Catchment Hydrology Introduction
36 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the purpose of a 'fully developed catchment'?

A fully developed catchment refers to the design of a drainage system that caters for flows discharged from a fully developed area.

The Rational Method is considered appropriate for the determination of peak design discharge for urban catchments exceeding 500 hectares.

False

Why is it essential to consider the 'sustainability' of existing surface storages when incorporated in drainage design?

The longevity (sustainability) of these surface storages must be ensured through appropriate measures like containment within easements or reserves to prevent potential issues like flood storage system failures.

What are the key factors to consider when choosing a hydrological method for a project?

<p>The chosen method should be suitable for the catchment conditions, meet the required accuracy level, and be capable of assessing critical changes in the specific condition being evaluated.</p> Signup and view all the answers

What considerations should be made when utilizing the Rational Method within complex catchments?

<p>The Rational Method may not be appropriate when dealing with areas of significant urban development.</p> Signup and view all the answers

What is the primary purpose of a runoff-routing model?

<p>Runoff-routing models are essential tools for analyzing and designing urban drainage systems, particularly in complex situations.</p> Signup and view all the answers

The 'critical storm duration' term is interchangeable with the 'time of concentration' when using the rational method.

<p>False</p> Signup and view all the answers

What factors contribute to difficulties in estimating future drainage conditions for a catchment?

<p>Assessing potential future conditions can be difficult especially when such conditions may be outside of the designer's direct control and knowledge.</p> Signup and view all the answers

What is the primary intent of choosing a hydrological method for a project?

<p>The intent is to select a method that is appropriate for the catchment conditions and provides the desired level of accuracy for the intended purpose of the project.</p> Signup and view all the answers

When undertaking a hydrologic analysis of a drainage catchment for the purpose of designing a drainage system, what is the 'intent'?

<p>All of the above.</p> Signup and view all the answers

The drainage designer must not assume, without appropriate investigation, that upstream inflows will not be altered from pre-development conditions once the catchment is fully developed.

<p>True</p> Signup and view all the answers

Which of the following is NOT a circumstance where the use of the Rational Method is NOT appropriate?

<p>Urban catchments with an area greater than 500 hectares.</p> Signup and view all the answers

The Rational Method is a simple hydrologic method with a high degree of accuracy compared to numerical runoff-routing models.

<p>False</p> Signup and view all the answers

In what circumstances is the use of computer-based, runoff-routing, numerical models preferred?

<p>All of the above</p> Signup and view all the answers

What is the recommended minimum time of concentration for the design of urban drainage systems (excluding roof water drainage)?

<p>5 minutes</p> Signup and view all the answers

Which of the following components is typically included in the total travel time for a small, non-piped catchment with no formal creek?

<p>Standard inlet time</p> Signup and view all the answers

The time of concentration (tc) is the same as the 'critical storm duration' or 'time to peak' as determined from runoff-routing models.

<p>False</p> Signup and view all the answers

What is the primary purpose of a 'standard inlet time'?

<p>To represent the travel time from the top of the catchment to a location where the first gully or field inlet would normally be expected to exist.</p> Signup and view all the answers

What is the recommended standard inlet time for urban residential areas where the average slope of land at the top of the catchment is greater than 10% and up to 15%?

<p>8 minutes</p> Signup and view all the answers

In cases where the use of a standard inlet time is considered appropriate, the following roof to drainage system flow travel times are recommended.

<p>False</p> Signup and view all the answers

Which of the following is NOT a scenario where overland flow travel times are used?

<p>The catchment is predominantly piped or channelized.</p> Signup and view all the answers

What does the 'n' variable represent in Friend's equation for calculating overland sheet flow time?

<p>Horton's surface roughness factor.</p> Signup and view all the answers

What is the formula for calculating kerb flow time using Manning's equation?

<p>t = 0.025 * L/S^.5 (minutes)</p> Signup and view all the answers

The 'Stream Velocity Method' uses the actual average stream velocity to determine the 'time of concentration'.

<p>False</p> Signup and view all the answers

The 'partial area effect' is a phenomenon that occurs when a shorter storm acting on a smaller section of the catchment results in a greater peak discharge compared to a longer storm acting on the whole catchment area.

<p>True</p> Signup and view all the answers

Which of the following is NOT a characteristic of a catchment that would warrant checking for a potential 'partial area effect' during hydrologic analysis?

<p>An elongated pipe system extending further upstream.</p> Signup and view all the answers

What type of data is required as input to the hydrologic model used for design?

<p>Intensity-frequency-duration (IFD) data</p> Signup and view all the answers

Which of the following is NOT a purpose for which runoff volume estimation is used in stormwater design?

<p>Determining the optimal type and size of pipes for a drainage channel.</p> Signup and view all the answers

The average annual runoff volume can be determined using which of the following methods?

<p>Both A and B</p> Signup and view all the answers

The volumetric runoff coefficient (Cv) is the same as the Rational Method coefficient of discharge (C).

<p>False</p> Signup and view all the answers

The 'single event volumetric runoff coefficient' is used to estimate the volume of runoff from a single storm event, while the 'average annual runoff volume' represents the average annual runoff generated from all storms in a year.

<p>True</p> Signup and view all the answers

When using the coefficients presented in Table 4.9.1, which adjustments must be applied?

<p>Both A and B</p> Signup and view all the answers

What is the formula used to adjust the runoff coefficients for urbanized catchments?

<p>Cv (composite) = Cv (pervious) * (A - A(imp.)) + A(imp.)</p> Signup and view all the answers

The Ksat value represents an initial loss rate for a particular soil type.

<p>False</p> Signup and view all the answers

What is the recommended volumetric runoff coefficient for compacted soils in temporary construction site sediment basins?

<p>1.0</p> Signup and view all the answers

What is the primary purpose of the 'Stream Velocity Method'?

<p>To compensate for flow attenuation effects caused by floodplain storage when using the Rational Method</p> Signup and view all the answers

Study Notes

Catchment Hydrology Introduction

  • Hydrologic analysis of drainage catchments is crucial for drainage system design.
  • The goal is to select appropriate hydrologic methods for a given catchment.
  • Considering catchment conditions is important when selecting and using key variables.
  • The design discharge should protect assets over the entire working life of the system.
  • Future drainage conditions of an upstream catchment should be considered, but are often uncertain.
  • Local government planning schemes and infrastructure plans often define future catchment conditions.

Design Discharge Considerations

  • Minimum fill or floor levels frequently require consideration of the worst-case scenario.
  • Best practice involves designing for 'fully developed' catchment conditions, unless a planning scheme or code specifies otherwise.
  • Considerations for flow attenuation systems (e.g., detention, WSUD) must be included if required by the planning scheme.

Choice of Hydrologic Method

  • The chosen method should be appropriate for the catchment conditions and desired accuracy.
  • The method should be suitable for evaluating changes in catchment conditions due to development.
  • The method should be reviewable by regulators or nominated third parties (if necessary).

Rational Method

  • The Rational Method is suitable for smaller urban and rural catchments (under 500 hectares and 25 km² respectively) with no significant stormwater storage.
  • Used for estimating peak discharges with simpler conditions.
  • Not applicable for urban catchments larger than 500 hectares, for determining flood levels for new development, for components with volume-based impacts (like detention basins), and for unusually shaped or complex catchments.

Runoff-Routing Models

  • Computer-based models are more suitable for complex catchments (over 500 hectares, with detention basins, and areas with diverse soil types).
  • A review of Australian Rainfall and Runoff guidelines on numerical models is recommended.

Regional Flood Frequency Analysis

  • Regional flood frequency analysis should be used in place of other methods for smaller rural catchments for more reliable discharge estimations.
  • This method is suitable for small to medium-sized rural catchments (8-1000 km²) with less than 10% urban area.

Catchment Area

  • Accurate assessment of catchment area is necessary.
  • The area should reflect historical, existing or future conditions.
  • Consider potential extensions to catchment limits due to development, roads, or flow diversion systems.

Coefficient of Discharge (C)

  • C should account for future development and local authority policies on detention and flow control.
  • Use table 4.5.1 to determine Fraction Impervious (fi) for the catchment in question.
  • Use tables 4.5.3 and 4.5.4 to determine the design discharge coefficient (C10.) for the 10-year return period event.
  • Adjust the basic discharge coefficient value (C10) with a frequency factor from Table 4.5.2 to achieve a design storm coefficient (Cy) for the desired return period.

Time of Concentration (tc)

  • tc is a critical parameter in the Rational Method.
  • Represents the time it takes for runoff from the furthest point of a catchment to reach a specific point.
  • It depends on various factors, including the travel time along overland flow paths, concentrated flow paths, piped/channeled flow paths, and, if applicable, creek flow paths.
  • Refer to the relevant tables to determine the typical time of concentration for specific types of catchments.
  • Standard inlet times and flow times from points like roofs and pipes, should be used if they are available.
  • Initial estimates can be taken using the flow charts provided.
  • A suitable runoff-routing model should be used if the catchment has unusual runoff characteristics.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

2017 Queensland Urban Drainage Manual - Hydrology Chapter 4 PDF

Description

This quiz covers key concepts in catchment hydrology, focusing on hydrologic analysis and design discharge considerations essential for drainage system planning. It emphasizes the importance of selecting appropriate hydrologic methods based on future catchment conditions and local government planning. Understanding these principles is crucial for effective drainage system design.

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser