Does flooding change rivers?

[steve2]

How does all this flooding alter your local river?
Do the fish always return to the places they were, are will they be downstream and find new homes.
Swims must change with tons of gravel and slit being moved around.
I remember returning to some of my favourite swims after a flood and finding the deep holes had become shallow gravel runs.
New fish may well turn up in your river section especially with flooded carp fisheries.
So those swims and fish you fished for years may no longer be there.

I suppose that is what makes river fishing so much more interesting than lakes which never alter from one year to the next.

 

[john step]

It also shifts horrendous snags around.

 

[sam vimes]

My local can, and usually does, change with almost every flood. Usually, the more significant the flood, the more obvious the changes. The very minimum I expect to see is shifted gravel/cobbles. The disappearance (or appearance) of large boulders, floodbanks, old bridge footings and huge old trees is not unusual. The river altering course fairly significantly is not especially unusual, especially in a big flood.

The most dramatic occurrence on one of the local rivers happened just before Christmas.
Angling: Something fishy going on along the River Ure | Yorkshire Evening Post
It didn't happen during a particularly big flood, though it's obviously the product of decades worth of flooding and erosion, not just the overnight event that it first appears to be. About a mile and a half of meander lost in a night.

 

[103841]

Been thinking exactly the same, some of the coast too. Walked along the beach this morning, the sea is turbulent and angry looking, at Hythe the two storms have washed away the shingle beach.

 

[108831]

I can remember fishing a swim on the H.Avon at Ellingham on the Somerley estate,this swim was around 12-13ft deep under your feet,good chub and barbel looked tiny when you looked in there with poloroids,for years the the swim never changed,then one August after heavy flooding during the previous winter i turned up to find the swim had filled in and was only 18ins deep,incredible....

 

[tigger]

Some rivers change much more than others. The substrate and bankings are a huge factor.

 

[nottskev]

It also shifts horrendous snags around.

It certainly does! I fished a favourite barbel swim - a few miles above where you go - last summer, and played the first one to the bank, where it snagged me up 3' below the surface (I could see my bomb) in 12' of water!. It seems a tree being carried downstream had lodged in the swim, making it too risky to fish.

The Dane, where I used to fish above Northwich, is a series of loops and meanders, and I was shocked to find one morning that the river had cut through and cut off a loop that had had some super swims for chub and barbel.

Apart from the effect on the river, I believe the access track to one stretch I fish these days has been wiped out, but I've yet to go and see what's become of it.

 

[sylvanillo]

Last year in south france, a trout river was left entirely empty.

We got 2 extreme flooding episodes in the thames valley, in January 2013 and in Januray 2014. From the following spring fishing results were awful. Whether for trout or perch notably. I suppose the river was literally washed out. Although the too hot summers that followed really did change rivers as well.

On this subject it's not only abnormal floodings but also heat waves that redistribute fish populations.

It's what I'm interested in when checking a river after something unusual. Then, whether the details of a river have changed, moved etc, it's almost every year anyway.

 

[bullet]

Most of my local rivers are very mobile, parts of them can be unrecognisable after winter floods.

 

[The bad one]

Kev the Dane is classed as the most Geomophically active river in the UK. This is due to the sandy/sandstone substraight soil it runs through and over.

50+ years ago before I understood how rivers work, and I had hair and good looks, I arrived at Swettenham and the river was in a big flood. I walked down from the bridge to the righthand bend at the bottom of what under normal conditions was a lovely glide of 50 yards and 3-4 ft deep of pristine stick float water.
The noise was deafening with a scrapping, grinding sound. As this section of river was to fast to fish I went up river to what was a slower deeper section.

The next time I fished this section of river I was shocked to find the pristine stick float run of 50 yards had gone completely and turned into a 50 yard length of course gravel and large football sized boulders. Clearly, the noise I'd heard in the flood was the gravel and boulders being moved from, I known not where, banging and crashing as they came to rest on what was the glide.
It was on seeing this awesome sight of what had happened under the flood that the penny dropped to he shear power of what floodwater can do to a rivers course. And probably the trigger to me setting off on the road to understanding the Geomorphology and Hydromorphology of how rivers really work.

 

[Aknib]

It certainly does! I fished a favourite barbel swim - a few miles above where you go - last summer, and played the first one to the bank, where it snagged me up 3' below the surface (I could see my bomb) in 12' of water!. It seems a tree being carried downstream had lodged in the swim, making it too risky to fish.

Yep and it's had a double dose a little over two months apart, I've a feeling that we'll be starting again with swim selection Kev.

I am toying with getting out and rolling some meat for a few hours tomorrow afternoon, the river stretch from the place I sent you the pictures of last night did look very inviting in its high water state.

Agree entirely on everything else that's been said about rivers altering in flood, on one occasion I was in a favourite Barbel swim as the river was coming up a few Summers ago and I too heard a very odd scraping, grating sound which seemed to be coming from underwater and beneath an overhanging willow just upstream of me.

Rising, very serpent like, out of the water directly in front of me was another large willow which had been washed down with the rising water and snagged in the willow above me which had the effect of almost standing it back up.

I've used some excuses in my time to justify moving swims but an instant tree has to be about the best so far.

 

[nottskev]

Kev the Dane is classed as the most Geomophically active river in the UK. This is due to the sandy/sandstone substraight soil it runs through and over.

50+ years ago before I understood how rivers work, and I had hair and good looks, I arrived at Swettenham and the river was in a big flood. I walked down from the bridge to the righthand bend at the bottom of what under normal conditions was a lovely glide of 50 yards and 3-4 ft deep of pristine stick float water.
The noise was deafening with a scrapping, grinding sound. As this section of river was to fast to fish I went up river to what was a slower deeper section.

The next time I fished this section of river I was shocked to find the pristine stick float run of 50 yards had gone completely and turned into a 50 yard length of course gravel and large football sized boulders. Clearly, the noise I'd heard in the flood was the gravel and boulders being moved from, I known not where, banging and crashing as they came to rest on what was the glide.
It was on seeing this awesome sight of what had happened under the flood that the penny dropped to he shear power of what floodwater can do to a rivers course. And probably the trigger to me setting off on the road to understanding the Geomorphology and Hydromorphology of how rivers really work.

Ha! I can imagine your surprise. I can remember standing on the bank scratching my head and checking I was where I thought I was. The bit with the new shape was just above the arches outside Northwich.

 

[trotter2]

Fingers crossed its moved the gravel to the clubs advantage. One of our club waters has shallower up significantly over the years let's hope its dug some holes in it.

 

[The bad one]

I've been thinking about writing what follows for a few days now, due to the fact I no longer go in for long posts. That stated, something that has come into common currency on the News and current affairs programmes, both radio and TV and is really getting under my skin. The Hue and Cry from the public, local and national politicians and farmers, that being, the rivers need dredging to sort the flooding problem out.

It's complete and utter nonsense in the vast majority of rivers cases, save for the man-made ones created as flood relief channels. And because the reporters, commentators, etc are so poorly briefed the exponents of this nonsense are getting a free pass and run at it, without being challenged.
One woman on Question Time last Thursday repeated the mantra and had the audience clapping like bloody seals!
Even the Secretary of State for the Environment, one George Useless, sorry Eustice, was that well briefed, even he didn't even pick her up on it.
What the head of his officials and the EA thought of him we can only speculate on. No doubt it was along the lines of, "What a Richard Head he is!"

The majority of rivers that have a natural course to them including those that have had “man-made flood improvement work” carried out are self-silt cleaning.
It's long been known and proven time and time again by river morphologists across the world that rivers work by bank and to a lesser extent bed sediment erosion, deposition of eroded sediments, then scarification and down river movement of those sediments under flood conditions. In effect the rivers work as a sedimentary conveyor system.
Anyone with half a brain cell and access to Google earth can see how the process works by looking in the estuaries and would see all the sandy/silty, mudflats deposits at the river mouth.
How do they think they got there? By the actions of the deep sea sand fairies may be?

Seriously to dredge the rivers that have flooded and keep flooding, you'd have to deepen the course of all of them, along most of the whole length, to a depth of around 10 ft. to keep the normal over topping floods in the channel. The exceptional floods we are experiencing at the present. perhaps 15-18 ft deeper. Even if it was achievable, which I doubt it is or could be, as you would in the main, be into the bedrock of the river bed, the costs of such work would be so prohibitive it would make HS2 look very cheap indeed!

 

[108831]

Also Phil lots of the biggest floods are on major rivers,ie the Severn,Y.Ouse etc where there is never an issue with siltation,both of these rivers and many others in similar positions have very high,scoured out banks,it makes no difference,not when you consider the unprecedented amount of rain thats fell since October...blimey the Ouse at York is an enormous river,how many feet,nay metres of floodwater is in it at its height?

 

[Mark Wintle]

As Phil says dredging is not the answer. In the 50s, 60s and 70s the old Avon and Dorset River Board/Authority/Wessex Water Authority dredged and straightened the Dorset Stour, canalising it so badly that in the 76 drought it all but dried up so that in 77 and 78 they had to install Gabian cage/cobble stone weirs just to bring back some depth. In late 79 the river had its revenge, flooding twice in 6 months at levels described as one in fifty year events, the latter of the two floods being higher than the latest recent flood. Subsequently the WWA as it now was first designed a scale model of the entire river valley to understand what was happening and secondly built flood defences in the form of earth banks and engineered walls with flood gates to protect various towns that had flooded.

The big observation, apart from the enormous quantities of gravel that were moved around in those big floods, was that when a major flood came up to a bridge which are usually built as part of a causeway across the flood plain was that the old bridges have a restriction on how much water can pass through them, including the capacity of flood arches on the causeway. Once the flood reached the top of the bridge arches then the level would rise very rapidly (often another 3 to 5 feet) to overwhelm the entire causeway and close the road as well as flood the entire plain, and close that road as well. This was so bad in the December 79 flood that at one stage every bridge from Sturminster Newton to the sea was closed (massive traffic jams), even the main A338 was shut(neither the Blandford or Wimborne bypasses had been built back then). So all digging the river very deep does is get the flood to the next bridge even quicker but you cannot increase the throughput of the bridge without totally replacing ancient listed bridges!

 

[108831]

Probably the best fix is to build balancing lakes,that lie relatively low during summer but fill during times of high water,possibly pumping water to reservoirs at times of need,lets not forget we were in a situation of severe water shortage before last October,maybe 14 months or more with hardly a drop here....

 

[theartist]

It's not just Joe public that gets drawn into the clamour for dredging, I've even had a club bailiff arguing it's need on a stretch of river that's almost perfect oblivious to all the rivers that have had this man made disaster forced upon them. The call for dredging and the modern blame culture work hand in hand in areas that have been flooded which isn't good for fish stocks who are much lower in priority.

Another thing that's happening in smaller streams is willow weave banking which is being put in place to naturally remove silt, however it also removes shallow areas where small fry shelter in times of flood.

Far too many rivers are unnaturally straight and uniform in depth, they need widening, with more bends and more gravel shallows and backwaters, it's win win both for flood relief and for the fish

Instead they are still making flood storage areas and trying to hold back the river, well the river is going to go feral one day regardless, any river can flood and it will

 

[nottskev]

It's weird how something like "dredging is the answer" get fixed in so many people's minds.
Why dredging, and not protecting wetlands, planting trees, creating water storage reservoirs, re-meandering straightened rivers, managing compacted soil and other things that would actually help? Is it because dredging seems like a simple one-shot answer for people who don't have the patience to understand the problem?

We shouldn't be surprised, I suppose, when Vox Pop interviews and programmes like Question Time reveal how little some of the most opinionated people actually know. It's especially depressing when ideas that are plainly wrong stand unchallenged by the interviewers or programme hosts. People are entitled to state their views but shouldn't be exempt from giving reasons or evidence for them.

 

[sam vimes]

I think at least part of the problem is the general idea that flooding has never been so bad. This is largely reinforced by the EA river level "records". I appreciate that they had to start somewhere, but the fact that there's no record level shown that's from prior to around 1990 gives a false impression. The reality is that there are no earlier records is because that's when the modern level monitors were installed. Earlier genuine records have either gone unrecorded, unremembered or simply unreliably remembered (and therefore discounted).

I've seen the Swale quite a bit higher than the current record suggests it has ever been. There's no way I can put an accurate measurement figure on it, but walls and buildings are rather obvious gauges. Due to circumstance, I can even narrow the memory to a school year of Sept 82 to July 83. Likewise, there's the bankside pub in York that has umpteen higher flood levels marked on its internal walls that go back centuries. Hardly an especially reliable gauge, but not one that can entirely discounted.

People believe that its never been as bad. They are told that's the case, they want to believe it's true. If you swallow that fib, it's very easy to believe that things are worse since large scale dredging stopped. When proper records don't go back further than the 90s and even living memory doesn't reliably exceed 75 years or so, this is what you get.