9

Chromium, dissolved as Cr μg/L EWI ICPMS 1

Cobalt, dissolved as Co μg/L EWI ICPMS 1

Copper, total as Cu μg/L EWI ICP, GFAA 10, 1

Copper, dissolved as Cu μg/L EWI ICP, ICPMS, GFAA 10, 1, 1

Iron, total as Fe μg/L EWI AA, ICP 10

Iron, dissolved as Fe μg/L EWI ICP, AA 3, 10

Lead, total as Pb μg/L EWI GFAA 1

Lead, dissolved as Pb μg/L EWI ICP, ICPMS, GFAA 10, 1, 1

Manganese, total as Mn μg/L EWI AA, ICP 10

Manganese, dissolved as Mn μg/L EWI ICP, ICPMS 10, 4, 1

Mercury, dissolved as Hg μg/L EWI CVAF 0.1

Molybdenum, dissolved as Mo μg/L EWI ICPMS 1

Nickel, dissolved as Ni μg/L EWI ICPMS 1

Selenium, dissolved as Se μg/L EWI ICPMS 1

Silver, dissolved as Ag μg/L EWI ICPMS 1

Zinc, total as Zn μg/L EWI ICP, AA 10, 31, 40

Zinc, dissolved as Zn μg/L EWI ICP, ICPMS 20, 3

Uranium, dissolved as U μg/L EWI ICPMS 1

Sediment

Sediment, suspended, concentration mg/L EWI gravimetric 1

Sediment, bedload, discharge T/d EWI gravimetric variable

Sediment, bedload, size fractions percent EWI dry sieve 1

Table 2. Laboratory methods and minimum reporting limits for samples collected during the study.—Continued

[ICP, inductively coupled plasma; ICPMS, inductively coupled plasma mass spectrometry; IC, ion chromatography; AA, atomic absorption; GFAA, 

graphite furnace atomic absorption; HPLC, high-performance liquid chromatography; MF, membrane filtration; CVAF, cold vapor atomic fluorescence; 

EWI, equal-width increment; mg/L, milligrams per liter; μg/L, micrograms per liter; °C, degrees Celsius; ft3/s, cubic feet per second; μS/cm, 

microsiemens per centimeter at 25°C; NTU, nephelometric turbidity units; T/d, tons per day]

Property or constituent Units Field method Analytical method

Minimum 

reporting 

limit
10 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

and the volume of water entering or leaving the reservoir during 

that month. Monthly masses were summed to compute annual 

mass. The assumption that one concentration can represent the 

entire month may not always be valid, as inflow and outflow 

volumes, degrees of stratification, and biological activity 

changed between sampling dates. These uncertainties led to an 

unquantified amount of error in the mass balance for the reservoir. Therefore, the mass balances presented in this report 

should be used with caution.

Reservoir water-quality data for field properties, nutrients, 

major ions, trace elements, and biological indicators were analyzed through the evaluation of general characteristics, spatial 

variability, surface and bottom variability, and seasonality 

through the use of time-series plots, statistics, and boxplots. 

Stratification patterns were evaluated by analysis of fieldproperty profiles to understand vertical variability in water 

temperature, specific conductance, pH, and dissolved oxygen. 

Nutrient budgets were used to evaluate loading and storage 

characteristics in the reservoir.

On the basis of data collected 1995–2001, Wolford Mountain Reservoir was classified using the method developed by 

Carlson (1977). 

Trophic-state index (TSI) values were calculated from the 

following equations:

(2)

(3)

(4)

where

SD is Secchi-disc depth, in meters;

TP is total phosphorus concentration, in micrograms per 

liter;

CHLA is chlorophyll-a concentration, in micrograms per 

liter; and

ln is the natural logarithm of the indicated variable.

The indices are meant to normalize the three indicators so 

that any of the three could be used independently to describe the 

conditions in the water body. Secchi-disc depths and concentrations of total phosphorus and chlorophyll-a (surface only) were 

averaged for each year to compute mean values. The annual 

mean values then were used to compute annual TSI’s.

Stream and reservoir water-quality data were evaluated by 

water-quality standards. In Colorado, water-quality standards 

specifies that hardness concentrations used to calculate the 

chronic trace-element standards be computed from the lower 

95-percent confidence limit of the mean hardness at the periodic 

low-flow criteria determined from regression analysis of sitespecific or regional data. The 85th percentile of available data 

then is compared to the standard. For this report, however, each 

hardness concentration and standard value was determined 

from analysis of water samples collected at the time of sampling 

and compared to the sample concentration. The standards comparison in this report, therefore, should be regarded as a general 

indicator rather than a rigorous statistical comparison of State 

standards. Laboratory minimum reporting limits (MRL’s) for 

trace elements such as ammonia, cadmium, mercury, silver, and 

lead commonly were too high to determine concentrations at the 

level of the standards. These constituents might be present in 

the sample at concentrations lower than the laboratory MRL but 

higher than the standard. Certain constituents listed in the Colorado water-quality standards were not analyzed in the samples 

(for example, chlorine, cyanide, and sulfide). 

Data-Set Construction

In order to obtain a continuous record of water-quality data 

downstream from the reservoir, data from two sites (S2 and S3) 

were combined. In July, August, and September 1995, monthly 

samples were obtained from each of the two sites, although they 

were not concurrent (table 3). Although three samples were not 

enough to compare the data statistically, a qualitative analysis 

indicated that water quality at the two sites was similar for 

major ions but somewhat dissimilar for nutrients and metals. 

These differences may have been a greater consequence of the 

timing of sample collection than of the site locations because 

the greatest differences between sites were in July (samples 

taken on July 11 at 09041500 S2 and July 13 at 09041400 S3), 

whereas the smallest differences were in September (samples 

taken on September 19 at both sites). This comparison indicates 

that some caution should be used when interpreting results 

based on the combined data.

Water-quality samples were collected at the most upstream 

site, Muddy Creek above Antelope Creek near Kremmling 

(USGS station number 09041090 S1), from April 1990 through 

September 2001. To directly compare the results of trend analyses at the upstream and downstream sites, the combined downstream data set was limited to match the time interval of the 

upstream data set.

Before January 1993, the type of a small number of analyses done by the USGS National Water Quality Laboratory was 

changed: total ammonia was replaced with dissolved ammonia; 

total nitrate plus nitrite was replaced with dissolved nitrate plus 

nitrite; total nitrite was replaced with dissolved nitrite; and total 

orthophosphate was replaced with dissolved orthophosphate. 

Between 1990 and 2001, several samples were analyzed concurrently for total and dissolved constituents (table 4). A Wilcoxon signed-rank test indicated that there were no statistically 

significant differences between the total and dissolved concentrations at an α-level of 0.01. Consequently, the total and dissolved constituent concentrations were combined in the final 

data sets both for the upstream and the downstream sites.

Trends in water quality were obtained using the seasonal 

Kendall trend (SKT) test with correction for serial correlation 

(Hirsch and Slack, 1984). The SKT is a nonparametric test for 

monotonic linear trend; it is resistant to outliers and is not 

dependent on the normality of the data set. In the test, data 

TSI SD ( ) = 60 14.41 ln SD – ( )

TSI TP ( ) = 14.42 ln TP ( ) + 4.15

TSE CHLA ( ) = 9.81( ) lnCHLA + 30.6
Methods of Investigation 11

Table 3. Comparison of samples taken concurrently at the two downstream sites —Muddy Creek at Kremmling (S2) and 

Muddy Creek below Wolford Mountain Reservoir near Kremmling (S3)—between August and September 1995.

[<, less than; --, sample not analyzed; mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; 

NTU, nephelometric turbidity units]

Constituent

Concentration

S2 S3

07-11-95 08-15-95 09-19-95 07-13-95 08-16-95 09-19-95

Dissolved oxygen (mg/L) 7.8 7.7 8.3 9 7.5 7.8

pH, field (standard units) 8.3 8.3 8.3 7.9 8.1 8.2

Specific conductance (μS/cm @ 25oC) 462 575 562 446 564 530

Water temperature (oC) 15.5 15.0 15.0 12.5 12.0 16.0

Hardness, total (mg/L as CaCO3) 190 260 250 370 250 240

Calcium, dissolved (mg/L as Ca) 54 70 66 98 68 63

Magnesium, dissolved (mg/L as Mg) 14 20 20 30 19 19

Potassium, dissolved (mg/L as K) 1.8 1.9 2.2 2.6 1.9 2.1

Sodium, dissolved (mg/L as Na) 13 18 19 23 17 17

Acid-neutralizing capacity, alkalinity, lab, as CaCO3 93 111 122 130 105 115

Chloride, dissolved (mg/L as Cl) 2.1 2.2 2 2.4 2 1.7

Fluoride, dissolved (mg/L as F) 0.1 0.2 0.1 0.2 0.1 0.1

Silica, dissolved (mg/L as SiO2) 8.6 8.4 7.7 9.4 9.8 7.7

Sulfate, dissolved (mg/L as SO4) 130 180 160 290 170 150

Nitrogen, ammonia plus organic, dissolved (mg/L as N) .3 .4 .3 .7 .5 .3

Nitrogen, ammonia plus organic, total (mg/L as N) .4 .5 .5 .7 .5 .5

Nitrogen, ammonia, dissolved (mg/L as N) .02 .15 .02 .28 .24 .02

Nitrogen, nitrite plus nitrate, dissolved (mg/L as N) <.050 <.050 <.050 .06 <.050 <.050

Nitrogen, nitrite, dissolved (mg/L as N) <.010 <.010 <.010 <.010 <.010 <.010

Phosphorus, dissolved (mg/L as P) <.010 0.02 <.010 0.06 <.010 <.010

Phosphorus, dissolved orthophosphate (mg/L as P) <.010 0.01 <.010 0.05 0.04 <.010

Phosphorus, total (mg/L as P) <.010 0.02 0.04 0.11 0.04 0.05

Carbon, organic, dissolved (mg/L as C) 6.9 -- 7.1 7.2 -- 7.1

Carbon, organic, total (mg/L as C) 7.7 -- 9 8.1 -- 8.6

Dissolved solids, residue at 180°Celsius (mg/L) 314 390 375 288 376 355

Dissolved solids, sum of constituents (mg/L) 279 368 351 533 351 330

Turbidity (NTU) 6.2 12 13 2.2 1.6 1.9

Aluminum, total recoverable (μg/L as Al) -- -- 340 -- -- 60

Arsenic, dissolved (μg/L as As) -- -- 1 -- -- <1

Arsenic, total recoverable (μg/L as As) -- -- 1 -- -- 1

Barium, dissolved (μg/L as Ba) -- -- <100 -- <100

Barium, total recoverable (μg/L as Ba) -- -- <100 -- -- <100

Beryllium, total recoverable (μg/L as Be) -- -- < 10 -- -- <10

Boron, dissolved (μg/L as B) -- -- 50 -- -- 60

Cadmium, dissolved (μg/L as Cd) -- -- <1.0 -- -- <1.0

Cadmium, total recoverable (μg/L as Cd) -- -- <1.0 -- -- <1

Chromium, dissolved (μg/L as Cr) -- -- <1.0 -- -- <1

Chromium, total recoverable (μg/L as Cr) -- -- <1 -- -- <1

Cobalt, total recoverable(μg/L as Co) -- -- <1 -- -- <1

Copper, dissolved (μg/L as Cu) -- -- 1 -- -- <1

Copper, total recoverable (μg/L as Cu) -- -- 2 -- -- <1

Iron, dissolved (μg/L as Fe) 60 110 40 160 160 50

Iron, total recoverable (μg/L as Fe) -- -- 660 -- -- 130

Lead, dissolved (μg/L as Pb) -- -- <1 -- -- <1

Lead, total recoverable (μg/L as Pb) -- -- <1 -- -- <1
12 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Lithium, total recoverable (μg/L as Li) -- -- 20 -- -- 20

Manganese, dissolved (μg/L as Mn) -- -- 80 -- -- 40

Manganese, total recoverable (μg/L as Mn) -- -- 110 -- -- 40

Mercury, dissolved (μg/L as Hg) -- -- <.1 -- -- <.1

Mercury, total recoverable (μg/L as Hg) -- -- <.1 -- -- <.1

Molybdenum, dissolved (μg/L as Mo) -- -- 1.6 -- -- 2

Molybdenum, total recoverable (μg/L as Mo) -- -- 1.6 -- -- 2

Nickel, dissolved (μg/L as Ni) -- -- 3 -- -- 2

Nickel, total recoverable (μg/L as Ni) -- -- 3 -- -- 2

Selenium, dissolved (μg/L as Se) -- -- 3 -- -- 3

Selenium, total recoverable (μg/L as Se) -- -- 3 -- -- 4

Silver, dissolved (μg/L as Ag) -- -- <1 -- -- <1

Silver, total recoverable (μg/L as Ag) -- -- <1 -- -- <1

Strontium, dissolved (μg/L as Sr) -- -- 590 -- -- 560

Zinc, dissolved (μg/L as Zn) -- -- <10 -- -- <10

Zinc, total recoverable (μg/L as Zn) -- -- <10 -- -- <10

Table 3. Comparison of samples taken concurrently at the two downstream sites —Muddy Creek at Kremmling (S2) and 

Muddy Creek below Wolford Mountain Reservoir near Kremmling (S3)—between August and September 1995.—Continued

[<, less than; --, sample not analyzed; mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; 

NTU, nephelometric turbidity units]

Constituent

Concentration

S2 S3

07-11-95 08-15-95 09-19-95 07-13-95 08-16-95 09-19-95

Table 4. Comparison of concurrent total and dissolved analyses and results of Wilcoxon signed-rank test.

[2-sided test; <, less than; --, sample not analyzed; all concentrations in milligrams per liter; p-values significant at greater than 90 percent confidence 

shown in bold]

Date Ammonia, 

total

Ammonia 

dissolved

Nitrite plus 

nitrate,

total

Nitrite 

plus 

nitrate, 

dissolved

Nitrite, 

total

Nitrite, 

dissolved

Orthophosphate, 

total

Orthophosphate, 

dissolved

S3 09041400

09-20-1989 0.04 0.03 <0.10 <0.10 -- -- <0.01 <0.01

05-9-1990 .03 .01 <.10 <.10 -- -- .04 <.01

09-25-1990 .05 .03 .20 <.10 -- -- <.01 <.01

05-30-1991 .05 .03 <.10 .052 .05 .01 .05 <.01

09-25-1991 .01 .01 <.10 <.05 .01 <.01 .02 <.01

09-3-1992 .02 .02 <.10 <.05 .02 <.01 .05 <.01

11-16-1992 .03 .02 .10 .13 <.01 .02 <.01 <.01

S1 09041900

05-10-1990 .04 .01 <.10 <.10 -- <.01 .05 <.01

09-27-1990 .03 <.01 <.10 <.10 -- <.01 <.01 <.01

05-30-1991 .04 .02 .052 <.05 .03 <.01 .03 .03

09-25-1991 <.01 .01 <.05 <.05 <.01 <.01 .01 <.01

05-7-1992 <.01 .02 <.05 <.05 <.01 <.01 <.01 .01

09-3-1992 .03 .02 <.05 <.05 <.01 <.01 .02 <.01

11-18-1992 .03 .01 <.05 <.05 <.01 .02 <.01 <.01

p-value 0.0110 0.3196 0.5295 0.0171
Methods of Investigation 13

60

5 10 15 20 25

Weighted total nitrogen

concentration = 2.2 mg/L

Observed total nitrogen

concentration = 1.0 mg/L

0

1

2

3

4

5

6

7

8

90

120

150

180

OCTOBER 1998

STREAMFLOW, IN CUBIC FEET PER SECOND

TOTAL NITROGEN CONCENTRATION, IN 

MILLIGRAMS PER LITER

Streamflow

Total nitrogen concentration

points are compared only to other points within the same season, reducing the effects of seasonality on concentrations. 

Trends were calculated for unadjusted and flow-weighted 

concentrations. Monthly flow-weighted concentrations are concentrations that have been weighted to reflect flow conditions 

throughout an entire month, not just the conditions on the day 

that a sample was collected (fig. 4). Flow weighting can produce a more representative monthly concentration than a single 

observed concentration alone. When the relation between flow 

and concentration is not statistically significant, however, flow 

weighting will lead to biased values. As a result, flow-weighted 

concentration trend results in this report are provided only for 

those constituents that are significantly correlated with flow.

Flow-weighted concentrations were calculated using the 

ordinary least-squares (OLS) regression model equation:

(5)

where 

ln is the natural log;

Ci

 is the ith observation of concentration;

Qi

 is the ith observation of mean daily discharge;

ß0 is the intercept;

ß1 is the slope; and

n is the number of samples.

Log-normal transformations were used in an effort to 

achieve homoscedasticity and normality of the residuals, two 

major assumptions of OLS regression. If these assumptions 

were not met for a given constituent, the constituent was 

excluded from the flow-weighting procedure. For the downstream sites, mean daily discharges were combined by date into 

one data set the same way the water-quality values were, so that 

concentrations obtained at one site were matched up with discharges measured at the same site. Slope coefficients and intercepts for OLS regression equations cannot be computed accurately with a large amount of censored data (Helsel and Hirsch, 

1992); consequently, constituents exceeding 10 percent of censored data were excluded from the flow-weighting procedure. 

Censored data for the constituents that remained were set equal 

to the detection limit in the OLS. The data set for each constituent remaining was tested for serial correlation using the "acf" 

function in S-Plus 2000© (Insightful Corp., 2000). If any values 

in the correlation matrix were above 0.20, serial correlation was 

deemed present at a level that would induce unacceptable type 

I error rates (Alden and others, 2000), and the corrected 

p-values from the SKT output were used.

The fitted OLS regression equation for each constituent 

was used to predict daily concentrations based on known mean 

daily discharge. The resulting concentrations were in lognormal space, so corrections for back-transformation bias were 

achieved using the equation:

ln Ci () β = 0 βlln Qi + ( ) i 1,2,...n =

Figure 4. Comparison of observed monthly concentration and a flow-weighted monthly concentration of total

nitrogen (adapted from Langland and others, 1999).
14 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

(6)

where 

ln is the natural log;

Ci is the ith observation of concentration;

Qi is the ith observation of mean daily discharge;

ß0 is the intercept;

ß1 is the slope;

s

2 is the sample variance; and

n is the sample size.

Monthly flow-weighted concentrations were calculated by 

taking the mean of the predicted daily concentrations each 

month. Flow-weighting procedures met criteria for most major 

ions at S2/S3 combined, and acid-neutralizing capacity (ANC), 

dissolved iron, and turbidity at S1. The SKT test then was run 

on the monthly flow-weighted concentrations using the 

"seaken" function in S-Plus 2000© (Insightful Corp., 2000).

For those constituents that were excluded from the flowweighting procedure because they did not meet the correlation, 

censoring, normality, or homoscedasticity criteria, the SKT test 

was used on unadjusted (observed) concentrations. Further, 

constituents with censoring between 5 and 50 percent can lead 

to biased estimates of the trend slope when an arbitrarily chosen 

value is substituted for the censored value (Helsel and Hirsch, 

1992). As a result, only the sign of the trend slope and not the 

magnitude was reported for constituents with censoring 

between 5 and 50 percent. The slope is reported in the tables in 

units of change per year in the median value. All censored data 

were set to the detection limit. When detection limits changed 

throughout the study period, all censored data were recensored 

to the highest reporting limit. This recensoring of the data 

caused a loss in statistical power, but leaving changes in reporting limits over time in a data set could have led to the detection 

of trends that did not exist. 

The SKT test requires one value per season per year. At the 

upstream site (S1), samples were collected only from April 

through December in some years and monthly in others. Due to 

the variation in sampling frequency, the seasons for the SKT 

test were defined on the basis of the lowest sampling frequency 

(Helsel and Hirsch, 1992). Therefore, nine seasons were used 

for the upstream site. For the years in which monthly samples 

were collected, the data were adjusted to nine seasons by taking 

the value from the sample collected closest to the midpoint of 

each season. At the downstream sites, monthly samples were 

collected throughout the study period, so 12 seasons were used 

in the SKT test. When multiple samples were collected in a 

given month, the median for that month was used. As with the 

flow-weighted concentrations, the unadjusted concentrations 

were tested for serial correlation and, if necessary, the corrected 

p-values from the SKT output were used. 

Spatial changes between the upstream and downstream 

sites were determined using a two-sided Wilcoxon rank-sum 

test to compare the two data sets before and after water storage 

began in the reservoir. The null hypothesis is that samples from 

both sites were from the same population, or accordingly, the 

samples are not statistically different (Helsel and Hirsch, 1992). 

Using data with censoring greater than 50 percent can invalidate 

the results of the hypothesis test; as a result, constituents with 

censoring greater than 50 percent were excluded from the 

Wilcoxon statistical test.

The first part of the testing for spatial differences was to 

determine if upstream and downstream differences in water 

quality existed before construction of the reservoir so that preexisting differences would not be mistaken for reservoir effects. 

Results of upstream/downstream differences at Muddy Creek 

above Antelope (S1) and Muddy Creek at Kremmling (S2) prereservoir, 1990 through 1995, were computed. Secondly, postconstruction upstream/downstream differences, 1995 through 

2001, also were computed. 

Hydrology

Hydrologic characteristics of the Muddy Creek watershed 

are important for understanding reservoir and streamflow water 

quality both upstream and downstream from the reservoir. 

Although some variation in hydrologic characteristics of 

Muddy Creek are due to natural changes, after 1995, when the 

dam was completed, the reservoir and control of outflows 

affected streamflow below the outlet of the dam. Daily mean 

discharge during the study was variable (fig. 5). The annual 

hydrograph for Muddy Creek was dominated by the magnitude 

and timing of snowmelt runoff. Snowpack melting represents 

about 88 percent of the average annual runoff 1990 through 

2001 during April through June (figs. 6–8). Daily fluctuations 

in streamflow during snowmelt are largely due to diurnal 

variations in air temperatures that influence melting and to 

the location, duration, and intensity of rainstorms. 

 Maximum instantaneous streamflow was 955 ft3/s, June 

20, 1994, before completion of the dam, when a localized storm 

dropped 3 inches of rain over a 1 to 2-mi2

 area in a tributary of 

Muddy Creek (Robert D. Jarrett, U.S. Geological Survey, written commun., 1994) (fig. 9). Attenuation of downstream peak 

streamflow was evident in the hydrograph. Minimum daily 

streamflow for the period of record at S1 was 0.96 ft3/s (fig. 7) 

and occurred in July 1994. 

The effects of Wolford Mountain Reservoir on downstream streamflow can be seen in flow-duration curves for 

Muddy Creek above Antelope Creek (upstream from the reservoir, site S1) and Muddy Creek below Wolford Mountain Reservoir (downstream from the reservoir, site S3) (fig. 10). In 

most years (water years 1996 to 2001) since the reservoir began 

filling, peak flows downstream from the reservoir were similar 

or slightly reduced as a result of reservoir storage when compared to those upstream. The upper first to fifteenth percentiles 

of flows downstream were decreased compared to prereservoir 

flow patterns. The fifteenth to one-hundredth percentiles of outflow duration generally were increased by operation of the 

reservoir compared to inflow duration.

Ci exp β0 + βl ln Qi ( ) 0.5s2 = [ ] + i 1,2,...n =
Hydrology 15

0

2,0001,000

DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

0

2,0001,000

0

2,0001,000

MUDDY CREEK ABOVE ANTELOPE CREEK (S1)

MUDDY CREEK AT KREMMLING (S2)

MUDDY CREEK BELOW WOLFORD MOUNTAIN RESERVOIR (S3)

1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 20011982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Figure 5. Daily mean discharge at stream gages along Muddy Creek.
16 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

0

1,800

800600400200

1,6001,4001,2001,000

STREAMFLOW, IN CUBIC FEET PER SECOND

MinimumMedianMaximum

Streamflows for each day of year representthe value of all the streamflows for that dayof the year for the period of record 

J FMAM J J A SO ND

2000

Figure 6. Daily streamflow statistics for period of record at Muddy Creek at Kremmling water years 1982–96.
Hydrology 17 2000 0

1,000

900800700600500400300200100

STREAMFLOW, IN CUBIC FEET PER SECOND

MinimumMedianMaximum

Streamflows for each day of year representthe value of all the streamflows for that dayof the year for the period of record 

J F M A M J J A S O ND

Figure 7. Daily streamflow statistics for period of record at Muddy Creek above Antelope Creek water years 1990–2002.
18 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

J FM A M J J A S O ND

2000

0

1,100

900800700600500400300200100

1,000

STREAMFLOW, IN CUBIC FEET PER SECOND

MinimumMedianMaximum

Streamflows for each day of year representthe value of all the streamflows for that dayof the year for the period of record 

Figure 8. Daily streamflow statistics for period of record at Muddy Creek below Wolford Mountain Reservoir water years 1995–2002.
Hydrology 19

Muddy Creek above

 Antelope Creek (S1) 

Muddy Creek

 at Kremmling (S2) 

2400 0600 1200 1800 2400 0600 1200 1800 2400 0600 1200 1800 2400

20 21 22

June 1994

1,000

200

400

600

800

INSTANTANEOUS STREAMFLOW, IN 

CUBIC FEET PER SECOND

0

0

0

1,000

200

400

600

800

STREAMFLOW, IN CUBIC FEET PER SECOND

EXPLANATION

0 120 20 40 60 80 100

PERCENTAGE OF DAYS FLOW WAS EXCEEDED

0

1,000

200

400

600

800

0 120 20 40 60 80 100 20 40 60 80 100 120

WATER YEAR 1996 WATER YEAR 1997 WATER YEAR 1998

WATER YEAR 1999 WATER YEAR 2000 WATER YEAR 2001

MUDDY CREEK ABOVE

 ANTELOPE CREEK (S1)

MUDDY CREEK BELOW

 WOLFORD MOUNTAIN

 RESERVOIR (S3)

Figure 9. Instantaneous discharge hydrographs for two Muddy Creek gaging stations 

during a localized storm with maximum rainfall in the range of 3 inches total over a 1- to 

2-square-mile area in a tributary of Muddy Creek.

Figure 10. Flow-duration curves for streamflow upstream and downstream from Wolford Mountain Reservoir, 1996 through 2001.
20 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Water Quality

This section presents chemical characteristics, sediment, 

and results of continuous water-quality monitoring of temperature, specific conductance, and dissolved oxygen (site S3 only) 

for streams. Chemical characteristics, profiles and stratification, 

nutrient mass balance, and trophic status of Wolford Mountain 

Reservoir are discussed after stream characteristics. 

Streamwater Quality

Seasonal and hydrologic factors such as precipitation distribution and bedrock geology affect variation in streamwater 

quality. Prereservoir water quality is an important baseline for 

evaluating postconstruction effects on water quality. Waterquality data available for analysis included field properties 

(water temperature, specific conductance, pH, dissolved oxygen, and turbidity), major ions, nutrients, trace elements, 

organic carbon, and suspended sediment. Continuous monitoring data for specific conductance, water temperature, and dissolved oxygen (site S3 only) also were collected and evaluated. 

To determine the effects of water storage in Wolford 

Mountain Reservoir on downstream water quality in Muddy 

Creek, changes in water quality along Muddy Creek before and 

after completion of the reservoir in March 1995 were examined. 

Temporal changes in water quality, due to natural variations 

over the entire study period, were determined based on trends in 

water quality at site S1 (Muddy Creek above Antelope Creek) 

upstream from the reservoir. Spatial changes in water quality 

due to natural variations were determined based on differences 

in constituent concentrations at the upstream (S1) and downstream sites (S2) before the initial storage of water in the reservoir. Temporal changes due to both natural variations and water 

storage in the reservoir were determined based on trends in 

water quality at the downstream sites (S2 and S3). Spatial 

changes due to natural variations and water storage in the reservoir were determined based on differences in concentrations at 

the upstream (S1) and downstream sites (S2 and S3) after the 

initial storage of water in the reservoir. By analyzing all results 

together, the effects of water storage in the reservoir can be separated out from those due to natural variations.

Field Properties

Summary statistics for field properties were compiled for 

S1, S2, and S3 (table 5). In the table, S1 is characterized for prereservoir (April 1990 to March 1995), postconstruction (April 

1995 to September 2001), and both periods combined (1990 to 

2001). S2 and S3, both downstream from the reservoir, are combined to create similar periods for comparison. Boxplots of 

selected constituents by site are in figure 11. Time-series plots 

of selected field properties from 1990 to present for upstream 

(S1), downstream (S3), and prereservoir down (S2) sites are 

shown in figure 12. Specific conductance for S1, S2, and S3 

ranged from 99 to 1,720 μS/cm (site S2); however, the median 

ranged from about 434 to 658 μS/cm from 1990 to 2001. Alkali 

Slough #2 (S4) had the largest specific conductance of 

3,470 μS/cm on April 12, 1995, probably due to the inflow of 

ground water in contact with saline marine shale and concentration by evapotranspiration. The lowest seasonal specific 

conductances (99 to 356 μS/cm) were measured during peak 

flow of snowmelt. 

Seasonal variation in daily mean specific conductance is 

illustrated in figure 13 for 1990 to 2001 at S1, S2, and S3. Daily 

mean specific conductance at sites unaffected by the reservoir 

(S1 and S2 pre-1995) ranged from less than 200 μS/cm during 

runoff to more than 1,500 μS/cm in late summer or early fall at 

low flow. Site S3, Muddy Creek below Wolford Mountain Reservoir had less annual variation between high and low specific 

conductance due to the stabilizing effect of mixing water from 

different parts of the hydrograph into a single pool within the 

reservoir.

Temporal variability of specific conductance was tested by 

SKT (table 6). At site S1, no temporal trend in specific conductance was determined. At S2/S3, there was a significant 

(p-value less than 0.10) downward trend in specific conductance. The downward trend downstream from the reservoir site 

probably is caused by the mixing of a large volume of snowmelt 

runoff with a low specific conductance in the reservoir that is 

subsequently released throughout the year. These releases have 

lower specific conductance than typical Muddy Creek streamflow (prereservoir) at low flow.

Spatial variability of specific conductance was significant 

(p-value less than 0.10) in prereservoir and postconstruction 

periods (table 7). The specific conductivity preconstruction was 

426 μS/cm upstream compared to 941 μS/cm downstream. 

Postconstruction was 435 μS/cm upstream compared to 627 μS/

cm downstream. This difference indicates that the marine shales 

and irrigation return flows have always added dissolved solids 

in the reach between S1 and S2/S3 but the larger concentrations 

downstream have been moderated by dilution during the postconstruction period (1995 to 2001).

Prereservoir water temperatures at Muddy Creek above 

Antelope Creek (S1) reached 26.7°C during summer low flow 

on July 7, 1999, and were near 0°C during the winter. Seasonal 

variation in daily mean water temperature for 1990 to 2001 at 

S1, S2, and S3 is shown in figure 14. In winter, sites unaffected 

by the reservoir had daily mean and instantaneous water temperatures ranging from 0° to 2°C. In summer, daily mean water 

temperatures at sites unaffected by the reservoir (S1 and S2 

pre-1995) ranged from about 14° to 22°C. Summer water temperatures at all three sites had a strong daily (diurnal) fluctuation that was influenced by air temperature. Spatial variability 

is illustrated by comparing S1and S3 (fig. 12), which shows less 

annual variation between high and low water temperatures after 

the reservoir was filled (post-1995) due to stability of water 

temperatures within the reservoir.
Water Quality 21

Table 5. Statistical summary of field-property data at S1 and S2/S3 from April 1990 through March 1995 before storage 

began in the reservoir, S1 and S2/S3 combined from April 1990 through October 2001, and S1 and S2/S3 from April 1995 to 

September 2001 after storage began in the reservoir.

[ft3/s, cubic feet per second; <, less than; --, sample not analyzed; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; oC, degrees Celsius; 

NTU, nephelometric turbidity units]

Constituent or property Minimum 25th 

percentile Median 75th percentile Maximum

Number 

of 

samples

Site S1 1990 through 2001

Discharge, instantaneous (ft3/s) 3.20 8.99 39 203 811 323

Dissolved oxygen, (mg/L) 3.3 8.0 8.9 10.2 13 132

pH, field (standard units) 7.1 8.2 8.3 8.4 8.7 135

Specific conductance (μS/cm @ 25oC) 99 268 434 512 851 137

Turbidity (NTU) 0.5 3.5 5.4 30 180 128

Site S2/S3 combined 1990 through 2001

Discharge, instantaneous (ft3

/s) 1.3 20 52.35 111 1,000 174

Dissolved oxygen, (mg/L) 5.4 8.1 8.8 9.65 15.6 139

pH, field (standard units) 7.3 8.1 8.3 8.4 8.9 137

Specific conductance (μS/cm @ 25oC) 164 575 658 814 1,720 144

Turbidity (NTU) .3 1.5 4.85 17.2 360 132

Site S1 pre-reservoir 1990 through 1995

Discharge, instantaneous (ft3/s) 1.31 10.0 150 267 777 143

Dissolved oxygen, (mg/L) 3.3 7.9 8.6 9.8 12.6 51

pH, field (standard units) 7.6 8.1 8.2 8.4 8.6 54

Specific conductance (μS/cm @ 25oC) 99 219 426 525 851 57

Turbidity (NTU) .5 3.2 5.6 26 110 53

Site S2/S3 pre-reservoir combined 1990 through 1995

Discharge, instantaneous (ft3/s) 1.3 9.4 22 106 709 81

Dissolved oxygen, (mg/L) 5.8 7.8 8.9 10.6 12.6 64

pH, field (standard units) 7.5 8 8.2 8.4 8.9 55

Specific conductance (μS/cm @ 25oC) 164 624 941 1,200 1,720 60

Turbidity (NTU) 1.2 10.8 19 32.8 360 56

Site S1 post-construction April 1995 through Sept 2001

Discharge, instantaneous (ft3/s) 3.20 8.50 16.0 85.0 811 180

Dissolved oxygen, (mg/L) 6.6 8.1 9.3 10.6 13 81

pH, field (standard units) 7.1 8.2 8.4 8.4 8.7 81

Specific conductance (μS/cm @ 25oC) 126 338 435 508 695 80

Turbidity (NTU) .6 3.6 5.2 30 180 75

Sites S2/S3 post-construction combined 1995 through 2001

Discharge, instantaneous (ft3/s) 3.50 28.0 58.0 111 1,000 93

Dissolved oxygen, (mg/L) 7.2 8.2 8.8 9.5 12.2 83

pH, field (standard units) 7.3 8.1 8.3 8.4 8.8 82

Specific conductance (μS/cm @ 25oC) 356 563 627 677 953 84

Turbidity (NTU) .3 1.0 1.8 3.2 190 76
22 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Reservoir

(112) (12) (52) (75)

Antelope

MuddyKremmlingMuddy-at

Reservoir

Below

MuddySloughAlkali

0

0.8

0.2

0.4

0.6

AMMONIA, DISSOLVED AS N,

IN MILLIGRAMS PER LITER

0

near dam

ReservoirWolford

Mid-Lake

ReservoirWolford

- Inflow

Reservoir

Wolford

Antelope

MuddyKremmlingMuddy-at

Below

MuddySloughAlkali

near dam

ReservoirWolford

Mid-Lake

ReservoirWolford

- Inflow

Reservoir

Wolford

(54) (54) (24)

0

SULFATE, IN MILLIGRAMS PER LITER

1.5

0.5

1.0

NITRITE PLUS NITRATE, DISSOLVED AS N,

IN MILLIGRAMS PER LITER

Antelope

MuddyKremmlingMuddy-at

Reservoir

Below

MuddySloughAlkali

near dam

ReservoirWolford

Mid-Lake

ReservoirWolford

- Inflow

Reservoir

Wolford

(112) (12) (24) (52) (54) (75) (54)

2,000

500

1,000

1,500

(139) (13) (24) (171) (53) (76) (54)

Antelope

MuddyKremmlingMuddy-at

Reservoir

Below

MuddySloughAlkali

near dam

ReservoirWolford

Mid-Lake

ReservoirWolford

- Inflow

Reservoir

Wolford

0

4,000

1,000

2,000

3,000

SPECIFIC CONDUCTANCE, 

IN MICROSIEMENS PER CENTIMETER 

AT 25 DEGREES CELSIUS

(136) (13) (24) (132) (54) (76) (54)

EXPLANATION

Minimum value

Lower fourth

Median

Upper fourth

Maximum value

(139) Number of observations

Figure 11. Selected water-quality constituents.
Water Quality 23

-

w

r

g r

i

r

EXPLANATION

Detection limit

10th percentile

Lower fourth

Median

Upper fourth

90th percentile

Number of observations

Muddy- Muddy-at Muddy- Alkal Wolford

Reservoir0

400

100

200

300

MANGANESE, DISSOLVED,

IN MILLIGRAMS PER LITER

Antelope Kremmlin

Reservoi

Below Slough

near dam

ReservoirMid-Lake

Wolford

- Inflow

Reservoi

Wolford

Antelope

MuddyKremmlingMuddy-at

Reservoir

Below

MuddySloughAlkali

near dam

ReservoirWolford

Mid-Lake

ReservoirWolford

- Inflo

Reservoi

Wolford

0

(80) (13) (24) (22) (50) (67) (54)

0

0.8

0.1

0.2

0.3

0.4

0.5

0.6

0.7

PHOSPHORUS, TOTAL AS P, 

IN MILLIGRAMS PER LITER

1,000

200

400

600

800

IRON, DISSOLVED,

IN MILLIGRAMS PER LITER

Antelope

MuddyKremmlingMuddy-at

Reservoir

Below

MuddySloughAlkali

near dam

ReservoirWolford

Mid-Lake

ReservoirWolford

- Inflow

Reservoir

Wolford

(135) (13) (24) (96) (51) (71) (49)

(135) (12) (24) (131) (54) (76) (53)

0

4.5

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

AMMONIA PLUS ORGANIC 

NITROGEN,TOTAL AS N,

IN MILLIGRAMS PER LITER

Antelope

MuddyKremmlingMuddy-at

Reservoir

Below

MuddySloughAlkali

near dam

ReservoirWolford

Mid-Lake

ReservoirWolford

Inflow

Reservoir 

Wolford

(135) (12) (24) (131) (54) (76) (53)

(135)

Figure 11. Selected water-quality constituents.—Continued.
24 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

1990 1992 1994 1996 1998 2000 2002

0

2,000

500

1,000

1,500

SPECIFIC CONDUCTANCE,

IN MICROSIEMENS PER CENTIMETER

AT 25 DEGREES CELSIUS

0

16

2

4

6

8

10

12

14

OXYGEN, DISSOLVED,

IN MILLIGRAMS PER LITER

1990 1992 1994 1996 1998 2000 2002

0

600

200

400

TURBIDITY, IN NEPHELOMETRIC

TURBIDITY UNITS

1990 1992 1994 1996 1998 2000 2002

EXPLANATION

Site S1 upstream

 from reservoir

Site S3 downstream

 from reservoir

Site S2 Muddy Creek

 at Kremmling

Continuous monitoring of stream pH was not done so it is 

not possible to describe variability of pH. At all sites, pH was 

near neutral to moderately alkaline ranging from 7.1 to 8.9 

(table 5). During the reservoir period, median pH at S1 and 

S2/S3 was the same, 8.2. During the postconstruction period, 

pH was 8.4 at S1 and 8.3 at S3 (table 5).

At site S3, downstream from the reservoir, dissolved-oxygen concentration data were collected continuously from late 

1995 to 2001 (fig. 15). Dissolved-oxygen concentration at all 

sites ranged from 3.3 to 15.6 mg/L (table 5). Daily minimum 

concentrations were usually greater than 5 mg/L and rarely less 

than 4 mg/L. Maximum daily dissolved-oxygen concentrations 

at S3 generally ranged from 7 to 12 mg/L. Seasonal lows generally occurred in late summer or early fall, coincident with 

summer hypoxia in the reservoir. Seasonal highs generally 

occurred during spring runoff. No multiyear temporal patterns 

were apparent in the S3 record. Meaningful interpretation of 

temporal and spatial variability for S1 and S2 is probably not 

possible due to the limited dissolved-oxygen data.

Turbidity, a measurement of the transparency of water, is 

related to fine-particle concentrations and sediment transport. 

Based on discrete sample data collected at S1 and S2, turbidity 

in prereservoir Muddy Creek was generally less than 10 NTU 

during low flow but ranged to more than 360 NTU during snowmelt. Turbidity in Muddy Creek downstream from the reservoir 

(S3) was substantially lower after 1995 [upstream (S1) median 

5.2 NTU, downstream (S3) median 1.8 NTU] because the reservoir acts as a sediment trap (fig. 12). Turbidity was the best 

indicator of the spatial variability in particle transport because 

suspended-sediment concentrations were not sampled at S3. 

Major Ions

Summary statistics for major ions were compiled for three 

streamwater-quality sites in this study (table 8). In the table, S1 

is characterized for prereservoir (April 1990 to March 1995), 

postconstruction (April 1995 to September 2001), and both 

periods combined (1990 to 2001). S2 and S3 are combined to 

create similar periods for comparison. Boxplots of selected 

constituents by site are shown in figure 11. Time-series plots of 

selected major ions from 1990 to present for upstream (S1), 

downstream (S3), and prereservoir downstream (S2) sites are 

shown in figure 16.

Cation compositions at two sites (S1, 1990 to 2001; and 

S3, 1995 to 2001) were mixed calcium-magnesium-sodium, but 

calcium is predominant (fig. 17). Cation composition at S4 was 

mostly calcium. Anion composition at S1 was primarily bicarbonate and sulfate, whereas S4 was almost completely a sulfate 

composition. Downstream from the reservoir (S3) anion composition tended toward more sulfate. This difference likely was 

caused by a source of dissolved solids rich in calcium and sulfate in the marine shales of the reservoir drainage area such as 

Alkali Slough #2 (S4). Anion composition varies seasonally in 

response to runoff and low-flow conditions. During snowmelt 

(high flow), Muddy Creek above Antelope (S1) tends to have 

relatively large concentrations of bicarbonate, whereas lowflow samples tend to have relatively more sulfate. Seasonal 

variation of ANC (mostly bicarbonate under these pH conditions) exceeds that of sulfate, causing relative differences in 

composition (fig. 16). Another explanation could be a result of 

the decay of algae in the reservoir and the emission of CO2, 

which could increase bicarbonate concentrations in the outflow.

Figure 12. Time-series plots of field properties at Muddy 

Creek above Antelope Creek (upstream from reservoir) 

and Muddy Creek below Wolford Mountain Reservoir 

(directly below reservoir), and Muddy Creek at Kremmling 

(site located approximately 7 miles downstream from 

reservoir.
Water Quality 25

0

3,000

800600400200

2,8002,6002,4002,2002,0001,8001,6001,4001,2001,000

DAILY MEAN SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER AT 25 DEGREES CELSIUS EXPLANATION Muddy Creek above Antelope Creek (S1) Muddy Creek at Kremmling (S2) Muddy Creek below Wolford Mountain Reservoir (S3)

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Figure 13. Daily mean specific conductance upstream and downstream from Wolford Mountain Reservoir.
26 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Table 6. Summary of field-property temporal variation upstream from reservoir by seasonal Kendall test 

for Muddy Creek above Antelope Creek (S1) and downstream combined data from Muddy Creek at 

Kremmling (S2) and Muddy Creek below Wolford Mountain Reservoir (S3), 1990 through 2001.

[ >, greater than; --, slope not computed; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; 

oC, degrees Celsius; NTU, nephelometric turbidity units; slope, units per year; -, downward trend; unadj,

not adjusted by flow-weighting; fwc, flow-weighted concentrations]

Constituent or property p-value

Significance 

> 90-percent 

confidence

Slope Type

Site S1 April 1990 through September 2001

Oxygen, dissolved (mg/L) 0.6684 No -- unadj

pH, field (standard units) .0750 Yes 0.01 unadj

Specific conductance (μS/cm at 25oC) .2698 No 2.33 unadj

Turbidity (NTU) .0427 Yes .32 fwc

Site S2/S3 April 1990 through September 2001

Oxygen, dissolved (mg/L) .0229 Yes -.02 fwc

pH, field (standard units) .6588 No -- unadj

Specific conductance (μS/cm at 25oC) .0228 Yes -19.55 fwc

Turbidity (NTU) .0012 Yes -2.00 unadj

Table 7. Summary of prereservoir and postconstruction upstream/downstream field-property 

differences at Muddy Creek above Antelope (S1) and Muddy Creek at Kremmling (S2), 1990 through 1995, 

and differences at Muddy Creek above Antelope (S1) and Muddy Creek below Wolford Mountain Reservoir 

(S3), 1995 through 2001 by Wilcoxon signed-rank test.

[<, less than; 2-sided test; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; oC, degrees Celsius; 

NTU, nephelometric turbidity units; p-values significant at greater than 90-percent confidence shown in bold]

Constituent or property p-value

Median

Upstream Downstream

April 1990 through March 1995

Oxygen, dissolved (mg/L) 0.5921 8.6 8.9

Specific conductance (μS/cm at 25oC) <.0001 426 941

Turbidity (NTU) .0006 5.6 19

April 1995 through-September 2001

Oxygen, dissolved (mg/L) .1213 9.3 8.8

Specific conductance (μS/cm at 25oC) <.0001 435 627

Turbidity (NTU) <.0001 5.2 1.75
Water Quality 27

0

26

8642

2422201816141210

DAILY MEAN WATER TEMPERATURE, IN DEGREES CELSIUS

EXPLANATION

Muddy Creek above Antelope Creek (S1)Muddy Creek at Kremmling (S2)Muddy Creek below Wolford Mountain Reservoir (S3) 

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Figure 14. Daily mean water temperature upstream and downstream from Wolford Mountain Reservoir.
28 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

1999 1995 1996 4

12

86

10

1997 1998 2000 2001

4

12

86

10

1995 1996 1997 1998 1999 2000 2001

4

14

86

1210

1995 1996 1997 1998 1999 2000 2001

DAILY MAXIMUM DISSOLVEDOXYGEN CONCENTRATION, IN 

MILLIGRAMS PER LITER

DAILY MEAN DISSOLVEDOXYGEN CONCENTRATION, IN 

MILLIGRAMS PER LITER

DAILY MINIMUM DISSOLVEDOXYGEN CONCENTRATION, IN 

MILLIGRAMS PER LITER

Figure 15. Daily minimum, mean, and maximum dissolved-oxygen concentrations at Muddy Creek below Wolford Mountain Reservoir.
Water Quality 29

Temporal variability in major ions was tested by SKT 

(table 9). At site S1 1990 to 2001, similar to the specific conductance results, calcium and sulfate (the predominant ionic 

species) had no significant temporal trend. Significant trends (p-value less than 0.01) were identified for ANC (downward), 

magnesium (upward), and silica (upward). For combined S2/S3 

1990 to 2001 data, all major ions except calcium and ANC 

(no significant trends) had downward trends (p-value less than 

0.10). These trends indicate that natural stream major-ion 

chemistry has not changed much during the period of record, 

and concentrations at downstream sites affected by the reservoir 

have decreased. As for specific conductance, the downward 

trend downstream from the reservoir site (table 6) probably was 

caused by the mixing of a large volume of relatively low-ionic 

strength water from runoff in the reservoir that subsequently 

was released throughout the year.

Spatial variability of almost all major ions was significant 

(p-value less than 0.10) in prereservoir and postconstruction 

periods (table 10). Median concentration for prereservoir 

upstream sulfate was 91.5 compared to 360 mg/L downstream. 

Median concentration for postconstruction upstream sulfate 

was 91.0 compared to 197 mg/L downstream. This similarity 

indicates that the marine shales and irrigation return flows have 

increased major ions in prereservoir and postconstruction 

periods in the reach between S1 and S2/S3, but the larger 

concentrations downstream have been moderated during the 

postconstruction period.
30 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Table 8. Statistical summary of major-ion data at S1 and S2/S3 from April 1990 through March 1995 before storage began in the 

reservoir, S1 and S2/S3 combined from April 1990 through October 2001, and S1 and S2/S3 from April 1995 to September 2001 

after storage began in the reservoir.

[<, less than; mg/L, milligrams per liter]

Constituent or property Minimum 25th 

percentile Median 75th 

percentile Maximum

Number 

of 

samples

Site S1 1990 through 2001

Hardness, total (mg/L as CaCO3) 24 140 190 220 370 133

Calcium, dissolved (mg/L as Ca) 7.4 38 52 60 99 133

Magnesium, dissolved (mg/L as Mg)) 1.3 9.7 15 18 30 133

Potassium, dissolved (mg/L as K) 0.7 1.4 1.8 2.2 8.4 133

Sodium, dissolved (mg/L as Na) 2.5 11 17 20 48 133

Acid-neutralizing capacity, alkalinity, lab, as CaCO3 27 101 138 153 280 133

Chloride, dissolved (mg/L as Cl) .2 1.0 1.8 2.3 14 133

Fluoride, dissolved (mg/L as F) <.1 0.1 0.2 0.2 0.5 133

Silica, dissolved (mg/L as SiO2) 2 7.3 8.4 10 12 133

Sulfate, dissolved (mg/L as SO4) 3 56 91 110 180 133

Dissolved solids, sum of constituents (mg/L) 38 191 266 318 535 134

Site S2/S3 combined 1990 through 2001

Hardness, total (mg/L as CaCO3) 71 250 290 390 790 140

Calcium, dissolved (mg/L as Ca) 21 64 72 92 170 140

Magnesium, dissolved (mg/L as Mg) 4.4 22 27 36 100 140

Potassium, dissolved (mg/L as K) .5 2.2 2.4 2.8 7 140

Sodium, dissolved (mg/L as Na) 4.7 23 28 39 120 140

Acid-neutralizing capacity, alkalinity, lab, as CaCO3 62 122 133 162 242 140

Chloride, dissolved (mg/L as Cl) .1 2.4 3 4.6 14 140

Fluoride, dissolved (mg/L as F) <.1 .2 .2 .2 1 140

Silica, dissolved (mg/L as SiO2) .1 7.4 8.1 9.1 14 140

Sulfate, dissolved (mg/L as SO4) 26 170 210 295 750 140

Dissolved solids, sum of constituents (mg/L) 107 375 434 595 1,220 139

Site S1 pre-reservoir 1990 through 1995

Hardness, total (mg/L as CaCO3) 24 96 190 228 370 54

Calcium, dissolved (mg/L as Ca) 7.4 28 52 62 99 54

Magnesium, dissolved (mg/L as Mg) 1.3 6.5 14 17 30 54

Potassium, dissolved (mg/L as K) .7 1.4 1.9 2.1 3.5 54

Sodium, dissolved (mg/L as Na) 2.5 6.7 16 20 48 54

Acid-neutralizing capacity, alkalinity, lab, as CaCO3 27 79 134 154 280 54

Chloride, dissolved (mg/L as Cl) .2 .8 1.7 2.6 5.8 54

Fluoride, dissolved (mg/L as F) <.1 .1 .2 .2 .5 54

Silica, dissolved (mg/L as SiO2) 4.7 7.0 8.1 9.2 12 54

Sulfate, dissolved (mg/L as SO4) 3 36 92 110 180 54

Dissolved solids, sum of constituents (mg/L) 38 134 264 317 535 54
Water Quality 31

Site S2/S3 pre-reservoir combined 1990 through 1995

Hardness, total (mg/L as CaCO3) 71 270 440 580 790 57

Calcium, dissolved (mg/L as Ca) 21 69 100 140 170 57

Magnesium, dissolved (mg/L as Mg) 4.4 24 45 55 100 57

Potassium, dissolved (mg/L as K) 1.1 2.4 2.9 3.6 7 57

Sodium, dissolved (mg/L as Na) 4.7 30 45 60 120 57

Acid-neutralizing capacity, alkalinity, lab, as CaCO3 62 150 167 188 242 57

Chloride, dissolved (mg/L as Cl) .1 3.6 5 6.8 14 57

Fluoride, dissolved (mg/L as F) <.1 .2 .3 .3 1 57

Silica, dissolved (mg/L as SiO2) .4 6.7 8.5 10 14 57

Sulfate, dissolved (mg/L as SO4) 26 180 360 500 750 57

Dissolved solids, sum of constituents (mg/L) 107 429 670 857 1,220 56

Site S1 post-construction April 1995 through Sept 2001

Hardness, total (mg/L as CaCO3) 51 160 190 220 330 79

Calcium, dissolved (mg/L as Ca) 15 44 52 57 92 79

Magnesium, dissolved (mg/L as Mg) 3.4 12 15 18 25 79

Potassium, dissolved (mg/L as K) .7 1.5 1.8 2.2 8.4 79

Sodium, dissolved (mg/L as Na) 3.7 12 17 20 30 79

Acid-neutralizing capacity, alkalinity, lab, as CaCO3 44 113 141 152 258 79

Chloride, dissolved (mg/L as Cl) .3 1.4 1.9 2.3 14 79

Fluoride, dissolved (mg/L as F) <.1 .1 .2 .2 .3 79

Silica, dissolved (mg/L as SiO2) 2 7.9 8.7 10 12 79

Sulfate, dissolved (mg/L as SO4) 14 66 91 110 160 79

Dissolved solids, sum of constituents (mg/L) 77 237 268 317 441 80

Sites S2/S3 post-construction combined 1995 through 2001

Hardness, total (mg/L as CaCO3) 88 250 270 300 390 83

Calcium, dissolved (mg/L as Ca) 26 63 69 74 98 83

Magnesium, dissolved (mg/L as Mg) 5.6 20 25 28 42 83

Potassium, dissolved (mg/L as K) .5 2.1 2.3 2.5 3.2 83

Sodium, dissolved (mg/L as Na) 7.8 22 25 29 56 83

Acid-neutralizing capacity, alkalinity, lab, as CaCO3 63 118 128 136 161 83

Chloride, dissolved (mg/L as Cl) .4 2.2 2.6 3.1 6.3 83

Fluoride, dissolved (mg/L as F) <.1 .2 .2 .2 .3 83

Silica, dissolved (mg/L as SiO2) .1 7.4 8.0 8.8 9.8 83

Sulfate, dissolved (mg/L as SO4) 36 170 197 223 320 83

Dissolved solids, sum of constituents (mg/L) 127 355 406 449 619 83

Table 8. Statistical summary of major-ion data at S1 and S2/S3 from April 1990 through March 1995 before storage began in the 

reservoir, S1 and S2/S3 combined from April 1990 through October 2001, and S1 and S2/S3 from April 1995 to September 2001 

after storage began in the reservoir.—Continued

[<, less than; mg/L, milligrams per liter]

Constituent or property Minimum 25th 

percentile Median 75th percentile Maximum

Number 

of 

samples
32 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

0

800

200

400

600

EXPLANATION

0

300

100

200

0

300

100

200

1990 1992 1994 1996 1998 2000 2002

1990 1992 1994 1996 1998 2000 2002

1990 1992 1994 1996 1998 2000 2002

ACID-NEUTRALIZING 

CAPACITY, IN MILLIGRAMS 

PER LITER AS CACO3

CALCIUM, DISSOLVED,

 IN MILLIGRAMS 

PER LITER 

SULFATE, DISSOLVED,

 IN MILLIGRAMS 

PER LITER 

Site S1 upstream

 from reservoir

Site S3, downstream

 from reservoir

Site S2 Muddy Creek

 at Kremmling, 7 miles

 downstream from

 reservoir

Figure 16. Time-series plots of selected major-ion constituents at Muddy Creek above Antelope Creek (upstream from 

reservoir) and Muddy Creek below Wolford Mountain Reservoir 

(directly below reservoir), and Muddy Creek at Kremmling 

(approximately 7 miles downstream from reservoir).
Water Quality 33

CALCIUM

SODIUM PLUS POTASSIUM

CARBONATE PLUS BICARBONATE

 100 

 80 

 60 

 40 

 20 

 0 

 0 

 20 

 40 

 60 

 80 

 100 0 

 20 

 40 

 60 

 80 

 100 

 0 

 20 

 40  60 

 80 

 100 

 100 

 80 

 60 

 40 

 20 

 0 100 

 80 

 60 

 40 

 20 

 0 

 0 

 20 

 40 

 60 

 80 

 100 

 0 

 20 

 40 

 60 

 80 

 100 100 

 80 

 60 

 40 

 20 

 0 

 100 

 80 

 60 

 40 

 20 

 0 

PERCENT

PERCENT

MAGNESIUM

SULFATE PLUS CHLORIDE

CALCIUM PLUS MAGNESIUM

SULFATE

CHLORIDE, FLUORIDE, NITRITE PLUS NITRATE

PERCENT

EXPLANATION

Muddy Creek above Antelope Creek (site S1)

Muddy Creek below Wolford Mountain Reservoir (site S3)

Alkali Slough #2 (site S4)

Figure 17. Major-ion composition of samples at selected sites.
34 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Table 9. Summary of major-ion temporal variation upstream from reservoir by seasonal Kendall test for 

Muddy Creek above Antelope Creek (S1), and downstream combined data from Muddy Creek at Kremmling (S2) 

and Muddy Creek below Wolford Mountain Reservoir (S3), 1990 through 2001.

[>, greater than; --, slope not computed; mg/L, milligrams per liter; oC, degrees Celsius; slope, units per year; -, downward trend; 

unadj, not adjusted by flow-weighting; fwc, flow-weighted concentrations; p-values significant at greater than 90-percent 

confidence shown in bold]

Constituent or property p-value

Significance 

> 90-percent 

confidence

Slope Type

Site S1 April 1990 through September 2001

Hardness, total (mg/L) 0.1755 No 1.25 unadj

Calcium, dissolved (mg/L) .2358 No 0.30 unadj

Magnesium, dissolved (mg/L) .0284 Yes .15 unadj

Potassium, dissolved (mg/L) .9817 No -- unadj

Sodium adsorption ratio .1139 No -- unadj

Sodium, dissolved (mg/L) .1883 No .13 unadj

Sodium (percent) .1743 No -- unadj

Acid-neutralizing capacity, dissolved (mg/L as CaCO3) .0416 Yes -1.95 fwc

Chloride, dissolved (mg/L) .5781 No .01 unadj

Fluoride, dissolved (mg/L) .8833 No -- unadj

Silica, dissolved (mg/L) .0425 Yes .08 unadj

Sulfate, dissolved (mg/L) .9823 No -- unadj

Residue, dissolved, at 180°C (mg/L) .0394 Yes 2.73 unadj

Dissolved solids, sum of constituents (mg/L) .2167 No 1.50 unadj

Site S2/S3 April 1990 through September 2001

Hardness, total (mg/L) .0228 Yes -9.25 fwc

Calcium, dissolved (mg/L) .2128 No -1.50 unadj

Magnesium, dissolved (mg/L) .0226 Yes -1.04 fwc

Potassium, dissolved (mg/L) .0181 Yes -.08 unadj

Sodium adsorption ratio .2775 No -- unadj

Sodium, dissolved (mg/L) .0215 Yes -1.20 fwc

Acid-neutralizing capacity, dissolved (mg/L as CaCO3) .1676 No -3.00 unadj

Chloride, dissolved (mg/L) .0985 Yes -.20 unadj

Fluoride, dissolved (mg/L) .0219 Yes -.00 unadj

Silica, dissolved (mg/L) .0087 Yes -.15 unadj

Sulfate, dissolved (mg/L) .0215 Yes -9.17 fwc

Residue, dissolved, at 180°C (mg/L) .0228 Yes -15.42 fwc

Dissolved solids, sum of constituents (mg/L) .0228 Yes -14.58 fwc
Water Quality 35

Nutrients

Summary statistics for nutrients and organic carbon were 

compiled for three streamwater-quality sites in this study 

(table 11). Boxplots of selected constituents by site are shown in 

figure 11. Time-series plots of selected nutrients and organic 

carbon from 1990 through 2001 for upstream (S1), downstream 

(S3), and prereservoir downstream (S2) sites are shown in 

figure 18.

Compounds of nitrogen and phosphorus are referred to as 

“major nutrients” because they are needed for plant growth. In 

excess quantities, nutrients can promote nuisance algae growth 

in streams and reservoirs (causing eutrophication). Natural 

sources of nutrients include precipitation and biochemical processes in the watershed. Anthropogenic sources of nutrients 

include urban runoff, domestic effluent, livestock waste, and 

erosion caused by development.

Nutrient concentrations at Muddy Creek sites generally are 

low (fig. 18) (table 11). Data censoring levels changed somewhat throughout the period of record and, at times, were of 

insufficient precision or too high to fully characterize nutrient 

concentrations. Median concentrations of ammonia plus 

organic nitrogen were less than 0.4 mg/L at all Muddy Creek 

sites. Median concentrations of dissolved nitrite plus nitrate 

were generally less than 0.13 mg/L. Median concentrations of 

total phosphorus were less than 0.05 mg/L at all sites. Concentrations of nitrite and orthophosphorus were rarely greater than 

minimum reporting limits. The smallest nutrient concentrations 

were generally measured at Muddy Creek above Antelope 

Creek (S1). Largest nutrient concentrations tended to be at 

Muddy Creek at Kremmling (S2) and Muddy Creek below 

Wolford Mountain Reservoir (S3). Concentrations of dissolved 

organic carbon ranged from 3.6 to 10 mg/L at S1 and S2/S3. 

Concentrations of total organic carbon ranged from 3.5 to 

21 mg/L. 

Table 10. Summary of upstream/downstream major-ion differences at Muddy Creek above Antelope (S1) and 

Muddy Creek at Kremmling (S2), 1990 through 1995, and differences at Muddy Creek above Antelope (S1) and 

Muddy Creek below Wolford Mountain Reservoir (S3), 1995 through 2001 by Wilcoxon signed-rank test.

[2-sided test; mg/L, milligrams per liter; p-values significant at greater than 90-percent confidence shown in bold]

Constituent p-value

Median

Upstream Downstream

April 1990 through March 1995

Hardness, total (mg/L) <0.0001 190 440

Calcium, dissolved (mg/L) <.0001 52.5 100

Magnesium, dissolved (mg/L) <.0001 14 45

Potassium, dissolved (mg/L) <.0001 1.9 2.9

Sodium, dissolved (mg/L) <.0001 16 45

Acid-neutralizing capacity, dissolved (mg/L as CaCO3) 0.0003 134 167

Chloride, dissolved (mg/L) <.0001 1.7 5

Silica, dissolved (mg/L) .3525 8.1 8.5

Sulfate, dissolved (mg/L) <.0001 91.5 360

Dissolved solids, sum of constituents (mg/L) <.0001 264 670

April 1995 through September 2001

Hardness, total (mg/L) <.0001 190 270

Calcium, dissolved (mg/L) <.0001 52 69

Magnesium, dissolved (mg/L) <.0001 15 25

Potassium, dissolved (mg/L) <.0001 1.8 2.3

Sodium, dissolved (mg/L) <.0001 17 25

Acid-neutralizing capacity, dissolved (mg/L as CaCO3) <.0001 141 128

Chloride, dissolved (mg/L) <.0001 1.9 2.6

Silica, dissolved (mg/L) .0009 8.7 8

Sulfate, dissolved (mg/L) <.0001 91 197

Dissolved solids, sum of constituents (mg/L) <.0001 268 406
36 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Table 11. Statistical summary of nutrient and carbon data at S1 and S2/S3 from April 1990 through March 1995 before storage began in 

the reservoir, S1 and S2/S3 combined from April 1990 through October 2001, and S1 and S2/S3 from April 1995 to September 2001 after 

storage began in the reservoir.

[<, less than; mg/L, milligrams per liter]

Constituent Minimum 25th 

percentile Median 75th 

percentile Maximum Number of 

samples

Site S1 1990 through 2001

Nitrogen, ammonia plus organic, dissolved (mg/L as N) <0.2 0.2 0.2 0.4 2 106

Nitrogen, ammonia plus organic, total (mg/L as N) <.2 .3 .4 .5 2.5 131

Nitrogen, ammonia, dissolved (mg/L as N) <.01 <.02 .02 .03 0.72 108

Nitrogen, nitrite plus nitrate, dissolved (mg/L as N) <.05 <.05 <.05 .08 .23 108

Nitrogen, nitrite, dissolved (mg/L as N) <.01 <.01 <.01 .01 .03 108

Phosphorus, dissolved (mg/L as P) <.01 <.01 <.01 .05 .32 108

Phosphorus, dissolved orthophosphate (mg/L as P) <.01 <.01 <.01 .01 .26 108

Phosphorus, total (mg/L as P) <.01 <.01 .04 .06 .51 131

Carbon, organic, dissolved (mg/L as C) 3.6 4.4 5 7.2 10 43

Carbon, total (mg/L as C) 3.5 4.9 7.4 8.6 15 23

Site S2/S3 combined 1990 through 2001

Nitrogen, ammonia plus organic, dissolved (mg/L as N) .2 .3 .3 .4 1.2 112

Nitrogen, ammonia plus organic, total (mg/L as N) .2 .3 .4 .5 1.3 139

Nitrogen, ammonia, dissolved (mg/L as N) <.02 <.02 .03 .05 .36 139

Nitrogen, nitrite plus nitrate, dissolved (mg/L as N) <.05 .08 .11 .19 .74 138

Nitrogen, nitrite, dissolved (mg/L as N) <.01 <.01 <.01 .01 .07 134

Phosphorus, dissolved (mg/L as P) <.01 <.01 .02 .05 .11 114

Phosphorus, dissolved orthophosphate (mg/L as P) <.01 <.01 <.01 .02 .26 139

Phosphorus, total (mg/L as P) <.01 .02 .04 .06 .61 140

Carbon, organic, dissolved (mg/L as C) 3.9 6.1 6.6 7.1 9.7 46

Carbon, total (mg/L as C) 4.1 6.3 8.2 9.6 21 24

Site S1 pre-reservoir 1990 through 1995

Nitrogen, ammonia plus organic, dissolved (mg/L as N) <.2 <.2 .2 .4 .5 28

Nitrogen, ammonia plus organic, total (mg/L as N) <.2 .3 .4 .6 .9 53

Nitrogen, ammonia, dissolved (mg/L as N) <.02 <.02 .02 .02 .05 29

Nitrogen, nitrite plus nitrate, dissolved (mg/L as N) <0.05 <.05 <.05 <.05 .17 29

Nitrogen, nitrite, dissolved (mg/L as N) <0.01 <.01 <.01 <.01 .02 29

Phosphorus, dissolved (mg/L as P) <0.01 <.01 <.01 .02 .04 29

Phosphorus, dissolved orthophosphate (mg/L as P) <0.01 <.01 <.01 <.01 .03 29

Phosphorus, total (mg/L as P) <0.01 .01 .02 .06 .18 52

Carbon, organic, dissolved (mg/L as C) 3.9 4.9 5.8 8.1 10 16

Carbon, total (mg/L as C) 3.5 4.9 7.4 8.6 15 18

Site S2/S3 pre-reservoir combined 1990 through 1995

Nitrogen, ammonia plus organic, dissolved (mg/L as N) <.2 .2 .3 .5 1.2 30

Nitrogen, ammonia plus organic, total (mg/L as N) .2 .3 .4 .6 1.3 56

Nitrogen, ammonia, dissolved (mg/L as N) .01 .02 .03 .06 .36 57

Nitrogen, nitrite plus nitrate, dissolved (mg/L as N) <.05 .09 .1 .12 .74 56

Nitrogen, nitrite, dissolved (mg/L as N) <.01 <.01 <.01 .02 .07 52

Phosphorus, dissolved (mg/L as P) <.01 <.01 <.01 .02 .11 32

Phosphorus, dissolved orthophosphate (mg/L as P) <.01 <.01 <.01 .02 .26 57
Water Quality 37

Site S2/S3 pre-reservoir combined 1990 through 1995—Continued

Phosphorus, total (mg/L as P) <.01 .02 .04 .07 .61 57

Carbon, organic, dissolved (mg/L as C) 3.9 5.7 6.8 7.4 9.7 18

Carbon, total (mg/L as C) 4.1 5.6 8.2 9.8 21 18

Site S1 post-construction April 1995 through Sept 2001

Nitrogen, ammonia plus organic, dissolved (mg/L as N) <.2 .2 .2 .3 2 79

Nitrogen, ammonia plus organic, total (mg/L as N) .2 .2 .3 .5 2.5 79

Nitrogen, ammonia, dissolved (mg/L as N) <.02 <.02 <.02 .03 .72 80

Nitrogen, nitrite plus nitrate, dissolved (mg/L as N) <.05 <.05 .05 .08 .23 80

Nitrogen, nitrite, dissolved (mg/L as N) .002 .01 .01 .01 .03 80

Phosphorus, dissolved (mg/L as P) <.01 <.01 <.01 .05 .32 80

Phosphorus, dissolved orthophosphate (mg/L as P) <.01 <.01 <.01 .02 .26 80

Phosphorus, total (mg/L as P) <.01 <.01 .05 .07 .51 80

Carbon, organic, dissolved (mg/L as C) 3.6 4.4 4.9 6.6 8.2 27

Carbon, total (mg/L as C) 4.5 4.9 5 8.5 12 5

Sites S2/S3 post-construction combined 1995 through 2001

Nitrogen, ammonia plus organic, dissolved (mg/L as N) .2 .3 .3 .4 .7 82

Nitrogen, ammonia plus organic, total (mg/L as N) .3 .3 .4 .5 .9 83

Nitrogen, ammonia, dissolved (mg/L as N) <.02 <.02 .03 .05 .28 82

Nitrogen, nitrite plus nitrate, dissolved (mg/L as N) .03 .08 .13 .2 .36 82

Nitrogen, nitrite, dissolved (mg/L as N) <.01 <.01 <.01 .01 .03 82

Phosphorus, dissolved (mg/L as P) <.01 <.01 .02 .05 .06 82

Phosphorus, dissolved orthophosphate (mg/L as P) <.01 <.01 <.01 .02 .05 82

Phosphorus, total (mg/L as P) <.01 <.01 .05 .05 .3 83

Carbon, organic, dissolved (mg/L as C) 5.7 6.3 6.4 6.9 8 28

Carbon, total (mg/L as C) 7.7 8.0 8.3 8.9 17 6

Table 11. Statistical summary of nutrient and carbon data at S1 and S2/S3 from April 1990 through March 1995 before storage began in 

the reservoir, S1 and S2/S3 combined from April 1990 through October 2001, and S1 and S2/S3 from April 1995 to September 2001 after 

storage began in the reservoir.—Continued

[<, less than; mg/L, milligrams per liter]

Constituent Minimum 25th 

percentile Median 75th 

percentile Maximum Number of 

samples
38 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

0

8

2

4

6

0

0.8

0.2

0.4

0.6

0

2.0

0.5

1.0

1.5

0

0.8

0.2

0.4

0.6

1990 1992 1994 1996 1998 2000 2002

1990 1992 1994 1996 1998 2000 2002

1990 1992 1994 1996 1998 2000 2002

1990 1992 1994 1996 1998 2000 2002

1980 1985 1990 1995 2000 2005

0

20

5

10

15

EXPLANATION

PHOSPHORUS, TOTAL 

AS P, IN MILLIGRAMS

PER LITER

NITROGEN, NITRITE PLUS 

NITRATE DISSOLVED AS 

N, IN MILLIGRAMS

PER LITER

NITROGEN, AMMONIA, 

DISSOLVED AS N,

IN MILLIGRAMS

PER LITER

NITROGEN, AMMONIA, 

PLUS ORGANIC, TOTAL 

AS N, IN MILLIGRAMS

PER LITER

ORGANIC CARBON, 

DISSOLVED, IN 

MILLIGRAMS PER LITER

Site S1 upstream

 from reservoir

Site S3, downstream

 from reservoir

Site S2 Muddy Creek

 at Kremmling, 7 miles

 downstream from

 reservoir

Figure 18. Time-series plots of selected nutrient and organic carbon constituents at Muddy Creek above Antelope Creek 

(upstream from reservoir) and Muddy Creek below Wolford Mountain Reservoir (directly downstream from reservoir), and 

Muddy Creek at Kremmling (site located approximately 7 miles downstream from reservoir).
Water Quality 39

Seasonal variability of nutrient concentrations generally 

was proportional to streamflow. Smallest concentrations for 

total ammonia plus organic nitrogen as N and total phosphorus 

as P occurred in late summer and winter low flow (July to 

March) (fig. 18). Largest concentrations were several times 

those at low flow and occurred during spring runoff (April to 

June). Concentrations of nitrite plus nitrate and ammonia 

tended to be largest in winter and early runoff and lowest during 

late summer and fall. Seasonal variability of organic carbon 

showed large concentrations in early runoff and high runoff and 

low concentrations during low-flow periods. Dissolved organic 

carbon is flushed from soils during runoff, and particulate carbon is transported during high flows when sediments enter 

Muddy Creek.

Temporal variability of nutrients were tested by SKT 

(table 12). Not all nutrient species had sufficient data greater 

than the MRL and, thus, were not tested. At site S1, an increasing temporal trend in total phosphorus was calculated, but insufficient data above MRL prevented the computation of slope. At 

S2/S3, there was a significant (p-value less than .10) downward 

trend in total ammonia plus organic nitrogen. This downward 

trend downstream from the reservoir site may have been caused 

by the settling of particulate organic nitrogen or biological 

uptake in the reservoir.

There were no statistically significant spatial trends for 

total ammonia plus organic nitrogen (table 13) indicating no 

statistical evidence of a difference in concentration between S1 

and S2/S3. Other nutrient species had insufficient data above 

MRL for testing.

An inflow/outflow mass balance of total nitrogen and total 

phosphorus was computed to indicate how the reservoir is 

affecting the transport of nutrients in Muddy Creek. The annual 

(1996–2001) mass-balance results are summarized in table 14. 

Graphical presentation of selected components of the mass balance is in figures 19 to 21. A more detailed listing of calculations is in the “Hydrologic and Water-Quality Data” section at 

the back of this report in tables 15 and 16.

Analysis of nutrient mass balance in Wolford Mountain 

Reservoir provided insight into the effect of the reservoir on 

nutrient transport. The following interpretations are made about 

the nitrogen mass balance during the growing season:

1. Inflow and outflow water discharge (a component of the 

load calculation) peaked in 1997 and generally has 

decreased through 2001;

2. Inflow and outflow mass of nitrogen generally decreased 

from 1997 to 2001, following patterns of inflow and 

outflow water discharge;

3. Mass of nitrogen in outflow from the reservoir 

substantially exceeded nitrogen in inflow from 1997 to 

1998 (years of larger outflow), whereas nitrogen was 

gained or approximately balanced in inflow and outflow 

during years of smaller outflows; and

4. Nitrogen mass in inflow generally was larger than mass in 

outflow during runoff and generally smaller than mass in 

outflow during low flow, indicating that some nitrogen 

was stored in the water column and gain/loss patterns for 

total nitrogen are related to reservoir storage.

The following observations can be made about the phosphorus mass balance:

1. Phosphorus was gained every year to the reservoir, and as 

a percentage, more phosphorus was retained than nitrogen 

in years when both were retained in the reservoir;

2. Phosphorus gained to the reservoir probably was related 

to settling or biological uptake;

3. Less phosphorus was gained to the reservoir in 1998, 

when outflow exceeded inflow by 27 percent;

4. Inflow mass of phosphorus generally followed patterns of 

inflow water discharge (fig. 19), which decreased from 

1997 to 2001, but the outflow mass of phosphorus had a 

poor relation to outflow; and

5. Phosphorus mass in inflow generally was larger than 

mass in outflow during all seasons (fig. 21), indicating 

that little phosphorus is available in the water column at 

the outflow, and reservoir water-column storage did not 

affect phosphorus outflow loading patterns as much as 

settling.

These observations indicate that, in general, nutrient transport in the inflow was proportional to the amount of water discharge in a given year. Some nitrogen was stored in the water 

column, and gain/loss patterns for total nitrogen were somewhat 

related to reservoir storage. Mass of outflow nitrogen was more 

proportional to outflow volume than mass of outflow phosphorus to outflow volume. Nitrogen tended to move through the 

reservoir, whereas phosphorus was trapped mostly within the 

reservoir. Little phosphorus was available in the water column 

at the outflow, and reservoir water-column storage did not 

affect phosphorus outflow loading patterns as much as settling.
40 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Table 12. Summary of nutrient temporal variation upstream from reservoir by seasonal Kendall test for Muddy Creek 

above Antelope Creek (S1), and downstream combined data from Muddy Creek at Kremmling (S2) and Muddy Creek 

below Wolford Mountain Reservoir (S3), 1990 through 2001.

[>, greater than; --, slope not computed; mg/L, milligrams per liter; slope, units per year; -, downward trend; p-values significant at greater than 90-percent 

confidence shown in bold; unadj, not adjusted by flow-weighting]

Constituent p-value

Significance 

> 90-percent 

confidence

Slope Type

Site S1 April 1990 through September 2001

Nitrogen, ammonia plus organic, (mg/L as N) total 0.1375 No -- unadj

Nitrogen, ammonia plus organic, (mg/L as N) dissolved .3263 No -- unadj

Nitrogen, ammonia, dissolved (mg/L as N) .2296 No -- unadj

Phosphorus, total (mg/L as P) .0935 Yes 0 unadj

Site S2/S3 April 1990 through September 2001

Nitrogen, ammonia plus organic, (mg/L as N) total .0237 Yes -0.02 unadj

Nitrogen, ammonia, dissolved (mg/L as N) .6266 No -- unadj

Phosphorus, total (mg/L as P) .7377 No -- unadj

Table 13. Summary of upstream/downstream differences in nitrogen Muddy Creek above Antelope (S1) and 

Muddy Creek at Kremmling (S2), 1990 through 1995, and differences at Muddy Creek above Antelope (S1) and 

Muddy Creek below Wolford Mountain Reservoir (S3), 1995 through 2001, by Wilcoxon signed-rank test.

[2-sided test; mg/L, milligrams per liter; p-values significant at greater than 90-percent confidence shown in bold]

Constituent p-value

Median

Upstream Downstream

April 1990 through March 1995

Nitrogen, ammonia plus organic, (mg/L as N) total 0.2115 0.4 0.4

April 1995 through September 2001

Nitrogen, ammonia plus organic, (mg/L as N) total .1128 .3 .4
Water Quality 41

Table 14. Mass-balance calculations for total nitrogen and total phosphorus 

in Wolford Mountain Reservoir, 1996 to 2001.

[From equation 1: Unaccounted-for mass (UMS) = Inflow mass (IMS) - Outflow mass (OMS); 

negative UMS is mass lost, positive UMS is mass gained by the reservoir; inflow and outflow in 

acre-feet per year; mass in kilograms per year; N, total nitrogen; P, total phosphorus; inflow and 

outflow of Muddy Creek in acre-feet during calendar year; mass terms are in kilograms during 

calendar year]

 (A) Nitrogen

Year Inflow Outflow IMS OMS UMS

Total nitrogen mass, in kilograms

a

1996 68,910 74,880 49,168 48,999 169

1997 82,273 104,080 66,363 71,681 -5318

1998 55,538 76,390 45,365 57,667 -12,302

1999 41,825 57,520 45,346 34,314 11,032

2000 47,978 62,820 43,784 40,481 3,303

b

2001 29288 39,450 21,935 23,319 -1,384

Total phosphorus mass, in kilograms

a

1996 68,910 74,880 14,989 2,942 12,047

1997 82,273 104,080 15,144 1,483 13,661

1998 55,538 76,390 9,302 7,129 2,173

1999 41,825 57,520 11,788 2,355 9,433

2000 47,978 62,820 10,980 513 10,467

b

2001 29288 39,450 3,351 875 2,476

a

April through December.

bJanuary through October.
42 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

1996 1998 2000 2002

NITROGEN OR PHOSPHORUS

MASS GAINED OR LOST

TO WOLFORD MOUNTAIN

RESERVOIR, IN KILOGRAMS

MONTLY MASS OF TOTALNITROGEN, 

IN KILOGRAMS

MASS OF TOTAL NITROGEN, IN KILOGRAMS, 

AND ANNUAL INFLOW AND OUTFLOW,

IN ACRE-FEET

MASS OF TOTAL PHOSPHORUS, IN KILOGRAMS, 

AND ANNUAL INFLOW AND OUTFLOW,

IN ACRE-FEET

MONTLY MASS OF TOTAL

PHOSPHORUS, IN KILOGRAMS

EXPLANATION

Nitrogen gained (+)

 or lost (–)

Phosphorus gained (+)

 or lost (–)

EXPLANATION

Mass in inflow

Mass in outflow

EXPLANATION

Mass in inflow

Mass in outflow

EXPLANATION

Mass in inflow

Mass in outflow

Inflow

Outflow

EXPLANATION

Mass in inflow

Mass in outflow

Inflow

Outflow

1994

0

120,000

20,000

40,000

60,000

80,000

100,000

1994 2002 1996 1998 2000

0

120,000

20,000

40,000

60,000

80,000

100,000

1994 2002 1996 1998 2000 -15,000

15,000

-10,000

-5,000

0

5,000

10,000

1994 1996 1998 2000 2002

-10,000

50,000

0

10,000

20,000

30,000

40,000

1994 1996 1998 2000 2002

-1,000

12,000

0

2,000

4,000

6,000

8,000

10,000

Figure 19. Nitrogen and phosphorus loads in Muddy Creek inflow and outflow to Wolford Mountain Reservoir (calendar years 1996 to 2001).

Figure 20. Monthly inflow and outflow mass of total nitrogen and total phosphorus (calendar years 1996 to 2001).

Figure 21. Total nitrogen and phosphorus load gained or lost in the reservoir mass balance (calendar years 1996 to 2001.
Water Quality 43

Trace Elements

Summary statistics for trace-element concentrations were 

compiled for three streamwater-quality sites in this study 

(table 17). Boxplots of dissolved iron and dissolved manganese 

by site are shown in figure 11. Time-series plots of dissolved 

iron, dissolved manganese, and dissolved copper from 1990 to 

present for upstream (S1), downstream (S3), and prereservoir 

downstream (S2) sites are shown in figure 22.

For the purpose of this report, trace elements are metal and 

transition metal elements generally occurring in small (less than 

1 mg/L) concentrations (table 17). Trace elements commonly 

detected at most sites in this study were aluminum, 

barium, copper, iron, manganese, nickel, selenium, and zinc. 

Trace elements infrequently detected at most sites were arsenic, 

boron, cadmium, chromium, cobalt, lead, molybdenum, and 

silver during the 1990 to 2001 period. For elements such as 

barium, copper, iron, manganese, and nickel, total-recoverable 

concentrations usually were larger than dissolved concentrations, indicating the presence of particulate-phase trace 

elements (greater than 0.45 microns). Trace elements are 

important indicators of water quality because, in large concentrations, they are toxic to aquatic life, and a large proportion of 

Colorado’s regulated constituents are trace elements (Colorado 

Department of Public Health and Environment, Water Quality 

Control Division, 2002). Sources of the more toxic trace 

elements are generally associated with ore deposits or urban 

runoff. The relative lack of ore deposits and the relatively low 

density of urban development in the drainage area of Muddy 

Creek may limit concentrations of trace elements to relatively 

low concentrations. 

Seasonal variability of concentrations of dissolved and 

total-recoverable iron and manganese seemed to be related to 

seasonal patterns of streamflow (proportional to flow) at S1 

(unaffected by reservoir) and prereservoir S2/S3. After reservoir completion (1995), seasonal fluctuations in dissolved iron 

and manganese concentrations stabilized at S2/S3 (fig. 22).

Temporal variability in dissolved and total-recoverable 

iron and manganese was tested by SKT (table 18). At site S1 

(1990 to 2001), dissolved iron had a significant (p-value less 

than 0.10) upward trend. At S2/S3 (1990 to 2001), dissolved 

and total-recoverable iron and manganese showed downward 

trends (p-value less than 0.10). This indicates that the downward trends downstream from the reservoir site probably were 

caused by settling in the reservoir and mixing of first-flush 

concentrations within the reservoir.

Spatial variability for iron and manganese is shown in 

table 19. Dissolved and total manganese increased significantly 

(p-value less than 0.10) from upstream to downstream during 

the prereservoir period (April 1990 through March 1995). 

These increases likely were caused by loads contributed by tributaries and ground-water inflow downstream. Total iron and 

dissolved and total-recoverable manganese medians were significantly decreased at the downstream site when compared to 

the upstream site in postconstruction (April 1995 through September 2001). These differences likely were caused by settling 

and mixing in the reservoir.

Biological Indicators

Bacteria were sampled only from 1999 through 2001. 

Summary statistics were compiled for two streamwaterquality sites in this study (table 20). Time-series plots of bacteria data from 1999 to 2001 for upstream (S1) and downstream 

(S3) are shown in figure 23.

E. coli counts ranged from less than 1 to 130 colonies per 

100 mL at S1 upstream from the reservoir and were not detected 

at S3 (table 20). Similarly, fecal coliform ranged from less than 

1 to greater than 120 colonies per 100 mL at S1 and less than 1 

to 1 at S3 with only two samples reported at 1 colony per 

100 mL. The higher bacteria counts occurred at S1 during the 

summer season (fig. 23). The comparison of S1 and S3 data 

indicates that bacteria do not survive in the reservoir or rapidly 

settle out with suspended material and, therefore, were not 

detected in the outflow at S3.

Suspended Sediment

Suspended sediment and turbidity were sampled at S1 and 

S2 because of concerns about the effect of substantial sediment 

loads to Wolford Mountain Reservoir. Suspended sediment is 

defined as particles (mostly rock fragments, soil, and some 

organic material) suspended in the water column by the turbulence of the water. Suspended-sediment discharge usually is 

only a portion of the total sediment discharge, which also 

includes the bedload. Bedload is the sediment transported by 

bouncing, rolling, and skidding along the streambed. Summary 

statistics of suspended-sediment concentrations are listed in 

table 21. Suspended-sediment concentrations ranged from 

small (4 mg/L) during low flow to as much as 

2,800 mg/L during high snowmelt (table 21). Median concentrations of suspended sediment at S1 and S2 (prereservoir) were 

approximately equal. Starting in 1996, suspended sediment was 

not sampled downstream from the reservoir. In general, suspended-sediment discharge was positively correlated with 

streamflow in Muddy Creek (fig. 25). 
44 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Table 17. Statistical summary of trace-element data at S1 and S2/S3 from April 1990 through March 1995, before storage began in the 

reservoir, S1 and S2/S3 combined from April 1990 through October 2001, and S1 and S2/S3 from April 1995 to September 2001 after

storage began in the reservoir.

[<, less than; μg/L, micrograms per liter]

Constituent Minimum 25

percentile Median 75

percentile Maximum

Number 

of 

samples

Site S1 1990 through 2001

Aluminum, total recoverable (μg/L as Al) 60 132 213 851 2,660 22

Arsenic, dissolved (μg/L as As) <1 <1 <1 1 2 23

Arsenic, total recoverable (μg/L as As) <1 <1 1 2 3 21

Barium, dissolved (μg/L as Ba) 25 38 59 57 100 23

Barium, total recoverable (μg/L as Ba) <100 <100 <100 100 200 23

Beryllium, total recoverable (μg/L as Be) <10 <10 <10 <10 <10 23

Boron, dissolved (μg/L as B) 10 20 45 60 72 23

Cadmium, dissolved (μg/L as Cd) <0.1 <1 <1 <1 <1 23

Cadmium, total recoverable (μg/L as Cd) <0.1 <1 <1 <1 <1 23

Chromium, dissolved (μg/L as Cr) <1 <1 <1 <1 <1 23

Chromium, total recoverable (μg/L as Cr) <1 <1 <1 2 6 22

Cobalt, total recoverable (μg/L as Co) <1 <1 <1 1 3 23

Copper, dissolved (μg/L as Cu) <1 <1 1 1 6 23

Copper, total recoverable (μg/L as Cu) 1 1 2 5 35 23

Iron, dissolved (μg/L as Fe) 3 16 40 51 220 132

Iron, total recoverable (μg/L as Fe) 30 340 430 1,110 5,670 71

Lead, dissolved (μg/L as Pb) <1 <1 <1 <1 5 23

Lead, total recoverable (μg/L as Pb) <1 <1 <1 6 66 23

Lithium, total recoverable (μg/L as Li) <10 <10 20 17 30 23

Manganese, dissolved (μg/L as Mn) 8 13 19 24 97 77

Manganese, total recoverable (μg/L as Mn) 19 26 40 54 450 74

Mercury, dissolved (μg/L as Hg) 0.1 0.1 0.1 0.1 0.2 22

Mercury, total recoverable (μg/L as Hg) <.1 <.1 <.1 .2 1.2 22

Molybdenum, total recoverable (μg/L as Mo) <1 <1 2 2 3 23

Nickel, total recoverable (μg/L as Ni) 1 2 3 4 10 23

Selenium, dissolved (μg/L as Se) <1 <1 <1 <1 2 23

Selenium, total recoverable (μg/L as Se) <1 <1 <1 1 3 21

Silver, dissolved (μg/L as Ag) <1 <1 <1 <1 2 23

Silver, total recoverable (μg/L as Ag) <1 <1 <1 <1 <1 23

Zinc, dissolved (μmg/L as Zn) 3 4 7 10 20 23

Zinc, total recoverable (μg/L as Zn) 1 10 10 18 60 23

Site S2/S3 combined 1990 through 2001

Aluminum, total recoverable (μg/L as Al) 38 60 90 720 8,200 23

Arsenic, dissolved (μg/L as As) <1 <1 <1 1 2 24

Arsenic, total recoverable (μg/L as As) <1 <1 <1 2 4 22

Barium, dissolved (μg/L as Ba) 30 50 57 70 120 25

Barium, total recoverable (μg/L as Ba) <100 <100 <100 <100 300 24

Beryllium, total recoverable (μg/L as Be) <10 <10 <10 <10 <10 24

Cadmium, dissolved (μg/L as Cd) <1 <1 <1 <1 2 25

Cadmium, total recoverable (μg/L as Cd) <1 <1 <1 <1 2 24

Chromium, dissolved (μg/L as Cr) <1 <1 <1 <1 8 24
Water Quality 45

Chromium, total recoverable (μg/L as Cr) <1 <1 <1 4 12 23

Cobalt, total recoverable (μg/L as Co) <1 <1 <1 1 8 24

Copper, dissolved (μg/L as Cu) <1 <1 <1 1 11 25

Copper, total recoverable (μg/L as Cu) <1 <1 2 3 32 24

Iron, dissolved (μg/L as Fe) <3 10 13 40 6,300 113

Iron, total recoverable (μg/L as Fe) 10 55 90 165 15,800 75

Lead, dissolved (μg/L as Pb) <1 <1 <1 <1 18 25

Lead, total recoverable (μg/L as Pb) <1 <1 <1 <1 40 24

Lithium, total recoverable (μg/L as Li) 10 20 24 32 110 24

Manganese, dissolved (μg/L as Mn) 1 4 6.9 29 370 79

Manganese, total recoverable (μg/L as Mn) 5 10 20 81 444 76

Mercury, dissolved (μg/L as Hg) <.1 <.1 <.1 <.1 .2 23

Mercury, total recoverable (μg/L as Hg) <.1 <.1 <.1 <.1 .3 23

Molybdenum, total recoverable (μg/L as Mo) <1 2 2 3 3 24

Nickel, total recoverable μg/L as Ni) 2 3 4 5 26 24

Selenium, dissolved (μg/L as Se) <1 2 2 3 6 24

Selenium, total recoverable (μg/L as Se) 2 2 3 4 7 22

Silver, dissolved (μg/L as Ag) <1 <1 <1 <1 2 25

Silver, total recoverable (μg/L as Ag) <1 <1 <1 <1 <1 24

Zinc, dissolved (μg/L as Zn) <3 4 8 20 41 25

Zinc, total recoverable (μg/L as Zn) <10 <10 <10 32 100 24

Site S1 pre-reservoir 1990 through 1995

Aluminum, total recoverable (μg/L as Al) 100 140 220 1,300 2,500 9

Arsenic, dissolved (μg/L as As) <1 <1 <1 <1 1 10

Arsenic, total recoverable (μg/L as As) <1 <1 <1 2 3 10

Barium, dissolved (μg/L as Ba) 25 34 54 66 79 10

Barium, total recoverable (μg/L as Ba) <100 <100 <100 <100 200 10

Beryllium, total recoverable (μg/L as Be) <10 <10 <10 <10 <10 10

Cadmium, dissolved (μg/L as Cd) <1 <1 <1 <1 <1 10

Cadmium, total recoverable (μg/L as Cd) <1 <1 <1 <1 <1 10

Chromium, total recoverable (μg/L as Cr) <1 <1 1 2 4 10

Cobalt, total recoverable (μg/L as Co) <1 <1 <1 1 3 10

Copper, dissolved (μg/L as Cu) <1 <1 1 2 6 10

Copper, total recoverable (μg/L as Cu) 1 2 2 5 35 10

Iron, dissolved (μg/L as Fe) 7 15 38 91 220 54

Iron, total recoverable (μg/L as Fe) 280 410 560 2,300 5,400 9

Lead, dissolved (μg/L as Pb) <1 <1 <1 <1 5 10

Lead, total recoverable (μg/L as Pb) <1 <1 2 4 66 10

Lithium, total recoverable (μg/L as Li) <10 <10 20 20 30 10

Manganese, dissolved (μg/L as Mn) 9 12 16 24 46 10

Manganese, total recoverable (μg/L as Mn) 20 42 60 70 140 10

Mercury, dissolved (μg/L as Hg) <.1 <.1 <.1 <.1 <.1 10

Mercury, total recoverable (μg/L as Hg) <.1 <.1 <.1 <.1 1.2 10

Table 17. Statistical summary of trace-element data at S1 and S2/S3 from April 1990 through March 1995, before storage began in the 

reservoir, S1 and S2/S3 combined from April 1990 through October 2001, and S1 and S2/S3 from April 1995 to September 2001 after

storage began in the reservoir.—Continued

[<, less than; μg/L, micrograms per liter]

Constituent Minimum 25

percentile Median 75

percentile Maximum

Number 

of 

samples
46 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Molybdenum, total recoverable (μg/L as Mo) <1 <1 1 2 3 10

Nickel, total recoverable (μg/L as Ni) 2 2 3 6 9 10

Selenium, dissolved (μg/L as Se) <1 <1 <1 <1 2 10

Selenium, total recoverable (μg/L as Se) <1 <1 <1 1 1 10

Silver, dissolved (μg/L as Ag) <1 <1 <1 <1 2 10

Silver, total recoverable (μg/L as Ag) <1 <1 <1 <1 <1 10

Zinc, dissolved (μg/L as Zn) <3 <3 4 9 14 10

Zinc, total recoverable (μg/L as Zn) <10 <10 10 20 60 10

Site S2/S3 pre-reservoir combined 1990 through 1995

Aluminum, total recoverable (μg/L as Al) 310 613 950 2,080 8,200 8

Arsenic, dissolved (μg/L as As) <1 <1 <1 1 2 9

Arsenic, total recoverable (μg/L as As) <1 1 1 2 4 9

Barium, dissolved (μg/L as Ba) 30 48 70 88 120 10

Barium, total recoverable (μg/L as Ba) <100 <100 100 200 300 9

Beryllium, total recoverable (μg/L as Be) <10 <10 <10 <10 <10 9

Boron, dissolved (μg/L as B) 20 20 75 140 180 10

Cadmium, dissolved (μg/L as Cd) <1 <1 <1 <1 2 10

Cadmium, total recoverable (μg/L as Cd) <1 <1 <1 <1 2 9

Chromium, dissolved (μg/L as Cr) <1 <1 <1 <1 8 10

Chromium, total recoverable (μg/L as Cr) <1 <1 2 5 12 9

Cobalt, total recoverable (μg/L as Co) <1 1 1 2 8 9

Copper, dissolved (μg/L as Cu) <1 1 2 2 11 10

Copper, total recoverable (μg/L as Cu) 2 2 3 5 32 9

Iron, dissolved (μg/L as Fe) <3 20 30 70 6,300 35

Iron, total recoverable (μg/L as Fe) 540 770 1,090 1,880 15,800 8

Lead, dissolved (μg/L as Pb) <1 <1 <1 <1 <18 10

Lead, total recoverable (μg/L as Pb) <1 1 2 5 40 9

Lithium, total recoverable (μg/L as Li) 10 20 60 70 110 9

Manganese, dissolved (μg/L as Mn) 13 20 56 89 200 10

Manganese, total recoverable (μg/L as Mn) 50 90 110 210 444 9

Mercury, dissolved (μg/L as Hg) <.1 <.1 <.1 <.1 <.1 9

Mercury, total recoverable (μg/L as Hg) <.1 <.1 <.1 <.1 <.1 9

Molybdenum, total recoverable (μg/L as Mo) <1 <1 2 3 3 9

Nickel, total recoverable (μg/L as Ni) 3 4 5 8 26 9

Selenium, dissolved (μg/L as Se) <1 2 2 4 6 9

Selenium, total recoverable (μg/L as Se) 2 2 3 4 7 9

Silver, dissolved (μg/L as Ag) <1 <1 <1 1 2 10

Silver, total recoverable (μg/L as Ag) <1 <1 <1 <1 <1 9

Zinc, dissolved (μg/L as Zn) <3 <3 6 8 41 10

Zinc, total recoverable (μg/L as Zn) <10 <10 20 40 100 9

Table 17. Statistical summary of trace-element data at S1 and S2/S3 from April 1990 through March 1995, before storage began in the 

reservoir, S1 and S2/S3 combined from April 1990 through October 2001, and S1 and S2/S3 from April 1995 to September 2001 after

storage began in the reservoir.—Continued

[<, less than; μg/L, micrograms per liter]

Constituent Minimum 25

percentile Median 75

percentile Maximum

Number 

of 

samples
Water Quality 47

Site S1 post-construction April 1995 through Sept 2001

Aluminum, total recoverable (μg/L as Al) 60 90 210 1,800 2,660 13

Arsenic, dissolved (μg/L as As) <1 <1 <1 <1 1 13

Arsenic, total recoverable (μg/L as As) <1 1 1 2 3 11

Barium, dissolved (μg/L as Ba) 31 42 68 77 100 13

Barium, total recoverable (μg/L as Ba) <100 <100 <100 100 114 13

Beryllium, total recoverable (μg/L as Be) <10 <10 <10 <10 <10 13

Cadmium, dissolved (μg/L as Cd) <1 <1 <1 <1 <1 13

Cadmium, total recoverable (μg/L as Cd) <1 <1 <1 <1 .5 13

Chromium, total recoverable (μg/L as Cr) <1 <1 <1 3 6 13

Cobalt, total recoverable(μg/L as Co) <1 <1 <1 2 3 12

Copper, dissolved (μg/L as Cu) <1 <1 <1 1 2 13

Copper, total recoverable (μg/L as Cu) 1 1 2 5 10 13

Iron, dissolved (μg/L as Fe) 3 17 40 69 180 78

Iron, total recoverable (μg/L as Fe) 30 340 420 1,100 5,700 62

Lead, dissolved (μg/L as Pb) <1 <1 <1 <1 <1 13

Lead, total recoverable (μg/L as Pb) <1 <1 <1 5 11 13

Lithium, total recoverable (μg/L as Li) <10 <10 14 20 30 13

Manganese, dissolved (μg/L as Mn) 8 13 20 28 97 67

Manganese, total recoverable (μg/L as Mn) 19 24 35 60 450 64

Mercury, dissolved (μg/L as Hg) .1 .1 .1 .1 .2 12

Mercury, total recoverable (μg/L as Hg) <.1 <.1 <.1 <.1 <.3 12

Molybdenum, total recoverable (μg/L as Mo) <1 <1 2 3 3 13

Nickel, total recoverable (μg/L as Ni) 1 2 2 7 10 13

Selenium, dissolved (μg/L as Se) <1 <1 <1 1 2 13

Selenium, total recoverable (μg/L as Se) <1 <1 <1 <1 3 11

Silver, dissolved (μg/L as Ag) <1 <1 <1 <1 <1 13

Silver, total recoverable (μg/L as Ag) <1 <1 <1 <1 <1 13

Zinc, dissolved (μg/L as Zn) <3 <3 <20 <20 <20 13

Zinc, total recoverable (μg/L as Zn) <10 <10 <10 24 40 13

Sites S2/S3 post-construction combined 1995 through 2001

Aluminum, total recoverable (μg/L as Al) 38 56 60 85 4,300 15

Arsenic, dissolved (μg/L as As) <1 <1 <1 <1 1 13

Arsenic, total recoverable (μg/L as As) 1 1 1 2 3 13

Barium, dissolved (μg/L as Ba) 41 50 56 60 100 15

Barium, total recoverable (μg/L as Ba) <100 <100 <100 <100 <100 15

Beryllium, total recoverable (μg/L as Be) <10 <10 <10 <10 <10 15

Boron, dissolved (μg/L as B) 29 37 48 58 63 14

Cadmium, dissolved (μg/L as Cd) <1 <1 <1 <1 <1 15

Cadmium, total recoverable (μg/L as Cd) <1 <1 <1 <1 <1 15

Chromium, dissolved (μg/L as Cr) <1 <1 <1 <1 2 14

Chromium, total recoverable (μg/L as Cr) <1 <1 <1 <1 7 14

Cobalt, total recoverable (μg/L as Co) <1 <1 <1 <1 4 15

Table 17. Statistical summary of trace-element data at S1 and S2/S3 from April 1990 through March 1995, before storage began in the 

reservoir, S1 and S2/S3 combined from April 1990 through October 2001, and S1 and S2/S3 from April 1995 to September 2001 after

storage began in the reservoir.—Continued

[<, less than; μg/L, micrograms per liter]

Constituent Minimum 25

percentile Median 75

percentile Maximum

Number 

of 

samples
48 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Sites S2/S3 post-construction combined 1995 through 2001—Continued

Copper, dissolved (μg/L as Cu) <1 <1 <1 <1 2 15

Copper, total recoverable (μg/L as Cu) <1 <1 1 2 11 15

Iron, dissolved (μg/L as Fe) <3 <10 <10 30 160 78

Iron, total recoverable (μg/L as Fe) 10 50 90 125 9,700 67

Lead, dissolved (μg/L as Pb) <1 <1 <1 <1 <1 15

Lead, total recoverable (μg/L as Pb) <1 <1 <1 <1 9 15

Lithium, total recoverable (μg/L as Li) 10 20 20 25 30 15

Manganese, dissolved (μg/L as Mn) 1 4 6 24 370 69

Manganese, total recoverable (μg/L as Mn) 5 10 20 37 390 67

Mercury, dissolved (μg/L as Hg) <.1 <.1 <.1 <.1 .2 14

Mercury, total recoverable (μg/L as Hg) <.1 <.1 <.1 <.1 .3 14

Molybdenum, total recoverable (μg/L as Mo) 1 2 2 2 3 15

Nickel, total recoverable (μg/L as Ni) 2 2 3 4 15 15

Selenium, dissolved (μg/L as Se) 1 2 2 3 3 15

Selenium, total recoverable (μg/L as Se) 2 2 3 3 4 13

Silver, dissolved (μg/L as Ag) <1 <1 <1 <1 <1 15

Silver, total recoverable (μg/L as Ag) <1 <1 <1 <1 <1 15

Zinc, dissolved (μg/L as Zn) <3 5 20 20 20 15

Zinc, total recoverable (μg/L as Zn) <3 6 10 10 60 15

Table 17. Statistical summary of trace-element data at S1 and S2/S3 from April 1990 through March 1995, before storage began in the 

reservoir, S1 and S2/S3 combined from April 1990 through October 2001, and S1 and S2/S3 from April 1995 to September 2001 after

storage began in the reservoir.—Continued

[<, less than; μg/L, micrograms per liter]

Constituent Minimum 25

percentile Median 75

percentile Maximum

Number 

of 

samples
Water Quality 49

0

600

200

400

IRON, DISSOLVED,

IN MICROGRAMS PER LITER

0

400

100

200

300

MANGANESE, DISSOLVED,

IN MICROGRAMS PER LITER

0

15

5

10

COPPER, DISSOLVED,

IN MICROGRAMS PER LITER

1990 1992 1994 1996 1998 2000 2002

1990 1992 1994 1996 1998 2000 2002

1990 1992 1994 1996 1998 2000 2002

EXPLANATION

Site S1 upstream

 from reservoir

Site S3 downstream

 from reservoir

Site S2 Muddy Creek,

 at Kremmling

Figure 22. Time-series plots of selected trace-element 

constituents at Muddy Creek above Antelope Creek 

(upstream from reservoir) and Muddy Creek below 

Wolford Mountain Reservoir (directly downstream from 

reservoir), and Muddy Creek at Kremmling (approximately 7 miles downstream from reservoir).
50 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Table 18. Summary of trace-element temporal variation upstream from reservoir by seasonal 

Kendall test for Muddy Creek above Antelope Creek (S1) and downstream combined data from 

Muddy Creek at Kremmling (S2) and Muddy Creek below Wolford Mountain Reservoir (S3), 1990 

through 2001.

[<, less than; μg/L, micrograms per liter; slope, units per year; -, downward trend; p-values significant at greater 

than 90 percent confidence shown in bold; unadj, not adjusted by flow-weighting; fwc, flow-weighted concentrations]

Constituent p-value

Significance 

> 90-percent 

confidence

Slope Type

Site S1 April 1990 through September 2001

Iron, dissolved (μg/L) 0.0435 Yes 0.82 fwc

Iron, total (μg/L) .3447 No -7.19 unadj

Manganese, dissolved (μg/L) .6185 No .15 unadj

Manganese, total (μg/L) .8950 No 0 unadj

Site S2/S3 April 1990 through September 2001

Iron, dissolved (μg/L) <.0001 Yes 0. unadj

Iron, total (μg/L) .0004 Yes -29. unadj

Manganese, dissolved (μg/L) .0403 Yes 0. unadj

Manganese, total (μg/L) .0207 Yes 0. unadj

Table 19. Summary of upstream/downstream trace-element differences at Muddy Creek above 

Antelope (S1) and Muddy Creek at Kremmling (S2), 1990 through 1995, and differences at Muddy Creek 

above Antelope (S1) and Muddy Creek below Wolford Mountain Reservoir (S3), 1995 through 2001 by 

Wilcoxon signed-rank test.

[<, less than; 2-sided test; μg/L, micrograms per liter; p-values significant at greater than 90-percent confidence shown in bold]

Constituent p-value

Median

Upstream Downstream

April 1990 through March 1995

Iron, total (μg/L) 0.3704 560 1,090

Manganese, dissolved (μg/L) .0209 16 56

Manganese, total (μg/L) .0138 60 110

April 1995 through September 2001

Iron, total (μg/L) <.0001 422 90

Manganese, dissolved (μg/L) <.0001 20 5.7

Manganese, total (μg/L) <.0001 35 20
Water Quality 51

EXPLANATION

Site S1 upstream

 from reservoir

Site S3 downstream

 from reservoir

0

150

50

100

0

150

50

100

1990 1992 1994 1996 1998 2000 2002

1990 1992 1994 1996 1998 2000 2002

E. COLI, TOTAL, IN 

COLONIES PER 

100 MILLILITERS

COLIFORM, FECAL, IN 

COLONIES PER 

100 MILLILITERS

Table 20. Statistical summary of bacteria data at S1 and S3 from December 1999 through 

September 2001, after storage began in the reservoir.

[<, less than; MF, membrane filtration; col/100 ml, colonies per 100 milliters]

Constituent Minimum Median Maximum

Number 

of 

samples

Site S1 1999 through 2001

Coliform, fecal (col/100ml) <1 1 >120 17

E. coli, urease, MF (col/100ml) <1 25 130 20

Site S3 1999 through 2001

Coliform, fecal (col/100ml) <1 <1 1 21

E. coli, urease, MF (col/100ml) <1 <1 <1 19

Figure 23. Time-series plots of bacteria data at Muddy Creek 

above Antelope Creek (upstream from reservoir) and 

Muddy Creek below Wolford Mountain Reservoir (directly 

downstream from reservoir), and Muddy Creek at Kremmling 

(site located approximately 7 miles downstream from reservoir 

1999 through 2001).
52 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Table 21. Statistical summary of suspended-sediment data at S1 and S2 from April 1990 through March 1995 before 

storage began in the reservoir, S1 from April 1990 through October 2001, and S1 from April 1995 to September 2001 after 

storage began in the reservoir.

[mg/L, milligrams per liter; tons/d, tons per day]

Constituent Minimum 25

percentile Median 75

percentile Maximum

Number 

of 

samples

Site S1 1990 through 2001

Suspended-sediment concentration (mg/L) 4 15 53.9 204 2,800 191

Suspended-sediment discharge (tons/d) 0.03 0.4 6.5 107 1,910 191

Site S1 pre-reservoir 1990 through 1995

Suspended-sediment concentration (mg/L) 4 35 113 265 2,800 93

Suspended-sediment discharge (tons/d) .03 .67 42 208 1,910 93

Site S1 post-construction April 1995 through Sept 2001

Suspended-sediment concentration ( mg/L) 4.3 11.3 19 96.8 1,290 98

Suspended-sediment discharge (tons/d) .08 .342 0.77 22 1,160 98

Sites S2 pre-reservoir 1990 through 1995

Suspended-sediment concentration (mg/L) 100 53 116 322 1,870 66

Suspended-sediment discharge (tons/d) .19 2.2 11 158 2,540 66
Water Quality 53

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

-200

2,000

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

SEDIMENT CONCENTRATION, IN MILLIGRAMS 

PER LITER 

1 2 5 10 20 50 100 200 500 1,000

STREAMFLOW, IN CUBIC FEET PER SECOND

0.01

10,000

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

50

100

200

500

1,000

2,000

5,000

SUSPENDED-SEDIMENT DISCHARGE, IN 

TONS PER DAY 

Figure 24. Time-series of suspended-sediment concentration at Muddy Creek upstream from 

Antelope Creek (site S1).

Figure 25. Suspended-sediment transport curve for Muddy Creek upstream from 

Antelope Creek (site 1).
54 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Reservoir Water Quality

Wolford Mountain Reservoir is an important water 

resource for recreation, aquatic habitat, and water storage. 

Understanding chemical characteristics, field-property profiles 

and stratification patterns, mass balance of nutrients, and 

trophic status provides a basis for interpreting the effects of 

Wolford Mountain Reservoir on downstream water quality.

Variation in reservoir water quality is affected by seasonal 

and hydrologic factors. Water-quality data available for analysis included field properties, major ions, nutrients, trace elements, bacteria, and chlorophyll. 

Field Properties

Statistics for field properties (medians) were compiled for 

three reservoir water-quality sites (L1 near the dam, L2 at midlake, and L3 near the inlet) (table 22) for July 1995 to September 2001. Boxplots of selected constituents by site are shown in 

figure 11. Time-series plots of selected data collected at the surface and near the bottom at L1 are shown in figure 26.

In natural, snowmelt-dominated mountain streams, one of 

the primary processes controlling specific conductance and 

major-ion concentrations is dilution. In general, specific conductance in the reservoir is characterized by minimums ranging 

from 99 to 356 μS/cm during peak snowmelt discharge and 

maximums ranging from 670 to 1,320 μS/cm occurring during 

winter low-flow conditions. In reservoirs, these fluctuations are 

dampened by mixing that occurs in the reservoir (fig. 26).

 Median specific conductance in Wolford Mountain Reservoir was generally less than 600 μS/cm (table 22). Water at 

Wolford Mountain Reservoir sampling sites are a blend of 

dilute high-elevation snowmelt runoff and more concentrated 

low-flow water, which have higher specific conductance related 

to exposure to marine shales and irrigation return flow or seepage. Median specific conductances generally were larger by at 

least 100 μS/cm in the near-bottom samples at L1 and L2 

(fig. 26). Median specific conductance at L3 near the reservoir 

surface was larger than at L1 or L2.

Water in Wolford Mountain Reservoir is subject to the 

cumulative effects of irrigation and evapotranspiration from the 

upper watershed. The reservoir is located at a lower elevation 

(higher evapotranspiration potential) and is exposed to saline, 

marine shale lithologies that may increase dissolved-solids 

content. All sampled reservoir waters had moderate specific 

conductivity and dissolved-solids content.

Water temperature varied seasonally; ice developed on the 

reservoir in winter, and temperatures approached 20°C in summer. The pH measured in the reservoir ranged from neutral to 

somewhat alkaline with median measurements of about 8.1 at 

all sites at the surface (table 22). Dissolved oxygen generally 

ranged from 4 to 8 mg/L, except in the hypolimnion of the 

reservoir, where seasonal stratification sometimes resulted in 

dissolved-oxygen concentrations approaching 1 mg/L or less. 

Dissolved-oxygen concentrations tended to be larger at the 

Table 22. A comparison of spatial differences in field-measurement data from Wolford Mountain Reservoir, July 1995 to

September 2001.

[--, constituent not measured; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; oC, degrees Celsius; NTU, nephelometric turbidity units]

Constituent or property Sampling site

Median concentration or value

Near reservoir surface Near reservoir bottom

Dissolved oxygen, (mg/L) L1 6.6 1.7

L2 6.8 2.6

1L3 7.2 --

pH, field (standard units) L1 8.1 7.5

L2 8.1 7.7

1

L3 8.2 --

Specific conductance (μS/cm at 25oC) L1 485 766

L2 491 614

1

L3 558 --

Transparency, secchi (inches) L1 113 --

L2 110 --

1L3 56 --

Turbidity (NTU) L1 1.2 2

L2 1.1 2.3

1L3 2.7 --

1L3 near the reservoir inlet was sampled at mid-depth only.
Water Quality 55

0

10

2

4

6

8

0

1,500

500

1,000

0

15

5

10

EXPLANATION

Surface samples L1

Bottom samples L1

1995 1996 1997 1998 1999 2000 2001

1995 1996 1997 1998 1999 2000 2001

1995 1996 1997 1998 1999 2000 2001

SPECIFIC CONDUCTANCE, IN

MICROSIEMENS PER CENTIMETER 

AT 25 DEGREES CELSIUS DISSOLVED OXYGEN,

IN MILLIGRAMS PER LITER

TURBIDITY, IN NEPHELOMETRIC

TURBIDITY UNITS

inflow and smallest near the dam in surface and bottom measurements (table 22). Turbidity was low at all sites but was 

highest at the L3 inflow site. Turbidity was higher in the nearbottom samples than the near-surface samples. Median transparency ranged from 56 to 113 inches below the surface. Transparency was largest at the dam and smallest at the inflow due to 

settling of suspended sediment at the inflow end of the reservoir 

(table 22).

Reservoir profiles of water temperature, specific conductance, pH, and dissolved oxygen were used to characterize stratification patterns of the reservoir. Profile measurements were 

collected in June, July, August, and October starting in July 

1995 and continuing through 2001. Plots of profiles measured 

in 1999 at Wolford Mountain Reservoir (figs. 27–30) show how 

these measurements generally vary with depth throughout the 

growing season.

Wolford Mountain Reservoir is probably dimictic (profile 

data generally did not extend to overturn periods in spring or 

fall), which means temperature stratification forms in summer 

and winter, and the lake contents mix during overturn in the 

spring and fall (Cole, 1994). Minor thermal stratification was 

evident in June and intensified through the summer. Specific 

conductance and pH data indicate moderate stratification with 

depth in June, but dissolved-oxygen concentrations were still 

relatively high (greater than 6 mg/L) and weakly stratified. In 

the fall (October 1999), the reservoir was in the process of overturn but was still stratified from summer heating. There was a 

very compact thermocline at the 60- to 70-ft interval (0.1°C/ft 

depth) relative to 0.02°C/ft depth in the 40- to 70-ft interval 

(fig. 28). During stratification, specific conductance generally 

increased with depth. This difference (fig. 26) may be due to 

seasonal routing differences through the reservoir but is also a 

result of mineral dissolution or ground-water inflow rich in dissolved solids. Dissolved oxygen commonly was depleted in the 

hypolimnion of the reservoir, and pH decreased with depth. The 

lowest dissolved-oxygen concentrations in the hypolimnion 

were measured in August when near-bottom oxygen concentrations approached zero. 

Spatial stratification between L2 (a transitional zone) and 

L1 (a deeper lacustrine zone) was relatively minor as both sites 

had similar patterns for all profile measurements in the 1999 

example (figs. 27–30). Site L3 at the inlet to the reservoir is a 

mixed riverine zone that is similar to Muddy Creek. Fieldproperty data were collected at one mid-point depth at L3. The 

seasonal differences in water temperature at the inflow can 

affect routing of water within the reservoir because of water 

density variation with temperature (Ford, 1990). Water of a 

given temperature at the inflow will tend to flow as a density 

current to depths within the reservoir of similar temperature. In 

Wolford Mountain Reservoir, spring-runoff temperatures and 

fall temperatures in Muddy Creek (essentially L3) are lower 

than in the reservoir (fig. 28). Thus, inflows tended to settle near 

the thermocline and plunge beneath the surface layer (epilimnion) in spring and fall of 1999. In summer, L3 water temperature was similar to the surface layer (fig. 28), and flows were 

routed through the reservoir near the surface.

In winter, stream temperatures were near 0°C, and surface 

water at the ice-cover interface was 0°C (profile not shown), but 

the temperature in the reservoir subsurface increased with depth 

to 4°C in the bottom waters (water is most dense at about 4°C). 

Winter stratification is assumed to be similar to other dimictic, 

montane reservoirs such as Lake Granby, Shadow Mountain 

Lake, and Grand Lake (Crowfoot and others, 2002). Thus, 

inflow will tend to be routed just under the ice. Flow patterns 

could be important because it could drastically reduce residence 

time in the event of a chemical spill upstream, and knowledge 

of probable vertical location of the plume would be important 

for outflow gate configurations.

Figure 26. Time-series plots of selected field properties 

from Wolford Mountain Reservoir, sampled near the dam (L1). 
56 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

0 500 1,000

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER

CENTIMETER AT 25 DEGREES CELSIUS

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER

CENTIMETER AT 25 DEGREES CELSIUS

0

120

20

40

60

80

100

DEPTH BELOW SURFACE, IN FEET

0 500 1,000

0

120

20

40

60

80

100

Site L1

Site L2

Site L3

0 500 1,000

0

120

20

40

60

80

100

DEPTH BELOW SURFACE, IN FEET

0 500 1,000

0

120

20

40

60

80

100

June 1, 1999 July 22, 1999

August 18, 1999 October 22, 1999

EXPLANATION

Figure 27. Specific-conductance profiles measured at Wolford Mountain Reservoir near the dam (L1) in 1999.
Water Quality 57

0

120

20

40

60

80

100

DEPTH BELOW SURFACE, IN FEET

0

120

20

40

60

80

100

Site L1

Site L2

Site L3

0

120

20

40

60

80

DEPTH BELOW SURFACE, IN FEET

100

WATER TEMPERATURE, IN DEGREES CELSIUS

WATER TEMPERATURE, IN DEGREES CELSIUS

0

120

20

40

60

80

100

June 1, 1999 July 22, 1999

August 18, 1999 October 22, 1999

5 20 10 15 25 5 20 10 15 25

5 20 10 15 25 5 10 15 20 25

EXPLANATION

Figure 28. Water-temperature profiles measured at Wolford Mountain Reservoir near the dam (L1) in 1999.
58 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

0

20

40

60

80

100

Site L1

Site L2

Site L3

0

120

20

40

60

80

100

DEPTH BELOW SURFACE, IN FEET

0

120

20

40

60

80

100

DEPTH BELOW SURFACE, IN FEET

June 1, 1999 July 22, 1999

August 18, 1999 October 22, 1999

pH, IN STANDARD UNITS

pH, IN STANDARD UNITS

78 9 9 7 8

789 9 7 8

0

120

20

40

60

80

100

120

EXPLANATION

Figure 29. pH profiles measured at Wolford Mountain Reservoir near the dam (L1) in 1999.
Water Quality 59

0

EXPLANATION

June 1, 1999 July 22, 1999

August 18, 1999 October 22, 1999

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

0

120

20

40

60

80

100

DEPTH BELOW SURFACE, IN FEET

120

20

40

60

80

100

0

120

20

40

60

80

100

DEPTH BELOW SURFACE, IN FEET

0

120

20

40

60

80

100

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

02468 0 02468 0

02468 0 0 02468

Site L1

Site L2

Site L3

Figure 30. Dissolved-oxygen profiles measured at Wolford Mountain Reservoir near the dam (L1) in 1999.
60 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

1995 1996 1997 1998 1999 2000 2001

0

200

50

100

150

1995 1996 1997 1998 1999 2000 2001

0

800

200

400

600

SULFATE, DISSOLVED,

IN MILLIGRAMS PER LITER

CALCIUM, DISSOLVED,

IN MILLIGRAMS PER LITER

Surface samples L1

Bottom samples L1

EXPLANATION

Major Ions

Statistics for median concentrations of major ions were 

compiled for three reservoir water-quality sites (L1 near the 

dam, L2 at midlake, and L3 near the inlet) (table 23) for July 

1995 through September 2001. Boxplots of selected constituents by site are shown in figure 11. Time-series plots of selected 

major-ion data collected at the surface and near the bottom at L1 

are shown in figure 31.

Major-ion composition of reservoir water was similar to 

the streamwater. Calcium was the predominant cation, whereas 

bicarbonate and sulfate were the primary anions. Concentrations of major ions in near-bottom samples usually were larger 

than those in surface samples (fig. 31) (table 23). A slight spatial trend decreasing from L3 to L1 is evident in median concentrations of surface samples (table 23); whereas, near-bottom 

median concentrations increased from inlet to dam. Similar patterns existed for specific conductance and dissolved solids. This 

pattern is probably a consequence of routing patterns during 

stratification. In summer, inflow is routed to the surface zone 

when specific conductance is higher in the inflow than in the 

main reservoir, which results in a chemical gradient that 

decreases from inlet to dam. During spring runoff, inflow is 

routed deeper within the reservoir when specific conductance is 

lower than in the deeper reservoir water, which results in a 

chemical gradient that increases from inlet to dam. 

Figure 31. Time-series plots of selected major-ions 

from Wolford Mountain Reservoir, sampled near the dam 

(site L1). 
Water Quality 61

Table 23. A comparison of spatial differences in major-ion data from Wolford Mountain Reservoir, July 1995 through September 2001.

[--, not sampled, mg/L, milligrams per liter]

Constituent or property Sampling site

Median concentration or value

Near reservoir surface Near reservoir bottom

Hardness, total (mg/L as CaCO3) L1 210 320

L2 210 250

1L3 245 --

Calcium, dissolved (mg/L as Ca) L1 54 78.9

L2 54 64

1L3 61 --

Magnesium, dissolved (mg/L as Mg) L1 19 28.1

L2 19 22

1L3 22 --

Potassium dissolved (mg/L as K) L1 1.9 2.5

L2 2 2.2

1

L3 2.0 --

Sodium, dissolved (mg/L as Na) L1 19 27

L2 18 21

1L3 22 --

Acid-neutralizing capacity, alkalinity, lab, as CaCO3 L1 108 124

L2 109 120

1L3 126 --

Chloride, dissolved (mg/L as Cl) L1 1.8 2.6

L2 1.8 2

1L3 1.9 --

Fluoride, dissolved (mg/L as F) L1 0.1 0.2

L2 .1 .2

1L3 .2 --

Silica, dissolved (mg/L as SiO2) L1 8 9.2

L2 8 8.4

1L3 7.9 --

Sulfate, dissolved (mg/L as SO4) L1 130 250

L2 130 170

1L3 154 --

Dissolved solids, sum of constituents (mg/L) L1 303 477

L2 306 364

1L3 347 --

1

 L3 near the reservoir inlet was sampled at mid-depth only.
62 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Surface samples L1

Bottom samples

NITROGEN, AMMONIA PLUS 

ORGANIC, TOTAL, IN 

MILLIGRAMS PER LITER

NITROGEN, AMMONIA 

DISSOLVED, IN 

MILLIGRAMS PER LITER

NITROGEN, NITRITE PLUS

NITRATE, DISSOLVED AS

N, IN MILLIGRAMS PER LITER

PHOSPHORUS, TOTAL

 IN MILLIGRAMS PER LITER

0.4

1.0

0.8

0.6

0.4

0.2

0

0.3

0.2

0.1

0

0

0.20

0.05

0.10

0.15

0

12

2

4

6

8

10

1995 1996 1997 1998 1999 2000 2001

1995 1996 1997 1998 1999 2000 2001

1995 1996 1997 1998 1999 2000 2001

1995 1996 1997 1998 1999 2000 2001

EXPLANATION

Nutrients

Statistics for median concentrations of nutrients were compiled for three reservoir water-quality sites (L1 near the dam, L2 

at midlake, and L3 near the inlet) (table 24) for July 1995 

through September 2001. Boxplots of selected constituents by 

site are shown in figure 11. Time-series plots of selected nutrient data collected at the surface and near the bottom at L1 are 

shown in figure 32.

Seasonal variation in nutrient concentrations differed in 

surface and near-bottom samples. Surface concentrations of 

total ammonia plus organic nitrogen, dissolved ammonia, dissolved nitrite plus nitrate, and total phosphorus showed few 

consistent seasonal patterns (fig. 32); whereas, near-bottom 

samples of the same nutrients had increased concentrations in 

fall samples. Near-bottom samples of ammonia and nitrite plus 

nitrate generally had larger concentrations than concurrent surface samples. (fig. 32). Surface-sample concentrations of nitrite 

plus nitrate were substantially depleted throughout the growing 

season. Temporally, surface and near-bottom concentrations 

tended to decrease and stabilize for ammonia plus organic nitrogen and ammonia throughout 1995 through 2001 (fig. 32). 

Nitrite plus nitrate seemed to increase in near-bottom samples 

with time (fig. 32). Spatial variation in nutrient concentrations 

from inflow to dam tended to decrease for total ammonia plus 

organic nitrogen and total phosphorus in surface samples; 

bottom-sample concentrations tended to increase from inflow to 

dam for nitrite plus nitrate. 

Figure 32. Time-series plots of selected nutrients from 

Wolford Mountain Reservoir, sampled near the dam (site L1). 
Water Quality 63

Table 24. A comparison of spatial differences in nutrient data from Wolford Mountain Reservoir, July 1995 through 

September 2001.

[<, less than; --, not sampled; mg/L, milligrams per liter]

Constituent or property Sampling 

site

Median concentration

Near reservoir 

surface

Near reservoir 

bottom

Nitrogen, ammonia plus organic, dissolved (mg/L as N) L1 0.3 0.3

L2 .3 .3

1L3 .3 --

Nitrogen, ammonia plus organic, total (mg/L as N) L1 .4 .4

L2 .4 .4

1

L3 .5 --

Nitrogen, ammonia, dissolved (mg/L as N) L1 .02 .04

L2 .02 .03

1

L3 <.02 --

Nitrogen, nitrite plus nitrate, dissolved (mg/L as N) L1 .05 .26

L2 .05 .16

1

L3 <.05 --

Nitrogen, nitrite, dissolved (mg/L as N) L1 <.01 <.01

L2 <.01 <.01

1

L3 <.01 --

Phosphorus, dissolved (mg/L as P) L1 <.01 <0.01

L2 <.01 <.02

1

L3 <.01 --

Phosphorus, dissolved orthophosphate (mg/L as P) L1 <.01 .01

L2 <.01 <.01

1

L3 <.01 --

Phosphorus, total (mg/L as P) L1 <.05 <.05

L2 <.05 <.05

1

L3 <.05 --

1

L3 near the reservoir inlet was sampled at mid-depth only.
64 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Surface samples L1

Bottom samples L1

0

400

100

200

300

IRON, DISSOLVED, IN 

MICROGRAMS PER LITER

MANGANESE, DISSOLVED, IN 

MICROGRAMS PER LITER

COPPER, DISSOLVED, IN 

MICROGRAMS PER LITER

-200

800

0

200

400

600

0

10

2

4

6

8

1995 1996 1997 1998 1999 2000 2001

1995 1996 1997 1998 1999 2000 2001

1995 1996 1997 1998 1999 2000 2001

EXPLANATION

Trace Elements

Statistics for median concentrations of trace elements were 

compiled for three reservoir water-quality sites (L1 near the 

dam, L2 at midlake, and L3 near the inlet) (table 25) for July 

1995 through September 2001. Boxplots of dissolved copper, 

dissolved iron, and dissolved manganese by site are shown in 

figure 11. Time-series plots of selected trace-element data 

collected at the surface and near the bottom at L1 are shown 

in figure 33.

Variation was difficult to describe for trace elements with 

concentrations near the MRL. Dissolved iron, manganese, and 

copper tended to increase in bottom samples during late summer or fall (fig. 33). This increase is probably the result of 

increased hypoxia at the end of the growing season, which 

causes redox-related increases in iron and manganese concentrations. The increases in copper concentrations also may be 

related to redox potential in that some trace elements may be 

adsorbed to iron and manganese particulates that have been 

remobilized and reprecipitated. 

Temporally, dissolved iron and manganese generally have 

decreased over the period of record (1995 to 2001) (fig. 33), 

whereas, the 2000 to 2001 data indicate increased copper concentrations. Spatially, total recoverable and dissolved iron and 

manganese, and total recoverable aluminum show decreasing 

median concentrations from inflow to dam (S3 to S1) in surface 

samples (table 25). Median concentrations of total recoverable 

iron and aluminum in near-bottom samples decreased from 

inflow to dam. The concentration increases in manganese along 

the reservoir axis probably are related to redox reactions in the 

hypolimnion, which release manganese from the bottom sediments during periods of hypoxia.

Figure 33. Time-series plots of selected trace elements 

from Wolford Mountain Reservoir, sampled near the dam 

(site L1) .
Water Quality 65

Table 25. A comparison of spatial differences in trace-element data from Wolford Mountain Reservoir, July 1995 through 

September 2001.

[<, less than; --, not sampled; μg/L, micrograms per liter]

Constituent Sampling site

Median concentration

Near reservoir surface Near reservoir bottom

Aluminum, total recoverable (μg/L as Al) L1 40 54

L2 43 70

1L3 100 --

Arsenic, dissolved (μg/L as As) L1 <1 <1

L2 <1 <1

1L3 <1. --

Arsenic, total recoverable (μg/L as As) L1 <1 <1

L2 <1 <1

1L3 <1 --

Barium, dissolved (μg/L as Ba) L1 55 58

L2 54 56

1L3 60 --

Barium, total recoverable (μg/L as Ba) L1 <100 <100

L2 <100 100

1L3 83 --

Beryllium, total recoverable (μg/L as Be) L1 <10 <10

L2 <10 <10

1

L3 <10 --

Cadmium, dissolved (μg/L as Cd) L1 <1 <1

L2 <1 <1

1L3 <1 --

Cadmium, total recoverable (μg/L as Cd) L1 <1 <1

L2 <1 <1

1

L3 <1 --

Chromium, dissolved (μg/l as Cr) L1 <1 <1

L2 <1 <1

1L3 <1 --

Chromium, total recoverable (μg/l as Cr) L1 <1 <1

L2 <1 <1

1L3 <1 --

Cobalt, total recoverable (μg/L as Co) L1 <1 <1

L2 <1 <1

1L3 <1 --
66 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Copper, dissolved (μg/L as Cu) L1 1 <1

L2 1 1

1L3 1 --

Copper, total recoverable (μg/L as Cu) L1 1 1

L2 1 1

1L3 1 --

Iron, dissolved (μg/L as Fe) L1 10 10

L2 10 <10

1L3 16 --

Iron, total recoverable (μg/L as Fe) L1 62 95

L2 70 140

1

L3 190 --

Lead, dissolved (μg/L as Pb) L1 <1 <1

L2 <1 <1

1L3 <1 --

Lead, total recoverable (μg/L as Pb) L1 <1 <1

L2 <1 <1

1L3 <1 --

Lithium, total recoverable (μg/L as Li) L1 20 28

L2 20 20

1L3 20 --

Manganese, dissolved (μg/L as Mn) L1 4 7

L2 4 5

1L3 21 --

Manganese, total recoverable (μg/L as Mn) L1 10 65

L2 10 36

1

L3 38 --

Mercury, dissolved (μg/L as Hg) L1 <0.1 <0.1

L2 <.1 <.1

1L3 <.1 --

Mercury, total recoverable (μg/L as Hg) L1 <.1 <.1

L2 <.1 <.1

1L3 <.1 --

Table 25. A comparison of spatial differences in trace-element data from Wolford Mountain Reservoir, July 1995 through 

September 2001.—Continued

[<, less than; --, not sampled; μg/L, micrograms per liter]

Constituent Sampling site

Median concentration

Near reservoir surface Near reservoir bottom
Water Quality 67

Molybdenum, total recoverable (μg/L as Mo) L1 2 3

L2 2 2

1L3 2 --

Nickel, total recoverable (μg/L as Ni) L1 2 3

L2 2 2

1L3 2 --

Selenium, dissolved (μg/L as Se) L1 2 3

L2 2 2

1L3 1 --

Selenium, total recoverable (μg/L as Se) L1 2 3

L2 2 2

1

L3 2 --

Silver, dissolved (μg/L as Ag) L1 <1 <1

L2 <1 <1

1L3 <1 --

Silver, total recoverable (μg/L as Ag) L1 <1 <1

L2 <1 <1

1L3 <1 --

Zinc, dissolved (μg/L as Zn) L1 <6 <5

L2 <6 <5

1L3 <4 --

Zinc, total recoverable (μg/L as Zn) L1 <10 <10

L2 <10 <10

1L3 <10 --

1

L3 near the reservoir inlet was sampled at mid-depth only.

Table 25. A comparison of spatial differences in trace-element data from Wolford Mountain Reservoir, July 1995 through 

September 2001.—Continued

[<, less than; --, not sampled; μg/L, micrograms per liter]

Constituent Sampling site

Median concentration

Near reservoir surface Near reservoir bottom
68 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

0

4

1

2

3

0

6

2

4

0

6

2

4

COLIFORM, FECAL, IN 

COLONIES PER 

100 MILLILITERS

E COLI, TOTAL, IN 

COLONIES PER 

100 MILLILITERS

CHLOROPHYLL–A, 

PHYTOPLANKTON, IN 

MILLIGRAMS PER LITER

1995 1996 1997 1998 1999 2000 2001

1995 1996 1997 1998 1999 2000 2001

1995 1996 1997 1998 1999 2000 2001

Biological Indicators

Statistics for median concentrations of chlorophyll and 

bacteria were compiled for three reservoir water-quality sites 

(L1 near the dam, L2 at midlake, and L3 near the inlet) 

(table 26) for July 1995 to September 2001. Time-series plots of 

selected chlorophyll and bacteria data collected at the surface 

and near the bottom at L1 are shown in figure 34.

The median concentration for chlorophyll-a was 1 μg/L 

(table 26). Large variation in concentrations occurred during the 

growing season (fig. 34). Median concentrations at L1 and L2 

were similar, indicating little spatial variation.

Bacteria counts were low to not detected in the reservoir 

samples (fig. 34) (table 26). Bacteria in Muddy Creek may be 

associated with suspended material that rapidly settles out in the 

reservoir.

Figure 34. Time-series plots of selected chlorophyll and 

bacteria data from Wolford Mountain Reservoir, sampled 

near the dam (site L1) 1995 through 2001.
Water Quality 69

Trophic Status

The relative fertility of a lake or reservoir can be evaluated 

by assessing the trophic status. Oligotrophic (nutrient-poor) 

lakes have characteristics such as high transparency, small 

organic-matter content, relatively large dissolved-oxygen concentrations, small nutrient concentrations, and small algal 

biomass. Eutrophic (nutrient-rich) lakes have the opposite characteristics (Woods, 1992). Mesotrophic lakes are intermediate 

in the continuum between oligotrophic and eutrophic lakes, 

exhibiting some characteristics of both. On the basis of data collected 1995–2001, Wolford Mountain Reservoir was classified 

using the method developed by Carlson (1977). The annual 

mean values then were used to compute annual trophic-status 

index (TSI) values (fig. 35). Censored values of total phosphorus were common in the 1990’s, therefore TSI’s were not computed. The Carlson (1977) index assumes phosphorus limitation. The boundary between oligotrophic (nutrient-poor) and 

mesotrophic (moderate nutrients) is a TSI of 30. The boundary 

between mesotrophic and eutrophic (nutrient-rich) is a TSI of 

50. Most of the index values for the reservoir are in the upper 

oligotrophic to mesotrophic ranges. Eutrophic conditions were 

indicated by some samples at L2 and L3 based on Secchi disc 

and total phosphorus. Computations based on chlorophyll-a at 

the dam (L1) indicated stable TSI’s, whereas the midlake site 

showed decreasing TSI’s. Generally, TSI’s based on Secchi 

disc and total phosphorus were greater than those of chlorophyll-a on the same sampling date, and TSI’s at the upstream 

end of the reservoir were greater than those computed for the 

site at the dam. This difference could be a result of turbid conditions caused by suspended sediment and turbidity from 

Muddy Creek that raise total-phosphorus and Secchi-depth 

TSI’s relatively but do not affect (and may even decrease) the 

chlorophyll-a index due to reduced light penetration. Other 

cyclic factors such as grazing of phytoplankton by zooplankton 

can make interpretation of chlorophyll-a indices ambiguous. 

Use of TSI can give a qualitative indication of relative status of 

water bodies, but it should not be used exclusively to evaluate 

whether lakes and reservoirs are meeting the water-quality 

classifications. 

Table 26. A comparison of spatial differences in biological data from Wolford Mountain Reservoir, 

July1995 through September 2001.

[<, less than; --, constituent not measured; μg/L, micrograms per liter; col/100 ml, colonies per 100 milliliters; 

MF, membrane filtration; col, colonies]

Constituent Sampling site

Median concentration

Near reservoir surface Near reservoir 

bottom

E. coli, urease, MF (col/100 ml) L1 <1 --

L2 1 --

1

L3 -- --

Coliform, fecal (col/100 ml) L1 <1 --

L2 1 --

1

L3 -- --

Chlorophyll-a (μg/L) L1 1 --

L2 1.3 --

1

L3 -- --

Chlorophyll-b (μg/L) L1 <0.1 --

L2 .1 --

1

L3 -- --

1 L3 near the reservoir inlet was sampled at mid-depth only.
70 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

1994

10

70

20

30

40

50

60

CARLSON TROPHIC STATUS INDEX

Secchi disc

 index value 

Total phosphorus

 index value 

Chlorophyll-a

 index value 

1994

10

70

20

30

40

50

60

CARLSON TROPHIC STATUS INDEX

1994

10

70

20

30

40

50

60

CARLSON TROPHIC STATUS INDEX

Reservoir near dam site L1

Reservoir midlake site L2

Reservoir inlet site L3

EUTROPHIC

EUTROPHIC

EUTROPHIC

MESOTROPHIC

MESOTROPHIC

MESOTROPHIC

OLIGOTROPHIC

OLIGOTROPHIC

OLIGOTROPHIC

1996 1998 2000 2002

1996 1998 2000 2002

1996 1998 2000 2002

EXPLANATION

Figure 35. Annual trophic status index (TSI) computations for Secchi depth, total phosphorus, and 

chlorophyll-a by the Carlson (1977) method.
Water-Quality Standards 71

Water-Quality Standards

Based on all samples collected during 1990 to 2001, 

Colorado standards for chloride, dissolved chromium, dissolved copper, dissolved nickel, nitrate, sulfate, and dissolved 

zinc were not exceeded at any of the sampling sites in the study 

area (table 27). Dissolved oxygen generally met minimum 

standards (6 mg/L) except for brief periods in late summer most 

years, when oxygen concentrations dropped slightly below 

6 mg/L at Muddy Creek below Wolford Mountain Reservoir 

(S3). Only in reservoir near-bottom samples was dissolved 

oxygen very low (less than 2 mg/L), but the reservoir water was 

well oxygenated in the mixed zone (epilimnion and metalimnion). The pH met standards at all sites. The standard for 

un-ionized ammonia was exceeded in only one sample at 

Muddy Creek below Wolford Mountain Reservoir (S3) in 

October 1995 during the first season of reservoir filling. Nutrients concentrated in the hypolimnion may have been released 

during mixing at fall overturn of the reservoir. 

Table 27. Summary of exceedances of Colorado aquatic water-quality standards, 1990 to 2001.

[>, greater than;--, not sampled; TVS, table value standard equation; ch, chronic standard; ac, acute standard; f, fixed standard; s, surface; b, near-bottom]

Constituent or property

Number of exceedances from 1990 to 2001

Type 1Standard S1 S2 S3 S4 L1 L2 L3

Dissolved oxygen, (mg/L) f,ch >6 0 0 8 0 2b00

pH, field (standard units) f,ch 6-9 0 0 0 0 0 0 0

Chloride, dissolved (mg/L as Cl) f,ch 250 0 0 0 0 0 0 0

Sulfate, dissolved (mg/L as SO4) f,ch 250 0 75 6 13 3b00

Nitrogen, unionized ammonia, dissolved (mg/L as N) ac TVS 0 0 1 0 0 0 0

Nitrogen, unionized ammonia, dissolved (mg/L as N) f,ch 0.02 0 0 0 0 0 0 0

Nitrogen, nitrite plus nitrate, dissolved (mg/L as N) f,ch 10. 0 0 0 0 0 0 0

Nitrogen, nitrite, dissolved (mg/L as N) f,ch .05 0 0 0 0 0 0 0

Coliform, fecal (colonies/100ml) f,ch 200 0 0 0 0 0 0 0

Arsenic, total recoverable (μg/L as As) f,ac 50 0 0 0 0 0 0 0

Boron, dissolved (μg/L as B) f,ch 750 0 0 0 0 -- -- --

Cadmium, total recoverable (μg/L as Cd) ac TVS 0 0 0 0 0 0 0

Cadmium, dissolved (μg/L as Cd) ch TVS 0 0 0 0 0 0 0

Chromium, total recoverable (μg/l as Cr) f,ac 50 0 0 0 0 0 0 0

Copper, dissolved (μg/L as Cu) ac TVS 0 0 0 0 0 0 0

Copper, dissolved (μg/L as Cu) ch TVS 0 0 0 0 0 0 0

Iron, dissolved (μg/L as Fe) f,ch 300 0 3 0 0 1 0 0

Iron, total recoverable (μg/L as Fe) f, ch 1,000 21 10 0 1 0 0 3

Lead, dissolved (μg/L as Pb) ac TVS 0 0 0 0 0 0 0

Lead, dissolved (μg/L as Pb) ch TVS 2 1 0 0 0 0 0

Manganese, dissolved (μg/L as Mn) f,ch 50 6 8 8 2 1s,8b 1s,7b 2

Mercury, total recoverable (μg/L as Hg) f,ch .01 0 0 0 0 0 0 0

Nickel, dissolved (μg/L as Ni) ac TVS 0 0 0 0 0 0 0

Nickel, dissolved (μg/L as Ni) ch TVS 0 0 0 0 0 0 0

Selenium, dissolved (μg/L as Se) ac TVS 0 0 0 12 0 0 0

Selenium, dissolved (μg/L as Se) ch TVS 0 2 0 12 6b 0 0

Silver, dissolved (μg/L as Ag) ac TVS 0 0 0 0 0 0 0

Silver, total recoverable (μg/L as Ag) ch TVS 1 1 0 0 0 0 0

Zinc, dissolved (μg/L as Zn) ac TVS 0 0 0 0 0 0 0

Zinc, dissolved (μg/L as Zn) ch TVS 0 0 0 0 0 0 0

1Colorado Department of Public Health and Environment, Water Quality Control Commission, 2002, Classifications and numeric standards for 

Upper Colorado River Basin and North Platte River (Planning Region 12) Regulation No. 33: Denver, Colorado Department of Health, Water Quality 

Control Commission Report, 3.8.0 (5 CCR 1002-33), variously paginated. 2Dissolved-oxygen concentrations in the hypolimnion were frequently less than 6 mg/L during late-summer stratification. 3

Sulfate concentrations often exceeded 250 mg/L in near-bottom samples.
72 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Selenium concentrations exceeded chronic standards twice 

at Muddy Creek at Kremmling site (S2). Six samples exceeded 

selenium chronic standards in near-bottom samples collected 

near the dam in Wolford Mountain Reservoir (L1) in 1995–97. 

Selenium concentrations in Alkali Slough #2 (S4) almost 

always exceeded computed chronic standards for selenium 

(12 samples). Acute standards for selenium at Alkali Slough #2 

were exceeded six times. Concentrations of lead and silver 

occasionally exceeded chronic standards. Most of these concentrations probably were near the precision of the method of analysis at the time, increasing the chance that poor precision could 

overrepresent some concentrations. More recent data of greater 

precision indicate that silver was present only at very low concentrations. The fixed standard for dissolved iron of 300 μg/L 

was exceeded 3 times at Muddy Creek at Kremmling (S2) and 

once at Wolford Mountain Reservoir (L1). The total-recoverable iron fixed standard of 1,000 μg/L was exceeded at Muddy 

Creek above Antelope Creek (S1), Muddy Creek at Kremmling 

(S2) (10 samples), Alkali Slough #2 (S4) (1 sample), and Wolford Mountain Reservoir (L3) (3 samples). The fixed standard 

of 50 μg/L for dissolved manganese was exceeded in six samples from Muddy Creek above Antelope Creek (S1), eight samples from Muddy Creek at Kremmling (S2), eight samples from 

Muddy Creek below Wolford Mountain Reservoir (S3 all 

before 1999), and two samples from Alkali Slough #2 (S4). 

Wolford Mountain Reservoir concentrations of dissolved manganese exceed the standard in nine samples from near the dam 

(L1), eight samples from midlake (L2), and two samples from 

the inlet (L3). Exceedances generally occurred in late-summer 

near-bottom samples, and primarily during 1995 to 1996, a 

period of water-quality adjustment after initial filling of the reservoir. Manganese is a common problem constituent in the bottom waters of Colorado lakes and reservoirs and can cause 

problems for drinking-water treatment, staining of laundry 

when used for washing, and stream-bottom precipitates that can 

smother aquatic life.

Summary and Conclusions

In March 1985, the U.S. Geological Survey, in cooperation 

with the Colorado River Water Conservation District 

(CRWCD), began a monitoring program on Muddy Creek in 

anticipation of the construction of Wolford Mountain Reservoir. A site upstream from the proposed reservoir (Muddy 

Creek above Antelope Creek, 09041090) and a site downstream 

(Muddy Creek at Kremmling, 09041500) were chosen to characterize preimpoundment conditions. Wolford Mountain Reservoir was constructed during 1992–94, and filling of the reservoir began in 1995. Water-quality monitoring of the reservoir 

began in July 1995 and in October 1995 at the reservoir outflow.

The purpose of this report was to describe inflow-, reservoir-, and outflow-water quality and assess the effects of Wolford Mountain Reservoir on downstream streamflow and water 

quality. Specific objectives were to:

1. Characterize and compare the upstream/downstream and 

prereservoir and postconstruction streamflow, waterquality characteristics, and temporal and spatial trends in 

Muddy Creek; 

2. Describe limnological and water-quality characteristics of 

Wolford Mountain Reservoir (1995–2000); and

3. Compare water-quality data to Colorado water-quality 

standards and guidelines.

A summary of the primary conclusions of the study are as 

follows:

1. Water quality was generally good in Muddy Creek and 

Wolford Mountain Reservoir throughout the period of 

record (collectively 1982 to 2001). Specific conductance 

ranged from 99 to 1,720 μS/cm. Dissolved-oxygen concentrations generally were in the range of 3 to 7 mg/L, 

except in the hypolimnion where concentrations were 

near 1 mg/L or less in late summer and early fall. Cation 

compositions at Muddy Creek sites were mixed calciummagnesium-sodium, but calcium typically was the predominant cation. Anion compositions were primarily 

bicarbonate and sulfate. After the reservoir was filled 

(post 1995), Muddy Creek downstream from the reservoir 

showed less annual variation in high and low water temperatures and specific conductance compared to prereservoir conditions. This change is likely due to the stabilizing 

effect of mixing within the reservoir. Turbidity in Muddy 

Creek downstream from the reservoir was substantially 

reduced after the reservoir was constructed as a result of 

sedimentation within the reservoir compared to prereservoir conditions. Concentrations of nutrients and trace 

elements generally were low (median total nitrogen less 

than 0.6 and median total phosphorus less than 0.05 

milligrams per liter) and trace elements (median dissolved 

copper less than 2, median dissolved lead less than 1, and 

median dissolved zinc less than about 20 micrograms per 

liter) at all stream and reservoir sampling sites. The 

paucity of ore deposits and the low density of urban development in the Muddy Creek drainage probably limit 

trace-element concentrations to low concentrations. 

2. The effects of Wolford Mountain Reservoir on 

streamflow are evident in flow-duration curves for 

Muddy Creek upstream and downstream from the 

reservoir. In most years, peak flows were the same or 

slightly reduced downstream from the reservoir due to 

storage effects. The upper first to fifteenth percentiles of 

flows were decreased compared to prereservoir flow 

patterns. Generally, the fifteenth to one-hundredth 

percentiles of flow were increased by operation of the 

reservoir outflow compared to prereservoir inflow.

3. Nutrient transport in the inflow is proportional to the 

amount of inflow-water discharge in a given year. Some 

nitrogen was stored in the water column, and gain/loss 

patterns for total nitrogen were somewhat related to 

reservoir storage. Nitrogen tended to be moved through 
References Cited 73

the reservoir, whereas phosphorus primarily was trapped 

within the reservoir in bottom sediments. Phosphorus 

was gained every year to the reservoir and, as a 

percentage, more phosphorus was retained than nitrogen 

in years when both were retained in the reservoir due to 

stronger phosphorus tendencies for adsorption, 

coprecipitation, and settling. Only small amounts of 

phosphorus were available in the water column at the 

outflow, and reservoir water-column storage did not 

affect phosphorus outflow-loading patterns as much as 

settling further upstream in the reservoir.

4. In most years, Carlson trophic-status index values for the 

reservoir were in the upper oligotrophic to mesotrophic 

ranges. Chlorophyll-a-based computations at the dam 

indicated stable Trophic Status Index (TSI) values, 

whereas the midlake site indicated decreasing TSI. 

Generally, the Secchi-depth and total-phosphorus TSI 

values were higher than those of chlorophyll-a on the 

same sampling date, and values at the upper end of the 

reservoir were higher than those computed for the 

reservoir site at the dam. This difference was probably a 

result of turbid conditions caused by inflow of suspended 

sediments and turbidity from Muddy Creek that raised 

the total-phosphorus and Secchi-depth TSI’s or maybe 

decreased the chlorophyll-a index by reducing light 

penetration.

5. Statistically significant temporal trends (p-value less than 

0.10) indicated by the seasonal Kendall test (SKT) for the 

upstream conditions (Muddy Creek above Antelope 

Creek, unaffected by the reservoir, 1990 to 2001) were 

for field properties of pH and turbidity; major ions and 

related calculated values that include magnesium, acidneutralizing capacity (ANC), silica, and dissolved-solids 

residue; and the trace element dissolved iron. The trends 

all have positive slopes, except for the negative slope of 

ANC. No nutrients trends were significant (p-value less 

than 0.10). Trends (p-value less than 0.10) determined by 

SKT for the downstream conditions at Muddy Creek at 

Kremmling (unaffected by the reservoir) and Muddy 

Creek below Wolford Mountain Reservoir (affected by 

the reservoir, 1995 to 2001) had negative slopes 

indicating relatively decreasing concentrations for field 

properties, major ions, total ammonia plus organic 

nitrogen, and iron and manganese.

6. Spatial comparisons indicating statistically significant 

(p-value less than 0.10) upstream/downstream 

differences in water quality before construction of the 

reservoir were tested by nonparametric Wilcoxon signedrank test for 1990 to 1995. Comparisons indicated that 

Muddy Creek was gaining dissolved solids, particulate 

matter (turbidity), and manganese as it flowed 

downstream before construction of the reservoir. Spatial 

comparisons indicating significant upstream/downstream 

differences also were determined for the period after 

construction of the reservoir (1995 to 2001). The 

comparisons indicated increased specific conductance 

and major ion concentrations downstream from the 

reservoir compared to concentrations upstream from the 

reservoir, which were similar to the differences in values 

and concentrations that existed before construction. 

Turbidity, total-recoverable and dissolved manganese, 

and total-recoverable iron decreased downstream from 

the reservoir. The increase in most major ions indicates 

that Muddy Creek was still gaining dissolved solids after 

reservoir construction; however, the difference between 

median concentrations was less when compared to the 

prereservoir period. This decrease is probably due to 

mixing within the reservoir. Particulate matter (indicated 

by turbidity) and the trace elements manganese and iron 

decreased in Muddy Creek downstream as a result of the 

construction of the dam. This decrease is probably due to 

settling of suspended particles within the reservoir. 

E. coli and fecal coliform bacteria were found in Muddy 

Creek upstream from the reservoir (S1, up to more than 

100 col/100mL). The comparison of upstream (S1) and 

downstream (S3) data indicate that bacteria do not 

survive in the reservoir or rapidly settle out with 

suspended material and, therefore, generally were not 

detected in the outflow at S3 or surface samples in the 

reservoir. Bacteria counts were low to not detected in the 

reservoir samples. Bacteria in Muddy Creek may be 

associated with suspended material that rapidly settles 

out in the reservoir.

7. Constituent concentrations generally met water-quality 

standards set by the State of Colorado. Selenium 

concentrations exceeded chronic standards twice at the 

Muddy Creek at Kremmling site (S2). Six samples 

exceeded selenium chronic standards in near-bottom 

samples collected from Wolford Mountain Reservoir 

near the dam (L1) in 1995–97.

References Cited

Alden, R.W., Perry, E.S., and Lane, M.F., 2000, A comparison 

of analytical techniques for determining trends in Chesapeake Bay Water-Quality Monitoring Program data: Norfolk, 

Va., Applied Marine Research Laboratory Technical Report 

No. 3114, 43 p.

Britton, L.J., and Greeson, P.E., eds., 1987, Methods for collection and analysis of aquatic biological and microbiological 

samples: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A4, 363 p.

Buchanan, T.J., and Somers, W.P., 1969, Discharge measurements at gaging stations: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 3, chap. A8, 65 p.
74 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 through 2001

Butler, D.L., 1990, Estimated water-quality conditions and 

potential downstream channel effects of the proposed Rock 

Creek and Wolford Mountain Reservoirs, north-central 

Colorado: U.S. Geological Survey Water-Resources Investigations Report 89–4177, 101 p.

Carlson, R.E., 1977, A trophic state index for lakes: Limnology 

and Oceanography, v. 22, no. 2, p. 361–369.

Cole, G.A., 1994, Textbook of limnology (4th ed.): Prospect 

Heights, Ill., Waveland Press, Inc., 412 p.

Colorado Climate Center, 1984, Colorado average annual precipitation map 1951–1980: Fort Collins, Colorado Climate 

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Colorado Department of Public Health and Environment, Water 

Quality Control Commission, 2002, Classifications and 

numeric standards for Upper Colorado River Basin and 

North Platte River (Planning Region 12) Regulation No. 33: 

Denver, Colorado Department of Health, Water Quality 

Control Commission Report, 3.8.0 (5 CCR 1002–33), 

variously paginated.

Colorado River Water Conservation District, 2000, Wolford 

Mountain Reservoir on Muddy Creek, the Wolford 

Mountain Project: accessed October 2000 at 

URL http://www.crwcd.gov/wolford/wolfnew.htm

Crowfoot, R.M., Boulger, R.W., and O’Neill, G.B., 2002, 

Water resources data, Colorado, water year 2001, v. 2, 

Colorado river basin: U.S. Geological Survey Water-Data 

Report CO–00–2, 559 p.

Edwards, T.K., and Glysson, G.D., 1988, Field methods for 

measurement of fluvial sediment: U.S. Geological Survey 

Open-File Report 86–531, 117 p.

Fishman, M.J., 1993, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of inorganic and organic constituents in water and fluvial 

sediments: U.S. Geological Survey Open-File Report 

93–125, 217 p.

Fishman, M.J., and Friedman, L.C., eds., 1989, Methods for 

determination of inorganic substances in water and fluvial 

sediments (3d ed.): U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 5, chap. A1, 545 p.

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1994, U.S. Geological Survey approved inorganic and 

organic methods for the analysis of water and fluvial sediment, 1954–94: U.S. Geological Survey Open-File Report 

94–351, 55 p.

Ford, D.E., 1990, Reservoir transport processes: in Thornton, 

K.W., Kimmel, B.L., and Payne, F.E., Reservoir limnologyecological perspectives: New York, John Wiley and Sons, 

Inc., p. 15–41

Friedman, L.C., and Erdmann, D.E., 1982, Quality-assurance 

practices for the chemical and biological analyses of water 

and fluvial sediments: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 5, chap. A6, 181 p.

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analysis: U.S. Geological Survey Techniques of WaterResources Investigations, book 3, chap. C1, 58 p.

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59 p.

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streamflow: U.S. Geological Survey Techniques of WaterResources Investigations, book 3, chap. A13, 53 p.

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R.E., 1999, Trends and status of flow, nutrients, and sediments for selected nontidal sites in the Chesapeake Bay 

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Report 99–451, 46 p.

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collection of water-quality data: U.S. Geological Survey 

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chapters A1 to A9, variously paginated.

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the effect of sedimentation rate on the proposed Wolford 

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87–4011, 22 p.

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Hydrologic and Water-Quality Data
76 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 Through 2002
Hydrologic and Water-Quality Data 77

Table 15. Nitrogen mass balance detailed computations.

[--, no sample or computation; mg/L, milligrams per liter; ac-ft, acre-feet; kg, kilograms; TN, total nitrogen]

Wolford 1996 Nitrogen Budget

Sample date TN in

(mg/L)

Water in

(ac-ft)

TN mass in 

(kg)

TN out

(mg/L)

Water out

ac-ft)

TN mass out

(kg)

1/11/96 -- 439 -- 0.96 970 1,149

2/27/96 -- 372 -- 0.70 1,210 1,045

3/27/96 -- 694 -- 0.64 2,450 1,935

4/22/96 1.32 8,960 14,595 0.68 14,830 12,444

05/22/96 0.56 39,080 27,006 0.54 21,440 14,287

06/10/96 0.33 14,730 5,907 0.52 9,750 6,256

07/16/96 0.45 1,250 694 0.43 3,720 1,974

08/28/96 0.33 853 342 0.59 9,430 6,866

09/03/96 0.23 528 147 0.52 6,150 3,946

010/17/96 0.23 492 137 0.42 2,170 1,125

11/13/96 0.13 641 99 0.71 1,410 1,235

12/10/96 0.23 871 242 0.52 1,350 866

Gained/lost = inflow - outflow

Total inflow mass (kg) 49,168 April to December only

Total outflow mass (kg) 48,999 April to December only

Mass gained (+) or lost from (-) reservoir 169 April to December only

Wolford 1997 Nitrogen Budget

Sample date TN in

(mg/L)

Water in

(ac-ft)

TN mass in 

(kg)

TN out

(mg/L)

Water out

(ac-ft)

TN mass out

(kg)

1/28/97 0.30 674 250 0.50 1,520 938

2/27/97 0.33 559 228 0.55 1,730 1,174

3/18/97 0.80 1,090 1,076 0.96 4,660 5,520

4/16/97 0.76 6,780 6,359 0.70 7,530 6,504

05/14/97 0.84 40,520 42,001 0.54 23,960 15,966

06/02/97 0.46 21,480 12,193 0.52 29,300 18,801

07/10/97 0.43 1,530 802 0.53 5,950 3,891

08/13/97 0.55 1,690 1,147 0.65 5,740 4,604

09/03/97 0.33 2,690 1,079 0.64 8,310 6,563

010/16/97 0.13 2,350 362 0.40 10,600 5,232

11/26/97 0.23 1,570 436 0.43 2,770 1,470

12/16/97 0.26 1,340 430 0.41 2,010 1,017

Gained/lost = inflow - outflow 

Total inflow mass (kg) 66,363

Total outflow mass (kg) 71,681

Mass gained (+) or lost from (-) reservoir -5,319
78 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 Through 2002

Wolford 1998 Nitrogen Budget

Sample date TN in 

(mg/L)

Water in 

(ac-ft)

TN mass in 

(kg)

TN out

(mg/L)

Water out 

(ac-ft)

TN mass out

(kg)

1/22/98 0.31 1,250 478 0.43 1,980 1,051

2/19/98 0.42 1,040 539 0.44 1,910 1,037

3/25/98 2.73 3,280 11,050 0.56 3,380 2,336

4/21/98 0.55 8,570 5,816 0.71 2,700 2,366

05/20/98 0.58 29,570 21,164 0.71 27,900 24,444

06/09/98 0.46 7,460 4,235 0.53 12,060 7,887

07/22/98 0.63 886 683 0.66 4,110 3,347

08/11/98 0.43 897 470 0.63 4,490 3,491

09/09/98 0.43 509 267 0.53 11,270 7,371

010/14/98 0.26 711 228 0.59 3,180 2,315

11/12/98 0.28 809 280 0.38 1,850 868

12/14/98 0.23 556 154 0.60 1,560 1,155

Gained/lost = inflow - outflow 

Total inflow mass (kg) 45,365

Total outflow mass (kg) 57,667

Mass gained (+) or lost from (-) reservoir -12,303

Wolford 1999 Nitrogen Budget

Sample date TN in 

(mg/L)

Water in 

(ac-ft)

TN mass in 

(kg)

TN out

(mg/L)

Water out 

(ac-ft)

TN mass out

(kg)

1/20/99 0.36 664 295 0.48 1,400 829

2/9/99 0.40 736 363 0.49 1,250 756

3/24/99 1.45 1,900 3,400 0.57 1,830 1,287

4/13/99 0.53 4,160 2,695 0.51 3,120 1,964

05/10/99 1.21 20,010 29,878 0.51 6,950 4,374

06/02/99 0.53 10,470 6,783 0.48 17,020 10,081

07/08/99 0.63 1,020 787 0.59 5,030 3,662

08/10/99 0.43 831 436 0.67 3,240 2,679

09/14/99 0.33 551 221 0.42 6,550 3,395

010/13/99 0.23 348 97 0.33 7,930 3,180

11/09/99 0.23 508 141 0.48 1,780 1,059

12/15/99 0.33 627 251 0.60 1,420 1,048

Gained/lost = inflow - outflow 

Total inflow mass (kg) 45,346

Total outflow mass (kg) 34,314

Mass gained (+) or lost from (-) reservoir 11,033

Table 15. Nitrogen mass balance detailed computations.—Continued

[--, no sample or computation; mg/L, milligrams per liter; ac-ft, acre-feet; kg, kilograms; TN, total nitrogen]
Hydrologic and Water-Quality Data 79

Wolford 2000 Nitrogen Budget

Sample date TN in 

(mg/L)

Water in 

(ac-ft)

TN mass in 

(kg)

TN out

(mg/L)

Water out 

(ac-ft)

TN mass out

(kg)

1/13/00 0.29 387 138 0.57 1,360 963

2/24/00 0.41 437 221 0.51 1,220 769

3/14/00 0.13 1,490 239 0.51 1,300 813

4/11/00 1.05 9,050 11,726 0.58 2,290 1,647

05/09/00 0.76 28,600 26,822 0.56 22,220 15,355

06/06/00 0.53 5,270 3,414 0.44 10,270 5,526

07/07/00 0.53 590 382 0.51 6,130 3,888

08/22/00 0.43 563 295 0.52 9,210 5,921

09/06/00 0.33 445 178 0.57 4,760 3,336

010/11/00 0.29 280 98 0.46 1,340 756

11/21/00 0.29 358 126 0.45 1,360 752

12/12/00 0.23 508 143 0.45 1,360 754

Gained/lost = inflow - outflow 

Total inflow mass (kg) 43,784

Total outflow mass (kg) 40,481

Mass gained (+) or lost from (-) reservoir 3,304

Wolford 2001 Nitrogen Budget

Sample date TN in 

(mg/L)

Water in 

(ac-ft)

TN mass in 

(kg)

TN out

(mg/L)

Water out 

(ac-ft)

TN mass out

(kg)

1/23/01 0.32 291 115 0.46 1,320 754

2/12/01 0.31 269 103 0.52 1,220 778

3/13/01 0.40 607 302 0.49 1,620 978

4/10/01 0.62 5,470 4,158 0.51 4,920 3,115

05/08/01 0.66 18,490 15,036 0.56 4,780 3,297

06/06/01 0.46 2,460 1,381 0.51 4,390 2,752

07/03/01 0.59 520 376 0.58 4,780 3,398

08/29/01 0.41 436 218 0.43 6,910 3,624

09/20/01 0.27 367 121 0.39 7,600 3,695

Oct estimate 0.27 378 125 0.39 1,910 929

Gained/lost = inflow - outflow 

Total inflow mass (kg) 21,935 January to October only

Total outflow mass (kg) 23,319 January to October only

Mass gained (+) or lost from (-) reservoir -1,384 January to October only

Table 15. Nitrogen mass balance detailed computations.—Continued

[--, no sample or computation; mg/L, milligrams per liter; ac-ft, acre-feet; kg, kilograms; TN, total nitrogen]
80 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 Through 2002

Table 16. Phosphorus mass balance detailed computations.

[mg/L, milligrams per liter; ac-ft, acre-feet; kg, kilograms] 

Wolford 1996 Phosphorus Budget

Sample date TP in

(mg/L)

Water in

(ac-ft)

TP mass in 

(kg)

TP out

(mg/L)

Water out

(ac-ft)

TP mass out 

(kg)

4/10/96 0.330 8,960 3,649 0.030 14,830 549

05/22/96 0.200 39,080 9,645 0.060 21,440 1,587

06/10/96 0.090 14,730 1,636 0.040 9,750 481

07/16/96 0.005 1,250 8 0.005 3,720 23

08/28/96 0.005 853 5 0.020 9,430 233

09/03/96 0.010 528 7 0.005 6,150 38

010/17/96 0.005 492 3 0.005 2,170 13

11/13/96 0.040 641 32 0.005 1,410 9

12/10/96 0.005 871 5 0.005 1,350 8

Gained/lost = inflow - outflow 

Total inflow mass (kg) 14,989 April to December only

Total outflow mass (kg) 2,942 April to December only

Mass gained (+) or lost from 

(-) reservoir

12,047 April to December only

Wolford 1997 Phosphorus Budget

Sample date TP in

(mg/L)

Water in

(ac-ft)

TP mass in 

(kg)

TP out

(mg/L)

Water out

(ac-ft)

TP mass out 

(kg)

1/28/97 0.005 674 3 0.005 1,520 9

2/26/97 0.080 559 108 0.080 1,730 171

3/18/97 0.060 1,090 502 0.060 4,660 345

4/16/97 0.005 6,780 250 0.005 7,530 46

05/14/97 0.220 40,520 11,000 0.010 23,960 296

06/02/97 0.120 21,480 3,181 0.010 29,300 362

07/10/97 0.005 1,530 9 0.005 5,950 37

08/13/97 0.020 1,690 42 0.010 5,740 71

09/03/97 0.005 2,690 17 0.005 8,310 51

010/16/97 0.005 2,350 14 0.005 10,600 65

11/20/97 0.005 1,570 10 0.005 2,770 17

12/16/97 0.005 1,340 8 0.005 2,010 12

Gained/lost = inflow - outflow 

Total inflow mass (kg) 15,144

Total outflow mass (kg) 1,483

Mass gained (+) or lost from 

(-) reservoir

13,662
Hydrologic and Water-Quality Data 81

Wolford 1998 Phosphorus Budget

Sample date TP in

(mg/L)

Water in

(ac-ft)

TP mass in 

(kg)

TP out

(mg/L)

Water out

(ac-ft)

TP mass out 

(kg)

1/22/98 0.005 1,250 8 0.005 1,980 12

2/19/98 0.010 1,040 13 0.005 1,910 12

3/25/98 0.510 3,280 2,064 0.020 3,380 83

4/21/98 0.040 8,570 423 0.030 2,700 100

05/20/98 0.170 29,570 6,203 0.180 27,900 6,197

06/09/98 0.050 7,460 460 0.005 12,060 74

07/22/98 0.050 886 55 0.005 4,110 25

08/11/98 0.005 897 6 0.005 4,490 28

09/09/98 0.010 509 6 0.040 11,270 556

010/14/98 0.025 711 22 0.005 3,180 20

11/12/98 0.025 809 25 0.005 1,850 11

12/14/98 0.025 556 17 0.005 1,560 10

Gained/lost = inflow - outflow 

Total inflow mass (kg) 9,302

Total outflow mass (kg) 7,129

Mass gained (+) or lost from 

(-) reservoir

2,173

Wolford 1999 Phosphorus Budget

Sample date TP in

(mg/L)

Water in

(ac-ft)

TP mass in 

(kg)

TP out

(mg/L)

Water out

(ac-ft)

TP mass out 

(kg)

1/20/99 0.025 664 20 0.005 1,400 9

2/9/99 0.025 736 23 0.005 1,250 8

3/24/99 0.220 1,900 516 0.005 1,830 11

4/13/99 0.080 4,160 411 0.005 3,120 19

05/10/99 0.360 20,010 8,889 0.030 6,950 257

06/02/99 0.140 10,470 1,809 0.090 17,020 1,890

07/08/99 0.025 1,020 31 0.005 5,030 31

08/10/99 0.025 831 26 0.005 3,240 20

09/14/99 0.025 551 17 0.005 6,550 40

010/13/99 0.025 348 11 0.005 7,930 49

11/09/99 0.025 508 16 0.005 1,780 11

12/15/99 0.025 627 19 0.005 1,420 9

Gained/lost = inflow - outflow 

Total inflow mass (kg) 11,788

Total outflow mass (kg) 2,355

Mass gained (+) or lost from 

(-) reservoir

9,433

Table 16. Phosphorus mass balance detailed computations.—Continued

[mg/L, milligrams per liter; ac-ft, acre-feet; kg, kilograms] 
82 Hydrology and Water-Quality Characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 

1990 Through 2002

Wolford 2000 Phosphorus Budget

Sample date TP in

(mg/L)

Water in

(ac-ft)

TP mass in 

(kg)

TP out

(mg/L)

Water out

(ac-ft)

TP mass out 

(kg)

1/13/00 0.025 387 12 0.005 1,360 8

2/24/00 0.025 437 13 0.005 1,220 8

3/14/00 0.025 1,490 46 0.005 1,300 8

4/11/00 0.200 9,050 2,234 0.005 2,290 14

05/09/00 0.230 28,600 8,117 0.005 22,220 137

06/06/00 0.070 5,270 455 0.005 10,270 63

07/07/00 0.025 590 18 0.005 6,130 38

08/22/00 0.040 563 28 0.005 9,210 57

09/06/00 0.025 445 14 0.005 4,760 29

010/11/00 0.030 280 10 0.030 1,340 50

11/21/00 0.030 358 13 0.030 1,360 50

12/12/00 0.030 508 19 0.030 1,360 50

Gained/lost = inflow - outflow 

Total inflow mass (kg) 10,980

Total outflow mass (kg) 513

Mass gained (+) or lost from 

(-) reservoir

10,467

Wolford 2001 Phosphorus Budget

Sample date TP in

(mg/L)

Water in

(ac-ft)

TP mass in 

(kg)

TP out

(mg/L)

Water out

(ac-ft)

TP mass out 

(kg)

1/23/01 0.030 291 11 0.030 1,320 49

2/12/01 0.030 269 10 0.030 1,220 45

3/13/01 0.042 607 31 0.030 1,620 60

4/10/01 0.068 5,470 459 0.030 4,920 182

05/08/01 0.118 18,490 2,692 0.016 4,780 94

06/06/01 0.036 2,460 109 0.030 4,390 163

07/03/01 0.013 520 8 0.007 4,780 41

08/29/01 0.028 436 15 0.009 6,910 77

09/20/01 0.016 367 7 0.014 7,600 131

October estimate 0.016 378 7 0.014 1,910 33

Gained/lost = inflow - outflow 

Total inflow mass (kg) 3,351 January to October only

Total outflow mass (kg) 875 January to October only

Mass gained (+) or lost from 

(-) reservoir

2,476 January to October only

Table 16. Phosphorus mass balance detailed computations.—Continued

[mg/L, milligrams per liter; ac-ft, acre-feet; kg, kilograms]