**SR 4 over Middle Fork Crow River near Manannah, MN**

SITE DESCRIPTION:

S.R. 4 runs north and south through low relief terrain of pastures and
meadows, with some areas of woody vegetation. The nearest town of
Manannah is located to the northwest. According to the MnDOT bridge plan
notes, "The channel appears to have been dredged and straightened. No
records at courthouse of it being a public ditch." The channel in 1997
still appear unusually straight, but banks were well vegetated and
appeared stable. There is no gaging station near this site, but
according to the bridge plans, local residents reported a historic high
water of 1124.9 ft MSL, which occurred in the spring of 1952. The
current bridge built in 1955 apparently replaced a smaller bridge
(having an opening of only about 25 ft), which was located about 20 ft
upstream. The construction plans indicated that the contractor was to
clean out the channel and dress slopes to the section shown in the
plans, for a distance of 60 ft both sides of the highway centerline. The
design cross section had a bottom width of 26 ft at an elevation of
1115.25 ft MSL with side slopes of 2:1.

Data collected in 1997 was collected after the flood peak had passed.
The time of the peak is not known but based on highwater marks the peak
appeared to be at 1122.1 ft MSL, approximately 1.86 ft higher than the
stage of 1120.25 ft MSL measured of April 4, 1997.

DESCRIPTION OF REFERENCE POINTS:

All elevations and stages are referenced to mean sea level, based on the
elevation of the finished bridge deck.

CONTACT:

David Mueller

U.S. Geological Survey

9818 Bluegrass Parkway

Louisville, KY 40299

PUBLICATIONS:

Mueller, D.S., and Hitchcock, H.A., 1998, Scour measurements at
contracted highway crossings in Minnesota, 1997: ASCE, Water Resources
Engineering '98, Memphis, TN, p. 210-215.

BED MATERIAL COMMENTS:

No sieve information for bed material samples was available. The
low-water survey completed in July 1997 noted that the bottom was
composed of firm rock and gravel and was uneven. The bridge plans did
not contain lithologic logs but did contain some penetration values,
suggesting that there was no bed rock in the area.

DESCRIPTION FOR THIS BRIDGE:

This bridge is a single-span structure with 45 degree wing-walls both
upstream and downstream. The bridge opening is smaller than both the
upstream and downstream channel top widths. The wing walls extend out to
the width of the upstream and downstream channels. The bridge and wing
walls are aligned with the channel.

PIER SCOUR COMMENTS:

none

ABUTMENT SCOUR COMMENTS:

none

CONTRACTION SCOUR COMMENTS:

There was no apparent scour at the bridge, either abutment or
contraction scour, despite the contraction present at the bridge.
However, there was a scoured area about a channel width downstream from
the bridge. This could have been caused by the flow contracted through
the bridge opening, which may have reached a maximum contraction
downstream from the bridge. This however, was not the flow pattern
observed on 4-8-97. The configuration of this scour hole and the channel
upstream and downstream from the bridge was nearly identical on 4-8-97
and in July 1997.

The contraction scour reference surface was determined by computing the
average bottom elevation of the each cross section collected on 4-8-97.
The scour area was located between 55 and 70 ft downstream. Thus the
sections near the hole were not used in the average. The average
elevation was about 1114.7 ft MSL. The minimum average bottom elevation
of a cross section was 1113.2 ft MSL. Thus, the depth of scour was 1.5
ft. Due to the variability of streambed elevation the accuracy is only
about 1 ft, with the majority of the error attributed to determining the
reference surface. A thalweg profile also showed a scour 1.5 ft.

There was about 0.1 ft of fall through the bridge on 4-8-97.

Analysis of cross sections collected on 4-8-97

Location Avg. Bot. Elev. Bottom width Top width

US 113 1114.95 30 55

US 78 1114.75 24 56

US 52 1114.5 30 50

US 24 1114.26 29 37

US 15 1114.83 20 35

DS 15 1115.29 18 35

DS 55 1113.86 30 60

DS 70 1113.16 \-- 70

DS 115 1115.6 \-- 67

The typical bottom widths for the upstream and bridge opening are
reported as the uncontracted and contracted widths. The average velocity
in the contracted section is the average velocity in the bridge opening.
No other criteria are reported due to the unusual configuration of the
scour and the possibility that the scour hole could be a result of
something other than the bridge contraction.

HYDROGRAPH:

No gage nearby.

SUMMARY OF FILES:

SR4CR.xls -- Excel 97 workbook containing the following worksheets:

Summary -- Summary of basic site and scour data

Note: All ranges are from right to left. The LOC is the approximate
distance upstream from the centerline of the highway. All elevations are
in ft MSL.

VEL-4897 -- Discharge measurement notes from 4-8-97

VEL-71497 -- Discharge measurement notes from 7-14-97

US98-4897 -- Cross section 98 ft upstream from bridge collected on
4-8-97

US75-71497 -- Cross section 75 ft upstream from bridge collected on
7-14-97

US63-4897 -- Cross section 63 ft upstream from bridge collected on
4-8-97

US37-4897 -- Cross section 37 ft upstream from bridge collected on
4-8-97

US25-71497 -- Cross section 25 ft upstream from bridge collected on
7-14-97

US9-4897 -- Cross section collected 9 ft upstream from bridge collected
on 4-8-97

US0-4897 -- Cross section collected at the upstream edge of the bridge
on 4-8-97

US0-71497 -- Cross section collected at the u/s edge of the bridge on
7-14-97

USLW-4897 -- Section collected along the left wing wall from 10 ft under
the bridge to the upstream end of the wing wall, collected on 4-8-97

USRW-4897 -- Section collected along the right wing wall from 10 ft
under the bridge to the upstream end of the wing wall, collected on
4-8-97

DS0-4897 -- Cross section at the downstream edge of the bridge on 4-8-97

DS17-4897 -- Cross section 17 ft downstream from bridge collected on
4-8-97

DS23-71497 -- Cross secton 23 ft downstream from bridge collected on
7-14-97

DS40-4897 -- Cross section 40 ft downstream from bridge collected on
4-8-97

DS50-71497 -- Cross section 50 ft downstream from bridge collected on
7-14-97

DS55-4897 -- Cross section 55 ft downstream from bridge collected on
4-8-97

DS100-4897 -- Cross section 100 ft downstream from bridge collected on
4-8-97

DS100-71497 -- Cross section 100 ft d/s from bridge collected on 7-14-97

DS-4897.jpg -- Photo looking downstream taken on 4-8-97

DS-71497.jpg -- Photo looking downstream taken on 7-14-97

DS-BRG-4897.jpg -- Photo of the downstream side of the bridge taken on
4-8-97

US-4897.jpg -- Photo looking upstream taken on 4-8-97

US-71497.jpg -- Photo looking upstream taken on 7-14-97

US-BRG-4897 -- Photo looking at the upstream side of the bridge taken on
4-8-97

Brg_Plan_1.jpg -- Scan of the bridge plans showing old bridge and site
drawing

Brg_Plan_2.jpg -- Scan of bridge plans showing bridge dimensions

AERIAL.jpg -- Satellite image of the study site from TerraServer

Topo.jpg -- Scan of the USGS topographic map