Instream Sand Mining Research Articles

Assessment of geomorphic status and recovery potential in anthropogenically altered river of Eastern India

ABSTRACT The study monitors chronological changes (1922–36 to 2023) in channel morphological status of the Mayurakshi River in Eastern India using the index of Geomorphic Status (GS). It encompasses Changes in Sedimentary Units (SU), Changes in Sediment Availability (SA), Changes in Bar Stability (BS) and Changes in Channel Flow (CF). The Index of Geomorphic Status (GS) reveals a sharp morphological degradation of the Mayurakshi River in the recent past. Therefore, a detailed checklist of channel width, bed-level, configuration dynamics and channel connectivity was prepared to identify medium- and short-term Channel Adjustment (CA). The study reveals that instream sand mining and structural interventions coupled with low discharge are the key factors hindering channel morphological recovery. Finally, a new Channel Recovery Potential Index (CRP) has been proposed by considering short-term channel adjustment, sediment connectivity, geomorphological setup and anthropogenic stresses. Preferred alternatives and optional groups assessed from the AHP-TOPSIS and AHP-VIKOR models were used to quantify the channel Recovery Potential. Outcome of the study reveals that reach 1 has more chance of channel recovery (TOPSIS: 0.77 and VIKOR: 0.00) compared to other sectors.

Evolution of the Chenglingji–Datong Channel in the Middle and Lower Reaches of the Yangtze River and Its Drivers

In recent years, the water–sand composition of the Yangtze River channel has changed due to the influence of human factors, especially the construction of water reservoirs such as the Three Gorges Project. Changing water–sand conditions have a long-term impact on the shaping of the river channel morphology in the middle and lower reaches of the Yangtze River, and the erosion retreat of local river sections has caused great harm to embankment projects. This paper focuses on the river evolution mechanism of the river channel from Chenglingji to Datong in the middle and lower reaches of the Yangtze River over the past 31 years. Landsat remote sensing images from 1989–2019 were used to extract and interpret water bodies, river shorelines, and central bars in the study area using the Modified Normalized Difference Water Index (MNDWI) combined with visual interpretation. We used near analysis to study the morphological evolution characteristics of the river, the channel, and selected typical river reaches for comparative analysis. We found out that the overall change in river morphology between 1989 and 2019 was small in the horizontal direction, but the local area changed significantly. Considerable scouring occurred in the vertical direction. Combining hydrological and meteorological data, we investigated the effects of the Three Gorges Dam, instream sand mining, boundary conditions, vegetation cover on both sides of the riverbanks, and aspects of storm flooding in the watershed on the evolution of the river. The study indicated that the geological conditions on both sides of the river, the implementation of the bank protection project, and the improvement of vegetation cover on both sides of the river have made the riverbanks more resistant to scouring. However, heavy rainfall floods, the operation of the Three Gorges Reservoir, and sand mining activities in the river channel make the river channel more susceptible to scouring. Based on the calculation of the slope change rate of the accumulated volume, it was found that the runoff is mainly influenced by precipitations, while the sand transport is mainly affected by human activities. This study shows that natural and anthropogenic activities affect the equilibrium state of the river’s water and sediment to varying degree.

In-Stream Sand Mining and Primary Productivity of Otamiri River in Owerri, South-East Nigeria

Sand mining involves the excavation of inland dune or river beds for the purpose of economic, developmental, constructional, etc., activities. Primary productivity therefore, is the frequency at which energy is transformed to organic substances by photosynthesis producers (photoautotrophs), which obtain energy and nutrients by requisite sunlight. Probable influence of sand mining on primary productivity of the mined ponds along the banks of the river was considered. The study undertakes an experimental research approach. Six (6) sampling locations were identified as WC1-WC6 along the course of the river. WCI-WC3 was established in area where active mining had ceased (unperturbed) whereas WC4-WC6 was established in area where active sand mining is ongoing (perturbed). The study utilized the light and dark technique to estimate primary productivity, and the set-up was incubated for four (4) hours in a sunny day. In situ measurement was carried out with HANNA 1H9828 pH/ORP/EC/DO meter and the average of the triplicate results obtained was recorded. Descriptive statistics, analysis of variance (ANOVA), student’s t-test and the structure detection of group mean were utilized for the organization of data. Results inter alia revealed that the actively mined ponds of the river had higher GPP (12.781*10-1 MgCL-1d-1) than the location where mining had ceased (i.e., GPP 5.986*10-1 MgCL-1d-1). The average GPP was 18.767*10-1MgCL-1d-1 while NPP and CR had 10.914*10-1 MgCL-1d-1 and 15.453*10-1MgCL-1d-1 respectively. The annual GPP of the study was 1144.800*10-1MgCL-1yr-1 which define low productivity. Thus, it was recommended that an enforcement of various environmental laws as it affects the preservation, maintenance and the sustenance of the aquatic environment be made in a bid to secure aquatic lives.

Assessment of suspended sediment load variability in the Tonle Sap and Lower Mekong Rivers, Cambodia

The Mekong River in Southeast Asia, one of the world’s great rivers, has been facing disruption of its sediment balance and resultant impacts on nutrient fluxes, aquatic ecology, floodplains and the delta. Using monitoring data from 1993 to 2018, we estimated the temporal variability of sediment loads in Tonle Sap and Lower Mekong Rivers in Cambodia, assessing the sediment linkage between the Tonle Sap Lake and the Mekong mainstem, which are connected by a seasonally reversing flow through the Tonle Sap River. We estimated the annual sediment in the Mekong mainstem of 72 ± 38 Mt/year at Kratie (upstream) and 78 ± 22 Mt/year at Chroy Changvar from 1993 to 2018 (just upstream of the Chatumuk confluence). Our sediment load estimation of the Mekong River is consistent with other recent estimates of sediment load on the Lower Mekong. However, the result is lower than reported in some older studies (prior to the 2000s), which is consistent with sediment trapping by dams on Upper Mekong mainstem and major tributaries. Our analysis indicates that Tonle Sap Lake provided 0.65 ± 0.6 Mt/year of sediment annually to the Lower Mekong River from 1995 to 2000. However, since 2001, Tonle Sap Lake has become a sink for sediment, accumulating an average of 1.35 ± 0.7 Mt annually. Net storage of sediment in Tonle Sap Lake reduces the annual sediment transport to the delta, further compounding the effects of reduced sediment delivery to the delta resulting from upstream dam development and instream sand mining.

Fingerprinting sediment sources of the Shouchang River in the Southeastern China

Identification of sediment sources within catchments is crucial for river and catchment management. A multivariate mixing model in conjunction with two sets of statistically verified composite fingerprints was employed to identify the main sediment source areas at five locations along the main channel of the Shouchang River, southeastern China. The fingerprint composite fingerprints derived from the principle component analysis (PCA) and discriminant function analysis (DFA) combination can better apportion the five types of potential sediment sources. This combination demonstrated that over 33.0% sediment at each location came from river bed, with the largest contribution of 42.9%. The contributions from construction lands ranged from 16.0 to 26.8%. Sediment contributions from forest lands ranged from 7.8 to 22.1%. A large portion of sediment came from paddy fields, varying from 8.7 to 31.4% at the five locations. The sediment from dry land was the smallest, with the largest contribution of 18.4%, and the least contribution of 4%. Similar findings were also identified using the composite fingerprints derived from KW-H and DFA combination. Land use, topography, precipitation, and human activities were responsible for the sediment source apportionments and their variations at the five sediment sampling sites. This study implies that the available sediment from road and bridge built as well as plant production should well be supervised, laws should be made to inhibit in-stream sand mining activity, and the connectivity between paddy fields and channels should be reduced.

Impact of instream sand mining on habitat destruction or transformation using coupling models of HSI and MLR

Several human activities like sand mining, dam construction have intensive effect on river ecosystem. Instream sand mining is one of them to hindrance on riverine biota. Hence, an attempt is made in this study to assess three tier habitat degradation or alteration caused by instream sand mining from channel bed to riparian and bank site in upper, middle and lower segments of Kangsabati River. Habitat Suitability Index (HSI) is applied to detect geo referenced ecological information on two different condition i.e. habitat suitability of two dominating species of Koeleria macrantha and Cynodon dactylon (pre mining) and degraded or altered habitat incorporated with mining responses (post mining). HSI prepared five different suitable class taken seven dominating variables i.e. river channel, sandchar, riparian zone, slope, elevation, dry and moist sand layer using multiple logistic regressions (MLR) under GIS platform. MLR denotes sandchar deposition, elevation as significant variables of Koeleriamacrantha dominance along the bank while moist sand layer, riparian zone signified on Cynodondactylon dominance across the riparian site. HSI indicates low-suitable class of Koeleriamacrantha and Cynodondactylon dominated in largest sand mining area as lower (82%, 86%), middle (58%, 89%) and upper segment (77%, 78%) whereas largest mining area under two dominant species reaches low-suitable class as lower (79%, 58%), middle (89%, 82%) and upper segment (92%, 70%) respectively. In spite of variables influence on species dominance, massive sand mining leads to destroy the habitat suitability. Therefore, in situ habitat suitability of dominant species either degraded or altered throughout the channel.

Effect of instream sand mining on hydraulic variables of bedload transport and channel planform: an alluvial stream in South Bengal basin, India

Sand mining adversely behaves with changing river system, especially in the bedload transport process. This study aims to find out the relationships between river water flows, sediment transport regime in bedload transport and also tries to determine how instream mining affect the sediment inflow and channel planform change. The field study has been conducted in three selected sites on Kangsabati River situated in the lower, middle and upper course. Several established equations were applied to derive the results from water flow and sediment regime. GSTAT was used to prepare coarse medium (CM) diagrams and tractive current deposits to analyze the trend of sediment throughout the river course. Sediment and bedload transport were measured using Ackers and White (J Hydraul Eng Div ASCE 99(hy11):2041–2060, 1973) and Meyer-Peter–Muller methods (IAHSR 2nd meeting, Stockholm, appendix 2. IAHR, 1948). Shear stress and critical shear stress were computed using Shields (Application of similarity principles and turbulence research to bedload movement, 1936) and DuBoys equations whereas Friend and Sinha’s method (Braiding and meandering parameters, vol 75, No 1, Geological Society, London, 1993) was used to detect irregular planform response caused by sand mining. Regression analysis denotes that mining intensity can be change the shear stress (R2 = 0.972); velocity (R2 = 0.683); grain diameter (R2 = 0.555) and sediment concentration (R2 = 0.997) on bedload transport. Mining activities can be changes of hydraulic responses as well as interruption of sediment and bedload transport throughout the channel. In context of sand mining, planform response denotes that thalweg shifting leads to massive sandchar deposition in upper course, huge channel incision causes river bank erosion in middle course and pool–riffle alteration expanded in channel and pit area in lower course.

Losing ground - scenarios of land loss as consequence of shifting sediment budgets in the Mekong Delta

With changing climate and rising seas, proliferation of hydroelectric dams, instream sand mining, dyking of floodplains, accelerated subsidence from groundwater pumping, accelerated sea-level rise, and other anthropic impacts, it is certain that the Mekong Delta will undergo large changes in the coming decades. These changes will threaten the very existence of the landform itself. The multiplicity of compounding drivers and lack of reliable data lead to large uncertainties in forecasting changes in the sediment budget of the Mekong Delta, its morphology, and the ecosystems and human livelihoods it supports. We compile information on key drivers affecting the sediment budget of the Mekong Delta and compare them to quantify the magnitude of effects from different drivers. We develop a set of likely scenarios for the future development of these drivers and quantify implications for the future of the Mekong Delta using a simplified model of the delta's geometry. If sediment supply to the delta is nearly completely cut off, as would be the case with full buildout of planned dams and current rates of sediment mining, and with continued groundwater pumping at current rates, our model forecasts that the delta will almost completely disappear by the end of this century due to increased rates of delta subsidence and rising sea levels. While local management cannot prevent global sea level rise, model results suggest that there are important management steps that could prolong the persistence of the delta ecosystem and the livelihoods it supports, including a reduction in ground water pumping and maintaining sediment connectivity between the basin and the delta.

Human interventions and consequent environmental degradation of a protected freshwater lake in Kerala, SW India

Sasthamkotta lake in the southwestern coast of India is the largest freshwater lake in the region. The lake has a water spread area of about 3.75 km2 and serves as a drinking water source for about seven lakh people in southern Kerala. Unfortunately, the lake is at the verge of severe degradation consequent to different kinds of human interferences. The Sasthamkotta lake receives water mainly from rainfall (2,350 mm/year) and surface run-off (3.33 million m3/ year). Apart from these, a significant quantity of water reaches the lake through underwater springs emerging from the Quaternary and Neogene aquifers as well. Rampant removal of construction grade sand using high power jet pumps from the Quaternary aquifers linking the lake with the adjoining river, over exploitation of lake water, unscientific engineering constructions, etc. are some of the externalities leading to degradation and ultimate drying up of the lake. The floodplain of the Kallada river, hosting the lake Sasthamkotta, was unaffected by sand extraction till early 1970’s. The results of the present study revealed that indiscriminate sand mining has turned floodplain area of about 3.57 km2 into fallow lands, during the past 3–4 decades. This together with the riverbed lowering due to instream sand mining has significantly reduced the groundwater replenishment of the lake system. The construction of embankment on the southern side of the lake has not only isolated the lake system from its natural settings, but has prevented the flood pulse contribution of monsoon waters to a considerable extent. The present paper examines in detail the pros and cons of the human induced environmental degradation of the Lake Sasthamkotta which is declared recently a Ramsar wetland of international importance. Based on the study, a set of recommendations are also drawn for improving the overall environmental quality of the Sasthamkotta lake in particular and the freshwater lakes in the coastal lands of densely populated tropics in general.

Accumulation and recovery capacity of heavy metals in sand mine ponds of the Otamiri River in Owerri, Nigeria

This study investigated the levels, index of accumulation and recovery capacity of heavy metals (Pb, Cd, Cu, Ni, Zn, Fe, Mn) in sand mine ponds of the Otamiri River in Owerri, Nigeria during the wet season of 2012. Water (WC) and sediment samples (SD) were collected from six sampling points, with WC 1-WC 3 and SD 1-SD 3 located within a derelict mine pond and WC 4-WC 6 and SD 4-SD 6 located within an actively mined pond. The pH was determined in situ and levels of heavy metals measured with the atomic absorption spectrophotometer. The student’s t-test, index of geoaccumulation (Igeo), accumulation factor (AF) and pond recovery capacity (PRC) were computed for the ponds. There was significant spatial heterogeneity in mean levels of the heavy metals in sediments (sig. t=0.029) at P Zn (4.932)> Cu (4.743) > Mn (4.326) > Pb (3.214) > Ni (2.483) > Cd (1.649), AF was Zn (1.513) > Cd (1.179) > Fe (1.082) > Ni (1.048) > Mn (1.042) > Cu (1.032) > Pb (0.987) and PRC was Zn (33.891) > Cd (15.165) > Fe (7.604) > Ni (4.608) > Mn (4.047) > Cu (3.052) > Pb (-1.373). Active mining led to extreme contamination of the ponds with Fe, strong to extreme contaminations with Cu, Zn and Mn, strong contamination with Pb, moderate to strong contamination with Ni and moderate contamination with Cd. However, Pb showed deficit recovery capacity and this could portend unfavourable ecological consequences on resident biota and raises public health concerns among resource dependants of the river. Strict enforcement of regulations on in-stream sand mining should be applied.

Spatial Fluctuations in Zooplankton Biotypes of the Imo River in a Niger Delta Area of Nigeria

<b> </b><b> </b>The study identified zooplankton biotypes of the increasingly in-stream sand-mined Imo River in Etche, a Delta area of Nigeria, as indicators of the health of the aquatic ecosystem. Plankton samples were collected with a 55μm mesh size plankton net that was hauled horizontally along the river course for 5 minutes at 7 sampling locations once monthly for 24 months (March 2007-February 2009). Samples were fixed/preserved in 4% formalin solution in labelled plastic containers. In the laboratory, a wide-mouthed pipette was used to withdraw 1ml of the plankton subsample and to place it on a Sedge-wick rafter-counting chamber. Standard keys were used for species identifications and counts made through direct microscopy. The ANOVA, post-hoc plots of group means, hierarchical cluster analysis (HCA), and the Margalef’s species diversity index were used to analyze data. Zooplankton had low diversity index (0.926 ± 0.100) and was made up of 7 taxa and a mean density of 433 organisms/ml; with order of dominance as Cladocera (25.87%)> Copepoda (20.55%)> Protozoans (19.17%)> Rotifera (18.71%)> fish eggs and larvae (9.24%)> Crab larvae (4.62%)> Beetle larvae (0.69%). Plankton abundance peaked in sampling location 1 (140 organisms/ml; 32.41%) and was least in location 3 (21 organisms/ml; 4.86%), even as there was marked spatial heterogeneity in the taxa composition[F<SUB>(11.94)</SUB>>F<SUB>crit(3.94)</SUB>] at P<0.05. The HCA revealed that crab larvae, fish eggs and larvae, beetle larvae, and copepods formed the first and richest cluster, while the rotifers, cladocerans and protozoans formed the sparse 2<SUP>nd</SUP>, 3<SUP>rd</SUP> and 4<SUP>th</SUP> clusters, respectively. The low biotic diversity recorded could be attributed to growth-limiting perturbations created by ongoing in-stream sand mining in water columns.