WSP09401

• File Number: 8056
• Description: Drought Preparedness
• State: CO
• Basin: Statewide
• Date: 8/28/1986
• Author: CDM
• Title: Phase I - Drought Study - City of Loveland Raw Water Supply System
• Water Supply Pro - Doc Type: Report/Study

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techniques vere used to supplement the existing Big Thompson River
streamflov record. The results of these efforts are described belovo A
brief description of the hydrology of the Big Thompson River Basin is first
provided as a background.

4.2 HYDROLOGY OF BIG THOHPSON RIVER BASIN

Much of the area drained by the Big Thompson River and its principal

tributaries - the North Fork of the Big Thompson River, Buckhorn Creek and

Little Thompson River - is in the Rocky Mountains to the vest of Loveland.

Spring runoff derived from snovmelt in the mountains is the single most

important factor affecting the quantity of vater available to the City and

other ovners of direct-flov vater rights. During an average year almost

three-fourths of the annual total streamf10v volume viII occur during

spring runoff during Hay through July.

The drainage area of the Big Thompson vatershed above the United States

Geological Survey (USGS) streamflov gauge at the mouth of the Big Thompson

Canyon, is 305 square miles. The total drainage area at its confluence

vith the South Platte River is 835 square miles. Tvo major tributaries

join the river betveen the Canyon mouth and confluence vith the South

Platte. Buckhorn Creek (contributing area of approximately 120 square

miles) joins the Big Thompson approximately 3 miles dovnstream from the

Canyon. The Little Thompson River (contributing area of approximately 190

square miles) joins the Big Thompson near Hilliken. Of the 16 irrigation

ditches or pipelines on the Big Thompson River, only the Evanstovn Ditch

headgate is dovnstream from the mouth of the Little Thompson. Most of the

remaining drainage area to the Big Thompson River lies along the Front

Range.

Streamf10vs on the Big Thompson vary significantly from one season to the

next. The irrigation season typically runs from Hay through October.

During May and June the spring runoff produces high streamf10vs even though

substantial irrigation vithdravals occur. During the July through October

4-3