Rivers flow into basins. The basin can be a sea like the Gulf of Mexico or an enclosed basin with no path to the ocean, such as the one into which the Truckee River flows to create Pyramid Lake in Nevada. As they reach their ultimate destinations and enter relatively quiet water, rivers lose the energy they acquired from their down slope flow. That loss of energy results in a deposition of whatever sediments the water carried in suspension during more turbulent flow. As the sediments drop from the water, they build deltas of sands, silts, and clays (all three, by the way, are size classifications, not necessarily particular substances).
Deltas develop in different shapes. Some, like the Nile Delta, are triangular like the Greek letter delta (Δ) from which the Nile’s shape gets its designation. Others are more irregular, like part of the Mississippi Delta, whose farthest reach into the sea is called a bird-foot delta.
As sands, silts, and muds settle, they can block a channel and divert a stream. Often, the stream of water bifurcates to flow past the barrier. Now two streams, either or both of which can block their journey to the sea, can undergo further splitting. Eventually, the process makes a surface feature through which water is distributed to the sea (or lake) in numerous channels, all the result of similar bifurcations. In a sense the water is being distributed to the sea, so the new channels that extend the zone of sedimentation are called distributaries.
The buildup of sediments extends a delta seaward. Depending on the size of the river and the amount of sediment it carries, a delta can develop relatively fast. I know, you want a ballpark figure. Just how much sediment can a river carry? Exact measurements are difficult to achieve and river capacities vary year to year because of rainfall, but here goes: The Mississippi River annually transports about 170 million tons of sediment from Cairo, Il, to the Gulf of Mexico.*
In just the past six or seven thousand years the Mississippi Delta spread over 7,000 square miles, extending the continent into the Gulf of Mexico and eventually becoming the site of not only small communities, but also New Orleans. Parts of today’s bird-foot delta did not exist in the eighteenth century. That’s how fast rivers can build a landscape by transporting sediments from highlands to the sea.
Because the river is a continuous conveyor of sediments, living on a delta is a high-maintenance process. The entire delta has numerous distributary channels, one being the Atchafalaya River, which is, in fact, the shortest path through the delta the water could take to get to the sea. Human intervention and a large dam across the Atchafalaya keep the main flow running past New Orleans. Whenever sediments pile up in an important shipping channel, engineers bring out the dredges. Can’t have Bourbon St. dry up because of an empty channel abandoned by the river.
Delta formation is a relatively good analog for the way we build the structure of our lives. Like a constantly changing delta, our lives are also ephemeral and require high maintenance. Frequently, we find our paths blocked by the very things we have carried along: The substances, ideas, and emotional responses we pick up and carry with energy can suddenly block our paths. What we pick up by way of obligations and cares during our energetic flow can also interrupt our path whenever we lose energy. We find ourselves at bifurcations, unexpectedly having to make decisions about which new path to take around obstacles composed of whatever we transported through a channel that runs from past to present. The basin into which we build a life delta is the future.
Turn around to look back upstream for a moment to know that whenever something you easily carried along in the past suddenly became an obstacle, you found a way around it. You cut a new channel, or you dredged a familiar one. Delta maintenance is a constant task if you want to build seaward with some control.
You have an ocean to fill as you build your delta with a lifetime supply of sediments.
*Thorne, C. R., O. P. Harmar, C. Watson, N. Clifford, D. Biedenharn, and R. measures. 2008. Current and historical sediment loads in the Lower Mississippi River. Final report, contract Number 1106-EN-01. London, England: United States Army, European Research Office of the U.S. Army. P. 3. Available online at http://www.dtic.mil/dtic/tr/fulltext/u2/a527428.pdf
Deltas develop in different shapes. Some, like the Nile Delta, are triangular like the Greek letter delta (Δ) from which the Nile’s shape gets its designation. Others are more irregular, like part of the Mississippi Delta, whose farthest reach into the sea is called a bird-foot delta.
As sands, silts, and muds settle, they can block a channel and divert a stream. Often, the stream of water bifurcates to flow past the barrier. Now two streams, either or both of which can block their journey to the sea, can undergo further splitting. Eventually, the process makes a surface feature through which water is distributed to the sea (or lake) in numerous channels, all the result of similar bifurcations. In a sense the water is being distributed to the sea, so the new channels that extend the zone of sedimentation are called distributaries.
The buildup of sediments extends a delta seaward. Depending on the size of the river and the amount of sediment it carries, a delta can develop relatively fast. I know, you want a ballpark figure. Just how much sediment can a river carry? Exact measurements are difficult to achieve and river capacities vary year to year because of rainfall, but here goes: The Mississippi River annually transports about 170 million tons of sediment from Cairo, Il, to the Gulf of Mexico.*
In just the past six or seven thousand years the Mississippi Delta spread over 7,000 square miles, extending the continent into the Gulf of Mexico and eventually becoming the site of not only small communities, but also New Orleans. Parts of today’s bird-foot delta did not exist in the eighteenth century. That’s how fast rivers can build a landscape by transporting sediments from highlands to the sea.
Because the river is a continuous conveyor of sediments, living on a delta is a high-maintenance process. The entire delta has numerous distributary channels, one being the Atchafalaya River, which is, in fact, the shortest path through the delta the water could take to get to the sea. Human intervention and a large dam across the Atchafalaya keep the main flow running past New Orleans. Whenever sediments pile up in an important shipping channel, engineers bring out the dredges. Can’t have Bourbon St. dry up because of an empty channel abandoned by the river.
Delta formation is a relatively good analog for the way we build the structure of our lives. Like a constantly changing delta, our lives are also ephemeral and require high maintenance. Frequently, we find our paths blocked by the very things we have carried along: The substances, ideas, and emotional responses we pick up and carry with energy can suddenly block our paths. What we pick up by way of obligations and cares during our energetic flow can also interrupt our path whenever we lose energy. We find ourselves at bifurcations, unexpectedly having to make decisions about which new path to take around obstacles composed of whatever we transported through a channel that runs from past to present. The basin into which we build a life delta is the future.
Turn around to look back upstream for a moment to know that whenever something you easily carried along in the past suddenly became an obstacle, you found a way around it. You cut a new channel, or you dredged a familiar one. Delta maintenance is a constant task if you want to build seaward with some control.
You have an ocean to fill as you build your delta with a lifetime supply of sediments.
*Thorne, C. R., O. P. Harmar, C. Watson, N. Clifford, D. Biedenharn, and R. measures. 2008. Current and historical sediment loads in the Lower Mississippi River. Final report, contract Number 1106-EN-01. London, England: United States Army, European Research Office of the U.S. Army. P. 3. Available online at http://www.dtic.mil/dtic/tr/fulltext/u2/a527428.pdf
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