Sustainable Watershed management aspects for Administrators in Sri Lanka

Transcription

1 Sustainable Watershed management aspects for Administrators in Sri Lanka By Chandima Gunasena BSc. In Agriculture, MSc, in Green Technology MPhil in Integrated Water Resource Management December

2 Table of Contents Session One Session learning objectives... 4 Session 1.1 Geographical features, historical background and land use change in Sri Lanka before and after colonial periods and population drifting from dry zone under hydraulic civilization to the wet zone. Land use changes happed with the population drifting (30 minutes)... 4 Session 1.2 Definitions and classification of watersheds, rivers, streams and basins, Identification of river components and basin characteristics, conflicts between natural ecological boundaries and manmade administrative boundaries, Problems confronted by administrators (120 Minutes)... 4 Session 1.3 Classroom simulations of problems forwarded by the participants and discussion... 4 (30 Minutes)... 4 Session 1.1 Geographical features, historical background and land use change in Sri Lanka before and after colonial periods and population drifting from dry zone under hydraulic civilization to the wet zone. Land use changes happed with the population drifting Introduction... 5 Unique Geographical features of Sri Lanka... 5 Hydrological network or the river network of Sri Lanka... 5 Hydraulic civilization of Sri Lanka... 7 Cascade system of ancient Sri Lanka Collapse of the Rajarata Civilization The Kandyan Kingdom Paddy ecosystem and its development in central hills The Colonial Period Establishment of new administrative boundaries Post colonial period Session 1.2 Definitions and classification of rivers, streams and basins, Identification of river components and basin characteristics, conflicts between natural ecological boundaries and manmade administrative boundaries, Problems confronted by administrators River basin, Drainage basin or watershed area River Basin or watershed classification Definition of a River Stream classification Particle size and its presence in stream segments

3 Riparian zone Conflicts between manmade boundaries or administrative boundaries with natural boundaries Problems confronted by administrators Environmental issues at residential level Simulation of problems confronted by the participants with a class room simulation

4 Session One 1. Session learning objectives To Familiar with the geographical features and hydrological network of Sri Lanka, discuss the watershed and river morphological characteristics and importance of watersheds for a sustainable resource mobilization To familiar with the problems confronted by administrators in relation to human settlements in Sri Lanka Session 1.1 Geographical features, historical background and land use change in Sri Lanka before and after colonial periods and population drifting from dry zone under hydraulic civilization to the wet zone. Land use changes happed with the population drifting. (30 minutes) Session 1.2 Definitions and classification of watersheds, rivers, streams and basins, Identification of river components and basin characteristics, conflicts between natural ecological boundaries and manmade administrative boundaries, Problems confronted by administrators (120 Minutes) Session 1.3 Classroom simulations of problems forwarded by the participants and discussion (30 Minutes) Session duration 180 minutes 4

5 Session 1.1 Geographical features, historical background and land use change in Sri Lanka before and after colonial periods and population drifting from dry zone under hydraulic civilization to the wet zone. Land use changes happed with the population drifting Introduction Unique Geographical features of Sri Lanka Sri Lanka has a central hill mass covered with natural forests, gradually flattening towards sea Figure 1. Figure 1: Central hills and surrounding flat landscape of Sri Lanka Source: Personal data and Hydrological network or the river network of Sri Lanka Most of the water source areas are at the central hills and rivers are flowing down radially through the central hill mass towards the flat land where fertile soils are located Figure 2. 5

6 Figure 2: Stream network and major river basins in Sri Lanka Source: AveI3-bg/UKIjVDcEMZI/AAAAAAAAHq8/8ViEv8SYaJE/s1600/Sri%2BLanka%2BGeo%2BMap%2B1.JPG and Forest and sponge effect Natural forest cover in the central hills captures the monsoon rains. This is identified as sponge effect Figure 3, of the forest cover and promotes gradual absorption of storm water into the soil mass and reduces the speed of water droplets and minimizes soil erosion in steep slopes. Canopy of the forest cover act as a sponge and absorb water from storms and clouds creating humid environment throughout the year. Water within the soils in central hills provides year round ground water supply to water springs, streams, tributaries and rivers while flourishing reservoir network at the flat lands. Figure 3: Central hills covered with clouds causing humid environment 6

7 Hydraulic civilization of Sri Lanka Hydraulic civilization of Sri Lanka thrived in fertile soils in dry zone area which is powered by two monsoons. Interconnected set of reservoirs identified as Cascades are the main ecological units operated by settlers to form villages, towns and kingdoms. Cascade system of ancient Sri Lanka A cascade is defined as a connected series of village irrigation tanks organized within a micro-(or meso-) catchment of the dry zone landscape, storing, conveying and utilizing water from an ephemeral rivulet. Water from the upper parts of the cascade was used and re-used several times before it reached the outlet. It may therefore, be argued that the village tank cascade systems only gave expression to the famous royal dictum that Let not a single drop of water go waste into the sea without benefiting the world ( King Parakramabahu, 12 Century AD) (Madduma Bandara 1985). These cascades are then clustered and formed regional administrative systems and finally the kingdom Figure 4. Figure 4: Cascade system in Dry zone of Sri Lanka 7

8 Ancient traditional village administration system under a village headman Figure 5: Traditional village tank system One tank and the surrounding landscape in a cascade system is identified as a village, As shown in the Figure 5, according to the Dharmasena P.B (2014) components of a tank in an ecological segment or a cascade system could be identified as tank bund (wewkandiya); downstream reservation (kattakaduwa); upstream side ridges (isweti or potaweti); high flood area (vangilma), where gasgommana and perana exist; upstream sediment trap (godawala), downstream drain (kiul-ela), village hamlet (gangoda), hamlet buffer strip (thisbambe); shrub land (landa), paddy field (wela); and paddy boarder zones (kurulupalu). Sustainability of the village tank system headed by a village headman maintained the long-term productivity for humans as well as to the surrounding environment. Ecological system also mitigates hazardous impacts of natural disasters like droughts by conserving the water and floods by absorbing excessive runoff of intensive rains to reduce floods. It also acts as a biological windbreak system to drive away the high winds and dynamic high bio-diversity helps to get rid of famine and epidemics. 8

9 Figure 6 shows the density of cascade systems spread in the Dry Zone of Sri Lanka. Figure 6: Ancient reservoir network Source: Manchanayake, P & Maddumabandara, CM

10 Figure 8 shows the reservoir density of Sri Lanka. Our ancestors established their kingdoms mostly in flood planes of major rivers located in dry zone areas. Ancient kingdoms: Ruhunu, Maya, Pihiti, demarcations or administrative boundaries were adjusted with reference to major rivers. Due to many reasons this hydrological civilization was collapsed with foreign invasions and many other local reasons. Figure 8: Ancient kingdoms of Sri Lanka Source: 10

11 1.1.2 Collapse of the Rajarata Civilization Ancient capitols of Sri Lanka which were established mainly in dry zone areas shifted time to time Figure 8. Due to many reasons Anuradhapura, capital shifted to Polonnaruwa and having few years in Dambadeniya, Kotte, Gampola and Sitavaka, respectively. Rajarata civilization or the ancient hydraulic civilization was disappeared after the twelfth century. Climatic change, Malaria, depletion of soil fertility, foreign invasions and famine are some of the reasons (Dharmasena P.B 2014). Figure 9: Forest cover change in central hills Source: Cascade system or the reservoir network was abundant due to lack of maintenance. People gradually moved to hilly areas seeking grounds to settle down for better livelihoods and protection form foreign invasions. Gradually natural forest cover decreased in central hills with the population pressure and Rajarata went under forest Figure 9. 11

12 1.1.2 The Kandyan Kingdom A scholar named Farmer, in the year 1957, mentioned about the push-pull effect that led to demographic shifts from the Dry Zone to the Wet Zone (Roberts, 1971), (Abeywicrama, and Baldwin 1991) Figure 10. Figure 10: Population drift and increment Source: Abeywicrama, and Baldwin

13 The capital was finally established in Kandy until the British conquest. Parallel to this capitol shifting from place to place, population shifted across different ecological zones, from the Dry Zone, to the Wet Zone, and to the hill country. People who came from dry zone lived with traditional dry zone agricultural systems gradually moved to hill country. Not like in dry zone paddy field areas Figure 11 they had to look for water in high lands where only streams and water springs are available. Figure 11: Dry zone paddy fields Sri Lankan agrarian society had to adjust to new environments in hilly areas with different technologies for managing land and water. Natural hydrological balance was changed with the modification of more wetter and rugged terrain features for their livelihood Paddy ecosystem and its development in central hills As shown in the Figure 12, paddy ecosystem started in the valley bottom and pushes towards the source areas with the population pressure. Figure 8, shows how these human settlements spread along the valley and towards top of these mountain regions with the population pressure as Hell Malu Paddy cultivation system. Water springs and streams provides water to these fields and these water sources are nourished with the infiltration, sub surface flows and deep percolation happening in ground water rechargeable areas where rain water received on these hilly terrine features. Clearing forest cover has altered the fluvial system of these areas. Figure 12: Spreading human settlements along the valley and top of mountain regions source: and 13

14 Figure 12 Spreading paddy fields along the vales of Sri Lankan central highlands Later in Kandy region these forest gardens became a man-made forest having various fruits and other economically useful tree species and identified as Kandyan Forest Gardens. Not like in dry zone environment the micro- environment of a Kandyan homestead provided a cool and pleasing 14

15 environment for the continuity of human settlements in a wet mountain setting (Abeywicrama,and Baldwin 1991) The Colonial Period Exploitation of natural resources in commercial scale started in early sixteenth century by the Portuguese, and then the Dutch, especially in maritime areas of the island excluding the hilly interior of the country, which continued under the monarchy. Kandyan kingdom fell to the British in 1815 and significant changes in the natural environment of the island began with the expansion of the commercial and plantation agricultural activities. 15

16 Establishment of new administrative boundaries During the colonial period new administrative system was introduces and land and ecological systems were divided based on the population density to manage the natural resources for the plantation and commercial agricultural activities. Total land area of the country was divided in to nine provinces and 25 districts. Districts are further divided in to Divisional Secretariat (DS) divisions and each (DS) division is further divided in to number of Grama Niladhari (GN) divisions which is the lowest administrative level in Sri Lanka Figure 13. Figure 13: Administrative boundaries of Sri Lanka Provincial, District and AGA boundaries Source: and personal data Crown Land Encroachment Ordinance With the implementation of a new land policy named as Crown Land Encroachment Ordinance, in 1840, vast extents of land including all forests, waste, unoccupied or uncultivated lands became directly under colonial administration. This encroachment facilitated the large-scale enterprises of plantation agriculture in Sri Lanka. The colonial government sold these lands cheaply to private parties. Within less than a half century hill country, became almost totally denuded and over four thousand elephants may have been killed in the process causing serious ecological disasters. 16

17 1.1.5 Post colonial period With the colonial administrative system, plantation agriculture was promoted in the central hills. Larger irrigation schemes were established in central highlands in many river basins for agricultural purposes and hydro power generation. 17

18 Session 1.2 Definitions and classification of rivers, streams and basins, Identification of river components and basin characteristics, conflicts between natural ecological boundaries and manmade administrative boundaries, Problems confronted by administrators River basin, Drainage basin or watershed area As shown in the Figure 14, a drainage basin or watershed could be defined as an extent or an area of land where surface water from rain, melting snow, or ice converges to a single point at a lower elevation, usually the exit of the basin, where the waters join another water body, such as a river, lake, reservoir, estuary, wetland, sea, or ocean. It is a natural boundary where all ecosystem functions take place without disturbances Figure 14: Watershed or River basin boundary and stream network of a basin Source: and Romania.jpg Figure 14: Conceptual watershed 18

19 River Basin or watershed classification The word watershed introduced in Watershed is that land area which drains or contributes runoff to a common outlet. Watershed is defined as a geo-hydrological unit draining to a common point by a system of drains. All lands on earth are part of one watershed or other. Watershed is thus the land and water area, which contributes runoff to a common point. Watershed is classified depending upon the size, a. Macro watershed: ,000 ha b. Micro watershed: ha c. Mini watershed: ha d. Mille watershed: 1-10 ha Fluvial process in a watershed or a river basin The hydrologic cycle Figure 15 illustrates the functions of the water in a watershed. Water evaporates from the ground and goes up and form clouds. Water discharge as rain droplets then hits the highlands, water tend to flow towards the lower elevations where streams are formed. Water generally moved from higher elevation to lowest by the force of gravity and while flowing water infiltrates the soil along its route, transpires into the atmosphere and/or collects into streams and forms a flowing concentrated body of water. This reaction between earth and water is dependent on the driving (slope of the flowing water, flow velocity, channel width and depth) and resisting forces (earth materials, roughness of a river system (presence of boulders, pebbles gravels, sands and sediments,) in response to erosion and transportation of debris sediment etc. Figure 15: Water cycle 19

20 This fluvial process could be categorized in to three zones namely, the upper sediment production zone, the middle sediment transfer zone and the lower sediment deposition zone. The upper sediment production functions as the initial runoff of water from higher elevations with steeper slopes allowing for deeper incisions and cuts into the earth. This zone sees the most erosion activity and develops steeper watercourses such as cascading streams and waterfalls. The middle transfer zone operates as a conveyor belt with softer slopes. This river reach is the longest of the three zones and human populations more commonly reside in these areas and see meandering or braided streams. The lower sediment deposition zone may be a lake, delta, or reservoir where the sediment load is dropped off Figure 16. Figure 16: The fluvial system in three zones: sediment source, transfer, and deposition (Living in the Environment: An Introduction to Environmental Science, 1990). 20

21 Definition of a River A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. Stream classification Figure 17: Stream classification system developed by Horton 1945 and Strahler, 1957 As shown in the Figure 17, number 1 denotes first order streams. Similarly number 2, 3 and 4 represents second order, third order and fourth order streams, First order streams are located mostly in water source areas, where second and third order streams could be identified as tributaries of main rivers. In this example 4 th order denotes the main river. 21

22 Figure 18: First order streams hold many insect species and few fish species Figure 19: Second order stream also has many insects and a few more fish species than first order streams 22

23 Figure 20: Third order streams have many plants and fish species Figure 21: Forth order streams have many plants and fish species than third order streams 23

24 As shown in the Figure 22 Type of the bed rock could also be used to identify these stream orders where poorly sorted large angular stone structures with smaller structures could be seen in water source areas or presence of first order streams. Sub angular and sub rounded partly sorted stone structures could be seen in second and third order streams. Well sorted smaller and rounded particles are in higher stream orders. Particle size and its presence in stream segments Figure 22: Particle size in a stream bed 24

25 25

26 Figure 22: The way of sediment transportation in a river bed 26

27 Types of channels, streams or rivers Figure 23: Straight streams Figure 24: Braided streams Braided channel or a stream has islands or eyots of deposited materials within the channel Meandering channels A meander is a bend in a sinuous or flowing watercourse. Meandering is the process when the fastermoving water in a river erodes the outer banks and widens its valley, and the slower-moving water on the inner side of the bend becomes a place where sediments are deposited (point bars). As a result, rivers tend to constantly change their course over a floodplain over time Point Figure 25: Meandering streams 27

28 An oxbow is a crescent lake on a stream floodplain formed when a meandering stream channel is cut off and isolated by changes in a stream channel. Components of a river Riparian zone Figure 26: Components of a river An acceptable riparian zone includes a buffer strip of a minimum of 18 m (Barton et al. 1985), from the stream on either side. The acceptable width of the riparian zone may also be variable depending on the size of the stream. Streams over 4 m in width may require larger riparian zones and it is also a natural boundary Figure 12. Figure 27: Riparian vegetation 28

29 Values of riparian vegetation and effects from its removal d.pdf 1. Shade controls in-stream temperatures by shading the water and prevent algal blooms. Removing shade increase the algal growth and blooms resulting decline in other invertebrates and fish species where temperature controls the lifecycle of these living beings. 2. Organic matter inputs are provided by the riparian vegetation as a carbon source providing energy to drive the aquatic food web. Effect of removing organic input like leaves, twigs, fruit and insects that form the basis of instream food webs changes the quantity and quality of energy in food webs and the functioning of the ecosystem and influence over the in-stream faunal and floral population abundance and biodiversity. 3. Channel stability will improve with the riparian vegetation and removal of bank vegetation and woody debris increase the flow rate causing flooding and downstream erosion. 4. In-stream habitat will improve directly with the input of woody debris like logs and branches from bank vegetation and indirectly through the formation of scour pools, around anchored tree trunks increase the biodiversity. Removing in stream habitat like woody debris from the river will reduce stream habitat complexity and decrease in-stream flora and fauna 5. Riparian vegetation act as buffer zones between terrestrial activities and aquatic ecosystems. The buffering includes filtering particles mobilized through anthropogenic activities and their subsequent delivery to the river via overland flow. Removal of buffer zones will increase the sediments and particle matter inflow to the river and will stimulate weed and algal growth. 6. Water filtering effect of the riparian vegetation will improve the inflow water quality with the help of Shallow rooted vegetation (grasses, herbs, sedges etc) can trap sediments and particulate matter, while deep rooted vegetation will absorb nutrients from subsurface flows. Effects of removing the water filtering capacity will diminishes this polishing or cleaning process 8. Riparian vegetation and salinity. 29

30 Pools and riffles Figure 28: Pools and Riffles Riffles Riffles are the distinguished feature of coldwater streams. They are at once a food source, a shelter from predators, a hedge against oxygen depletion, and many species of insects reproduce or grow to maturity in riffles. Riffles also oxygenate the water. Pools Pools are one of the most obvious features of a stream. The pool provides the two things depth and still water. The deep water of a pool provides habitats for many fish species. 30

31 1.2.4 Conflicts between manmade boundaries or administrative boundaries with natural boundaries With this new administrative system introduced by the foreign invaders during the colonial period and natural ecosystems or river basins or watersheds were divided for the purpose of administration to support commercial agricultural activities, shifting cultivation and residential purposes, neglecting the natural boundaries like river basins boundaries. Situation is aggravated due to illegal deforestation and timber production. As shown in the Figure 29, Mahaweli river basin was sub divided in to several districts. Water source area of the Mahaweli River was deforested for commercial agricultural purposes, and larger reservoirs were constructed in central highlands for the purpose of power generation. In many occasions riparian zone of the river was encroached by the expanding human settlements for residential and commercial purposes and started sand mining and to dump fecal matter, hospital waste and other organic and inorganic waste directly in to the river altering the river functions and adjoining ecological functions. Figure 29: Mahaweli river basin and manmade administrative boundaries Due to lack of coordination among districts decision making in relation to protect Mahaweli River as a watershed or a river basin was neglected. Considering only the administrative boundaries like provinces, districts, AGA divisions, new settlement schemes, plantations were established in ecologically sensitive areas. Natural hydrological balance was altered with the devastating impacts on landscape and serious environmental problems became prominent during this period namely; soil erosion, landslides and siltation of stream and reservoir beds and these ecological implications significantly altered the surface hydrology. Colonial government had to react this and forest department was established to start soil conservation in the highlands. Laws were brought in to action to preserve the area above 1,500 meters. 31

32 Protection of natural forest cover was not properly addressed by the crown ownership and forest cover accounted for some 45 percent of Sri Lanka by the time of National Independence. Later on plantation agriculture sector was able to introduce soil conservation technologies namely, contour drains and stone terracing. Soil erosion problems prevailed even in the in the last years of the colonial rule (Abeywicrama, and Baldwin 1991). Even after the colonial period same development pattern took place with the same administrative structure causing Sevier environmental destructions. As shown in the Figure 30, satellite images of Kandy, Nuvaraeliya, Bandarawela illustrates the population density and deforestation, constructions etc. Figure :30 Satellite images of Kandy and Nuvaraeliya showing the impact of heman settlements Source: Google maps Similarly satellite images of Anuaradapura, Polonnaruwa, Yala, willpattu, Ampara etc. in Figure 31, shows the abundant reservoir network and forested areas those were civilized during the ancient past. Figure :31 Satellite images of Anuaradapura, Polonnaruwa, Yala, willpattu, Ampara showing the impact of human settlements Source: Google maps 32

33 1.2.6 Problems confronted by administrators Environmental resources were managed and resource mobilization was carried out by administrators with manmade administrative boundaries developed based on the population density. As shown in the Figure administrators had to follow the rules and regulations imposed based on the foreign administrative system which is not compatible with the natural boundaries. 33

34 With the rapid development took place during 70s, 80s, and 90s, we have now achieved infrastructural, industrial, agricultural development with the scientific and technological advancement. In contrast, even though Sri Lanka has these institutional and infrastructural and livelihood change, Sri Lanka is now confronted with many environmental, social and economical issues. In the long run land water and air pollution is increasing, reservoirs, irrigation canals, road side drainage networks are silting very quickly than earlier and need frequent rehabilitation due to lack of proper overland flow and sediment control measures. Most of the cities in hill country are experiencing higher population growth and faced with many environmental problems. 34

35 Figure 32: Silted reservoirs and irrigation canals Source: Personal data Figure 33: Disturbed environmental flows and silting road side drainage network Source: Personal data 35

36 1.2.5 Environmental issues at residential level As shown in the Figure15, due to unplanned building and access road construction cause soil erosion and land degradation in upper catchment areas. Furthermore, construction of buildings and toilets near small streams cause dying of these first order streams in water source areas. When a particular land owner is having larger land parcel as a residential area, home garden is considered as the home and the surrounding land parcel and rest of the land keep unproductive casing many environmental issues. Figure 34: Impacts of home gardens or human settlements at micro catchment level Source: Personal data 36

37 Overland flows, sediment transportation, ground water recharging, conservation of bio diversity etc. are not properaly addressed in human settlements. As shown in the Figure 16, land and environmental flow management in home gardens and access roads are neglected nationally. Figure 35: Seasonal environmental flows appear in home gardens and access roads Reconsideration of river basin boundaries as administrative boundary During the late 70s again basin approach was considered as a sustainable management concept and Mahaweli authority was established to promote the basin level resource mobilization expecting better institutional coordination. It was the major multipurpose development scheme in Sri Lanka Figure 18. Figure 36: Mahaweli River Basin of Sri Lanka Source: Unavailable 37

38 1.3 Simulation of problems confronted by the participants with a class room simulation Problems of the participants will be discussed with respect to an administrative point of view highlighting methods of generating solutions in relation to the theory discussed. 38

39 Home work Questioner (bring a hard copy of your homework to the class) Name:.. Date: Administrative details: Province:...District:...AGAdivision:... GN Division:.. 1. Different animals live in different environments and these environments are identified as habitats. We all know that elephant lives in forests areas and flood planes of rivers and those areas could be identified as elephant habitats. Similarly, leopards live in forests and mostly they rest on trees, Lions live near grasslands in forests, honey bee has its own bee hive to live. Do they have administrative boundaries like you and what are those? Do they confront environmental problems due to their own living standards? Now try to define human habitat? What are the boundaries of human habitats?.. 3. What are the difficulties you faced when you try to define the human habitat?.. 4. Identify an environmental problem in your home town or village. Your problem may be related to water pollution, air pollution, pollution of a wet land or river, soil degradation, deforestation, flooding, drought, or any other problem. 3a. Define your problem. Draw sketches to illustrate the site condition and get few photographs of your problem site and paste to this document as an attachment... 3b. Who is responsible for the problem? Government, any privet industry, individual etc. 3c. How old the problem is? Why it is still not solved? (Explain according to your knowledge) 39

40 Right side chairs Left side chairs 3d. If you are asked to provide a practical solution for the problem, what would be the solution? 5. Problem simulations - After your arrival to SLEDA for the training program, try to be familiar with your group mates having similar problems (Question 4) and their solutions before this presentation. Figure bellow shows a stream flowing from higher grounds to lower grounds. Now think of the location of your home town or your village, if your home town is near the sea come and sit left side of the class room. If your home town is at some where middle come and sit in middle of the room. Similarly if your home town is located at higher grounds you have to sit right side of the class room. Note: If you enter from the front door your right hand side is the left side of the class. Your left hand side is the right side of the class room. If you enter from the back door right hand side is the right side of the class room and left hand side is the left hand side of the classroom. Class Room Middle chairs Entrance Figure 1: Our class room People seated in the right side are the head waters. Your class room is now an eco-system or a river basin and you can identify the direction of the water flow and your problems could be simulated. 40

41 Annex 1: Sketches and photographs of the site selected 41