I believe withdrawal of river sand has some advantages and some disadvantages. Advantages - Flood mitigation by providing more storage capacity

- Construction Material e.g. Fine Aggregate supply, etc.

Disadvantages - Lowering Water Level which may increase pumping cost for water supply and irrigation.

- Unplanned withdrawal of river sand may trigger river bank/bed erosion

- Degrade River Water Quality by adding Suspended Solid. etc.

The key word in that case is certainly the moderation of withrawal taking into account the capacity of the river to renew the taken volumes and the greedy level of the exploitation which may deteriorate the environment, yielding floods and creating pollution accumulation zones...

In most cases it can be negative if not well planned and managed. I am referring to semi arid areas in particular. If it impact on the river bank it will result in increased erosion of the river bank. In many areas the sand will lower the flood retention during increased flow events and good stable river banks with good riparian vegetation will ensure that water velocity is decreased.

In addition, the sand will ensure that subsurface flow is maintained during low flow periods. If the sand in mined, it will expose the subsurface water resulting in increased evaporation of the water.

One may also add that mainly in arid and semi arid areas, river beds are hosting green zones made of well adapted vegetation. This has the advantage of slowing the flow of the rivers during flooding periods and boosting the infiltration towards the whallow watertables located below, while protecting them from any direct polluting factors..;

Agree with the comments above. Sand mining will alter the groundwater table will potentially adverse impacts on the riparian veg if the root systems can no longer access that water. In my experience once you let a miner in they take the lot, it takes very strict control (e.g. onsite environmental officer with clout) to limit the amount removed. Where the groundwater sustains permanent pools it can have marked impacts on the ecosystems

I do agree with all of you

In the south of Spain, we had/have a huge problem at the Guadiaro river mouth because the sand mining for construction purposes alterated all the morphodynamics of the zone

For further details you can see

- Environmental restoration of the Guadiaro river estuary, Cadiz (Spain), 2000.

JJ Muñoz-Perez, A de la Casa, G Gomez Pina, A Acha

Periodicum Biologorum 102, 333-338

- Reversal in Longshore Sediment Transport without Variations in Wave Power Direction, 2010. JJ Muñoz-Pérez, I Caballero, B Tejedor, G Gomez-Pina

Journal of Coastal Research, 780-786

Neverhteless, on the other hand, we usually dredge the sand of the river mouths on summer for maintenance of the adjacent beaches for tourism purposes. Data about methodology and cost of this system can be found for instance in

- Cost of beach maintenance in the Gulf of Cadiz (SW Spain), 2001.

JJ Muñoz-Perez, B Lopez de San Roman-Blanco, JM Gutierrez-Mas, L Moreno, GJ ...

Coastal engineering 42 (2), 143-153

- A critical review of beach restoration projects in the northern coast of Cadiz (Spain) after thirteen years, 2006.

G Gomez-Pina, L Fages, JL Ramirez, JJ Muñoz-Perez, J Enriquez

COASTAL ENGINEERING CONFERENCE 30 (4), 4167

I'd appreciate if anyone could let me know about some other similar data

What I feel is not good if river sand is mined in excess quantities. The following impacts are possible.

1. Bank erosion - severe bank erosion could happen during the next rainy season as the bank is not stable now due to sand mining.

2. As the river bed is deeper with sand mining, the water level in the river goes down. This will lower the water table in the adjacent areas affecting the wells.

3. As the river bed is decreased, salt water can intrude (if the sand mining is done in a place which is closer to sea outfall). Even in the rainy seasons, a salt water layer can exist in the deeper layers of the river (if the river is lower than the sea level due to sand mining)

4. As bottom sediments are removed, that can affect the organism living on the river bed.

5. Deep pits can cause harm to animal and human (due to falling in the pits)

6. Of cause some economic values.

Unless there is a need to remove river sand, there will be several negative impacts as discussed by my respective colleagues. It is also worth to mention that surface water is more vulnerable to pollution and in most of the cases the river sand works as a natural filter.

It is clear we understand the problem. What we need is ways to convince those who authorise such mining to the full costs involved, so often they only see the value to the mining company and not the costs to those affected by the mining.We need to document what was lost and the value of it, an I am not just talking about monetary value.

I think David's comment has value. He refers to to formal mining process are here there is a form of control or management. The controlling agents can enforce an EIA and some management strategies which is fine - if policing is effective.

A much larger concern is the non-approved activities. The small illegal operation in rural areas. I have seen many examples over the last few years in South Africa and the damage is huge.

If the local authorities (at what local level is present) are not onto the problem, the negative issues raised by the learned colleagues will result in ecological disasters.

I agree with all the previous comments, but I must add that the river sand is not just sand. The river bottom is sandy and contains mud. During the excavation of sand organic sludge is raised as well. Anaerobic conditions are common in that sludge, hence the sludge reacts on contact with the oxygen from the water in an oxygen-consuming reaction. Reducing the concentration of oxygen in the water, which is already on a very low level, you will agree, will have a negative impact on the enviroment.

... Not to mention other negative things, such as the formation of harmful, or even poisonous chemical compounds.

Thanks a lot to all for the inputs

The reason behind my question is that near by institution (Brahmaputra river,Guwahati,Assam,India), there is a much exploitation of the river sand whenever the water level goes down. The locals near the river bank are illiterate and not aware of the pros and cons. The major exploiters are rich and far from the river. I just want to know so that I can make aware the locals about the negative side of river sand removal.

a very good question, and great replies. Given that it is very hard to prohibit sand mining in such places due to the politician-contractor nexus, the question is how much can be tolerated. The Brahmaputra near Guwahati aleady has large floodplains, with a lot of himalayan sediment depositing out. Perhaps some of the sedimnet can be taken annually, equal to what deposits each year, thereby maintaining some sort of steady state in deposition and withdrawal via mining. The positive would be maintaining channel depth and thereby flood control. Negatives would be increased turbidity downstream, disturbing the local aquatic ecosystem as well as bank erosion as mentioned earlier, since the mining would happen in concentrated areas forminh pits etc. Its a difficult scene given the boom in construction in the region and nationwide.

There is little to add here, but I would like to point to the fact that large quantities of deposited sediments do cause inundations in the vicinity of the river. Here mining is encouraged to diminish material loss. There are cases where organised and controlled mining is necessary in order to maintain equilibrium, or by other words prevent those nearby towns and settlements being frequently flooded. This seems somewhat similar to what Juan Muñoz-Pérez wrote about above.

I do really think Peter is right.

Because beach-nourishment requirements on the southwestern Spanish coast have led to a significant increase in offshore dredging, assessment of changes recorded in physicochemical and biological parameters due to dredging and dumping operations was performed. Turbidity, salinity, pH, dissolved oxygen, temperature, and suspended-sediment data were collected and a three-campaign monitoring program was implemented for 1 year to assess the possible effects on biological communities and sediment properties. Methodology, data and discussion can be obtained from

- Turbidity and Other Effects Resulting from Trafalgar Sandbank Dredging and Palmar Beach Nourishment (2011). J Roman-Sierra, M Navarro, JJ Muñoz-Perez, G Gomez-Pina. Journal of Waterway, Port, Coastal, and Ocean Engineering 137 (6), 332-343

http://ascelibrary.org/doi/abs/10.1061/(ASCE)WW.1943-5460.0000098

Hakeem,

Are you talking about the suspended load or the bedload?

@ Rosenheim - Fine sand particles along side the river shore - then i believe suspended load !!!

There will be much more suspended load in the river when the discharge is high, so you will have an easier time collecting the sand. Also grain size distributions change - more fine grains during low discharge and a higher proportion of coarse grains during higher discharge. See the following references:

Nittrouer, J.A., Mohrig, D., Allison, M.A., Peyret, A.-P.B., 2011. The lowermost Mississippi River: a mixed bedrock-alluvial channel. Sedimentology 58, 20.

Allison, M.A., Demas, C.R., Ebersole, B.A., Kleiss, B.A., Little, C.D., Meselhe, E.A., Powell, N.J., Pratt, T.C., Vosburg, B.M., 2012. A water and sediment budget for the lower Mississippi-Atchafalaya River in flood years 2008-2010: Implications for sediment discharge to the oceans and coastal restoration in Louisiana. Journal of Hydrology 432-433, 84-97.

There is a lot to consider when answering this question. The answer will depend on the specific situation. Let's consider a river that flows through an unpopulated region, which has not been altered significantly by human enterprises such as farming. Taking sand will alter the river's natural condition and will surely be negative.

Now let's consider a river which flows through a densely populated region with farming on steep slopes in the uplands and hardened surfaces promoting rapid runoff in the lowlands. This river has artificially high sediment loads and is excessively prone to flooding in its lower reaches. Regulated removal of sand is probably beneficial in this case because it will tend to restore the river's prior structure and hydrological conditions. But if the sand is removed carelessly (without regard to effects on the channel) it could exacerbate the situation rather than improve it (such as by causing unwanted erosion of river banks by altering the channel).

So, regardless of the circumstance, the situation needs to be studied, modeled, monitored, and regulated so that properly informed decisions can be made. In addition to considering the physical conditions, attention will need to be paid to the biological communities that are present to ensure that (a) entire communities are not removed, thereby losing sources for plant community regeneration, and (b) there are no impacts on rarities. Since river sands are very unstable, their biological communities are generally resilient, so sand removal can probably be achieved at rates and in patterns that are sustainable provided the modeling and monitoring are done properly, and the (socio-political) regulatory system is not corrupt.

It is all about scale. Size of the river and the amount and depth of removal. Mostly negative in natural flowing systems. The advantages is limited and must be well managed.