October 10, 1963
SURFACE WATER BRANCH MEMORANDUM NO. 64.18
To: District Engineers and Staff Officials (SW)
From: Chief, Surface Water Branch
Subject: Review of indirect measurements and bridge-site reports
A meeting of the Branch Area Chiefs, hydraulics specialists, and other staff officials was held recently in St. Louis to discuss changes in operation procedures required by the recent reorganization of the Surface Water staff. Decisions made at this meeting regarding the review of indirect measurements of flood flow and bridge-site reports are given in this memorandum.
Standard procedures for making indirect measurements of peak flood flow have been developed during the past ten years. During this period of development all indirect measurements have been review by the flood specialists. This review assured the application of the proper methods and techniques and provided training for district personnel in this important area of our work. However, because of the increased number of engineers who have now had experience in making indirect measurement and because the methods have been largely standardized, the review of all measurements by a specialist outside the district is not longer desirable. The following review procedure will be used in the future.
A copy of all bridge-site reports prepared in the districts will be sent to the appropriate Branch Area Chief. The services of the hydraulic specialist may be utilized as needed in hydraulic analysis or in training district personnel where a new program of this type is initiated.
Although representing the Hydraulics Section in most of his technical activities, the hydraulics specialist is under the administrative direction of the Branch Area Chief.
Melvin R. Williams
A, B, S-2, FO-2, SL
Sample Indirect Measurement Summary
11-5180.5 East Fork Kalihi River at Callahan, California
Kamath River Basin
Par 11 1963 Regular Station
or Crest-gage station
or Miscellaneous Site
Flood of February 12, 1963
Type of Measurement: Contracted opening, Type IV; or Flow through Culvert Type III; or 3-section Slope-Area; or Flow over dam; etc.
Location of Site: Give location with respect to the gaging station or if a miscellaneous site, give lat., long., land line location, distance from nearest tributary and nearest community.
Survey of site: List the following information:
Example: Site was selected on February 14, 1963 by S.H. Hoffard. Highwater profiles were surveyed February 17 by R. Chinn, B.R. Davies and R.H. Hansen. X-Sections were run on February 18 by R. Chinn and B.R. Davies. Gage datum + 10 feet was used and survey was referenced to RM2 and RM3 at the station. Instrument was checked by two-peg test on February 7, 1963.
Discharge and gage height: 93,400 cfs; Recorded peak gage height 17.93 feet; HWM in well 17.98 feet; and 18.35 feet from well defined highwater profile past gage (Note this paragraph MUST give both inside and outside gage heights and how they were obtained.)
Drainage area: Give Drainage area at measurement site and at gage site, and if pertinent, how discharge was adjusted to gage site.
Unit discharge: (Discharge in cfs divided by drainage area).
Nature of flood: Very brief description of the storm that caused the flood rainfall (etc.) and any other pertinent remarks.
Field conditions: Describe the reach (dam, culvert, embankment, etc.) with particular emphasis on composition of the bed material, banks, trees, vegetation, overflow. Describe in detail any evidence of scour or fill. Give a general description of the type and quality of highwater marks. List n values. Were x-sections subdivided, and if so on what basis? State specifically whether x-sections were located after the highwater profiles were plotted. State how many pictures were taken and type.
For dams describe conditions of the dam crest at the time of the peak (debris, flashboards, gage settings). Also how much water was bypassing the main spillway through power releases, fishways, irrigation diversion, water supply, etc.
For culverts give n value used, and reason (size of corrugations, condition of concrete, etc.), presence of debris or fill, entrance conditions and other pertinent facts.
For contracted openings describe approach section, contracted section, n values, scour, debris, skew, type of opening, submergence.
B Culverts and contracted openings
C Dams, embankments and critical depth.
Describe the dam (or embankment or critical depth section) in detail and state specifically how the discharge coefficient was obtained (Circular 397; USBR Bul No. 3; Kings Handbook, etc.). State what the static head is and the velocity head. Give the percent of submergence. Discuss other factors that affect the computations.
Example: The dam is broad-crested, rock-crib, timber sheathed structure. The crest is 10 feet wide and is horizontal. The upstream face is on a slope of 1 ½ to 1 and the downstream face is on a 2 to 1 slope. The average static-head of 11.53 feet was determined 35 feet upstream, from well-defined highwater profiles along both banks. The velocity head is only 0.34 feet. Tailwater elevation was poorly defined but still good enough to prove that there was no submergence. Base coefficient of 3.63 was determined from Figures 10 and 11 in Circular 397 and then raised to 3.74 because of the 6 radius of rounding of the upstream edge. Froude number in the approach section is 0.43.
Evaluation: Briefly review the conditions affecting accuracy and rate the measurement.
Example: Use 86,400 cfs and consider it a good reliability. Profiles are well defined, reach is slightly contracting, there is little evidence of excessive scour or fill and the results from the two subreaches agree within 8%.
Previous computations: List previous indirects by date of peak, type, and evaluation.
Date of Peak
Type of Measurement
|December 21, 1953||Slope-area||Poor|
|February 14, 1959||Contracted opening||Fair|
Remarks: Discuss how well the indirect looks on the rating and anything else that may be pertinent.
Signature (Part of sample)