CUE 3235 Flashcards
Difference between urban hydrology and rural hydrology?
Precipitation falls in greater amounts and in greater intensity in urban areas than in the surrounding rural areas.
Natural landscapes eg forests, wetlands, grasslands trap precipitation and allow it to infiltrate slowly into the ground, reducing surface runoff. In contrast, impermeable urban surfaces like roads, car parks and rooftops prevent precipitation from infiltrating; most of it remains above the surface where it runs off in unnaturally large amounts.
Why are urban and rural hydrology’s different?
Urban areas are designed to shed water quickly. Sloping roofs, smooth rounded gutters and cambered roads all contribute to the rapid movement of water away from the surface.
Water is then gathered in smooth storm sewers which act like a high density drainage system.
It gathers speed and erosional power as it travels underground. When the water leaves the storm drains and empties into streams, they fill rapidly.
What is the result of precipitation being unable to infiltrate the urban surfaces?
Groundwater and soilwater levels are reduced. Since this is the water that feeds streams during dry periods, base levels flows are reduced.
What’s an alternative to hard engineering for catchment in rural areas?
SUDS
What are SUDS?
SUDS is a relatively new approach to managing rainfall using natural processes in the landscape to reduce flooding, control flooding, and provide amenity for the community.
BIOSWALE is an example of a SUDS system: it is a rain garden is a sloped retention area designed to capture and convey water while allowing it to infiltrate the ground. Eg:
- LOCATION: rain gardens are usually located at the end of a roof gutter, as a buffer between the street and the lawn.
- SOIL AMENDMENTS: a good soil mixture is 50% sand, 30% compost, 20% topsoil.
- DEPTH: a typical rain garden is between 6 - 9 inches deep. This depth, proportionate to SA, helps to assure water will infiltrate quickly and not pond.
- PLANT CHOICES: plants are chosen based on their need for light, moisture and soil. Vary plant structure, height and flower colour for seasonal appeal and butterfly habitat. The use of native plants is encouraged.
- SIZE: a raingarden is typically 20% of the size of the impervious surface that generates runoff.
Other components of SUDS include:
- roof water is collected in butts for use in gardens
- Swales are located around the settlement. These will fill up during heavy rainfall and store the water downstream.
This water storage in the local landscape also provides an attractive place for wildlife.
- permeable block paving is used on paths and roads - this means water falling onto these surfaces is filtered and stored in the ground below before it enters the rest of the SUDS system.
Define SUDS.
A relatively new approach to managing rainfall by using natural processes in the landscape to reduce flooding, control flooding and provide amenity for the community.
Define hydrology.
The scientific study of the movement, distribution and quality of water on Earth, including the Earth cycle, water resources and environmental watershed sustainability.
Define storm hydrograph.
A graph of discharge of a river over the time period when the normal flow of a river is affected by a storm event.
Define discharge.
The amount of water in a river flowing past a particular point. Expressed in cumecs.
Define base flow.
This represents the normal day-to-day discharge of the river.
It is the consequence of slow moving soil throughflow and groundwater seeping into the river channel.
Define hard engineering.
These are river management strategies that involve the use of man made structures in order to prevent or control natural river processes from taking place.
Define soft engineering.
River management strategies which aim to work alongside natural river processes to manage flood risk.
They do not involve building artificial structures or trying to stop natural processes.
They aim to reduce and slow the movement of water into a river channel to help prevent flooding.
