The major threat that a river irrigation project system faces during its life time is reduction in its storage capacity owing to the process of sedimentation, which means reduction in the potential ayacut of the project. When it comes to the hydropower projects, this problem extends even to the water conveyance systems leading to inefficiency in the operations of power generation. Although soil erosion and movement of soil particles and deposition of sediment are natural hydrological process, sedimentation is accelerated by the change in land-use pattern, deforestation, adoption or no adoption of soil conservation techniques, etc., in the catchment area.

Therefore, it is essential to collect information on the rate and extent of reservoir sedimentation for not only assessing the probable life of a reservoir, but also to initiate appropriate preventive measures for keeping sedimentation of reservoirs under check. Secondly, realistic assessment of reservoir’s available storage capacity based on the so collected information enables the management of the reservoir to draft an optimum reservoir operation schedule. There are of course several methods including empirical and numerical simulation models developed to predict deposition pattern of sediments. With the advent of remote sensing techniques, assessment of reservoir sedimentation has of course become highly cost-effective, besides being less time-consuming vis-à-vis conventional methods.

We have R K Jaiswal, T Thomas, R V Galkate and S Singh, authors of the first paper of the issue, ”Revised Capacities and Sediment Pattern Assessment in Rajaval and Kharo Reservoirs of Gujarat (India)”, who made an attempt to compare the revised storage capacities of Rajaval and Kharo reservoirs of southern Gujarat using the image analysis technique of remote sensing data. The authors have used seven Linear Image Self-Scanning digital data of IRS ID/P6. The analysis carried out using the normalized difference water index, band ratio, and slicing to classify the water and non-water pixels from the images using ILWIS 3.0 GIS software has revealed that the sedimentation rate increased significantly during 2000-07 in both the reservoirs. The authors have also opined that the Rajaval reservoir needs immediate measures to arrest the sedimentation.

Moving away from sedimentation to predicting rainfall runoff in a watershed, we have, Kuok King Kuok, Po-Chan Chiu, Chai Min Chung and Tiong Huo Chuang, presenting their simulation studies of hourly rainfall-runoff relationship carried out in three selected catchments in the southern region of Sarawak using appropriate hydrologic parameters in the second paper, “Relationship Between Storage Coefficient and Catchment Area Using Hec-Hms for Southern Region of Sarawak”. The authors have selected Hydrologic Engineering Center—Hydrological Modeling System (HEC-HMS) as the model and optimized the model parameters with combination of initial and constant laws, Clarke unit hydrograph, recession baseflow and Muskingum routing methods. The accuracy of simulation results was then measured with coefficient of correlation and peak error. The analysis revealed that the optimized time of concentration and storage coefficient are very close to the calculated results. Based on the results, the authors have established relationship between storage coefficient and catchment area through a linear equation which is set to be useful to the hydrologists to estimate the time of concentration and storage coefficient values for the ungauge catchments at southern region of Sarawak.

Moving on to the next paper, “Effect of Fencing on Morphological, Chemical and Physical Attributes of Soils in an Agricultural Catchment in N-W Tract of India”, we have its authors, M S Hadda, Dapinder Pal Singh, M Vashistha and Narinder Mohan, presenting the affect of fencing on morphological, chemical and physical attributes of soils of northwestern tract of India. This tract is ecologically degraded and terrain is undulating because of which soil erosion has became a serious threat to agricultural productivity. Fencing is found to be effective in retaining more organic carbon content, total soil nitrogen content, and phosphorous content besides increased clay content.

Moving on from soil erosion to flood modeling, we have Ting Sie Chun, Frederik Joseph Putuhena and Salim Said presenting the findings of their study to identify the causes of inundation in Sibu town of Sarawak state in the next paper, “InfoWorks Collection System-Based Hydrodynamic Modeling in Sibu Town”. The authors have used infoworks Collection System (CS) that is embedded with Geographic Information System (GIS) to develop one-dimensional hydrodynamic modeling tool to identify the causes of flooding in the area. From the reconstruction studies carried out using the model and the analysis thereof revealed that it can be used to effectively produce a clear view of one-dimensional flood scenarios of the drainage system and thereby undertake effective inundation mitigation.

Moving on to tropical forest soil, we have Ahmad Makmom Abdullah, Nurul Azzura Shahadan and Marzuki Ismail presenting their findings on the physicochemical properties of forest soil in their paper, “Physicochemical Properties of Tropical Forest Soil”. The study revealed that there is no dramatic change in soil chemistry of the area studied over three decades.

To conclude we have B Mamatha, T N Shivananda, K Sudhir, A N Ganeshamurthy and Savitha M Murthy presenting the findings of their study on FYM application on plant growth and biomass accumulation in their research note, “Evaluation of Biofertilizers on Growth and Biomass Accumulation of Coleus vettiveroides”.

-- GRK Murty
Consulting Editor