Block 1: Watershed Management - Definitions and Approaches

Block 1: Watershed Management - Definitions and Approaches
1.1. Principles and basic concepts of watershed management

1.1. Introduction to Watershed Management
Key Words Watershed watershed management effect of watershed on community Principles of watershed management watershed characteristics

Learning outcomes At the end of the topic students are be able to:
define watershed and watershed management Know historical overview of watershed management Know basic principles of watershed management explain rationale for using watershed for planning and development Classify watershed (based on size and stability) Know watershed characteristics which affect watershed function

Scope of the Topic The purpose of this topic is to give students insight on watershed definitions and its management, effect of watershed on the community, objectives and basic principles of watershed management, Rationale for using watershed for planning and development and watershed characteristics which affect watershed function

1.1.1. Definition of watershed
Definition: watershed can be defined in different ways “Watershed is a unit of area covers all the land which contributes runoff to a common point or outlet and surrounded by a ridge line”. Technically, a watershed is the divide separating one drainage area from another (Chow, 1964). It is the drainage area on the earths surface from which runoff resulting from precipitation flows past a single point into a larger stream, a river or ocean A watershed or catchment or basin or drainage area refers to any topographically delineated area that can collect water and is drained by river system with an outlet (brooks, et al 1981) The groundwater flow may not coincide with the surface drainage boundaries because the phereatic divide does not always coincide with the topographic divide

Definition cont’d The common point towards which all the water tends to converge flowing in the drainage network is the outlet of the watershed. A drainage divide is the boundary that physically separates two drainage basins from each other. Precipitation on one side of a divide will drain into one basin, whereas, precipitation on the other side will drain into another basin.

Definition cont’d In general there is a quit resemblance between a tree and a watershed. Different leaves leads to small branches that leads to larger branches and a larger branches leads to trunk of the tree as different small watershed leads to larger watershed and existing drainage network.

1.1.2. Concepts of Watershed Management
Watershed includes: All natural resources (water soil and vegetation), people, farming system, livestock, and the interaction among the components. All land everywhere is part of some watershed. Watershed vary greatly in size and it could be only few ha as drainage area for filling small ponds or hundreds of square kilometers for rivers. Small watersheds together form large watershed Soil, vegetation and water are most important vital natural resources for the existence of the man and his animals. These three interdependent resources can bee managed collectively, conveniently, simultaneously and efficiently on watershed basis (unit of management.)

Fig. Typical watershed and drainage system

Watershed Management …
Can be referred to as the planned use of drainage basin in accordance with predetermined objectives. It includes the analysis, protection, development, operation or maintenance of the land, vegetation and water resources of the drainage basin to benefit its residents. Watershed management involves management of land surface so as to conserve and utilize the water that falls on the watershed, and to conserve the soil and vegetation for immediate and long term benefits to the farmer, his community and society. The tasks of watershed management includes the treatment of the land (soil, water and vegetation) by using most suitable biological and engineering measures in such a manner that the management work must be economically and socially accepted

1.1.3. Effect of watershed on the Community
A Watershed has wide ranging effects on the lives of people at large as soil, water and vegetation are the most vital natural resources and Watershed affects them all. The sustained productivity of food, fuel, fodder, forage, fiber, fruit and small timber can be ensured by judicious and effective management of soil, water and vegetation.

1.1.3. Effect of watershed on the Community...
Soil: The rate and magnitude of soil erosion and sedimentation are vital for watershed community i.e. people and animal. Accelerated erosion. Adversely affects the productivity and production on agricultural horticultural, forest lands and grasslands; (at higher elevation). Results in higher production due to transportation of silt and sediments into the rivers and reservoirs and then on agricultural land but also results into the reduction of life and benefits of the reservoir; (in plains). Results in siltation of streams and rivers which causes flash floods; Results in severe drought due to low soil infiltration, excessive runoff etc; Results in damage to property.

1.1.3 Effect of watershed on the Community….
WATER: Water quality, quantity and regime are influenced by watershed conditions. Rivers, streams and lakes are the "lifeblood" of our environment. The quality and quantity of water in streams are generally characterized by the influence of natural conditions such as the underlying geology, topography, and soils, and the adjacent vegetation, combined with the long history of human influence – with the initial forest clearing, agricultural use, construction of mills, dams and ponds, road and building construction, and modern development, conservation and restoration..

1.1.3 Effect of watershed on the Community….
Vegetation: It provides food, fruit, fuel, fodder, forage, small timber NWFPs etc. to the community which is vital for the survival of humanity. Vegetation is also a very crucial factor that affects erosion, runoff and climatic factors of the area. Floods and drought: This again is the function of the watershed and affects the people greatly. This is one of the sever problem, if it happens, and takes the attention of the people more than any other item. Drought might appear due to low productive potential of the watershed as well as due to flooding. Both effects can be mitigated by sound watershed management programmes aiming moisture conservation and flood protection.

1.1.4. Objectives of watershed management
In general watershed management is aimed to improve the standard of living of human being in the watershed by increasing his earning capacity, by supply water for different purposes (irrigation, drinking, hydroelectric power), by increasing the productivity of the land (increasing the fertility of the soil), freedom for fear of floods and drought The objective will vary from place to place, from watershed to watershed, but the following are some of the most common objectives:- To rehabilitate the watershed through proper land use and protection/conservation measures in order to minimize erosion and simultaneously increase the productivity of the land and the income of the farmers. To protect, improve or manage the watershed for the benefit of water resources development (domestic water supply, irrigation, hydropower)

Objectives of watershed management….
To manage the watershed in order to minimize natural disaster such as flood, drought and land slide etc To develop rural areas in the watershed for the benefit of the people and economies of the region. To minimize siltation of reservoir/dam. The objective could also be a combination of the above. Note: different objectives call for different techniques, manpower, inputs and approaches in planning. The monitoring and evaluation criteria will also be difficult. Therefore, main objectives should be identified and defined as early as possible.

1.1.5. Principles of watershed management
1) Watershed as natural system that we can work with. A system can be defined as complex whole formed from related parts or a combination of related parts organized into a complex whole. Similarly, watershed can be regarded as a complete system and it entails several components. Entities that define the system may include products or outputs leaving the system, inputs coming to the system and interaction (+, -) between its components. The various parts of the watershed are physically and operationally linked i.e. the various resources are linked not only spatially but also functionally, and the potential benefit from integrated use can be large.

1.1.5. Principles of watershed management….
2) Watershed management must be participatory Participatory means involving method where the community is motivated to function and contributes as a group to perform various tasks. The management must involve local farmers and other land users and wide community who depend on the land. The adequacy of planning depends on the human element and not only on physical or technical aspects. Therefore, planning must start from people living on the land. The watersheds communities must involve in all stages of implementation of watershed development activities.

3) Should follow multi-disciplinary approach and it is a continuous process Watershed management is inter-disciplinary approach. Watershed planning is a coordinated analysis by a team of technicians representing various disciplines like hydrology, geology, engineering, soil science, forestry, agronomy, and economists. Each disciple is inter-related with each other.

4) Watershed management must be gender sensitive: Women's are the most affected by environmental hardship; for example, they need to walk long hours to fetch increasingly scarce water, firewood and animal dung in addition to attending livestock, to name a few. Their involvement in watershed development planning, implementation and management is the key to ensure that they equally benefit from the various measures

5) Watershed management must be build up on local experience, strength. Local knowledge is essential to improve the existing technologies, to adopt new ones and to manage natural measures once they are introduced and established

6) Watershed management must be realistic, integrated, productive and manageable. It must be realistic based up on local capacity, available resources and of government and partner support. Integrated conservation and development base is the guiding principles of watershed management. The watershed activities must be tangible and quick benefits the households. The measures must accommodate both production and conservation. Management is not only for the sake of conservation it must include both conservation and production.

7) Watershed management must be flexible at different level Flexibility is needed during the selection of community based, their size (slightly smaller or flexibility or higher than the ranges indicated), and clustering and during the steps of the producer. Flexibility is also essential when considering the choice and design of measures with in agreed criteria of quality and integration 8) Watershed management must be cost-sharing and empowerment/ownership building Cost-sharing by stakeholders contributes to the sustainability of the projects for establishing the responsibility of various stakeholders in the management of the resource. Various forms of local contributes are possible upon social networks and groups formation mechanisms.

9) Watershed management must be complementary to food security and rural development mainstream (like HIV, health, education and others) Watershed deployment planning should incorporate additional elements related to basic services and social infrastructure.

10) Flexible approach is always need One should never look for a rigid, step-by-step ‘’cookbook recipe’’ for watershed management. Different regions have watershed that function in very different way, and even neighboring watersheds can have major differences in geology, land use, or vegetation that imply the need for different management strategies. Different communities vary in benefits they want from their watersheds. Therefore, watershed management is a dynamic and continually readjusting process that is build to accommodate these kinds of changes

11) Watershed management framework support partnering, using sound science, taking well-planned action, and achieving results When you are designing a house, you first think about all the functions you want it to serve. The same is true for designing a watershed management framework. A strong watershed framework uses sound science, facilitates communications and partnership, fosters actions that are well planned and cost effective. Among the three common elements of successful watershed management framework, Geographic management units (the watershed itself) is the first one, which agreed up on by partners to provide a functional, practical basis for integrating efforts. Secondly, stakeholders (anyone who can impact or is impacted by decisions in the watershed are involved through the processes, with clearly defined roles and responsibilities.

Thirdly, partners agree on a management cycle, including activities they will work on together and a fixed time schedule for sequencing these activities. importantly, the cycle signals that watershed management is a never ending job. remember, these steps can be initiated by a local watershed associations, basin group, or regional or federal agency.

Catchment; Watershed and Basin
Catchment is often used as a synonym for watershed- watershed (USA), catchment (British) A watershed is differentiated from a river basin in that a river basin may encompass hundreds of watersheds. Example: Nile basin, which encompasses 9 or 10 riparian countries. River basins cannot be considered as units for development simply because it encompasses a variety of agro-ecological zones.

Watershed size There is no restricted size of a watershed. It can be a large river basin or small stream basin. But, for appropriate resource development and management, a watershed can be divided into sub-watersheds referring to a micro-watershed and mini-watersheds. For ease of implementation of watershed management programmes, a small watershed is preferred. The main criteria for sub-division is decided based upon the availability of finance and other resources to attain the development objectives within a defined project period. Again the nature of the problem or objectives also force to determine size of manageable watershed

1.1.6. Watershed classification
According to their size watersheds may be classified into: Major watersheds Watersheds, and Sub-watersheds The major watersheds are tributaries to river basins and may cover areas ranging between 20,000 and 500,000 hectares. There may be a variety of eco-systems/agro-ecological zones in each major watershed. Therefore, major watersheds can be used mainly for broad planning but not for intensive planning.

Watershed classification ….
Watersheds Watersheds are units of more or less similar ecological conditions and may vary in size from 5,000 to 20,000 hectares. A watershed may be used as a unit for development planning as improved practices are identified for different land uses. However, detailed work plans cannot be worked out for these watersheds. Sub-watersheds The area covered by sub-watershed varies, in general, between 2,000 and 5,000 hectares. The sub-watersheds can be used for detailed development planning, including detailed work plans showing erosion control structures, dams, gully plugs, reforestation and grazing improvements.

Classification of watersheds based on stability indicators:
The main goal of classifying watersheds based on stability indicator is to:- Identify critical watershed areas and concentrate limited financial and manpower resources onto the most seriously affected lands first. Based on their stability watersheds can be classified into: Fragile Instable Moderately stable and Stable This classification is based on evaluation of biophysical (rainfall, slope, forest cover and watershed shape) and socio-economic (population density, proportion of arable land affected by erosion, average farm size and per capita food crop production) indicators which are easy to obtain and suitable to evaluate the stability of the watershed.

1.1.6. Rationale for using watershed for planning and development
It enables complete understanding of overall conditions in an area and the stressors which affect those conditions (system thinking). The various parts of the watershed are physically and operationally linked i.e. the various resources are linked not only spatially but also functionally, and the potential benefit from integrated use can be large. Besides driving results towards environmental benefits, the system approach can result in savings time and money- it can have the added benefit of saving time and money (monitoring, modelling, reporting and other opportunities to simplify and streamline workloads by eliminating duplicative trips and efforts

1.1.8. Watershed characteristics
No two places are exactly alike (similar) so each watershed has its own distinctive characteristics or “watershed attributes”. These define the watershed potentials and problems of the watershed. Watershed geomorphology refers to the physical characteristics of the watershed. Certain physical properties of watersheds significantly affect the characteristics of runoff Watershed area: is used to indicate the potential for rainfall to provide a volume of runoff, where as the length indicates the time of travel through watershed. Accordingly, high area of watershed indicates high volume of runoff and long watershed indicates low runoff. The drainage area (A) is the probably the single most important watershed characteristic for hydrologic design.

1.1.8. Watershed characteristics….
Factors responsive to size: Overland flow, more in small watersheds as there is less network of drainage systems while in large watersheds channel flow is dominant Sheet and rill erosion is dominant in small watersheds while in large watersheds gully erosion could be more significant Channel storage, more significant in larger watersheds land use affects flow in small watersheds while in larger watersheds it is counteracted by channel predominance Intense rainfall, more responsive in small watersheds

Watershed Length Watershed length (L) is usually defined as the distance measured along the main channel from the watershed outlet to the basin divide. The straight-line distance from the outlet point on the watershed divide is not usually used to compute L because the travel distance of floodwaters is conceptually the length of interest. Thus, the length is measured along the principal water flow path and also it is called hydraulic length.

Shape of the watershed: Watersheds have an infinite variety of shapes, and the shape supposedly reflects the way that runoff will “bunch up” (gathered) at the outlet. A circular watershed would result in runoff from various parts of the watershed reaching the outlet at the same time. Long and narrow watersheds are likely to have longer time of concentration, resulting in lower runoff rates than broad and compact watersheds of the same size. The quantitative expression of the drainage basin shape was predicted in different forms: form factor, circulatory ratio, elongation ratio.

FF is form factor, A is basin area (km2) and L basin length (km)
Shape The shape of a watershed influences the shape of its characteristic hydrograph. For example, a long shape watershed generates, for the same rainfall, a lower outlet flow, as the concentration time is higher. A watershed having a fan-shape presents a lower concentration time, and it generates higher flow than an elnogated shape. Form Factor FF is form factor, A is basin area (km2) and L basin length (km) Circulatory ratio A is basin area (km2), total area of the circle (Ac) having equal parameter as the perimeter of the drainage basin (km2). How do you find Diameter?

In general terms, in more compact watershed, the runoff hydrograph is expected to be sharper with a greater peak and shorter duration. For a watershed that is partly long and narrow and partly compact the runoff hydrograph is expected to be a complex composite of the above mentioned hydrographs Slope of watershed: determines the flood magnitude and speed: Naturally, the steeper the slope of a field, the greater the amount of runoff. Soil erosion by water also increases as the slope length increases due to the greater accumulation of runoff.

Slope …. the average slope of the watershed can be determined from the topographic map of the watershed by using the following formula Where S percent watershed slope (average) M = total length of contours within the watershed (m) N = contour interval (m) A = size of watershed For very small watershed, the average slope can be taken as the ratio of difference in elevation between the watershed outlet and the most distant ridge (delta H) and approximate average length of the watershed (L)

Time of concentration (Tc): the time taken by the runoff to reach the outlet from the most hydrological distant ridge Tc= L 0.77 Sg-0.385 where Time of concentration in minute, L is maximum length of flow m, Sg the watershed gradient or the difference in elevation between the outlet and the most remotest point in the watershed divided by the length, L

Relief is defined as the elevation difference between the reference points located in the drainage basin Maximum relief is the elevation difference between the highest point and the lowest points Maximum basin relief is the elevation difference between the basin outlet and the highest point located on the perimeter of the basin Rh is the relief ratio H is the relief (m) HL is the horizontal distance (m)

Stream Order Stream order is as measure of the degree of stream branching of streams within a Watershed. First order stream are defined as those channels that have no tributaries. In this case, the flow is depend entirely on surface overland flow to them. The junction of two first order stream forms a second order channel. Please note that when a low order stream segment joins to the height order stream segment, then the order of the stream remained as it is

Second order channel receives flow from the two first order channel that that form it and from overland flow from the ground surface and might receive flow from another first order channel that flow directly in to it. Third order channel is formed by the junction of two second order channels. It receives flow not only from the two second order channels that form it, but also direct overland flow and possibly from first order channels that flow directly in to it and possibly from other second order stream that might join it. In general, an nth order stream is a tributary formed by two or more streams of order (n-1) and streams of lower order. Numerical ordering begins with the tributaries at the streams headwaters being assigned the value one.

Fig. Stream/channel and basin Order

Stream/channel and basin Order
The bifurcation ratio (Rb) is defined as the ratio of the number of streams of any order to the number of streams of the next highest order. Values of Rb typically range from the theoretical minimum of 2 to around 6. The bifurcation ratio is calculated as Rb = Ni/Ni+1 The bifurcation ratio of a watershed is the average of the bifurcation ratios of each stream order

Drainage: it is the discharge of water through a system of natural watercourse like river. It is characterized by its density which is the total length of stream within a watershed divided by the area, the length of channel per unit area as: Where, Dd drainage density (km km-2) L length of stream segment (km) A basin area (km2), K and N trunk order of stream segments and total number of streams, respectively. A high drainage density reflects highly dissected basins, and relatively rapid response to a rainfall input, while low drainage density reflects a poorly drained basin with low hydraulic response.

Stream density – also known as stream frequency over the basin, and it is expressed as the ratio of the total number of stream to the area of the basin. Stream density (Sd) = No. of stream/Basin Area. It is also possible to calculate Sd of first order streams over the watershed, as Sd1 = No. 1st order streams/basin Area

Drainage patterns This refers to the arrangement of streams in a drainage, which often reflects structural and/ or lithological control of underlying rocks. Drainage patterns tell much about the substance of which the land surface is made, with little practice, interpretation and identification of geologic structures and rock types in an area can be made from analysis of stream patterns on air photos or topographic maps Dendritic patterns are an index of the homogeneous nature of underlying bed rock and lack of structural control; they are characterized by the branching of stream valleys at acute angles Radial patterns, consequent streams flowing from a central area in all direction. They are usually developed on high, recently formed land surfaces such as volcanic cones.

Dendrite drainage pattern Develops in area where the type of rocks remain the same all over the basin and where no geological processes, like folding or faulting have created structures that would control the development of river system Weak rock structure usually form dendrite drainage pattern Is characterized by the fact that tributaries flow in the same direction as the main stream, joining at an acute angle Trellis drainages pattern It develops in area where softer and harder rocks alternates with one another or where folding and faulting results in the formation of structures that control the development of river system Radial drainage system -it is made up of a pattern of stream flowing outward, down the slopes of a dome or cone-shaped up land

Drainage patterns

Radial Drainage patterns

Ruggedness number It is the product of relief (H) and Drainage density (Dd). It indicates that if Dd is increased keeping relief (H) constant, then average horizontal distance from the drainage divide the adjacent channel is reduced. If H is increased by keeping Dd constant, then elevation difference between the divide and the adjacent channel will also be increased. An extremely high value of ruggedness number is encountered, particularly when both H and Dd are large i.e. when slope is steep and long.

h is a height of a given contour
H is the relief (i.e. basins height) a is the cross- sectional area at contour and A is the total basin area Fig. Hypsometric integral (HI) for different stage of watershed

Hypsometric integral (HI)
HI, a fraction is the portion of the area that lies below the hypsometric curve. It represents the fraction of volume that remains after the erosion of a hypothetical reference figure whose base is the planimetric area of the basin and whose height is the relief of the basin The ineqilibrum stage is also refereed as young stage, which reveals that the basin is under development The equilibrium stage is less the mature stage of the basin development i.e. development is reached at steady-state conditions The Monadnock phase occurs particularly when isolated bodies of resistant rock from prominent hills are found above the subdued surface

Hypsometric integral (HI)
According to Strahler (1965), equilibrium is attained after erosion has removed enough material that the hypsometric integral stabilizes Stable HI are in the range , HI larger than this are characteristics of basins in an early stage of sculpture where much of the area of the basin is as yet at high altitude. The significance of the stable HI is in the implied stabilization of the basin form. Forms are stable to the extent that the pattern of channels, slopes and divides is established, and from that time on, even tough all these elements may lose material, the ratio of area to altitude is fixed.

Watershed geology The geology of the watershed must be known in order to estimate the watershed’s hydrological reaction. The geology of the watershed substrate influences both the runoff and the groundwater flow. For the runoff, the main geologic characteristic is the permeability of the soil substrate. In case of rainfall, a watershed that has an impermeable substrate presents a faster and more violent increase of the runoff in comparison to a watershed with a permeable substrate. A watershed with a permeable substrate will provide a base runoff during dry periods that will last longer. Watershed geology is essential for groundwater flow.

Soil: Taking infiltration as one parameter, four groups of soil can be recognized for primary classification of watershed. Group A: it is soil having high infiltration rate when thoroughly wetted, having low runoff potential and having high rate of water transmission, very deep soil, it has course texture Group B: moderate infiltration rate when thoroughly wetted, moderately deep to deep, moderately well drained to well drained, moderately fine to moderately course texture, moderately transmission rate. Group C: slow rate of infiltration, soils with layers that impede the downward movement of water, moderately fine to fine texture, and water transmission rate is low. Group D: very slow rate of infiltration, have high runoff potential, clay soil, water transmission is very slow.

Table: watershed characteristics and their importance for watershed management

Land use and vegetation: Depending upon the type of vegetation and its extent, this factor regulates the functioning of watershed example, Infiltration, water retention, runoff production, erosion, sedimentation, rate of evaporation etc. Vegetation protects and shade the soil through its leaves and it also anchor the soil particles through its roots.

Land use and vegetation ….
It has also effects on infiltration rate by adding organic matter to the soil and root opening Type of land use, its extent and management are the key factors which affect watershed behavior. Judicious land use by users [human beings] is of vital importance to watershed management and functioning

Climate: Climate parameters affect watershed functioning and its manipulation in two ways. Rain provides incoming precipitation along with its various characteristic like intensity, frequency and amount of rainfall, distribution (space and time). Parameters like rainfall, temperature, humidity, wind velocity, etc. regulates factors like soil and vegetation.

Block 1: Watershed Management - Definitions and Approaches

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