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STABILITY AND TAILWATER CALCULATIONS

FOR GRADE STABILIZATION STRUCTURES

Details about the Structure: Project:

Inlet Elevation: ft Structure Hydrology: Assisted by:

Proposed Outlet Elevation: ft Q25: cfs Date: 6/9/2014

Lowest Channel Elevation: ft Q50: cfs

Structure Design Flow: cfs

Structure Entrance Head: ft

Stability Check:

Stability will be checked at the conditions on the Calculation page. Make sure that the flow, depth and velocity

represents a "worst case" condition that would be experienced for downcutting of the channel. The channel-full

condition is the most conservative. Select a less conservative condition only when you have determined that

the channel full condition will rarely if ever be experienced.

Existing Channel Slope: 0.000000 ft/ft = 0.000 %

Channel Flow Depth: (channel full)Channel Flow:

Channel Velocity: for stability checking

Allowable Channel Velocity: ft/sec (from EFH Table 14-3)

Visual Observations of Stability: (evidence such as well-vegetated banks, no downcutting, etc)

Distance downstream of structure site that was visually inspected: ft.

Stable Outlet Elevation Prediction: (To be used when the channel will DEGRADE)

Stable Downstream Point: Elevation, ftDistance from Structure, ft

Predicted Stable Structure Outlet Elevation: 0.0 ft or lower

Make sure the outlet is AS LOW or LOWER than the lowest part of the cross section where the structure joins the channel.

If the outlet channel is a drainage ditch, consider submerging the structure outlet to prevent undermining during cleanout.

Tailwater Check:

Tailwater must be at least: 2.0 ft (2 ft. or the entrance head during the design storm, whichever is less)

RECALCULATE

Flow to check tailwater: 0 cfs structure design flow

Channel depth at tailwater flow:

Tailwater will flood the structure entrance apron during desig

Consider an island structure design.

NOCFwin - version 1.08 (Rev. 1/10)

Side Inlet (to a main channel or ditch)


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Date Version

Aug-02 1.00

Aug-02 1.01

Sep-02 1.02

Oct-02 1.03

Oct-02 1.04

Apr-05 1.05

Aug-05 1.06

Jan-06 1.07

Jan-10 1.08


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Programming Notes

Created program using DOS-based NOCF as a reference. This program uses Manning's equation to

determine channel capacity and flow depth using survey data as inputs.

R.Book Champaign, Illinois

Display all rod readings and calculated results to the nearest 0.1, not 0.01.Add comma separator for thousands if answers are large.

Display natural ground with a thicker line on plot for visibility.

Change "Offset Distance" to "Distance" for clarity.

Added "assuming uniform, steady flow" as a caption to the equation box.

Restricted flow depth entry so that it can't exceed the maximum depth.

Limited entry of slope to 0.5 (50%) and rod readings to 30 ft.

Changed display of "maximum flow depth" to display selected depth but default to max. if none specified

Corrected data validation checking procedure.

Added box at the bottom of the Calculation page for user-entered notes

Changed display of horizontal distances in the survey data to allow tenths of a foot, and velocity in

hundredths of a ft/sec.

Corrected the "Clear Cells" macro to include all user-input cells.

Added functionality to work in Elevations as well as Grade Rod

Added "Replot" button & macro for custom plotting according to choice of data type

Added "Stability & Tailwater" page with associated calculations

Clarified "Stability & Tailwater" calculation procedure:

added inputs for structure details such as inlet and outlet elevations, hydrology, side inlet

modified tailwater check in a side inlet situation to account for some additional channel flow

added discussion of channel conditions for checking stability

added description of stable downstream point to alert the designer to the importance of proper selection

added visual observation notes section to describe channel stability

added warning note on predicted stable outlet elevation to make sure outlet is low enough for ditch

cleanout and channel thalweg migration

added alert for user to recalculate tailwater if inputs have changed

added warning note to alert user when structure inlet is submerged during design storm.

Added conditional formatting on proposed structure outlet when higher than the low in the channel

Corrected tailwater calculations for situations where design flow exceeds channel capacity

Changed submergence calculation to use low in channel rather than predicted stable elevation

Corrected stability calculation to refer to hydraulic radius from Calculation page rather than result_R

Blanked out "Channel is Stable" note when no entries have been made

Adjusted plot routine to accommodate Excel 2007 security

Documents

Natural Open Channel Flow