This compendium by Mihir Kumar Maitra is a valuable resource for all practitioners engaged in watershed management activities in the field. The first part of the book addresses the technical and engineering aspects useful in developing natural resources like land, surface water, groundwater, crops and forest while the second part discusses aspects related to formulation, appraisal and implementation of watershed projects by involving the beneficiaries in the process.
Please view some of the important questions that the book addresses in the context of watershed development below:
A watershed is defined as a topographically delineated geographical area in which the entire run off tends to converge through the existing drainage system to the common outlet of the area for subsequent disposal. One watershed is separated from another by a natural boundary known as the water divide or the ridge line. In short, a watershed is an independent drainage unit for surface water runoff.
Watershed management is the process of formulating and carrying out a course of action involving the manipulation of natural, agricultural and human resources in a watershed to provide goods and services that are desired by and suitable to society, under the condition that soil and water resources are not adversely affected. Watershed management must consider the social, economic and institutional factors operating within and outside the watershed (FAO, 1987).
The common physical components in a watershed development project or programme are:
A number of activities under integrated watershed development projects mobilise community participation to create sustainable outcomes. These involve:
Hydrology is the science that deals with the occurrence, distribution and movement of water within the earth and its atmosphere. The hydrological cycle is a dynamic water transfer system of nature, wherein the water is continuously moving and changing from one form to another, while its sum total remains the same.
<p style="color: #000000;">The hydrological cycle determines the amount of water available and the movement of water in the watershed.</p>
After reaching the earth’s surface, rainfall (or snow) continues to move and change its form. The part that enters the soil is infiltration; the part which flows along the surface is run-off; the part which goes back to the atmosphere as water vapour is evaporation and the part that is transpired by the plants back to the atmosphere is transpiration. Further, the part which is intercepted by leaves and stems of existing vegetative cover is interception, the part which is collected on the surface is surface storage, the part which is retained in the soil is soil moisture and the part which percolates below the soil zone to join the saturated zone is groundwater.
Thus, the static water balance equation in its simplest form, may be written as: Precipitation = Run off + Evapo-transpiration + Change in Storage
Water occurring in subsurface formations can broadly be divided into two horizontal segments. The upper horizon is the zone of aeration and the lower segment is the zone of saturation. The zone of aeration remains filled partly with air and partly with water. The water occurring in this zone is known as soil water. In the zone of saturation, all the pores remain saturated with water. Water occurring in this zone of saturation is known as groundwater. The upper surface of the zone of saturation is the water table.
A third zone - the unsaturated zone, often exists between the zone of aeration and the zone of saturation, particularly when the water table is deep. This intermediate unsaturated zone however, gets saturated temporarily during the monsoon, when groundwater is recharged from rainfall. The zone of saturation containing groundwater, on the other hand, extends downwards till the bedrock in hard rock areas or till an impervious clay layer is encountered in alluvial areas. More such saturated zones may occur underneath the first one in case of multi-aquifer systems common to thick alluvial deposits.
<p>Water occurring in the pores and interstices of sub-surface formations, to its level of saturation, is groundwater. Groundwater occurs much below the zone of soil moisture. A porous and permeable formation capable of holding and transmitting a sufficient quantity of water under gravity (normal field condition) is an aquifer. </p>
Like human beings, plants too need the right kind and amount of sustenance for their growth and development. In addition to light, air, heat and water, plants require nutrients to synthesize their food. Soil acts as a storehouse for nutrients, which not only support plant life but also are an important determinant of crop productivity.
Agricultural lands lose their productivity very rapidly when they are subject to loss of topsoil due to erosion. Land rapidly deteriorates qualitatively due to poor soil management. Proper management of land (soil) therefore, assumes great importance, especially in a country like India where agriculture is the main occupation.
Soil erosion can affect crop growth in many ways. It can reduce soil nutrients and soil moisture-holding capacity due to loss of soil depth, soil organic matter and clay contents. It can also reduce available soil water due to increase in run-off, surface crusting, greater bulk and density of soil. Soil erosion can cause a reduction in rooting depth due to decreased top-soil depth; in soil microbes involved in nutrient recycling and soil aeration and in seed germination.
Soil erosion can also cause an increase in the washing away of seeds and fertilizer from the soil surface, thus increasing the amount of time that needs to be spent on farming operations. Variability in soil fertility can cause within-field variations in crop maturity, resulting in harvest loss.
The above effects of soil erosion on crop growth are iterative and cumulative in nature. The extent to which erosion actually reduces yield is also impacted by a number of other factors. Shallow-rooting crops tend to be more sensitive to the effects of erosion on yield. Crop management systems can, however, compensate for the effects of erosion on yields through increased fertilizer application, adoption of different cultivation practices and use of irrigation water.
The principle of soil conservation is based on the adoption of methods that will make the soil more cohesive at its place of occurrence, thus making it less detachable in one hand and reduction of velocity of run-off and the wind, that leads to soil erosion, on the other. Conservation and management of rainwater plays the most important role in soil conservation. This is why soil and water conservation measures are generally dealt with together as a common activity.
Soil conservation is generally done through vegetational and mechanical measures. Vegetational measures include growing of trees, shrubs, grasses, crops etc. Vegetational measures can further be divided into two sub groups namely Agrostological practices and Agronomical practices like tillage operation, use of organic manure, crop rotation, strip cropping. Mechanical measures include construction of earthen, stone and masonry barriers and ditches for retarding velocity of run-off, as well as land levelling and construction of field bunds.
The vegetational measures take time to show results while mechanical measures give immediate result. From a sustainable watershed development perspective, vegetational measures are considered more permanent and/or sustainable than mechanical measures. In an ideal situation, mechanical measures are introduced simultaneously with vegetative measures so as to facilitate the vegetative measures to take their roots and replace the functions of most of the mechanical measures over the course of time. In arid regions, these measures serve the purpose of run-off harvesting while in humid regions, they retard the run-off to prevent soil erosion.
Rainwater harvesting (RWH) is a simple method by which rainfall is collected for future use. Water harvesting structures store rainwater or surface run-off; they are usually small in size for in situ use of tapped water e.g. field bunds, gully plugs, contour trench. Water retention or storage structures like reservoirs and tanks are generally larger structures, constructed for the purpose of storing large quantities of surface and stream run-off.
While large reservoirs are created by raising earthen bunds in large seasonal streams, small tanks may be created even by raising bunds across small and large gullies or depressions. From the construction point of view, all reservoirs and tanks have two main components, namely the earthen bund and the spillway. While the earthen bund is the structure which impounds the desired quantity of water, the spillway permits excess water to flow away, thus protecting the earthen bund from damage. Although the spillway or the waste weir should preferably be a masonry structure, a katcha outlet or pipe outlet may also be provided, particularly in the case of small tanks.
<p>Therefore, water harvesting structures refer to all physical structures, small and big, constructed in the field for the purpose of storage of surface water flow. Large water retention structures require special engineering knowledge and skills for their design and construction. These are expensive, give immediate and visible results and have a limited life span. <a href="https://www.indiawaterportal.org/articles/kuhl-kohli-and-lost-tradition" target="_blank">Smaller water retention structures</a> are easy to construct, have longer effective life span and <a href="https://www.indiawaterportal.org/articles/saved-tanks-story-puducherrys-bahour-commune" target="_blank">yield more sustainable results</a>.</p>
The different kinds of water harvesting structures are:
Every crop requires a certain quantity of water during its period of growth. If rainfall is sufficient and timely, then no irrigation is required to raise a crop. Plants meet most of their water needs from rainfall. The need for additional water through irrigation is required only when there is no or inadequate rainfall, or when rainfall is distributed unevenly.
<p>Plants can get their water requirement through a combination of irrigation, Effective Rainfall (EF) and Soil Water (SW) contribution in various proportions. Therefore,<br> WR = Effective Rainfall (ER) + Irrigation Water (IR) + Available Soil Water (SW)<br> Or, IR = WR – (ER + SW)</p>
In other words, the minimum quantity of irrigation water required to be added to plants is equal to the crop’s Water Requirement (WR) less Effective Rainfall (ER) and available water in the soil (SW). Factors controlling irrigation requirement therefore depend broadly upon the climatological conditions (for consumptive use), soil conditions (for soil moisture status), crop types and irrigation management practices.
Afforestation refers to planting of new trees. The major component of afforestation activity is the plantation of new seedlings. In an ideal situation, unless there is severe soil erosion and high biotic interference, forest lands can be restored through the process of natural regeneration by allowing the root stock already present in the land to grow, by providing adequate protection. But biotic interferences, i.e. the pressure on forest from man and animals, are ever increasing and must be dealt with by creating alternatives.
<p>The very fact that forest degradation continues unabated is an indication that natural regeneration alone is unable to cope with the pressure and artificial planting is necessary to reverse the trend. </p>
Several factors should be kept in mind while carrying out afforestation:
A project may be formulated on the basis of a skeletal plan (concept paper) developed after a PRA or after conducting an elaborate survey and investigation. A simple project proposal without necessary details is not likely to meet the criteria of a funding agency. Conversely, formulation of an elaborate project proposal down to its minute details without an assured source of funding is also untenable. Moreover, preparation of a very elaborate plan well in advance does not necessarily guarantee successful implementation of the project at a later stage. This dilemma needs to be navigated through discussions with the funding agency.
Most funding agencies have their own guidelines or formats for appraisal of a project proposal. In order to do a perfect job, especially while dealing with larger funding, these formats sometimes seek answers to many aspects of resource endowments and project implementation, much before the initiation of project formulation. For the sake of initial screening, a format should be made such that the answers to many of the queries can be provided meaningfully without going through the process of conducting an elaborate survey. A format which asks questions that cannot be answered without carrying out a detailed survey must be used only after a preparatory or an inception phase has been allowed and funded.
It is, however, prudent to first submit a proposal in a descriptive form (concept paper). A revised proposal may be submitted later in the standard format, which will eventually be supplied by the funding agency, if the proposal appears to them worth considering. While considering a project proposal, many funding agencies place emphasis on the project approach, based on which the project is formulated as well as implemented later. While some funding agencies may insist upon the adoption of a process approach, allowing the project to develop as it goes, others may prefer a well laid down work plan and monitoring plan in place following a Result Based Management approach.
Whatever the implementation strategy, necessary definitions and clarification of the basic elements of the project, viz. the project goal and purpose, beneficiaries, problem identification, location of the project area, funding requirement etc., is required in all cases.
Criteria for enrolment of membership to the committee.
The project team should initiate the formation of the watershed committee and provide managerial inputs to sustain the committee during the project period. A watershed committee, to begin with should:
When a funding agency supports a large number of projects, it is likely that the funding agency will not be able to monitor all these projects, with equal attention. Some common problems encountered by such funding agencies are:
Joint monitoring workshops are useful to monitor a large number of similar projects as a group. Project Implementing Agencies (PIAs) are required to present their reports on certain common aspects e.g. progress made, problems faced, lessons learned, funds utilised, documentation prepared, contribution raised etc. When all the agencies report in a common format, it becomes possible not only to compare relative merits and demerits of each project but also to discuss common problems and seek solutions jointly.
India Water Portal is grateful to Dr Mihir Kumar Maitra for sharing the document with us, and allowing us to publish this in the public domain.
The full text of the document can be downloaded as a PDF from below: