Normal Flow vs Gradually-Varied Flow

In normal flow the down-slope component of weight balances bed friction. As a result, the
water depth h and velocity V are constant and the total-head line (or energy grade line) is
parallel to both the water surface and the channel bed; i.e. the friction slope Sf is the same as
the geometric slope S0.

As a result of disturbances due to hydraulic structures (weir, sluice, etc.) or changes to
channel width, slope or roughness the downslope component of weight may not locally
balance bed friction. As a result, the friction slope Sf and bed slope S0 will be different and
the water depth h and velocity V will change along the channel.
The gradually-varied-flow equation gives an expression for dh/dx and allows one to predict
the variation of water depth along the channel.

Types of Open channel flow

Steady Flow:

For open channel, the flow is steady if the depth of flow does not change with respect to time at a particular location or section.

Uniform flow:

For open channel flow, the flow is uniform if the depth of flow remains constant along a certain length of the channel.

Non Uniform flow:

For open channel flow, the flow is non uniform if the depth of flow does not remains constant along a certain length of the channel.

Gradually Varied flow:

If the depth of flow changes over a relatively long distance along the length of a channel, then the flow is called gradually varied flow.

Rapidly Varied flow:

If the depth of flow changes over a relatively short distance along the length of a channel, then the flow is called rapidly varied flow.

Modeling procedure for separate channel splits

 1. For a split flow optimization, first of all we need to estimate the initial supplies of the total flow in both separate channels. HEC-RAS will then uses these initial flow estimates to perform computation from downstream to upstream on both the channels.

2. From Steady Flow Analysis click on Options and select Flow Optimization and under the Flow Optimizations dialog box you need to select the check box for Junction.

3. When the junction tab is selected, perform the analysis by computing the water surface profiles for all the reaches.

4. Then compare the computed energy grade lines for the cross section just downstream of the junction.

5. If the energy in all the reached below the junction is not within a specified tolerance (0.02 feet). Then the flow going to each reach is re-distributed and the profiles are re-calculated.

6. The methodology continues until a balance is reached.