On a hydrograph, isolated storm is represented as
single peak
Understanding Hydrographs for Isolated Storms
A hydrograph is a graphical representation showing the flow rate (discharge) of a river or stream over a period of time. It helps us understand how rainfall events affect the flow in a river basin.
What is an Isolated Storm?
An isolated storm refers to a single, distinct rainfall event that occurs over a drainage basin with sufficient time before and after it for the resulting runoff to rise and fall back towards the base flow condition.
Representing Isolated Storms on a Hydrograph
When an isolated storm occurs over a basin, the rainfall generates surface runoff. This runoff travels through the basin, eventually reaching the river channels and increasing the flow. Initially, the flow rises from the base flow condition as the runoff reaches the gauging station. This rising limb culminates in the peak flow, which is the maximum discharge recorded during the event. After the rainfall stops and the runoff contribution decreases, the flow gradually declines back towards the base flow. This declining part is known as the recession limb.
For a single, isolated storm event, this process typically results in a hydrograph with a single prominent rise to a peak flow followed by a recession. Therefore, an isolated storm is represented as a single peak on a hydrograph.
| Storm Type | Typical Hydrograph Representation |
|---|---|
| Isolated Storm | Single peak |
| Multiple Storms in Close Succession | Multiple peaks or a complex shape |
| Continuous Rainfall (for S-curve) | Cumulative flow reaching equilibrium |
Analyzing the Options
- s-curve: An S-curve hydrograph represents the response of a basin to a continuous effective rainfall of constant intensity. It is used in the development of unit hydrographs, not for representing a single isolated storm event directly.
- complex peak: A complex peak or hydrograph with multiple peaks usually indicates that the basin response is due to multiple rainfall events occurring in close succession, or it might reflect complex characteristics of the drainage basin itself.
- multi peaks: Similar to complex peak, this describes a hydrograph showing more than one peak flow, typically resulting from separate rainfall bursts or events within a short period.
- single peak: This is characteristic of the hydrograph resulting from a single, isolated rainfall event, showing a distinct rise to one maximum flow and subsequent recession.
Based on the nature of an isolated storm and how a basin responds to a single input of rainfall, the resulting hydrograph will display a single peak.
Revision Table: Hydrograph Basics
| Term | Definition |
|---|---|
| Hydrograph | Plot of discharge vs. time at a point on a river. |
| Isolated Storm | A single, distinct rainfall event. |
| Rising Limb | The part of the hydrograph showing increasing discharge. |
| Peak Flow | The maximum discharge on the hydrograph. |
| Recession Limb | The part of the hydrograph showing decreasing discharge. |
| Base Flow | The groundwater contribution to river flow. |
Additional Information: Factors Affecting Hydrograph Shape
While an isolated storm typically produces a single-peak hydrograph, the exact shape and timing of the peak can be influenced by several factors, including:
- Rainfall characteristics: Intensity, duration, and spatial distribution of the rainfall.
- Basin characteristics: Size, shape, slope, drainage density, and storage capacity of the basin.
- Antecedent conditions: Soil moisture content before the storm.
- Land use: Urbanization, vegetation cover, etc.
These factors can affect the time it takes for runoff to reach the river (lag time), the speed of the flow, and the amount of storage within the basin, all of which modify the shape of the resulting single-peak hydrograph.
Important Questions from Hydrograph
The use of unit hydrographs for estimating floods is generally limited to catchments of size less than?
What are the lower and upper limits of catchment area for applicability of the use of unit-hydrograph?
Select the correct option with regard to the following two statements (H1 and H2) pertaining to the hydrograph of a storm in a catchment.
H1: The rising limb of the hydrograph depends on the catchment characteristics only.
H2: The recession limb of the hydrograph depends on the storm characteristics and catchment characteristics.
Basin lag in hydrology is the time difference between the ______.
Isolated storm is represented in a hydrograph with
