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EXECUTIVE SUMMARY
On
UGC Major Research Project Report entitled
‘ESTIMATION OF SUSPENDED SEDIMENT YIELD FROM
THE MORA DHANSIRI RIVER CATCHMENTS OF
DARRANG DISTRICT OF ASSAM’

Dr Rana Sarmah
PRINCIPAL INVESTIGATOR
and
Associate Professor, Department of Geography,
Pandu College, Pandu, Guwahati-781012
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The principal aspects which have focused in this report are soil erosion, soil loss, sediment yield, and soil nutrient loss from the Mora Dhansiri River catchments. The rates of soil erosion and sediment yield are also highlighted for having their wider consequenses in landscape change and agricultural productivity.

It is measured that the study area (Mora Dhansiri River basin), covering an area of 151.87 km2, spreads over the districts of Udalguri and Darrang occupying 98.63 km2 (62.61%) and 53.24 km2 (37.39%) of area respectively. The Mora Dhansiri River is a floodplain river and one half of its basin falls in the piedmont region while the second half occupies the younger floodplains of the northern Brahmaputra valley. The basin is devided into four physiographic/geomorphological units viz. (a) piedmont zone (area 32.46 km2), (b) younger alluvial plain (area 64.48 km2), (e) older alluvial surfaces (area 17.40 km2), and (f) floodplain zone (area 37.53 km2). The average annual rainfall in the valley part of the basin is 200 cm. About 71% of total annual rainfall is received during the monsoon months (May to October). The average rainfall intensity in the study area is recorded to be 12 mm/hr. The study made on land use pattern that most of the areas of the study area are occupied by agricultural lands followed by forest land, wastelands, and built-up lands. Four drainage density classes are earmarked in the study area. These are very low (0-0.40 km per km-2), low (0.41-0.80 km per km-2), medium (0.81-1.20 km per km-2), high (1.21-1.60 km per km-2), and very high (1.61-2.10 km per km-2). In case of drainage frequency too four classes are earmarked. These drainage frequency classes are very low (0-0.80 No. per km-2), low (0.81-1.60 No. per km-2), medium (1.61-2.40 No. per km-2), high (2.41-3.20 No. per km-2), and (3.21-3.60 No. per km-2). It is found that the average discharge during the wet monsoon months (July to October) were 1.72 m3s-1, 4.14 m3s-1, 5.97 m3s-1, and 7.96 m3s-1 at Bhairabkunda (source), Mora Dhansiri village, Lalpul bridge, and confluence respectively in 2009; the same were 1.95 m3s-1, 4.73 m3s-1, 6.89 m3s-1, and 9.63 m3s-1 at Bhairabkunda (source), Mora Dhansiri village, Lalpul bridge, and confluence respectively in 2010; and 1.73 m3s-1, 4.19 m3s-1, 6.27 m3s-1, and 9.51 m3s-1 at Bhairabkunda (source), Mora Dhansiri village, Lalpul bridge, and confluence respectively in 2011. Mora Dhansiri River does not record any significant flood event during the period under study. The Mora Dhansiri River transported an amount of 4258 tons, 10623 tons, 20030 tons, and 30147 tons of suspended sediment at Bhairabkunda (source), Mora Dhansiri village, Lalpul Bridge, and confluence respectively during July to October in 2009; 6678 tons, 16825 tons, 27051 tons, and 39645 tons at Bhairabkunda (source), Mora Dhansiri village, Lalpul Bridge, and confluence respectively during July to October in 2010; and 6044 tons, 14310 tons, 24290 tons, and 36043 tons at Bhairabkunda (source), Mora Dhansiri village, Lalpul Bridge, and confluence respectively during July to October in 2011. In other months, suspended sediment transportation is found to be not significant. It is found that the first reach covering 34% of the river has stored 25% of sediment, the second reach covering 22% of the river has stored 36% of sediment, and third reach covering 43% of the river has stored 39% of sediment in 2009. This scenario in 2010 is found to be 29%, 33%, and 38% respectively in the three reaches. In 2011 the same are calculated to be 40%, 20%, and 40% respectively. The low medium and high percentages of storage of sediment in upper, middle, and lower river reaches are attributable to corresponding low (49%), medium (38%), and high (65%) percentage coverage of catchment area under these reaches. However, the only exception is in the first reach because of hydrogeomorphological conditions where suspended sediments are less produced. Besides, nature of use of lands in the catchment area is also found to be an important factor of this trend. It is found in this study that the lands covered under the first reach are mostly forest land, grass land, and barren land. Human interventions on these lands are less compared to the lands under lower reaches and thus sediment transportation and storage in the channel is found to be less in percentage. On the other hand, lands under the middle and lower reaches are agricultural lands mostly devoted to production of summer crops. Catchments of this part of the Mora Dhansiri River reach occupies floodplain areas and is primarily devoted to production of summer crops like rice, orange, jute, etc. Land tillage during high rainfall period is high and thus sediment flow too is high. This is why, sediment storage in the middle and lower reaches are found to be propotionately high.

The study made on soil loss following a proposed conventional method reveals that magnitude of soil loss is mostly triggered by anthropogenic forces. This study has estimated that magnitude of soil loss in the Mora Dhansiri River catchment from built-up land, agricultural land, forest land, and waste land are in the order of 3767, 39824, 534, and 1952, tons respectively in 2009; 4674, 56704, 624, and 1664, tons respectively in 2010;.and 5646, 45369, 1258, and 3422 tons respectively in 2011. Rates of soil erosion from built-up land, agricultural land, forest land, and waste land are estimated to be 2.00, 3.09, 1.10, and 1.85, tons/hectare respectively in 2009; 2.39, 4.61, 1.30, and 1.87, tonnes/hectare respectively in 2010;.and 2.83, 4.23, 2.60, and 3.73 tons/hectare respectively in 2011. Average magnitude of soil erosion from built-up land, agricultural land, forest land, and waste land during 2009-2011are estimated to be 4696, 47299, 805, and 2346 tons respectively. Average rate of soil erosion from built-up land, agricultural land, forest land, and waste land during 2009-2011are estimated to be 2.41, 3.98, 1.67, and 2.48 tons/hectare respectively. Rate of soil erosion from the catchment of the Mora Dhansiri River is estimated at 3.67 tons/hectare/year.

Amount of soil loss, mostly triggered by anthropogenic forces, is also estimated following Revised Universal Soil Loss Equation (RUSLE). Amount of soil loss in the Mora Dhansiri River catchment from built-up land, agricultural land, forest land, and waste land are estimated to be 2768, 17586, 1692, and 6830, tons respectively in 2009; 6555, 53380, 2009, and 8836, tons respectively in 2010;.and 6112, 52818, 1941, and 8768 tons respectively in 2011. Rates of soil erosion from built-up land, agricultural land, forest land, and waste land are estimated to be 1.47, 1.76, 3.61, and 4.63, tons/hectare respectively in 2009; 3.35, 5.28, 4.19, and 6.27, tons/hectare respectively in 2010;.and 3.07, 5.09, 4.05, and 6.17 tons/hectare respectively in 2011. Average magnitude of soil erosion from built-up land, agricultural land, forest land, and waste land during 2009-2011are estimated to be 5145, 41261, 1881, and 8145 tons/year respectively. Average rate of soil erosion from built-up land, agricultural land, forest land, and waste land during 2009-2011are estimated to be 2.63, 4.04, 3.95, and 5.69 tons/hectare/year respectively. Rate of soil erosion from the entire catchment of the Mora Dhansiri River is estimated at 4.08 tons/hectare/year. Principal Component Analysis done on factors of soil erosion considered in RUSLE reveal that cannopy cover, average rainfall, and rainfall intensity are the principal factors of soil erosion.

Suspended sediment yield (ton/km2/second) from catchment of Mora Dhansiri River is estimated following a proposed conventional method. It is found that amount of sediment yield in 2009 is 5811ton, 4784 ton, 5503 ton and 4007 ton at sediment Outlet No.1, Outlet No.2, Outlet No.3, and Outlet No.4 respectively. The total sediment load transported is estimated to be 20105 ton in 2009. The rate of sediment yield through the four outlets of the Mora Dhansiri River is worked out to be 436 ton/km2/year in 2009. It is also estimated that the amount of sediment yield in 2010 is 7476 ton, 5737 ton, 7612 ton and 5015 ton at outlet-1, outlet-2, outlet-3, and outlet-4 respectively. The total sediment load is estimated to be 25840 ton in 2010. The rate of sediment yield is worked out to be 560 ton/km2/year in 2010. Magnitude of sediment yield in 2011 is estimated to be 5494 ton, 4757 ton, 8748 ton and 3411 ton at outlet-1, outlet-2, outlet-3, and outlet-4 respectively. The total sedimentload is estimated to be 22410 ton in 2011. The rate of sediment yield is calculated to be 486 ton/km2/year in 2011. The amount of sediment yield in the three years period (2009, 2010, and 2011) is calculated to be 68355 ton with the rate of sediment yield 494 ton/km2/year.

Studies made on soil nutrient loss reveal that high the intensity of rainfall high the loss of soil nutrient. It is also found that high the number of days of rainfall high the loss of soil nutrient. Average rate of sodium loss from built-up land, agricultural land, forest land, and waste land are found in the order of 0.04, 0.04, and 0.07, ton/hec in 2009, 2010, and 2011 respectively; 0.05, 0.06, and 0.08 ton/hec in 2009, 2010, and 2011 respectively; 0.02, 0.03, and 0.07 ton/hec in 2009, 2010, and 2011 respectively; and 0,03, 0.03 and 0.04 ton/hec respectively in 2009, 2010, and 2011 respectively. It is estimated that the average rate of potassium loss from built-up land, agricultural land, forest land, and waste land are in the order of 0.04, 0.04, and 0.06, ton/hec in 2009, 2010, and 2011 respectively; 0.04, 0.06, and 0.07 ton/hec in 2009, 2010, and 2011 respectively; 0.04, 0.06, and 0.07 ton/hec in 2009, 2010, and 2011 respectively; and 0,03, 0.03 and 0.04 ton/hec respectively in 2009, 2010, and 2011 respectively. The estimated average rate of calcium loss from built-up land, agricultural land, forest land, and waste land are in the order of 0.03, 0.03, and 0.06, ton/hec in 2009, 2010, and 2011 respectively; 0.05, 0.07, and 0.09 ton/hec in 2009, 2010, and 2011 respectively; 0.04, 0.05, and 0.07 ton/hec in 2009, 2010, and 2011 respectively; and 0.03, 0.04, and 0.04 ton/hec respectively in 2009, 2010, and 2011 respectively. Finally the average rate of organic matter loss from built-up land, agricultural land, forest land, and waste land are in the order of 0.006, 0.007, and 0.012, ton/hec in 2009, 2010, and 2011 respectively; 0.009, 0.012, and 0.016 ton/hec in 2009, 2010, and 2011 respectively; 0.01, 0.01, and 0.02 ton/hec in 2009, 2010, and 2011 respectively; and 0.008, 0.009, and 0.011 ton/hec respectively in 2009, 2010, and 2011 respectively. It is found that rate of loss of soil nutrients is highest in 2011 followed by 2010 and 2009. Our study reveal that rate of loss of organic matter has a direct bearing on rainfall intensity. It is evident in this study that average rainfall intensity is increased from 23.81 mm/hr to 31.11 mm/hr during 2009 to 2011. This reflects the conformity in the increase of rate of loss of organic matter with that of rainfall intensity. Some discrepancies in this rule are noticed in some LULC categories. This may be because of nature of use of a particular plot of land.

This study reveals that soil erosion is mostly triggered by anthropogenic forces. Anthropogenic activities viz.deforestation, earth cutting and filling for construction of settlements and transport lines, land tillage during high runoff, poor crop rotation practice are found to be the principal factors of soil erosion which to a great extent contributes to sediment yield. Sediment yield is found to be mostly contribution from agricultural lands through floodplain gullies.

Based on the findings mentioned above, following measures are proposed for checking soil erosion and better management of land use practices and land cover areas.

* Deforestation must be stopped by means of community participation and providing environmental  education. Forest density is required to be increased by plantation.

* Barren lands existed in the upper part of the catchments be reclaimed by means of plantation. This is reported to be effective and mentioned in clause 3.3.26 of Chapter III.

* Land tillage at high runoff must be stopped through proper training to the peasents. Scientific method of land tillage has to be adopted.

* Scientific method of crop rotation and agricultural land use practices have to be adopted by means of advice of the block level government agricultural workers (Gram Sevak).

 

Executive summary
on
UGC Major Research Project Report entitled
Evaluation of Wastelands for Sustainable Development of Jia Bharali river Watershed in Sonitpur District, Assa
 
Dr. Sujit Deka
Pricipal Investigator
and 
Assistant Professor, Department of Geography,
Pandu College, Pandu, Guwahati-781012

The research work focuses on the study of evaluation of wastelands for sustainable development of Jia Bharali river watershed in Sonitpur District of Assam. The study was carried out with the objectives – (i) to identify wastelands and watershed development sites of the Jia Bharali river, (ii) to identify the magnitude of various problems, forest status, soil loss and run off, over utilization of agricultural land, over grazing and browsing etc, (iii) to analyze land suitability and land capability of wastelands and  recommend landuse, (iv) to develop spatial model for operational uses in  wasteland development planning based on spatial and non-spatial data of the Jia Bharali watershed using GIS technology, (v) to evolve an Integrated  Sustainable Wasteland Development Plan for the Jia Bharali river watershed.
To arrive at these objectives the analysis of wastelands in terms of  their definition and classification has been done. The findings of the analysis carried out under the project have been incorporated in the chapters of the project report. The report contains six chapters including summary and conclusion. Chapter I carry introduction of the report including discussion on statement of the problem, review of research and development in the subject, significance of the study, objectives, data base and methodology.
                  Chapter II describes the study area in respect of its location, the course of the river, shifting of the river, geology and tectonics, geomorphology, climate, ground water, natural vegetation, transport and socio-economic condition of the inhabitant of the study area. Chapter III contains terrain analysis of the study area. Chapter IV discusses the wastelands classification and distribution. Chapter V deals with conservation of wastelands for sustainable development of the study area, while the chapter VII discusses the summary and conclusion of the study area. In the present study for preparation of base map from conventional sources like Indian Remote Sensing (IRS)-P6 Satellite Linear Image Self Scanning (LISS) - 3 sensor data of 29th February, 2008 were collected and registered to Survey of India (SOI) topographical sheets at 1:50,000 scale in the Super Map Express version 10. Considering the definition of wasteland
given by the National Wastelands Development Board (NWDB) and the National Remote Sensing Agency (NRSA), Department of Space,
Government of India a suitable scheme of wasteland classification has been proposed based on the definition adopted for present study. Intensive field works have been carried out in order to examine the present status and potentiality of wastelands and also for verifying wasteland and landuse mapping. The soil samples are collected from different locations of the study area to access the soil properties, wasteland fertility and potentiality. Aspect pertaining to the distributional patterns, types, status have been examined  and analyzed thoroughly. Terrain analysis of the Jia Bharali river watershed in the Sonitpur district of Assam has been performed by obtaining the findings of river morphometry analysis besides determining of depth of ground water table, landuse pattern, soils and geomorphology of the study area with the help of Spatial Analysis GIS System (ArcGIS version. 9.3). For this purpose, the toposheets (1:50,000) of the study area are scanned and retrieved in digital form to execute necessary steps for further analysis in GIS system. Finally, the suitability of the study area and capability of wastelands for best landuse option has been analyzed for sustainable development of the study area.
Further, GIS technique has been applied to show the digital elevation model of the study area. The results derived under the project have been pointed out in the following statements -
(1) The Jia Bharali river watershed in Sonitpur District of Assam covers an area of 89.84 km2 that lies between 260
36'45''N and 270 02’18’’N latitudes and 920 36'07''E and 920 59'58'' E longitudes.
(2) The Jia Bhrali river in its downstream diversion of the channel could be observed at Potasali and Kolabari where the river get shifted around 0.45 km towards north east and around 1.96 km towards south west direction.
(3) In the study area the Jia Bharali river possesses a total of 781 numbers of streams including all orders. Out of which 560 are of first
order, 153 are of second order, 50 are of third order, 15 are of fourth order, 2 are of fifth order and 1 is sixth order.
(4) The values of bifurcation ratio for first order , second order, third order, fourth order, fifth order and sixth order streams are found as
3.66, 3.06, 3.33, 7.5, 2.0 and 0 respectively. (5) The total stream length of the river in Sonitpur district is found 1152.34 km with differential length for first order ( 529.31 kms),second order (210.06 kms), third order (188.69 kms), fourth order (144.52 kms), fifth order (59.03 kms) and sixth order (20.73 kms).
(6) It is found that the stream frequency value decreases as the order increases. The derived stream frequency values are 0.63 km, 0.17 km, 0.06 km, 0.02 km, 0.02 and 0.001 km for first, second, third, fourth, fifth and sixth order respectively. It indicates that stream population
increases with respect to increase in drainage density.
(7) The length of overland flow of Jia bharali river watershed in Sonitpur
district has been derived and 0.645 km/km2 is found as its mean value.
(8) The drainage density values in the study area are dispersed within the range of values between low to high such as 0-0.5, 0.51-1, 1.01-2, 2.01-3, 3.01-4 covering an area of 33.42, 16.85, 27.17, 17.66 and 4.9 per cent respectively.
(9) The relative relief map shows that the relief of the study area is classified into six categories such as less than 100 m, 100-150 m,
151-200 m, 201-250 m, 251-300 m, 301-350 m which constitutes 59.05%, 20.63%, 15.87%, 3.18%, 0.95% and 0.32% of the total area
respectively.
(10) In the study area, slope values vary from 0 to 9º. The slope values have been categorized in to five groups namely less than 10
, 1.10 -30, 3.10 -50, , 5.10-70, , 7.10-90 and above 9º. Nearly level slopes (0-1º) are observed in the downstream and valley fill zones covering 82.33% of the total area. These slopes are found in the plains of the river valley extending in plains of the watershed.
(11) The water table having the depth of less than 3 m, 3-5 m, 5.1-7 m, 7.1-9 m, 9.1-11 m and more than 11 m are representing 27.25%,
31.06%, 17.05%, 23.46%, 1.17% and 0.01 % of the study area respectively.
(12) On the basis of the study and analysis of relief, slope, drainage and geological formations, the study area can be divided into three main geomorphological divisions, viz. (a) Structural landforms, (b) Denudational landforms and (c) Depositional landforms.
(13) The major soil groups identified in Jia Bharali river watershed in Sonitpur district of Assam includes 1. Course-loamy , Typic
Fluvaquents, 2. Fine-loamy, Typic palevdalfs, 3. Fine-silty, Typic Haplaquepts, 4. Fine-loamy, Typic Haplaquents, 5. Coarse-loamy,
Aeric Fluva quents.
(14) In the study area wastelands occupy 25.57% of which cropland covers 21.47%, built up land 16.81%, water bodies 6.3% and other
types 1.55%. (15) The wastelands of the study area include culturable wastelands. The sub-category are classified as (1) Undulating uplan with or without scrub, (2) Surface waterlogged land and marsh, (3) Degraded notified forest land, (4) Degraded pasture/grazing land and (5) Sand bar.(16) It is observed that all the five categories of wastelands, viz. scrub land, marshy land, degraded pastures / grazing land, underutilized degraded notified forest land have been occupying 0.67%, 0.13%, 0.29%, 4.97% and 19.51% of the total wastelands of the study area respectively.
(17) To determine suitability for certain land use option of the study area some elements of terrain are taken as input for modal formulation.
The results are displayed on maps which highlight the areas of high to low suitability.
(18) Further, in order to formulate a landuse option of the fertility status of the wastelands types of the project site has been examined. For that purpose soil samples of different wasteland categories are collected and analyzed by using laboratory technique. From the results of soil fertility status it is found that each category of wasteland there is deficiency in productive ability and these require proper conservation.
(19) Based on the analysis of soil quality of the study area the capabilities of the wastelands have been examined. Further to attain sustainable development of the study area the fertility of soil could very nicely be applied in the developmental projects of those locations. For this purpose the available wasteland resources effectively be used based on the suitability of the area.

 

EXECUTIVE SUMMARY

UGC sponsored Major Research Project entitled “Flood and its Impact on People and Environment in Nanoi River Basin, Assam"
 
PI : Dr.Niranjan Bhattacharjee
Asst.Professor, Pandu College, Guwahati-12

Water is the life line of living being, but sometimes it may create havoc to the living being as discussed and found in the present research work. Many vital aspects like river basin morphology, morphometric, climatic, hydrological, biological and socio-economic characteristics are discussed in this research work.

The river Nanoi originates from the Bhutan hill. That is Tangchar southern part of the Bhutan hill (2000m). In the hilly area its takes numbers of small tributaries. Total length of the Nanoi River is 104.275 kilometer with the basin area of 959.46 sq km. extending from 260 15/ 45.14// N to 270 04/ 57.84// N latitude and 910 48/ 59.66// E to 910 58/ 42.536// E longitude. The basin area is steeply downward towards the southern part. From the analysis of basin shape measurement indicators it is found that the basin is semi circular shape where sinuous index is fund 1.16, the form ratio (0.0882), and the lemniscates (K=2.27) value shows that the Nanoi basin unlike other basins of the districts is semicircular. Due to medium Dd (0.62 Km/Km2) and Fs (0.19 No./Km2) value of the basin it can be assess that the river is moderately suffered by the flood (some time it is severe as record revealed) during heavy rainy season as indicates by the hydrological data. Channel gradient is 50.06 at foothill area where near the active flood plain the gradient is only 1.7. Considering the physiographic divisions the region may be divided into three divisions, namely the Bhutan Himalayan foothill zone (Bhabar- Tarai Zone), the Built up plain zone and the alluvium plain or active floodplain zone. The extreme northern part has the maximum elevation is 2000 m above the mean sea level. In the extreme south the maximum elevation is 50 m above the mean sea level. Such elevation indicate that the land of the basin abruptly sloping upward in the juncture of the hills and plains. The hydrograph drawn by taking 25 years stage and discharge data which indicates that, during dry period (winter) the stream flow decreases exponentially. As such times discharges consist solely of base flow. For example during winter months of 1989 the water levels goes down to the extent of 49 meter but during rainy season the water level went up to the 54.37meter where the danger level is 52.74 meter. This happened during August to September. Discharge during winter season was of the under of base flow measured at 1.00 cumecs, which rise to 239.22 cumecs during the summer season’s. The landforms are developed and modified by the water bodies and channels of Nanoi river which are being heavily fed by rainfall and partly by the snowmelt water due to climatic variations. The catastrophic effects of the great earthquake of 1950 have also been rendering great impact on the landform of the entire river basin. The effect also help to frequently change the channel course from place to place which have again rendered communication gap between one place to another by destroying the road and bridges during the period of floods. The floods in the Nanoi river basin occur or get enhanced both naturally and artificially. From the record of various sources and field observation it is found that there were four great flood periods found during the last 25 years (1989 to 2013). In this tenure the great floods occurred in 1988, 2000, 2002, 2004 and 2008. The floods of 2000, 2004 and 2008 were the bigger ones. The affected the entire basin, specially the downstream part of the river. The average peak floods of Nanoi recorded 53.49 m during the last 25 years. The result of this flood was found mostly to tally most with the result of observed situation. To know the intensity and magnitude of various floods with varying recurrence intervals and probabilities of occurrences, flood frequency method is applied on water levels data. It reveals that high floods are almost common in every river. The river Nanoi frequently changes her courses from place to other (channel shifting ranging from 1 km to 8 km) by causing serious geomorphic problem like serious bank erosion. Based on the above discussion and field observation, the whole of the basin area may be divided into three major flood zones as described below: Zone of high or chronical floods - This zone is characterized by recurrent floods, generally ranging from 3 to 4 occurrences in a year.  Areas of medium floods - These areas are having floods of medium frequency and intensity.  The areas under moderate floods are confined within the lower part of the built-up plains. Low flood or flood free zone – The areas under this flood are confined in the areas of old built-up plains and piedmont zones of the Udalguri districts of the basin. The bank erosion, channel shifting and deposition of sediment are the important aspects that can reflect the change of landform features in the basin. Due to continuous sedimentation many spots in the agricultural fields have turned to barren land. The sand for example, got deposited up to 2 m in some places of the Khas-Dipila village during the floods of 2002 and 2008. The analysis of causes of flood in the river basin is mainly natural and anthropogenetic. They are fully responsible for the development and enhancement of flash flood in the basin area. Among all other factors climatic characteristics is the major one. Heavy and prolonged rainfall is the main factor of genesis of flood in the concerned region. Anthropogenetic factors are also responsible for enhancing the flood problems. The land use and occupational patterns and development of infrastructure in the floodplain have been deeply influenced by the frequency and intensity of flood events. Regarding human response and perception most of them (flood plain dwellers) are sure about the future flood and they are going on by adjusting themselves with floods at their best efforts. They are totally depressed regarding the assistance of government or any other organizations as revealed by the analysis of survey work.

For sound management of floods a number of factors and parameters are to be dealt with. However, some measures are suggested here to check or minimize the problem. Among them two main approach can be used i) Engineering approach ii) Regulatory approach.

Various structural measures such as dams, reservoirs, levees, flood walls may be constructed specially in the areas of low slope gradient and water congestion to fulfill the long term aim of flood control/amelioration, etc. The beels, wetland, marshes, swamps, abandoned channels may fulfill such objectives. They may be interlinked with rivers to check floods and enhance land use potentials and practices. Development of wastelands as watershed units for in-situ retention of rainwater, most effective utilization of soil moisture and proper land use for optimum and sustained productivity through various self-help user groups are the main objectives of this programme. Such types of programmes are namely Integrated Wasteland Development Project (IWDP), National Watershed Development Project in Rainfed Areas (NWDPRA) and Integrated Watershed Management Programmes (IWMP). Appropriate measures are to be taken to increase the capacity to pass the excess discharge of water along and across the rivers and its tributaries considering the basin catchment, drainage net, channel and basin configuration and the supply of water to the basin. Design tranches, ditches, or pipes on the soil can be to control soil water content and ground water level on agricultural land etc. This will help in checking soil erosion and avoiding sediment deposits on river bed. Soil tillage and choice of crops to be planted should be in a befitting manner in the river catchment in order to check rapid run-off and erosion processes in the agricultural field. Embankment cum roads can be constructed along the banks of the more vulnerable places. Afforestation especially in the upstream and more flood vulnerable spots and places, is to be executed to mitigate strongly rushing down-flow of water, slope wash and sedimentation on the channel bed so as to check these problems and protect the areas from flood. Floodways can be built to provide an outlet from a stream in order to allow streams flood to go in an area. A floodway is the area where no construction is allowed. It is the land which is used for agricultural or recreational purposes, where there is no threat from a flood. It provides an outlet for flood waters during the periods of high discharge.  A floodway is the area identified in the main channel of a stream that allows water conveyance without increasing the BFE (Base Flood Elevation) by more than 1 foot.  HECRAS (Hydrologic Engineering Centers River Analysis System) is one of the hydraulic models approved by the NFIP (National Flood Insurance Program) to perform floodway modeling.

Regulatory Approaches to Reduce Vulnerability laws can be passed that restrict construction and human habitation on floodplains.  Instead floodplains can be used for agricultural uses, recreation, or other uses wherein lives and properties are not endangered or lost when flood waters re-occupy the floodplain. Any kind of manmade structures that are allowed within the floodplain could be restricted to those that can withstand the high velocity of flood waters and are high enough off the ground to reduce risk of contact with water. In the areas that have been recently flooded, it may be more cost effective on the part of the government while pying to the victims the damage cost either through subsidized flood insurance or direct disaster relief, to buy the rights to the land rather than pay the cost of reconstruction and then have to pay again the next time the river floods. Lending institutions could refuse to give loans to buy or construct dwellings or businesses in flood prone areas. But this can be made earlier and effective if appropriate agents of planning, development, etc adopt befitting steps. However, technology no matter how expensive or efficient cannot prove to be of any help, without a well-drawn policy that can ensure its implementation. Necessary steps and follow-up action shall have to be made to train up the flood plain dwellers with the knowledge of eco adjustment on the one hand, and to save the land from flood and erosion disaster caused at the time of heavy downpour on the other. All these need well planned and well organized strategies formulated wisely in consideration of the topographic, hydrologic, geomorphic and socio-economic factors in Nanoi river basin.

 

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