This project is assessing the hydrologic
impact created by installing a series of small in-stream structures on flow
regimes and ground water levels in two West Virginia headwater
watersheds. Structures designed to enhance bank and alluvial
storage of water, for the purpose of increasing stream flow during base
flow, are installed on first and second order streams.
Data collected for this project include flow, groundwater
"level", stream height, precipitation, and water temperature.
Changes in the system will be detected based on comparisons between sites, in particular,
between control and experimental sites, and between upstream and
downstream locations within the experimental study areas.
The schematic drawing at right shows the
standard layout of the most
important elements of this project: the streams, groundwater stations
(piezometers), flow stations and structures. Click on any of these
to learn more.
We are conducting a pilot study in which structures designed to enhance
bank and alluvial storage of water, for the purpose of increasing stream
flow during base flow, are installed on first and second order streams.
Three watersheds were selected for study. One stream remains unaltered
to serve as a control. One stream has two segments receiving treatments,
a meadow with a broad floodplain, and an upland forest. The second
experimental site is an upland meadow that is enrolled in USDA-CREP.
The following table provides a brief description of each of the four
study sites, including a list of data points.
Stream Length (ft)
# Flow / Precip.
# Piezometer Nests
# Structure Grids
2 / 1
2 / 2
The SRE Forest site is totally forested, with a small amount of
pasture at the headwaters of the drainage. The lower end is
roughly 2000' upstream of SRE Meadow. The stream has a
slope of 2.7%.
The Meadow site is in a broad
floodplain with extensive wetlands. The stream has a slope of
1.7%. An important "feature" of this meadow is
abundant multiflora rose that often slump into the stream
2 / 2
The control site has only a small, forested section and is
mostly grassy. It winds through a narrow valley, and passes back
and forth across a road. The stream has a slope of 3.2%. There
is a pond near the headwaters of this stream - a pond that has
had a tendency over the years to blowout and create some
scouring downstream flows.
This site is an upland meadow, and is enrolled in the USDA
Conservation Reserve and Enhancement Program (CREP). The stream
has a slope of 2.4% and a narrow area with alluvial deposits.
This site has a sizeable side stream that delivers significant
flow to the system roughly 400 feet above the bottom of the
study reach. Flows are taken there as well as at the top and
bottom of the main stream.
flow is the product of the speed of the water and the cross section of
water at a stream site. When you multiply the speed (for example: in
feet per second) by the wetted area (for example: in square feet), the
result is a volume of water moving past a site over some period of time
- such as cubic feet per second. We're interested in flow for this
project because an increase in flow between experimental and control
sites will tell us if we are having the effect we are trying to
achieve. Flows are taken at the top and bottom of each study area.
The very small, meandering streams selected for this project provide
particular challenges for accurate measurement of stream flow across all
ranges of flow, and a mixture of methods suitable for different
conditions have been utilized. Flow measurement equipment includes a
Global Flow Probe Model FP101 and the "Insta-Weir." The
portable Insta-Weir was developed for this project because of our need
to measure flow at very low levels, where stream depth or flow rate
precludes use of the Flow Probe and really any other device we have
seen. The Insta-Weir works by backing up the stream and
constraining the outflow through a V or box -shaped weir; outflow is
collected in a waterproof bucket or bag for direct volumetric
measurement. It captures most of the flow of the stream (if the bottom is
firm and does not have deep cobble or gravel or undercut banks), and the volume of water
is measured in a calibrated Tidy CatTM bucket at the
outlet. Looks silly as can be, but it works in many
locations. Many thanks to Meredith Pavlick for all her
efforts testing various iterations of this device, and to Bob Markley
and Pat Bowen for helping to develop the concept.
Highly significant statistical relationships between control and
experimental sites, and between upstream and downstream locations within
the experimental study areas during the pre-installation phase of this
project, are essential in understanding changes in flow that occur due
to structure installation. Fortunately, very strong correlations
were found between the four flow stations in the Experimental Site 1,
with r-values ranging from 0.940 to 0.997. These sites were all also
significantly correlated with the two flow stations in the control area,
with r-values ranging from 0.88 to 0.98, and also very strongly
correlated with the upper two flow stations at experimental site 2, with
r-values ranging from 0.935 to 0.994.
The flow correlation results, and the results of regression analysis,
indicate that a strong predictive relationship exists between flows in
upstream and downstream sites, as well as control and experimental
sites. Graphs of this data (such as the one below at right) show a tight
cluster of data points along the regression line, particularly at lower
flows; this is very good, because lower flows are where we expect to see
the largest change. Very preliminary data indicate that both the
slope and the y-intercept are higher in post structure data than in
pre-structure data, which tells us that the flow at the downstream site
was higher than at the upstream site after structures were installed
than before. As noted, this is very preliminary - but encouraging
- data. Ultimately, we expect the y-intercept to increase more, and the slope
actually to decrease due to a greater effect at low than high flows.
Insta-Weir - measuring flow where all other flow equipment fails.
compares flow at an upstream site (SRE3) with a downstream site
are we interested in groundwater? Because the ground is our
project's reservoir. Rather than creating dams to create large
surface reservoirs, we are using the spaces between soil and rocks in
the ground to store our water. We do this by installing small
structures in the stream channel that raise the water level just a bit,
to increase contact with the soil and allow water to flow into the
floodplain. Later, when the streams drop, the stored water can
flow back into the stream channel and keep the stream flowing. The
structures are intended to mimic the hydrological effect of small beaver
dams . . . and beavers provide the appropriate ecological context for
Alluvial groundwater is being measured using a network of
piezometers. Piezometers are like groundwater measuring wells,
except they only have a hole(s) at the bottom instead of up and down the
sides. They can provide information about the direction of water
movement in the ground, instead of only elevation. Our piezometers were constructed from 1¼ inch PVC pipe, with
nylon mesh placed on the bottom end of the pipe and secured in place using a
1¼ inch PVC cap which is perforated with six 1/4 inch holes. Spring
steel measuring tapes were cut to length and inserted in the piezometers,
and a water-soluble ink daubed on the tapes serves as a crest height
recorder between sampling trips.
Piezometers were installed
according to two protocols.
The first is a
longitudinal network of piezometers spaced every 100 ft along the length of the
stream segment, 10 ft from the edge of the stream (if possible),
with the bottom of the piezometer level with the stream's thalweg
(lowest point in the channel).
nests were installed every 400-ft of stream length (where
possible). In nests, each piezometer is a different depth in
the ground, and the relative water elevation in the three
piezometers tells us if the water in the ground is rising, falling,
The second piezometer
protocol is called a Structure Grid, which consists of a grid
of three rows of three piezometers (if possible) used to measure
changes in groundwater levels across a width of floodplain area
caused by the installation of a structure. One row is centered
on a structure, one is upstream, and one is downstream.
Although there are useful correlations between a number of the sites,
the piezometer data is far less predictable than the flow data discussed
previously, at least when viewed in mass. There are four major patterns.
usually have water, with little difference between
daily and maximum levels, and a relatively small range of water levels;
usually have water, with little difference between daily and maximum
levels, and a relatively large range of water levels;
are often dry,
with large difference between daily and maximum levels, and a relatively
large range of water levels; and
are in a condition of dynamic change
that has nothing whatsoever to do with the installation of structures
(may include the defining characteristics of 1-3 above).
in 1-3 appear to relate to the speed of the hydraulic connection to the
stream, and piezometers in close proximity to one another may
behave very differently (see graphs below). A mosaic of statistical and visual methods will
be used to assess the piezometer data.
installation - Greg and Bob digging holes with a gas-powered
removes measuring tape from piezometer at nest.
the tape. Water soluble ink tells us how high the water is .
. . and how high it has been.
graphs below illustrate piezometer patterns No. 1 &
3. Piezometer data is far less predictable than the
flow measurements discussed previously. The two graphs below
illustrate this point in a number of ways. These SRE Meadow
piezometers are located only ten feet apart, both ten feet
from the edge of the stream, and the depth of the piezometers in
the ground differs by only 0.04 ft. And yet, the patterns of
current and maximum water elevations, and the relationships
between maximum and current, are quite different. Water levels in
SB190 (top graph) range narrowly through less than 0.5 feet, and
the current and maximum levels are usually very close. Water
levels in SB200 (bottom graph) range over nearly one foot, and the
current and maximum levels are often quite different.
is no missing data in these graphs; when no bar appears on the
graph it means there was no water in the piezometer. The
piezometer at SB200 was dry on 10 of the 25 visits shown here,
while SB190 was dry only four times (during a very dry period in
August). We think the differences are caused by a difference
in the speed of the hydraulic connection to the stream. The
piezometers with water levels that rise and fall quickly along
with stream levels probably have a nearly open channel,
underground connection to the stream. Those that rise and
fall more slowly are probably buffered from rapid changes in
stream height by well consolidated alluvial soils. That
these two conditions can, and do, occur in such close proximity
was quite a surprise.
By the way, a "dry pipe"
is not "no data", it is the rather oxymoronic
unquantifiable data. The information that you don't get from
a "dry hole" is very different from a
below-detection-limit result in a chemical analysis. In the latter
case, you always have a known, absolute lower limit -zero, while a
dry piezometer only tells you that the water level is somewhere
below the bottom of the pipe. This creates some interesting
challenges in data analysis.
graphs below illustrate piezometer pattern No. 4 - a
condition of dynamic change that has nothing whatsoever to do with
the installation of structures (well, until the end). The following two graphs
provide a wonderful, and our most extreme, example of this. This
site has a multiflora rose dam in the stream, immediately upstream
of the piezometer nest at SREM 1600; this natural dam is probably the source of what we
see here. The top graph shows daily and maximum water levels in
the SB (stream bottom elevation) piezometer, and the trend of
increasing water level over time is unmistakable. We are fortunate
that this is one of the piezometer nest sites, and Graph B
provides a closer look at what is happening here. The relatively
high water in the low piezometer for sampling period from 2-11
clearly indicates a rising water level in the ground during this
time. After this, groundwater "direction" appears to
vacillate between steady, rising, and falling, and appeared to
have stabilized roughly between elevation 1889.60 and 1989.80 . .
. until sampling period 28-30, which occurred after a pair of
structures were installed at this site to preserve the elevated
groundwater impact of the multiflora dam that was rapidly
disintegrating. You can see these 2 structures in the
structure slide show.
installed longitudinally in series in the experimental streams to create
a progression of small pools, rather than single isolated structures. We
expect that alluvial water storage caused by upstream pools will extend
periods of stream flow further downstream and create a multiplier
effect, like batteries wired in series.
Structures were modeled after a variant of the cross vane that we
observed during a visit to a stream restoration project in Big Bear, PA.
Log structures at this site
had been installed on a sizeable, high-gradient stream by two men in one
day, using no heavy equipment, and have successfully withstood a number
of major floods. Biological studies at this site found that neither
their stone nor log cross vanes created an impediment to movement of
stream life. Structures are built to or below bankfull elevation at the
edges and lower in the center of the stream to provide a spillway. The
cross vane’s inverted-V design directs the force of the water away
from the banks and toward the center of the channel, reducing bank
erosion and enhancing long-term stability. They can be built
symmetrically to center the flow, or asymmetrically to direct the flow
of water through a bend in the stream. Click
here to see all the structures that have been installed so far.
While construction methods at each site vary somewhat, in general the
method is as follows: 1) The primary members of the cross vane are
driven or cut into the stream banks at the appropriate angle and
elevation. 2) The upstream edges of the logs are trimmed and fitted to
each other, and then either wired, through-bolted, or nailed together.
3) At the point where the cross vane members enter the bank, model
68-DB-1 duckbill earth anchors (1,100 lbs. holding capacity) are driven
into the bank at a right angle to the member, with the cable fastened to
the member using a cable clamp. 4) Galvanized wire mesh and erosion
cloth are stapled to the upstream edge of the exposed portions of each
member, and run 1'-2’ upstream of the structure. The erosion cloth is
included to reduce seepage through the structure, and is held below the
line of sight for aesthetic reasons. 5) A layer of leaves or hay is
placed on top of the erosion cloth and then rocks of cobble and larger
size are placed on the full length of the wire mesh upstream to the
height of the top of the members.
possible by funding from The Norcross Wildlife Foundation, the
National Fish and Wildlife Foundation, Virginia Environmental
Endowment, NOAA-BWET, USEPA, The MARPAT Foundation, and our generous