Watercourse Depth

[robs1]

Trying to get us to “hold water back” or slow it down is all very well on worthless amenity land but makes agriculture as we know it almost impossible. Their plans to spill flow over a wide area to slow it down will also have a limited effect in my view. The town still sits at the neck of a funnel and whether the flow arrives narrow and fast or slow and wide, once the ground is saturated it’s still the same amount of water that has to get through the town. And with all these dams and restrictions, ground will remain saturated for longer and actually have less transient water buffering capacity in my view.
I’d prefer a chain of properly engineered and controlled winter storage reservoirs to take peak winter flows and allow irrigation in the summer but looks like it ain’t going to happen. A return to unproductive swamp and marsh looks more likely.

I've had this argument with well qualified people several times, it's only when you explain to them that once a sponge is full it cant hold any more water they grasp it, the look on their face when it dawns on them is priceless, then it again dawns on me that these sort of idiots are actually running the country

 

[yellow belly]

the problem could be more rainfall events of 12mm or more that lead to high water flow
high water flow has much greater carrying capacity the the same voluume of water over an extended period

ie 20 mm one weekend compared to 5 by 4mm rainfall events in 2 weeks

here at the source of the river witham we have more rain in the may to december period than we had 30 to60 years ago average is up 3 inches with most extra in bigger rainfall events in the may to december months januarry to may are no wetter

 

[thesilentone]

It seem's these days, the planning is now for 100/200/300 houses, so a whole new development. The footprint (in real terms) is quite small as developers like to ' squeeze em in ' however the ability to absorb (or slow down) water from that footprint is lost.

I am strongly of the view that all these should be forced to also build a lake that takes all the run-off from these developments, acting as a buffer for the rivers where it will all end up, as well as becoming a wildlife haven and recreation area.

In addition, a water treatment plant.

 

[thesilentone]

the problem could be more rainfall events of 12mm or more that lead to high water flow
high water flow has much greater carrying capacity the the same voluume of water over an extended period

ie 20 mm one weekend compared to 5 by 4mm rainfall events in 2 weeks

here at the source of the river witham we have more rain in the may to december period than we had 30 to60 years ago average is up 3 inches with most extra in bigger rainfall events in the may to december months januarry to may are no wetter

12mm/20mm ?

What about 341.4mm in 24 hours !!

Storm Desmond

5 - 6 December 2015 - Storm Desmond brought strong winds and heavy rainfall with the worst impacts in Cumbria.

www.metoffice.gov.uk

 

[yellow belly]

It seem's these days, the planning is now for 100/200/300 houses, so a whole new development. The footprint (in real terms) is quite small as developers like to ' squeeze em in ' however the ability to absorb (or slow down) water from that footprint is lost.

I am strongly of the view that all these should be forced to also build a lake that takes all the run-off from these developments, acting as a buffer for the rivers where it will all end up, as well as becoming a wildlife haven and recreation area.

In addition, a water treatment plant.

i agree but eh design has to be fit for purpose all the balancing ponds on land i used to farm do not work built by the highays

the one on private industrial area always works

 

[BrianV]

It seem's these days, the planning is now for 100/200/300 houses, so a whole new development. The footprint (in real terms) is quite small as developers like to ' squeeze em in ' however the ability to absorb (or slow down) water from that footprint is lost.

I am strongly of the view that all these should be forced to also build a lake that takes all the run-off from these developments, acting as a buffer for the rivers where it will all end up, as well as becoming a wildlife haven and recreation area.

In addition, a water treatment plant.

Building a lake doesn't actually solve the problem once full, the answer is a lake with an appropriate size pipe in the bottom to allow a manageable amount of water to escape whilst any surplus is retained until later.

 

[DrWazzock]

And at a practical level would I be doing any good or wasting my time by installing a few small dams to raise the water level retained in our watercourses, so the bed width is greater, flow slower and more silt settles out? I’m only talking about 24” or so, nothing major.
My only reservation about this approach is that our culvert pipes for gateways etc already serve as dams yet have not stopped the watercourse deepening either side of them. There are such high flows in winter that the turbulence seems to kind of hoover up the silt and carry it away.

(Dad had noticed this deepening and he used to reckon the Earth or landscape here had tilted more so there was a steeper slope across the place.)

 

[DrWazzock]

Building a lake doesn't actually solve the problem once full, the answer is a lake with an appropriate size pipe in the bottom to allow a manageable amount of water to escape whilst any surplus is retained until later.

Absolutely right. Here with a high winter water table where under drains are poor or non existent, a lake fills up anyway from groundwater so has no reserve capacity to cope with a big rain event.
Without pumps, properly engineered reservoirs that hold water above ground level and a decent control system, we aren’t doing much good messing about with “sacrificial” flood plains, particularly if it’s your business that’s being sacrificed.

 

[thesilentone]

Absolutely right. Here with a high winter water table where under drains are poor or non existent, a lake fills up anyway from groundwater so has no reserve capacity to cope with a big rain event.
Without pumps, properly engineered reservoirs that hold water above ground level and a decent control system, we aren’t doing much good messing about with “sacrificial” flood plains, particularly if it’s your business that’s being sacrificed.

Not sure it would be of any benefit to build a lake without sufficient volume and freeboard to take additional capacity. Why would you ?

 

[robs1]

I sometimes wonder whether these ponds help or not, when rain falls on to land some runs off some is absorbed, even that which runs off on levrlish ground can take a fair while to reach rivers and cause flooding down stream, we are 25 or so miles from Avonmouth which the rivers here memory into the sea, it is normally at least 24 hours( depending on tides) before serious flooding occurs here due to the slow build up, perhaps if rain from built up areas went quicker to the river it would be out of the river into the sea before the flows from land built up whereas if rain from newly built areas goes via ponds and releases slowly into rivers this might coincide with peak flows from farmland.

 

[br jones]

the fact you have been at the address for along time means you notice stuff ,water washes stuff away ,grand canyon anyone

 

[thesilentone]

I sometimes wonder whether these ponds help or not, when rain falls on to land some runs off some is absorbed, even that which runs off on levrlish ground can take a fair while to reach rivers and cause flooding down stream, we are 25 or so miles from Avonmouth which the rivers here memory into the sea, it is normally at least 24 hours( depending on tides) before serious flooding occurs here due to the slow build up, perhaps if rain from built up areas went quicker to the river it would be out of the river into the sea before the flows from land built up whereas if rain from newly built areas goes via ponds and releases slowly into rivers this might coincide with peak flows from farmland.

I agree, however the problems arise when it doesn't stop raining.

 

[DrWazzock]

Another thing you notice is that banks slowly move in to the watercourse so essentially get steeper and steeper and the channel gets narrower and narrower as the years go by, unless reshaped. We have some grass banks that have almost closed in over the watercourse which runs in a deep undercut beneath them until we reshape it.

 

[Tubbylew]

Anyone had a go at willow spiling to stop bank erosion? always fancied a go but not had the opportunity.

Spiling - Wikipedia

en.m.wikipedia.org

 

[wanton dwarf]

Another thing you notice is that banks slowly move in to the watercourse so essentially get steeper and steeper and the channel gets narrower and narrower as the years go by, unless reshaped. We have some grass banks that have almost closed in over the watercourse which runs in a deep undercut beneath them until we reshape it.

A few things come to mind.

Could try gravel or rock ballast in the base of the watercourse ? If jagged enough this should hold silt back but might be a pain when cleaning the ditch. Obviously won't work if too large.

Two stage dams, small gap lower down to give low flow and overflow higher up - rather than just a dam. Adjustable would be brilliant I guess ?

Silt ponds. Might provide a bit of shooting or fishing ?

 

[Longlowdog]

Youtuber Upstate Brush Control makes a lot of his money keeping vegetation out of (and Letsdig 18 from dredging) the almost ubiquitous retention ponds that are mandatory with any development of size in the states. U.K planning seems to end at the area purchased to build on and doesn't factor in water management from impermeable surfaces as a basic necessity.
Surely speeding and deepening of waterways must be a natural occurrence as observable by features such as The Grand Canyon that formed way before men started messing with anything.

 

[Doing it for the kids]

It seem's these days, the planning is now for 100/200/300 houses, so a whole new development. The footprint (in real terms) is quite small as developers like to ' squeeze em in ' however the ability to absorb (or slow down) water from that footprint is lost.

I am strongly of the view that all these should be forced to also build a lake that takes all the run-off from these developments, acting as a buffer for the rivers where it will all end up, as well as becoming a wildlife haven and recreation area.

In addition, a water treatment plant.

They do!

Building a lake doesn't actually solve the problem once full, the answer is a lake with an appropriate size pipe in the bottom to allow a manageable amount of water to escape whilst any surplus is retained until later.

Exactly.

the lake is sized to take a flash flood over the land in question.

depending on ground type you either use semi permeable surfaces or pipe it all to a lake. That lake has a small pipe at the bottom (well almost) with a hydro brake on that lets the water out slowly.

the theory is the spike in rain fall is ironed out over the coming days by a trickle out. So Long as it’s maintained is the best solution to stop flash flooodng.

where possible when heavy rain is forecast they should open up every pipe and get as much out as soon as possible so they can use the storage and throttle it back once it gets to ‘flood level’ lower down.

too simple perhaps!?

 

[Exfarmer]

They do!

Exactly.

the lake is sized to take a flash flood over the land in question.

depending on ground type you either use semi permeable surfaces or pipe it all to a lake. That lake has a small pipe at the bottom (well almost) with a hydro brake on that lets the water out slowly.

the theory is the spike in rain fall is ironed out over the coming days by a trickle out. So Long as it’s maintained is the best solution to stop flash flooodng.

where possible when heavy rain is forecast they should open up every pipe and get as much out as soon as possible so they can use the storage and throttle it back once it gets to ‘flood level’ lower down.

too simple perhaps!?

This is how it works in an ideal situation, however in the uk two things are standard, the pond / lake etc either is hi jacked for recreation and left permanently filled for fishing / nature/ sailing/ even water skiing or it ends up filled with shopping trolleys, stolen cars etc. the drain blocks and the same effect after ten years it has no value at all for flood prevention

 

[wanton dwarf]

where possible when heavy rain is forecast they should open up every pipe and get as much out as soon as possible so they can use the storage and throttle it back once it gets to ‘flood level’ lower down.

Said exactly the same thing to visitor from one of the Environment divisions .. why don't they use remote controlled sluice gates linked to rain forcasts.

The observation was quickly dodged, "How about using some land for a wet land area ?" - to which I thought "Bog off".

 

[zero]

We have alot of moorland upstream from us, if the peat is damp before heavy rain it soaks rainfall up better than if it's as dry as fibreboard when the rainfall bounces off and heads our way. You might be better just battering your watercourses at a shallow angle with a digger and just let the water flow past without causing too much erosion as the weather's all or nowt these days rather than little bits and often..