What is a flashy hydrograph?
A hydrograph is a graph of the flow in a stream over a period of time. Reading horizontally to the left, you can determine the discharge of the stream for that date. “Flashy” To say that a hydrograph is flashy means that the graph depicts sharp vertical jumps and equally steep vertical declines.
What factors create a flashy hydrograph?
Interacting factors affecting the shape of two different storm hydrographs
| Factor | ‘flashy’ river |
|---|---|
| Shape | Circular basins have shorter lag times |
| Drainage density | High drainage density means more streams and rivers per unit area, so water will move more quickly to the measuring point. |
Why are urban hydrographs flashy?
The Urban Hydrograph A Hydrograph is a graph which shows the discharge of a river, related to rainfall, over a period of time. As a result of the changes to urban drainage basins, urban hydrographs tend to be flashy, where rivers are more likely to flood due to lower interception and infiltration rates.
What are the two types of hydrograph?
Types of hydrographs include: Storm hydrographs. Flood hydrographs. Annual hydrographs a.k.a. regimes.
What are hydrographs used for?
In its simplest form, a hydrograph is a graphical representation of runoff rate against time (Figure 1). It shows the time distribution of runoff at the point of measurement or computation, reflecting the complex characteristics of the watershed by a single curve.
Why do hydrographs differ?
Hydrographs can take different shapes dependent upon the characteristics of the drainage basin. The various flows and stores of the drainage basin are affected by these characteristics, and these in turn will affect the shape of the hydrograph and the volume of water in a river.
What factors affect hydrographs?
Physical factors affecting flood hydrograph dynamics
- Shape. A circular shaped drainage basin leads to rapid drainage whereas a long drainage basin will take time for the water to reach the river.
- Topography & relief.
- Heavy Storms.
- Lengthy rainfall.
- Snowfall.
- Vegetation.
- Rock type.
What can hydrographs be used for?
Basically, a hydrograph shows you the ways in which a river is affected by a storm. This helps us to understand discharge patterns of a particular drainage basin and helps to predict flooding and plan flood prevention measures. As you can see in the graph below, the peak rainfall is the time of highest rainfall.
How does vegetation affect hydrographs?
Vegetation intercepts precipitation and slows the movement of water into river channels. This increases lag time. The amount precipitation can have an affect on the storm hydrograph. Heavy storms result in more water entering the drainage basin which results in a higher discharge.
How does soil type affect hydrographs?
Soil type – clay soils do not drain easily and become saturated very quickly. This results in rapid overland flow and shorter lag times. Dry soils slow down water transfer leading to longer lag times. Slope – steep slopes lead to rapid water transfer and shorter lag times.