Sand mining lowers the riverbed in the water storage love, thereby, effecting physical and biological environments of the river system..

sand mining in excess of annual sediment loading can cause shift in local grade control and rejuvenate upstream degradation (downcutting) of channel system.  If there are good upstream channel grade controls, the effects upstream are less.  If upstream channel system degrade such as bullying, the runoff is increased, baseflow reduced as adjacent water tables lower on effected reaches.  Downstream of inchannel sand mining can produce a clean water effect (Kondolf is a good author explaining this) that increases bank erosion downstream resulting in a wider and thus somewhat shallower river.  Riparian bank erosion can also undercut bank trees, leading to bank failures.  As mentioned, Matt Kondolf (California) has a paper on the Clean water effect of insteammining.  I have personally seen some of these effects in Broad River in South Carolina from deep channel dredging.  Similar effects of local dredging in smaller tributaries was also found.  Upstream indications in Broad River I have seen with aerial photos are truncated (eroded) point bars on downstream end especially, as the channel adjusts (degrades).  If you have an aggrading system from too much sediment loading, perhaps some sand mining could even be beneficial.

The effects are apt to be greatest in sand substrates without good channel controls such as coarse shoals or bedrock.  Also streambanks without deep, dense root systems also more prone to effects.  Soils that are deeply weathered, highly erosive or tendency for bullying or chemical imbalance such as marine terraces may also be subject to greater effect.  It would be however best to evaluate each circumstance on its own merits, and of course reauire mining companies to be awar of thesee possible impacts and produce a performance  bond to help with mitigation or damages. 

Dredging of sediments in reservoirs may be soother option to help maintain capacity, and remove highh quality materials for construction.  Carefully designed dredging in a braided channel system may be beneficial or at least less impactive, to dredge an maintain a stable bank full channel.  

Sand mining lowers the riverbed in the water storage love, thereby, effecting physical and biological environments of the river system..

Dear Respondents,

thank you for the answers.

Sand mining on the river bed, of course, reduces bed level. Due to the continuous cyclic process of erosion and deposition,  there may not be much trouble to the environment when with in safe depth. Consider this If we are not dredging/mining the sand deposits in the river bed then finally they will be deposited on the sea bed. In that case dredging the sand deposits for using as construction material will not be an issue when we maintain the safe depth of dredging.  

Safe dredging depth- depth to which only possible minimal effect on the biota(micro and macro organisms environment)

The question is still alive and fully not answered.

Yes I agree with you Velusamy. I think, ecology of  the river is badly affected with sand mining..

Sand mining and its impact on water resources is an important issue. Sand mining is related to removal of sand in excess of its depositional rate along the river beds. The sand bed in the river beds is a potential aquifer and it stores portion of the river water which otherwise would have been lost to sea. Now a days lot of studies are being carried out to estimate the annual rate of sand deposit along the river courses and also safe level of sand removal from the river beds. 

This subsurface water stored in the river bed material (sand bed) is used in summer months in many places through infiltration wells or galleries for domestic water supply schemes. Once this sand bed is removed or reduced due to sand mining, the performance of these water supply schemes will be affected due to reduction in the saturated thickness of the aquifer.

The other effect of sand mining is in the reduction of summer flows/lean flows in the rivers and furtherance of salinity intrusion in the coastal region.

Because of the water table gradient change in the river bed material due to sand mining, it is expected that there will be fall in groundwater level in the wells situated on the banks (higher elevations/higher slopes).

I think that there is a negative relationship between sand mining in river and river water availability due to the increased amount of sediment sand in along the river which mean more and more river water escaping to the sea and as a result decreased available river water.

Sand Mining certainly alters the river regimen, and impacts environment adversely. There is however a natural erosion pattern as well that occurs.I think there has to be a balance between resource use & conservation, for preservation of nature. 

Sand "excavation" is important along the river course, otherwise with the continued sand deposit there can be river bank erosion or floodplain problems. However sand "mining" is hazardous, as it is expected to create many adverse effects like reduction in the saturated thickness affecting the river based water supply schemes; salinity intrusion due to reduction in the river flow during lean period; reduction in natural sediment discharge to seas; etc. Presently lot of studies are being carried out to assess the annual sand deposit and feasible sand removal from the river stretches.

Sand mining should be balanced with river sand transport which is potentially deposited to replace sand excavated. Otherwise, the river bed will be degraded resulting in decreasing water profile of the river. This condition will affect the groundwater table, making possibility sea water intrusion.   

I would like to tell that the whole issue of this sand mining is very tricky and complicated. The whole activity related to sand mining involves researchers to assess the quantity of safe removal of sand; bureaucrats to monitor & control the unregulated sand mining; labourers involved in mining of sand; Government to auction the resource & collect revenue; Politicians in managing the conflicting issues between various sections of public; and most importantly building industry.

Assessing the removal of sand is very difficult as it is not removed uniformly along the river course. In some places the river bed has been excavated to such depths under the water body that, people have even died unknowingly falling into  these trenches. There are Dos and Donts of sand mining but it is hardly followed by the lorry owners. Though there are reports on the ill-effects of sand mining in a given watershed such as bank erosion; turbid water; lowering of water table; salinity ingression in the lower reaches; poor performance of the river bed based public water supply schemes; no body cares because of the reasons such as no alternative construction material; great demand for river sand and every body wants their own home. Government agencies have also utterly failed in controlling the miners, for various compulsions and limitations.