A rectangular concrete channel (n = 0.015) is 10.5 ft wide, has a slope of 0.006, and a discharge rate of 200 cfs. Compute the normal depth and critical depth. If the depth of flow is 5.7 ft, is the flow subcritical or supercritical? What is the type of profile?

Structural Analysis
6th Edition
ISBN:9781337630931
Author:KASSIMALI, Aslam.
Publisher:KASSIMALI, Aslam.
Chapter2: Loads On Structures
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### Problem Statement: Hydraulics in Rectangular Channels

**Channel Characteristics:**
- **Type:** Rectangular concrete channel
- **Width:** 10.5 feet
- **Slope:** 0.006
- **Discharge Rate:** 200 cubic feet per second (cfs)
- **Manning's Roughness Coefficient (n):** 0.015

**Tasks:**
1. **Compute the Normal Depth**:
   - Use the Manning's equation for open channel flow to determine the normal depth.
   
2. **Compute the Critical Depth**:
   - Use the appropriate formula to find the critical depth for the rectangular channel.

3. **Determine the Flow Condition**:
   - Given the depth of flow is 5.7 feet, evaluate if the flow is subcritical or supercritical by comparing it with the critical depth.

4. **Identify the Flow Profile Type**:
   - Based on the flow depth and the critical depth, determine the type of flow profile in the channel.

### Explanation of Concepts

**Normal Depth (y_n):**
- The depth of flow in a channel where the flow is uniform and steady. It's calculated using Manning's equation:
\[ Q = \frac{1}{n} A R^{2/3} S^{1/2} \]
  Where:
  - \( Q \) is the discharge (200 cfs),
  - \( n \) is the Manning's roughness coefficient (0.015),
  - \( A \) is the cross-sectional area of flow,
  - \( R \) is the hydraulic radius,
  - \( S \) is the slope of the channel (0.006).

**Critical Depth (y_c):**
- The depth of flow where the specific energy is at a minimum for a given discharge. It's calculated using:
\[ Q^2 = g A^3 / B \]
  Where:
  - \( g \) is the gravitational acceleration (32.2 ft/s²),
  - \( A \) is the cross-sectional area,
  - \( B \) is the top width of the flow.

**Flow Conditions:**
- **Subcritical Flow:** Occurs when the flow depth is greater than the critical depth (\( y > y_c \)).
- **Supercritical Flow:** Occurs when the flow depth is less than the critical depth (\( y < y_c \)).

**Flow Profile Types:**
Transcribed Image Text:### Problem Statement: Hydraulics in Rectangular Channels **Channel Characteristics:** - **Type:** Rectangular concrete channel - **Width:** 10.5 feet - **Slope:** 0.006 - **Discharge Rate:** 200 cubic feet per second (cfs) - **Manning's Roughness Coefficient (n):** 0.015 **Tasks:** 1. **Compute the Normal Depth**: - Use the Manning's equation for open channel flow to determine the normal depth. 2. **Compute the Critical Depth**: - Use the appropriate formula to find the critical depth for the rectangular channel. 3. **Determine the Flow Condition**: - Given the depth of flow is 5.7 feet, evaluate if the flow is subcritical or supercritical by comparing it with the critical depth. 4. **Identify the Flow Profile Type**: - Based on the flow depth and the critical depth, determine the type of flow profile in the channel. ### Explanation of Concepts **Normal Depth (y_n):** - The depth of flow in a channel where the flow is uniform and steady. It's calculated using Manning's equation: \[ Q = \frac{1}{n} A R^{2/3} S^{1/2} \] Where: - \( Q \) is the discharge (200 cfs), - \( n \) is the Manning's roughness coefficient (0.015), - \( A \) is the cross-sectional area of flow, - \( R \) is the hydraulic radius, - \( S \) is the slope of the channel (0.006). **Critical Depth (y_c):** - The depth of flow where the specific energy is at a minimum for a given discharge. It's calculated using: \[ Q^2 = g A^3 / B \] Where: - \( g \) is the gravitational acceleration (32.2 ft/s²), - \( A \) is the cross-sectional area, - \( B \) is the top width of the flow. **Flow Conditions:** - **Subcritical Flow:** Occurs when the flow depth is greater than the critical depth (\( y > y_c \)). - **Supercritical Flow:** Occurs when the flow depth is less than the critical depth (\( y < y_c \)). **Flow Profile Types:**
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