A hydrograph is a graphical representation of the flow rate of a river or stream over time. There are several factors that can affect the shape and characteristics of a hydrograph, including precipitation, infiltration, evapotranspiration, channel geometry, and land use.
Precipitation is a major factor that can affect the flow rate of a river or stream. When it rains, the water from the precipitation can either infiltrate into the ground or run off into nearby waterways. If the ground is saturated with water, or if the soil has a low infiltration rate, then more of the precipitation will run off into the river or stream, causing the flow rate to increase. Conversely, if the soil has a high infiltration rate, then more of the precipitation will be absorbed into the ground, causing the flow rate to decrease.
Infiltration is the process by which water seeps into the ground. The rate of infiltration is influenced by factors such as the type and structure of the soil, the slope of the land, and the presence of vegetation. Soils with a high clay content or that are compacted tend to have a low infiltration rate, while looser, more porous soils have a higher infiltration rate. Similarly, slopes that are steep or have a hard, impermeable surface will have a lower infiltration rate than gentler slopes or those with a porous surface. Vegetation, particularly grass and other shallow-rooted plants, can help to increase the infiltration rate by intercepting and slowing down runoff, allowing it to soak into the ground.
Evapotranspiration is the process by which water is returned to the atmosphere through the transpiration of plants and the evaporation of water from the surface of the ground and bodies of water. The rate of evapotranspiration is influenced by factors such as temperature, humidity, and wind speed. In general, evapotranspiration rates are higher in warmer, dryer conditions, and lower in cooler, more humid conditions.
Channel geometry refers to the physical characteristics of the river or stream channel, such as its shape, size, and slope. These factors can affect the flow rate of the water by influencing how quickly it moves through the channel. For example, a wide, shallow channel will have a lower flow rate than a narrow, deep channel of the same length, because the water has more space to spread out and slows down as it moves through the channel. Similarly, a channel with a steep slope will have a higher flow rate than one with a gentle slope, because the water will be moving more quickly as it flows downhill.
Land use can also affect the flow rate of a river or stream. For example, if an area is heavily developed with roads, buildings, and other impermeable surfaces, more of the precipitation will run off into the river or stream, increasing the flow rate. On the other hand, if the land is covered in vegetation or has permeable surfaces, more of the precipitation will be absorbed into the ground, decreasing the flow rate. Land use can also affect the rate of evapotranspiration, as vegetation tends to have a higher rate of evapotranspiration than other land covers.
In summary, there are several factors that can affect the shape and characteristics of a hydrograph, including precipitation, infiltration, evapotranspiration, channel geometry, and land use. Understanding these factors can help us to better predict and manage the flow of rivers and streams, and to make informed decisions about land use and development in the surrounding areas.