Watershed Management: Objective, Practice and Monitoring

1 year ago

Atiqur Rahman

14 minutes

Objectives of Watershed Management

The broad objective of watershed management is the promotion of the overall economic well-being and the social improvement of the people within the watershed, along with the maintenance of the watershed. The watershed management activities focus on enhancing the viability and quality of rural livelihood support systems.

To achieve these objectives and fulfil the focus of watershed management, watershed managers should be well aware of the watershed characteristics, watershed input and output variables, and the status of watershed input and output interactions.

Managing the watershed means healing wounds, treating various types of land diseases, and improvement of the quality of the inhabitants. Before starting treatment (i.e., management) of a disease, operation research is needed to determine its cause(s) and effects on the entire system. Then only the disease can be rooted out from the entire system.

Approach of Watershed Management

To ensure the best use of resources in the watershed, the approach of watershed management should be:

a) preventive, to control the deterioration of existing relationships between the use of natural resources within the system, and

b) restorative, for restoring sustainable relationships which had been destroyed due to actions in the past.

For this purpose, various watershed management practices are used, described briefly in the following paragraphs.

Watershed Management Practices

For wise management of watersheds, massive soil and water conservation treatment practices are required. Morgan (1986) has suggested various soil and water conservation practices which are divisible into three major groups. These are related to soil management practices, crop management practices and soil erosion control measures. A brief account of these practices and measures based on Morgan (1986) is presented in the following paragraphs.

1. Soil Management

The soil management practices aim to maintain the fertility and structure of the soil. The fertile soils not only give good yield, but they also minimize the erosive effects of raindrops, runoff and wind. Soil fertility is thus also seen as the key to soil conservation. The various soil management practices used so far in different areas can be divided into three groups. These are using organic matter and various tillage practices.

a. Organic Contents– The use of organic materials improves the cohesiveness of the soil, increases its water retention capacity and promotes a stable aggregate structure. The major organic materials which may be added are green manure, straw or manure which has already undergone a high degree of fermentation. Green manures have a high rate of fermentation and yield a rapid increase in soil fertility. Straw decomposes less rapidly and so it takes longer to affect soil stability.

b. Tillage Practices– Tillage is an important soil management technique. The standard tillage operations maintain soil fertility and retain its stability. Tillage provides a suitable seedbed for plant growth and helps to control weeds. The tillage practices which are used for soil management may be divided into two different types. These are – conventional tillage and conservation tillage.

Conventional Tillage– Ploughs made of wood being used over the years as the traditional implement of tillage. Ploughs invert the plough furrow and lift and move all soil in the plough layer usually to a depth of 15 to 30cm. Disc cultivator is another traditional piece of equipment for tillage. With disc cultivators, the soil is broken up by the passage of saucer-shaped metal discs mounted on axles.

Conservation Tillage– Conventional practices are not useful for all types of soils. For example, fine sandy soils; very heavy sticky soils; and structureless soils. On fine sandy soils, particularly when dry, conventional tillage practice tends to produce many failure planes, pulverising the soil near the surface and creating a compacted layer at plough depth, reducing infiltration and increasing infiltration runoff. The soil is then rapidly eroded by water and, on drying into fine dust, also by wind.

Thus whilst tillage can improve the coarse structures on heavy soils, it can destroy the structure on non-cohesive soils. Under such soils, to overcome these problems, tillage operations are restricted either by cutting down on their number by carrying out as many operations as possible in one pass, as with mulch tillage and minimum tillage or by concentrating them only on the rows where the plant grows and leaving the inter-row areas untilled, as with strip-zone tillage.

2. Crop Management

Plants themselves play a significant role in reducing soil erosion. Because of differences in their density and morphology, plants differ in their effectiveness in protecting the soil from erosion. In designing a soil conservation strategy based on agronomic measures, raw crops must be combined with protection-effective crops in a logical cropping pattern.

The agronomic measures for soil conservation are based on the role of plant cover in reducing erosion by various practices such as crop rotation, cover crops, strip cropping, multiple cropping, high-density planting and mulching.

a. Rotation– The simplest way to combine different crops is to grow them consecutively in rotation. The frequency with which raw crops are grown depends upon the severity of erosion. In low erosion areas, they may be grown every other year, but in the erodible areas, they must be grown only in five or seven years. Suitable crops for use in rotation are legumes and grasses. These provide good ground cover and help to maintain or even improve the organic status of the soil, thereby contributing to soil fertility and enabling a more stable aggregate structure to develop in the soil.

b. Cover Crops– Cover crops are grown as a conservation measure either during the off-season or as ground protection under trees. They are grown as winter annuals and, after harvest, are ploughed in the form of green manure. Ground cover is grown under tree crops to protect the soil from the impact of water drops falling from the canopy.

c. Strip-Cropping– Under strip cropping, raw crops and protection-effective crops are grown in alternating strips aligned on the contour or perpendicular to the wind. Erosion is largely limited to the row-crop strips and soil removed from these is trapped in the next strip downslope or downwind which is generally planted with a leguminous or grass crop. This practice of soil management is best suited to well-drained soils because the reduction in runoff velocity if combined with a low rate of infiltration on poorly drained soil, can result in waterlogging.

d. Multiple Cropping– The multiple cropping practices involve either sequential cropping, growing two or more crops a year in sequence, or intercropping, growing two or more crops on the same piece of land simultaneously. This practice aims to increase the production from the land while protecting the soil from erosion.

e. High-Density Planting– By increasing the density of plants, the intensity of soil erosion can be mitigated. This practice is used to obtain the same effect for a monoculture crop that multiple cropping achieves with two or more crops. The high-density planting increases the infiltration capacity of soil and controls the overland flow; consequently, erosion is controlled.

f. Mulching– To protect the soil from rain splash and sheet wash erosion, mulching practice is used. Mulching is the covering of soil with crop residues such as straw, maize stalks, palm fronds etc. Such cover controls raindrop impact and reduces the velocity of runoff and wind. Mulching also reduces soil temperatures and increases soil moisture. This practice is very useful for semi-humid tropical areas to increase the yield of coffee, banana and cocoa.

g. Revegetation– To control the process of erosion on landslides, rilling, gullied, road and other construction sites, dunes and mine spoil areas, vegetation plays a significant role. Revegetation is also necessary for the deforested areas and areas cleared by patch-cutting. Various methods and measures are described by Morgon (1986) for the restoration of gullied land, restoration of landslide scars and restoration of pastures.

h. Agroforestry– To control soil erosion, land which is not suitable for agriculture, such as along river banks, on terraces and contour bunds, on areas being revegetated to control erosion as windbreaks and shade trees may be used for planting within a farming system.

3. Soil Erosion Control

Mechanical field practices are used to control the movement of water and wind over the soil surface. Studies have suggested several mechanical techniques to reduce the velocity of runoff and wind, increase the surface and groundwater water storage capacity or safely dispose of the excess water. Such important mechanical measures include contouring, contour bunds, terraces, waterways, stabilization structures, windbreaks and geotextile (Morgan,1986).

a. Contouring– Carrying out ploughing, planting, and cultivation on the contour can reduce soil loss down to 50% compared with the cultivation of sloping land by –and-down the slope. The effectiveness of contour farming varies with slope steepness and slope length, for it is inadequate as the soil conservation measure for lengths greater than 180m at 1⁰ steepness.

b. Contour Bunds– Contour bands are earth banks of 1.5 to 2m wide, built across the slope to act as a barrier to runoff from a water storage area on their upslope side and to break up a slope into segments shorter in length than is required to generate overland flow.

c. Terraces– Terraces are earth embarkments constructed across the slope to intercept surface runoff and convey it to a stable outlet at a non-erosive velocity and a shortened slope length. These terraces can be classified into three main types: diversion terraces, retention terraces and bench terraces. Diversion terraces intercept overland flow and channel it to a suitable outlet across the slope. Retention terraces are used where it is necessary to conserve water by storing it on the hillside. Bench terraces consist of a series of alternating shelves and risers and are employed where steep slopes, up to 300, need to be cultivated.

d. Waterways– The purpose of waterways in a conservation system is to convey runoff at a non-erosive velocity to a suitable disposal place. Normally its dimension must provide sufficient capacity to confine the peak runoff from a storm with a ten-year return period. Three types of waterways can be incorporated into a complete water disposal system. These are diversion channels, terrace channels and grass waterways.

e. Stabilization Structures– For gully reclamation and gully erosion control, stabilization structures play an important role. Small dams, usually 0.5 to 2.0 m in height, made from locally available materials such as earth, wooden plank, brushwood or loose rock, are built across gullies to trap sediment and thereby reduce channel depth and slope.

f. Windbreaks– To control the erosive winds, shelterbelts placed at the right angle are very useful in reducing wind velocity. The shelterbelts are spaced at regular intervals to break up the length of open wind blow. Inert structures such as stone walls, salt and brushes fences and cloth screens can be used to perform similar functions on a smaller scale. A shelterbelt is designed so that it rises sharply on the windward side and provides both a barrier and a filter to wind movement.

g. Geotextile– Several types of netting woven from natural fibres such as jute or made from artificial fibres such as nylon are used in erosion control. They are supplied in rolls, unrolled over the hillslope from the top and anchored with large pins or stapled. They are designed to give temporary stability on roadsides and on steep slopes not used for agriculture until the vegetation cover grows.

Watershed Instrumentation For Monitoring

Because watershed provides an opportunity to estimate the amount of erosion and water balance through measurements of hydrometeorological parameters and by knowing the area of the watershed and by assuming a diversity of material, the rate of land erosion and water balance over the whole watershed may be deducted before watershed treatment, during watershed treatment and after watershed treatments.

Therefore, to define the responses of various management activities in the watershed, watershed instrumentation is an essential part of watershed management. For this purpose two permanent monitoring stations within the watershed are needed.

First, to monitor watershed responses or outputs, i.e., water discharge and sediment and solute flow, a hydrological station at the mouth of the watershed and Second, to monitor climatic input parameters, i.e., rainfall, temperature, evaporation, wind velocity etc, a meteorological station within the same watershed (Fig.) is required.

History of Watershed Management in India

The Government of India has launched Watershed Management projects from the early 1970s onwards. Different watershed management programmes like DPAP (Draught Prone Area Progress), DDP (Dessert Development Program), RVP (River Valley Project), NWOPRA (Nainital Watershed Development Project for Rain-fed Areas) and IWDP (Integrated Watershed Development Programme) were launched subsequently in venous environmental regions, these were consistently being affected by water stress and drought-like situation.

During the mid-1980s and early 1990s, the integrated watershed development programme was emphasised with a participatory approach. This approach focused on rising crop productivity and livelihood improvement in watersheds.

In 1974, the Government of India constituted a committee under the Chairmanship of Prof. C.H. Hanumatha Rao. This Committee recommended new guidelines in 1975 which emphasized collective action and community participation, including the participation of primary stakeholders through community-based organizations, non-government organizations and Panchayati Raj Institutions (PRIs).

The watershed development programmes were reviewed and revised again in 2001 and developed guidelines known as the Hariyali Guideline to make further simplification and involvement of PRIs more meaningful in planning, implementation, evaluation and community improvement.

In the year 2005, the Heeranchal Committee evaluated the entire Government sponsored NGO and donor-implemented watershed development programmes in India and suggested a shift in focus away from a purely engineering and structural focus to the deepest concern with livelihood issues. The major objectives of the watershed management programme are:

Conservation, up-gradation, and utilization of natural endowments such as land, water, plant, animal and human resources in a harmonious and integrated manner with low-cost, simple, effective and replicable technology.
Generation of massive employment reduction of inequalities between irrigated and rain-fed areas and poverty alleviation.

Watershed Management: Objective, Practice and Monitoring

Objectives of Watershed Management

Approach of Watershed Management

Watershed Management Practices

1. Soil Management

2. Crop Management

3. Soil Erosion Control

Watershed Instrumentation For Monitoring

History of Watershed Management in India

Read More in Geomorphology

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Objectives of Watershed Management

Approach of Watershed Management

Watershed Management Practices

1. Soil Management

2. Crop Management

3. Soil Erosion Control

Watershed Instrumentation For Monitoring

History of Watershed Management in India

Read More in Geomorphology

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