10/09/2025
https://www.facebook.com/share/p/1Gx72pPp5Z/
A creek bed that is dry on the surface in autumn almost always has water flowing underground. The visible surface flow has just dropped below the level of the streambed.
This phenomenon is so common it has specific names. A creek that flows seasonally is called an intermittent or seasonal stream. One that only flows after heavy rain or snowmelt is called an ephemeral stream.
Here’s a breakdown of what's happening:
1. The Water Table Drops
Think of the ground beneath the creek as a giant sponge saturated with water. The top of this saturated zone is called the water table.
· Spring: With melting snow and spring rains, the water table is high. It often rises above the bottom of the creek channel, causing water to flow on the surface.
· Summer/Autumn: As precipitation decreases and plants draw more water from the ground (transpiration), the water table slowly drops.
· The "Switch": When the water table falls below the bottom of the creek bed, the surface water can no longer be sustained. It seeps down into the ground, and the surface flow "disappears." The water continues to flow, but now it's moving slowly through the sand, gravel, and sediments underneath the dry creek bed. This is often called the hyporheic zone (meaning "under the flow").
2. Infiltration and Groundwater Flow
The creek bed itself is often made of porous materials like sand, gravel, and cobbles. When the water source from upstream diminishes, this porous material acts like a drain, allowing the remaining surface water to infiltrate and join the groundwater flow. The water doesn't stop; it just changes its path from an open channel to a subterranean one.
3. Evidence You Can Look For
Even when the surface is dry, you can find clues that water is not far away:
· Damp Sand/Gravel: Dig a small hole in the creek bed. Just a few inches down, you will likely find wet, dark sand or gravel.
· Green Vegetation: Look at the plants growing in and along the creek bed. They will often be lusher and greener than the surrounding vegetation because their roots can tap into the shallow groundwater.
· Isolated Pools: You might find deeper sections of the creek (called pools) that still hold water, while the shallower sections (called riffles) have gone dry.
The Exception: "Losing" vs. "Gaining" Streams
· Losing Stream: This is what you are describing. The stream is "losing" its water to the groundwater system. This is common in arid regions and during dry seasons.
· Gaining Stream: This is a stream that is fed by the groundwater. The water table is high enough that it constantly contributes water to the stream, keeping it flowing year-round. Many large, perennial rivers are gaining streams.
The creek is not truly "dry." The driver of the flow hasn't stopped; the water has just taken a different, hidden route. The creek is still "flowing" in a hydrological sense, just underground through the sediments. It's a vital part of the water cycle and a crucial hidden reservoir that sustains plant life and will eventually feed the surface flow again when the rains return.
