Dredging does it work

Seastoke

Seastoke

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Well watching our marina dredge and pump it in to the estuary as tide is going out ,does it work or does it stop in estuary ,then come back in the marina .it just seems an ongoing issue ,how does your marina del with it
 
It doesn't stop what's removed being brought back in by the tide over time but dredging is always ongoing in certain areas
 
I think they need a licence to dredge and the conditions that apply specify where it is to be dumped, normally that would take account of tidal flows. However, silting will reoccur over time.
 
We kept various boats in Conwy Marina during the 90s. Silting was a very big problem then and a number of hydraulic studies were undertaken. These resulted in the installation of the marina lifting sill. This did a bit to alleviate the problem but, as you have observed, it is no cure. In the early days they were not allowed to pump the silt but had to dredge and take the foul well out to sea for dumping. This meant that only one barge load could be dumped on each tide. In between times many of the berths, including ours, became mud berths at Springs.

I think dredging or pumping will be needed for the foreseeable future.
 
The quantities of mud that are dredged just for a small marina are colossal. But the rate some silt up is pretty scary as well. We're fortunate to be berthed in a natural harbour where it doesn't get chance to silt up!
 
If it was dredged in the past and needs dredging now it will probably need dredging forever.
In the Medway dredging was carried out on a regular basis and was probably helped by the sheer amount of commercial traffic moving around in the port.
The river is now silting up very fast.
Piers which once gave access at all states of tide are now high and dry a couple of hours after HW.
In Rochester town centre extreme caution is needed navigating around low water especially when going through bridge.
The centre arch is now off limits due to risk of grounding as several boats have discovered.
 
To answer the original question, certainly much of it goes out: fast flowing water will hold and carry much of the silt (and larger particles), which will then fall to the bottom when the current slows (which is why you usually find a bar across the mouth of a river where it widens). Less of it comes back in because there isn't the flow speed outside to pick it (or as much of it) up. (Local circumstances will vary, of course, but the basic mechanisms at work remain.

But it's not just the amount or type of dredging (and commercial traffic) in the harbour itself that affects silting. Much is caused by changes in land use upstream over long periods. Changes in agriculture (direction of ploughing on slopes for horses vs. tractors, greater extent of ploughing, reduced field margins and fewer hedges, etc.) mean more soil is washed into rivers than in earlier days; water abstraction for agriculture, housing and industry reduces the normal flows of rivers (so they can't carry away the same volume of silt); etc..
 
LittleSister said:
To answer the original question, certainly much of it goes out: fast flowing water will hold and carry much of the silt (and larger particles), which will then fall to the bottom when the current slows (which is why you usually find a bar across the mouth of a river where it widens). Less of it comes back in because there isn't the flow speed outside to pick it (or as much of it) up. (Local circumstances will vary, of course, but the basic mechanisms at work remain.

But it's not just the amount or type of dredging (and commercial traffic) in the harbour itself that affects silting. Much is caused by changes in land use upstream over long periods. Changes in agriculture (direction of ploughing on slopes for horses vs. tractors, greater extent of ploughing, reduced field margins and fewer hedges, etc.) mean more soil is washed into rivers than in earlier days; water abstraction for agriculture, housing and industry reduces the normal flows of rivers (so they can't carry away the same volume of silt); etc..
Click to expand...

Water extraction has most certainly affected the Medway. Although industry (esp paper) has declined to virtually nothing suspect that water for domestic use is responsible for the majority now,
In living memory many small feeder streams have virtually vanished form the surface with most reduced to a trickle.
All that indicates their existance is the pumping station.
Think some streams ,such as the Dart had water pumped into them near the source to maintain flow.
Old extraction permissions granted decades ago to water boards and agriculture are proving hard to revoke especially on the Thames which supplies London.
NIMBY objections to planned reservoirs in Kent did not help.
 
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