Silver Lake
0 0
POOR
2
FAIR
1
GOOD
4
Secchi Disc Transparency Depth (meters)
Secchi Disc Transparency Depth (feet)
Significant Trend 2000-2009
EXCELLENT -0.233 meters (-0.76 feet) / year
6
2
8
3
10
12
4
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
Year
SILVER LAKE
SUMMER AVERAGE WATER CLARITY
Valley Branch Watershed District
Silver Lake
Average Summer Epilimnetic (0-2 meters) Total Phosphorus
Concentrations
200
n=2 POOR
180
160
n=number of samples collected
June through August
140
n=2 n=2
120
TP (ug/L)
n=1 n=2 n=10
n=32
100
n=24 FAIR
80
n=8
60 n=10 n=19
n=1 n=16 n=14n=5 n=8 n=10
n=23 n=8
40 GOOD n=8
n=10 n=8
n=10 n=4
n=14 n=5
20
n=8n=8
n=10 n=5 n=8
n=8 n=6
EXCELLENT
0
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
Year
Silver Lake
Average Summer Epilimnetic (0-2 meters) Chlorophyll a Concentrations
70
POOR
n=2
60
n=2
50
n=number of samples collected
June through August
Chl-a (mg/cu.m)
40
n=1
n=1
n=10
30 FAIR
n=10
20 n=2
n=9
GOOD n=8
n=33 n=5
10 EXCELLENT n=24 n=4
n=16 n=8 n=14
n=10n=8
n=8 n=10 n=8 n=5
n=23 n=14
n=8 n=10 n=9n=8
n=6 n=6
0 n=4n=7
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
Year
SILVER LAKE
HISTORIC WATER QUALITY DATA
Valley Branch Watershed District
Silver Lake
Carlson TSI Index Based on Summer Average Water Clarity
70
POOR
65
FAIR
60
GOOD
Carlson TSI Index
55
EXCELLENT
50
45
40
35
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
Year
Silver Lake
Minimum Summer Secchi Disc Transparency
0 0
2
Secchi Disc Transparency Depth (m)
Secchi Disc Transparency Depth (ft)
1
4
Guideline for Excellent Water Quality:
Minim um Secchi Disc
Transparency ≥ 1.1 m eters 6
2
8
3 10
12
4
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
Year
SILVER LAKE
HISTORIC WATER QUALITY DATA
Valley Branch Watershed District
Silver Lake
Secchi Disc Transparency Depths
0.0
Avg. Summer (Jun-Aug) Values
0.5
Secchi Disc Transparency Depth (m)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
Mann-Kendall/Sen’s Slope Trend Test
(Test Period – 2001 to 2010)
Confidence Test Statistic = -35
Level Test Significance
99% -35 < -30 Significant (Declining)
95% -35 < -23 Significant (Declining)
90% -35 < -20 Significant (Declining)
80% -35 < -16 Significant (Declining)
Sen’s Slope -0.233 meters/year
Notes:
1. Points shown in the graph are the summer average (June-August) Secchi disc
transparency depths. Only years with a calculated summer average based on at least 4
measured values are plotted. At least 5 data points were required to complete the trend
test.
SILVER LAKE
MANN-KENDALL TREND ANALYSIS
OF SECCHI DISC TRANSPARENCY
Valley Branch Watershed District