A crest-stage network has been installed in cooperation with the Missouri Department of Transportation to cost effectively provide data for smaller drainage basins (less than 100 square miles) in Missouri.
Benefits of such a network are as follows:
Advance definition and research of hydrologic-similar regions throughout the state.
Essential in developing robust regression equations for smaller basins.
Beneficial in the assessment of scour-critical bridges.
| Objective | |||||
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| The objective of the 10-year effort is to define the hydrologic characteristics of smaller drainage basins and to aid in the evaluation and design of bridge structures. The study data base is essential for research projects involving flow characteristics and simulations of streams at or near roadway crossings. Current progress may be viewed within the current annual data report. Discharge at Partial-Record Stations (PDF File 408 KB) or the Entire Annual Data Report—Water Year 2002 | |||||
| Approach | |||||
| The following steps will be taken to accomplish the objective of the study: | |||||
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Determine drainage area range and spatial distribution of gage sites. | ||
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Install 38 gaging stations (PDF File) and collect pertinent information at each site to develop preliminary rating. | CSG at North Carolina Creek near Marshfield, Missouri. Photo courtesy of Paul Rydlund. |
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Operate and maintain equipment at fixed intervals. | |
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Make discharge measurements to verify the preliminary rating and to determine the annual peak discharge at each site. | |
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| Crest-Stage Gage | |||||
| Typical gages consist of a 2-inch galvanized pipe containing a wood staff held in a fixed position with relation to a datum reference.The bottom cap has six intake holes positioned to minimize nonhydrostatic drawdown or superelevation inside the pipe. Tests have concluded this arrangement of intake holes to be effective with velocities up to 10 ft/sec and at angels no greater than 30 degrees. The bottom cap contains regranulated cork. As the water rises inside the pipe, the cork floats on the water surface. When the water begins to recede, the cork adheres to the staff inside the pipe, thereby retaining the crest stage of the flood. |  |
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Crest-Stage Gage Diagram
Installations at Selected Sites
Agee Creek near Savannah
Big Muddy Creek near Bethany
Upper Peavine Creek near Belle
Selvage Hollow near Lebanon
Indirect Measurement and Supplemental Installation of Monuments
The storm hydrographs (flow rate as a function of time) associated with the 38 crest-stage gage sites occurs much faster than other streams with larger drainage areas. The narrow "window of opportunity" makes direct streamflow measurement at many crest-stage gage sites difficult. To compensate for the lack of direct measurements of streamflow, indirect measurements involving step-backwater, slope-area, contracted opening and slope conveyance (normal depth) computations using 1-D models such as WSPRO or HEC-RAS are applied to peak stages acquired by the crest-stage gage. To indirectly measure flow rate at a stream location, it is necessary to establish the hydraulic slope (slope of the water surface) of the peak stage. The slope must be established no less than the distance between a location approximately one bridge length upstream of the gage to a location approximately one bridge length downstream of the gage. Typically, the hydraulic slope of a peak event may be established by high water marks in the form of drift or seed lines.
Monuments are typically defined as objects that mark a property line or the like. In this case, monuments are essentially smaller crest-stage gages installed upstream and downstream of the pre-existing gage at the bridge. The monuments are typically bracketed to trees and are surveyed to identify the index (gage datum) and associated floodplain and channel transect. The monuments are installed partially within and partially above the channel banks. As such, the CSG monument can provide an accurate reading of water-surface for within-channel flow events (channel control flow regime), where flow velocities typically prohibit the establishment of well-defined high-water marks, as well as events with out-of-bank flow (floodplain control flow regime).
During the installation of each monument, a survey of associated channel and floodplain transects, bridge detail and road embankment is completed. This is a tremendous benefit at more remote locations where it may take up to a day to arrive at a site. When a site visit is conducted, marks are collected at all (3) gage locations (downstream, bridge, and upstream) and submitted for an indirect analysis.
It is rare that a subsequent survey is needed to define channel bed change. Often channel bed scouring or aggradation resulting from peak events effects flows within the sectional control flow regime and is often submerged for peak measurements (within channel or floodplain control flow regimes). The primary objective of this study is to determine the annual maximum peak discharge which is only concerned with a clearly defined rating (discharge vs. stage) at higher flows.
Installation of Monuments at Selected Sites
Big Muddy Creek near Bethany
Little Tarkio Creek near Tarkio
Smokey Creek near Linneus
Special Case-Dry Crane Creek Near Crane
Occasionally, gages may reflect a "dry" basin. In the case
of Dry Crane Creek near Crane, a Special-Area-Land-Treatment (SALT) project
was introduced in 1995 by the Missouri Department of Natural Resources, Soil
and Water Conservation Program, Stone County District, to mitigate soil
erosion and protect and enhance the riparian corridor of Dry Crane Creek. As
a result, the project has affected the rainfall-runoff hydrograph for this
basin by providing considerable storage in the upstream end of the basin. Dry
Crane Creek has had minimal flows since the beginning of this 10-year effort.
As a result, a small network of supplemental monuments has been introduced
at this site to adapt to lower flows. Four monuments have been placed upstream
from the gage (at the bridge) where the channel was identified as straight, uniform,
and slightly contracting downstream. In addition, transects have been surveyed
at each monument. The monuments will represent a study reach necessary to obtain
indirect measurements. In the rare event of a substantial peak, it is assumed
the channel-bed survey will have to be redefined at each monument considering
the majority of flows may be concentrated on the lower end of the rating curve.
Monuments - 2,3,4
Monuments - 1
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Updated: February 27, 2004
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