WSP03634

• File Number: 8102.400
• Description: Arkansas River Hydrology - Transmountain Diversions-Imports
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 2/10/1998
• Author: USGS
• Title: Methods to Determine Transit Losses for Return Flows of Transmountain Water in Fountain Creek Between Colorado Springs and the Arkansas River-Colorado
• Water Supply Pro - Doc Type: Report/Study

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Channel Storage

Channel storage is the volume of water in a reach of a stream at any
given time. The introduction of a water wave results in an increase in
channel storage in the reach. The volume of water lost to channel storage,
however, is only a temporary loss because after passage of the water wave,
channel storage rapidly decreases, forming a part of the downstream flow. In
regard to the transportation of transmountain return flows d'lwn Fountain
Creek, changes in channel storage can have a substantial effect on the
quantity of return flows reaching the Arkansas River on any given day.
Although this effect was determined in the present study, channel storage was
not considered to be a permanent loss of transmountain return flows.

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Evaporation

Transmountain return flows are evaporated either by (1) direct
evaporation from the stream surface or by (2) indirect evaporation through
soil surfaces of water in bank storage. Transit loss resulting from direct
evaporation was considered to be a permanent transit loss and waS included
in the present study, Only the increase in evaporation resulting from the
increase in stream width because of transmountain return flow was considered.
Transit losses resulting from indirect evaporation were not considered to be
substantial; moreover, these losses would, to some extent, be derived from
transmountain return flows permanently lost to bank storage.

Transpiration

Transpiration is the process by which water vapor escapes from the
tissues of plants and enters the atmosphere, For purposes of this discussion,
the actual use of water by plants for growth and development of tissue is
included in the process of transpiration. Only transpiration from naturally
growing riparian vegetation along Fountain Creek, much of which consists of
phreatophytes, was considered in the present analysis. The quantity of water
transpired by phreatophytes depends, to some extent, on the depth to water in
the alluvium.

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Introduction of transmountain water into fountain Creek increases head in
the stream and induces flow into the alluvium; this flow results in a head
increase in the alluvium and a decrease in depth to water below land surface,
Head increase in the stream because of transmountain return flow could be as
much as 0,5 ft; often it would be much'.iess. Head increases in the alluvium,
on the other hand, are considerably less than head increases in the stream.

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Studies to determine the rate of water use by phreatophytes as a function
of depth to water below land surface indicate that very small decreases in
depth to water do not result in substantial increases of water use by
phreatophytes (Robinson, 1958, p. 18, 22). Therefore, tbe increase in
transpiration by riparian vegetation along Fountain Creek owing to a decrease
in depth to water resulting from head increases in the stream caused by trans-
mountain return flows was assumed not to be substantial. Again, some of these
losses would be derived from transmountain return flows that are permanently
lost to bank storage.

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