Upper Los Pinos Watershed Report

• Document ID: hr_0016
• Contract/PO #: PO 06-51
• County: La Plata
• County: Hinsdale
• County: San Juan
• Stream Name: Los Pinos River
• Basin: San Juan/Dolores
• Sub-Basin: Upper San Juan 14080101
• Water Division: 7
• Title: Rainfall Runoff, Flood Hazards, and Water-Quality Data for the Upper Los Pinos River Watershed, Southwestern Colorado, 2006
• Date: 3/1/2007
• Prepared For: CWCB
• Prepared By: Southwest Hydro-Logic
• Watershed Pro - Doc Type: Planning Report

On October 6, 2006, warm rain fell on an
early snowpack in the San Juan Mountains, The
SNOTEL sites (operated by the Natural
Resources Conservation Service) indicated that
the San Juan Basin was at 400 percent of the
average snow water equivalent. At the USGS
raingage site A-4 in Jack Creels, 1.21 inches of
rain were recorded. At the CoCoRAHS site north
of Vallecito Lake, 1.32 inches of rain fell. There
had been numerous rainfall events of that
magnitude throughout the summer of 2006;
however, the rain-on-snow triggered high flows in
streams that had snowpack in the headwaters.
Streamflow discharge in Vallecito Creek
increased from 135 ft'/sec on October 5, 2006, to
3,700 ft'/sec on October 6, peaking at 10:45 PM
(Figure 9). By the morning of October 7, several
houses and properties along the flood plain of the
Vallecito Valley had been flooded (see photos,
Figure 2).
4.000
z
O 3,500
w
y
~ 3,000
w
a
w 2,500
W
LL
U 2,000
m
U
z 1,500
w
~ 1,000
a
x
cq 500
0
RAINFALL RUNOFF WATER-QUALITY DATA
Water-quality samples were collected of
rainfall runoff from selected streams draining the
Missionary Ridge wildfire area (Figure 3).
Samples were analyzed for total iron, total
manganese, dissolved ammonia, dissolved nitrate,
and total mercury. Samples for total iron and
manganese were acidified after collection, and the
samples were digested before analysis. Digestion
consisted of adding 2.5 mL,s of concentrated nitric
acid to 25 mLs of sample (10 percent acid), then
heating the sample to 160°F using a microwave
oven (EPA Method 3015). Digested, or total
recoverable, samples were then filtered and the
samples brought between pH 3 and 5 using
sodium hydroxide before analysis. Iron,
manganese, ammonia, and ntrate analyses were
analyzed by spectrophotometry. Mercury
samples were analyzed by cold-vapor atomic
fluorescence by the U. S. Geological Survey,
Mineral Resources Branch in Denver, Colorado.
Sample results are shown in Table 1, and graphs
of water-quality data for the rainfall runoff are
shown in Figure 10.
VALLECITO CREEK
USGS STREAMFLOW GAGING STATION 09352900
HIGH FLOW EVENT, OCTOBER 6-7, 2006
STREAMFLOW
RAINFALL
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^o~o~ti ^o~~~ti ^o~~~ti ^o~o~ti ^o~~ti ^o~~~ti ^o~o~ti o\^o~ti o\^,~~ti o\^~~ti o\^o~ti
~ ~ ~ ~
Figure 9. Flood hydrograph for Vallecito Creels and rainfall at site A-4.
1.4 ~
D
1.2 ~
1.0 T
D
r
r
0.8 O
D
0.6 ~
D
D
0.4 p
z
0.2 =
m
10 Rainfall Runoff, Flood Hazards, and Water-Quality Data for the /n cooperation with the Colorado Watershed Protection Fund and
Upper Los Pinos River Watershed, Southwestern Colorado, 2006 the San Juan Resource Conservation and Developrnent Council