FLOOD02650

• County: La Plata
• Stream Name: Animas River
• Basin: San Juan/Dolores
• Title: Hydrology Addendum to FIS La Plata County Unincorporated Areas
• Date: 5/21/2002
• Prepared For: La Plata County
• Prepared By: Montgomery Watson
• Floodplain - Doc Type: Floodplain Report/Masterplan

From the San Juan Mountains, the Animas River flows southerly
through steep, narrow canyons into the nearly I-mile wide Animas
Valley, which extends for approximately 15 miles to Durango.
Elevations in the Animas River drainage basin vary from more than
14,000 feet along the wese~rn slopes of the San Juan Mountains to
approximately 6500 feet at Durango. The Animas Valley north of
Durango is wide, gently sloping, and shallow. The drainage area of
the Animas River at the northeast corporate limits of Durango is
649 square miles.

The Lightner and Junction Creek watersheds, which are tributaries of
the Animas River at Durango, cover approximately 66 and 39 square
miles, respectively. Lightner and Junction Creeks rise in the La
Plata Mountains to the northwest of Durango at elevations greater
than 12,000 feet. The watersheds consist of high, mountainous terrain
with steep to moderately steep slopes. Within the study areas, both
Lightner and Junction Creeks have well-defined channels and sufficient
channel capacities to pass minor floodflow without significant
property damage.

The drainage basin of Dry Gulch Creek, which covers approximately
4 square miles, is situated between the lower portions of the basins
of Lightner and Junction Creeks. The headwater elevation is in excess
of 8000 feet and it joins Junction Creek approximately 0.5 mile
upstream from the Animas River.

Los Pinos River flows through typical glaciated mountains from the
Needle Mountains at approximately 14,000 feet. Vallecito Creek joins
Los Pinos River at Vallecito Reservoir at an elevation of 7665 feet.
In general, slopes on Vallecito Creek are steep upstream from the
reservoir. Stream gradients of 100 to 300 feet per mile are common.
The drainage area above Vallecito Dam is approximately 270 square
miles. Downstream from the Vallecito Reservoir, the Los Pinos River
watershed consists of high mountainous terrain with steep to moderately
steep slopes. The drainage area of the Los Pinos River is 349 square
miles at Bayfield.

Vallecito Creek and Grimes Creek are located upstream from the
Vallecito Reservoir in a wide valley. All of these watersheds empty
into the Vallecito Reservoir. The drainage areas for these creeks
are 90 and 5 square miles, respectively.

The study area of the Animas River and Hermosa Creek in the vicinity
of Hermosa extends along the Animas River from near the end of the
river's canyon reach upstream to near the southern boundary of the
San Juan National Forest, and along the lower 2.8 miles of Hermosa
Creek. Hermosa Creek joins the Animas River from the west in the
Animas Valley, southeasterly of Hermosa. The Animas valley is on
the southern slopes of the San Juan MOuntains in the southwest
corner of Co.lorado. The Hermosa area is on the western side of the
valley, approximately 10 miles north of Durango.

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