ESC265: Water Erosion

Water Erosion Defined

• Water erosion occurs when rain or snowmelt displaces soil on the ground
• The more water flows over land, the more soil particles are moved away
• Land without vegetation is especially vulnerable to water erosion
• Without vegetation, water is not absorbed, dirt is not held in place, and the energy of raindrops is not broken up, leading to increased runoff and erosion
• Intense weather (heavy rains, flash floods, and rapid snowmelt) leads to rapid soil erosion
• In 2019, intense spring rainstorms in the Midwest eroded the fertile landscape
• Water flowing across fields with sand was observed in northern Missouri, impacting farms

Factors Influencing Water Erosion

• Rainfall intensity and water runoff during storms significantly impact soil erosion
• Soil type, quality, and texture (soil particle size and compaction) influence erodibility
• The length and slope of the land affect the speed and strength of water runoff
• Farms on steep hillsides are susceptible to devastating soil erosion and washouts because of limited arable land
• Vegetation buffers the impact of water on farm fields
• Land managers can mitigate soil erosion through selective tillage practices
• Reducing mechanical disturbance to farm fields helps preserve soil

Common Forms of Water Erosion

• Water is vital but can be corrosive
• Every raindrop has the potential to impact soil structure
• Four common types: sheet, rill, gully, and bank erosion

Sheet Erosion

• Thin, uniform layers of soil are removed by raindrop impact and shallow water flow
• Sheet erosion is hard to detect unless soil is deposited or damage is severe
• Removing fine soil particles that contain nutrients and organic matter

Rill Erosion

• Erosion results in small, well-defined channels
• Rill erosion channels are typically smaller than gully erosion channels
• After some time, rill erosion may fade away, or be smoothed over with tilling

Gully Erosion

• The washing away of soil occurs through deep grooves or channels across unprotected land
• Gully erosion can refer to soil being washed away through human-made drainage lines or grooves created by hard rains
• Farmers fill these grooves with fresh soil to temporarily fix the issue
• Gully erosion hinders the ability to plow fields and grow crops

Bank Erosion

• Progressive undercutting, scouring, and slumping of natural rivers/streams and drainage channels by the movement of water
• Removing vegetation or livestock overgrazing near streams/riverbanks exacerbates the problem
• Claylike soil in southwestern Bangladesh is vulnerable to erosion during the rainy season
• Riverbank erosion displaces tens of thousands of people and impacts regional framing

Effects of Water Erosion

• Soil loss depends on the type and depth of the topsoil lost
• Topsoil loss reduced the soil's ability to hold nutrients and moisture
• Crop emergence, growth, and yield is greatly reduced
• Seriously eroded soils are not usable for crop production
• Erosion reduces the soil's ability to absorb water, which increases flooding and standing water
• Water accumulation can delay or impede planting new crops
• Agricultural runoff leads to dire consequences beyond farm fields
• A larger-than-usual "dead zone" in the Gulf of Mexico has been contributed by excessive fertilizer and agrochemicals
• High levels of manure and fertilizer are responsible for harmful algal blooms that kill marine life and render fresh water undrinkable/unsafe
• In 2014, 500,000 users of Toledo, Ohio's water were advised to avoid tap water due to unsafe levels of toxins from Lake Erie algal blooms