Meghalaya

Organizers:

• Indian Space Research Organisation (ISRO)
• North Eastern Space Application Centre (NESAC)

Venue: North Eastern Space Application Centre (NESAC), Shillong

This report by Kalpavriksh, Aaranyak and ActionAid India deals with the large dams’ juggernaut, which happens to be the biggest ‘development’ intervention in this ecologically and geologically fragile, seismically active and culturally sensitive region in the coming days. With the Northeast identified as India’s ‘future powerhouse’ and at least 168 large hydroelectric projects set to majorly alter the riverscape, large dams are emerging as a major issue of conflict in the region.

Although the current scale of dam-related developments far outstrips anything which took place in the past, the region has been no stranger to dam-related conflicts. For example, the Kaptai dam, built in the Chittagong Hill Tracts of East Pakistan (now Bangladesh) in the 1960s, submerged the traditional homelands of the Hajong and Chakma indigenous communities, and forced them to migrate into parts of Northeast India.

The report presents flood plain mapping of Phulbari area within the flood plains of Brahmaputra basin in the States of Assam and Meghalaya using satellite data. Flood is a natural calamity in which most parts of the north-eastern region are ravaged. Management of the problem in these disastrous flood affected areas often requires flood plain mapping for protection and resource development. This has mostly being done in real time on the basis of time consuming and often hazardous ground based surveys.

In the study, the hydrogeomorphological parameters of Myntdu basin have been estimated from a digitized basin map where basic map data could be retrieved and manipulated quickly and accurately. The estimated geomorphological parameters of the basin covering linear, areal and relief aspects will be helpful in estimating and modeling the flow process in the basin.

The study attempts to do field and laboratory determination of soil classification properties in the Dudhnai river basin of Assam and Meghalaya. Point infiltration tests using double ring infiltrometer were conducted at various locations (forty-four sites) in respect of different land use conditions. Soil samples were collected from these infiltration testing sites.

The saturated hydraulic conductivity was determined in the field using Guelph Permeameter for the selected sites. The undisturbed soil samples and disturbed soil samples (50 cm below the ground) were collected and subjected to elaborate laboratory tests. 

The study develops a precipitation network design for the Myntdu-Leska basin, which lies near Cherrapunji, the zone of highest rainfall in the world. Network design offers an estimation of the number and location of the rain gauge stations to provide adequate information regarding rainfall falling over the catchment. 

The study applies the methodology developed by United States Department of Agriculture’s (USDA), Soil Conservation Services (SCS) for the nine subwatersheds of the representative Dudhnai basin in Assam & Meghalaya and estimates the runoff volume on a daily basis for the period 1986-1991. The method is widely adopted for the estimation of runoff from rainfall depths and takes into account the important physical aspects of a basin on which runoff depends such as land-use, hydrological soil cover and antecedent moisture condition.

The study attempts to develop a computerized model for Geomorphological Instantaneous Unit Hydrograph (GIUH) for estimation of flood hydrographs resulting from intermittent storms of varying intensity. The model applied to the rainfall-runoff data of the Myntdu-Leska basin of Meghalaya infers that the channel network and geomorphological features are closely related to the retention and discharge characteristics of the basin.

The theory of GIUH assumes that rainfall that occurs over a basin is assumed to be composed of infinite number of non-interacting drops of uniform size. After spending some time in one state in the channel or overland region, the drop makes transitions to another state to reach the basin outlet. Assuming one parameter, exponential time distribution of one drop chosen at random from the basin defines the IUH of the basin.

The study applies advanced models of design storm like Flood Analysis and Protection Systems (FLAPS) and HEC-1 for rainfall-runoff simulation employing selected short-term events of three basins of the north-eastern region – Myntdu-Leska (Meghalaya), Krishnai and Dudhnai (Assam). The results are used to study the sensitivity of the model parameters with respect to different hydrological parameters of the basin. The performance of these methods is evaluated by analyzing the isolated events. An attempt has been made to evaluate the non-linearity in rainfall-runoff response, using a simple storage-runoff dynamic model. The relationship of incipient soil moisture and transmissivity with direct runoff and recharge is studied.

Guest Post by: Amitangshu Acharya The Umiam Lake Conservation - Stakeholder Dialogue and Future Strategies was held on 9th and 10th March 2009 in Shillong. The presentations and some videos from the conference can be viewed here -https://www.indiawaterportal.org/data/conf/ULC.html To give help learn more about the Lake Umiam in Shillong, here is a backgrounder about Lake Umiam and its importance to Shillong. You can join the discussion forum about Umiam Lake here https://www.indiawaterportal.org/Network/forum/viewtopic.php?t=3044 Umiam Lake ( also known as Barapaani) originated as an artificial reservoir for the Umiam Umtru Hydro Electric Power project, the first of its kind in the North East. For a long time, this project had supplied the bulk of its power needs to the State of Meghalaya. The state's love affair with this lake spans 43 years. With approximately 12,000 mm of rainfall each year and a catchment area of 221.5 sq km (almost double the size of Chandigarh) Umiam rarely saw any dry days. Until now, that is. For two years now, Shillong has confronted one of the worst power crises ever. The reason is not hard to imagine: Umiam doesn't have enough water. Officially, inadequate rainfall has been cited as the sole reason, and a correlation does exist between decreasing water levels (about 39 feet over 3 years) in the lake and lesser rainfall since 2005. And once the water level falls below 3150 feet, there can be no power generation. However, the question is, whether the role of rainfall is being overplayed while the other issues remains unaddressed.