Coquille River Estuary EarthCache
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The Bandon Marsh National Wildlife Refuge is a place to observe and enjoy the Coquille River estuary. It was developed by and is maintained by the US Fish & Wildlife Service. This location is open from sunrise to sunset. Pets are not allowed in order to protect the wildlife. Waterfowl hunting and clamming are allowed in this area under current Oregon regulations. Please observe the rules.
For more information about visiting this area visit the Bandon Marsh Wildlife Refuge webpage. Thank you to the National Wildlife Refuge for allowing this Earthcache.
Estuaries in Oregon
According to the Oregon Coastal Management System “an estuary is defined as a semi-enclosed body of water, connected to the ocean, where salt water is measurably diluted with fresh water from the land.” Additionally, it is a zone of transition between the marine-dominated systems of the ocean and the upland river systems, a zone which yields one of the most biologically productive areas on Earth. Oregon has 22 major estuaries and many other minor estuaries along its coast.
The distribution of estuaries along the Oregon coast reflects the geology and topography of the mountains that meet the ocean. Between the Salmon River estuary at Cascade Head and the Coquille River far to the south are the estuaries of Siletz Bay, Yaquina Bay, Alsea Bay, the Siuslaw and Umpqua rivers, and Coos Bay. Along this portion of the coast, the mountains are mostly older marine sediments and sands, clays, and muds eroded from ancient mountains to the south and east. Deposited on the ocean floor in a great trough from the Klamath Mountains to Vancouver Island, these sediments were uplifted by the force of colliding continents and eroded once again to create relatively wide river mouths. Rising seas filled these river valleys with sediments and created the conditions for present-day estuaries.
Classifying Estuaries by Geology
The features of an estuary are determined by a region's geology, and influenced by physical, chemical, and climatic conditions. For example, movements in the Earth’s crust elevate or lower the coastline, changing the amount of seawater that enters an estuary from the ocean. The coastal elevation also determines the rate of fresh water that flows into an estuary from rivers and streams. The amounts of seawater and fresh water flowing into an estuary are never constant. The quantity of seawater in an estuary changes with the changing tides, and the quantity of fresh water flowing into an estuary increases and decreases with rainfall and snowmelt.
Estuaries are typically classified by their existing geology or their geologic origins. The five major types of estuaries classified by their geology are coastal plain, bar-built, deltas, tectonic and fjords.
• Coastal plain estuaries are formed when rising sea levels flood existing river valleys.
• Bar-built estuaries are characterized by barrier beaches or islands that form parallel to the coastline and separate the estuary from the ocean. Barrier beaches and islands are formed by the accumulation of sand or sediments deposited by ocean waves.
• A delta, characterized by large, flat, fan-shaped deposits of sediment at the mouth of a river, occurs when sediments accumulate more rapidly than ocean currents can carry them away.
• Tectonic estuaries are formed when the Earth’s tectonic plates run into or fold up underneath each other creating depressions.
• Fjords are steep-walled river valleys created by advancing glaciers, which later became flooded with seawater as the glaciers retreated.
Classifying Estuaries by Geography
There are several types of estuaries on the Oregon coast.
• River dominated: Some, like the Columbia River and Rogue River, are dominated by the freshwater flow of the river and have relatively small tideland areas.
• Drowned river mouth: The majority, like Coos Bay, Siletz Bay, Yaquina Bay, and Coquille River, are the drowned river mouth variety, where winter's floods discharge high volumes of sediments through the estuary. In summer, seawater inflow dominates the estuary because the streamflow is low.
• Bar-built: Others, like Sand Lake and Netarts Bay, are "bar-built," where a sand spit creates a separate estuarine environment which receives very little freshwater inflow. Sand Lake has a watershed of only 14 square miles.
• Blind: Some of the smaller estuaries, like Elk River and Sixes River in Curry County, are "blind" estuaries where low river flow in summer results in a sand bar completely closing off the mouth of the estuary.
The Coquille River Estuary is a Drowned River Mouth estuary.
To claim credit for the Earthcache answer these questions from the information provided and through you observations. Please send me the answers to these questions through my Geocaching profile. All reasonable attempts will be accepted.
1. Knowing that the Coquille River Estuary is defined geographically as a Drowned River Mouth estuary, how is it defined geologically?
2. According to the information on site, what are two factors that make the health of the estuary vulnerable?
3. Tell about two observations you made on your visit such as wildlife you see or the current exposure level of the mud flats.
Sources:
Oregon Coastal Management Program
Inforain
NOAA
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