ISFAPP01508

• Year: 1996
• Title: Development of Instream Flow Recommendations in Colorado Using R2CROSSDevelopment of Instream Flow Recommendations in Colorado Using R2CROSS
• CWCB Section: Stream & Lake Protection
• Author: Gregory D. Espegren
• Description: Overview of Colorado's ISF Program and documentation for the R2CROSS Lotus macro
• Publications - Doc Type: Historical

flow control. Riffles are most easily visualized
as the stream reaches which would dry up most
quickly should streamflow cease.
Biologically, riffles are essential to the
production of benthic invertebrates and the
passage, spawning, egg incubation, feeding, and
protective cover of fISh. Riffles are also the
stream habitat-type most sensitive to changes in
hydraulic parameters with variation in discharge
(Nehring 1979). Riffles are critical to a healthy
aquatic environment because small reductions
in streamflow may result in large reductions in
water depth and the amount of wetted perimeter
available for aquatic habitat. Maintaining
adequate streamflow in riffles also preserves the
natural environment in other important stream
habitat-types such as pools and runs (Nehring
1979).
Hydraulic engineers have developed
several mathematical models and equations to
predict instream hydraulic parameters (Chow
1959). Manning's equation is one such model
that is well-s\lited to the rime -stream habitat-
type (Grant et ale 1992); In order to maximize
the reliability of Manning's equation, transects
are placed within a rime so that streamflow is
uniform across the transect (Grant et ale 1992).
The transect represents the average stream
width, depth, and cross-sectional area within the
riffle being characterized. Transects should be
located in areas that exhibit natural banks or
grasslines and concentrated water flow, free
from braiding. They should not be located on
eroded or undercut streambanks.

Hydraulic Data Collection
Stream discharge is measured using
standardized procedures established by the
United States Geological Survey (USGS)
(Buchanan and Somers 1969). On streams less
than 50 feet in width, channel geometry is
typically measured using sag-tape methodology
(Silvey 1976; Ray and Megahan 1979). Larger

streams typically require the use of a land
survey level and stadia rod (Benson and
Dalrymple 1967). A list of required field
equipment for making streamflow
measurements is provided in Table 1.
The sag-tape methodology consists of
suspending a steel tape from bank to bank
across the stream channel, perpendicular to the
streamflow (Figure A). Metal cross section
stakes are driven into the ground above the
grassline. The steel tape is suspended by
attaching the zero-end of the tape to one of the
metal stakes, stretching the tape across the
stream, and then attaching the other end to a
tape clamp and spring scale fastened to the
metal stake on the opposite streambank. A
minimum of 15 pounds of tension is applied to
the tape, as the tape is drawn up and clamped.
A survey level and stadia rod are used to adjust
the ends of the tape up or down until they are
level, thereby producing a consistent datum
from which vertical distance measurements can
be read
The R2CROSS program uses the
standard weight of a one-foot section of the
steel tape, tape tension, and the length of tape in
suspension to correct horizontal distance and
vertical depth measurements made from the
sagging tape. The program adjusts the
coordinates at each cross section vertical so that
the corrected measurements correspond to a
level datum from stake to stake and not the
curved datum created by the sagging tape
(Figure A).
an larger streams, vertical
measurements between the suspended tape and
the stream channel may be replaced with
readings using a survey level and stadia rod.
The suspended tape is then used to measure
only the horizontal location of each cell
vertical. There is no need to precisely level the
ends of the suspended tape or to record the tape
tension as no sag corrections are required.

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