BOARD01651

• Board Meeting Date: 5/22/2000
• Description: Flood Section - Approximate Hydrology Guidelines
• Board Meetings - Doc Type: Memo

. On the north by the Dolores River - Colorado River basin divide;
. On the east by the Dolores River - Gunnison River basin divide;
. On the south by the Dolores River - San Juan River basin divide; and
. On the west by the Colorado - Utah state line.

The regression equation for this subregion is only valid for natural tributary streams that have
drainage areas between 2 mi2 and 1,080 mil. A detailed study or other hydrologic analysis must
be performed for projects involving streams with drainage areas that fall outside of the applicable
range.

The equation for subregion DLR-l is:
Q = 213.8(A)601
Where:
A = Drainage Area, square miles (2<A<1,080)
Q = 100 year peak flow, cfs

Eastern San Juan River Subregion:
This subregion includes the San Juan River mainstem and its tributaries in southwestern Colorado.
Streams in this subregion are located in portions of La Plata County, San Juan County, Archuleta
County, Hinsdale County, and Mineral County. Major tributaries in this subregion include the San
Juan River, Animas River, La Plata River, and Los Pinos River. The subregion is bounded as
follows:

. On the north by the San Juan River - Gunnison River basin divide;
. On the east by the San Juan River - Gunnison River basin divide;
. On the south by the Colorado - New Mexico state line;
. On the west by La Plata River - Mancos River basin divide; and
. On the northwest by the Animas River - Dolores River basin divide

The regression equation for this subregion is only valid for natural tributary streams that have
drainage areas between I mi2 and 760 mil. A detailed study or other hydrologic analysis must be
performed for projects involving streams with drainage areas that fall outside of the applicable
range.

The equation for subregion SAN-l is:
Q = 589.2(A)"5Il
Where:
A = Drainage Area, square miles (1 <A <760)
Q = 100 year peak flow, cfs

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