Hydrograph

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Stream hydrograph

Hidrograma

Raster hydrograph

Lag-1 hydrograph

Hydrograph is a graphical representation of the flow rate of water in a particular stream or channel at a specific point over a set period of time. Hydrographs are essential tools in hydrology and water resources management, providing critical information for the planning and design of water supply and flood control systems, as well as for understanding natural river dynamics and the impact of human activities on aquatic ecosystems.

Overview

A hydrograph plots the flow rate of water, typically in cubic meters per second (m³/s), against time. The shape of a hydrograph can reveal much about the temporal distribution of precipitation over the drainage basin and the basin's response to rainfall or snowmelt. Key features of a hydrograph include the rising limb, the peak flow, the falling limb, and the base flow or groundwater contribution.

Components

• Rising Limb: The portion of the hydrograph where the discharge begins to increase following a rain event.
• Peak Flow: The maximum flow rate following a precipitation event.
• Falling Limb: The part of the hydrograph where the flow rate starts to decrease, returning to base flow conditions.
• Base Flow: The portion of the streamflow that is not directly affected by precipitation events and is contributed by groundwater seepage into the river or stream.

Factors Influencing Hydrograph Shape

Several factors can influence the shape of a hydrograph, including:

• Rainfall Intensity and Duration: Intense and short-duration rainfall events tend to produce hydrographs with steep rising limbs and high peak flows.
• Catchment Size and Shape: Larger and more elongated catchments tend to have longer lag times and more prolonged peak flows.
• Soil Type and Land Use: Permeable soils and areas with significant vegetation cover can absorb more water, reducing runoff and peak flows.
• Urbanization: Urban areas with impervious surfaces like roads and buildings generate more runoff, leading to higher and quicker peak flows.

Types of Hydrographs

• Direct Runoff Hydrograph (DRH): Represents the portion of the hydrograph that is directly attributable to a precipitation event, excluding base flow.
• Unit Hydrograph: A theoretical hydrograph that represents the runoff response of a catchment to a unit of rainfall (e.g., one inch) over a specified duration.
• Synthetic Hydrograph: Constructed using empirical formulas and catchment characteristics, used when observed data is not available.

Applications

Hydrographs are used in various applications, including:

• Flood Forecasting and Management: By analyzing hydrographs, engineers and hydrologists can predict the timing and magnitude of floods, aiding in the design of flood defenses and evacuation plans.
• Design of Hydraulic Structures: Hydrographs are used to design structures such as dams, levees, and stormwater management systems to ensure they can handle peak flows.
• Water Resources Planning: Understanding the flow regime of rivers and streams helps in the allocation of water for irrigation, drinking water supply, and environmental conservation.

Challenges

Interpreting hydrographs and predicting hydrological responses require understanding the complex interplay of meteorological, hydrological, and land use factors. Changes in climate and land use can significantly alter hydrograph characteristics, making the management of water resources more challenging.