Mitigation and Intervention Techniques Related to Micro-hydro Power (MHP) Projects
Overview
The identification of appropriate mitigation and intervention techniques on the basis of the Environment Assessment is crucial for the implementation of a successful Watershed Action Plan in order to achieve a sustainable use of the catchment area and thus the MHP project.
Biophysical as well as political mitigation and intervention techniques are presented in this article.
Biophysical Measures[1]
Gully Control
Stone Checkdams
Objectives: A stone checkdam is a structure across the bottom of a gully or a small stream, which reduces the velocity of runoff and prevents the deepening and widening of the gully. Sediments accumulated behind a checkdam could be planted with crops or trees/shrubs grass and thus provide additional income to the farmer. |
Brushwood Checkdams
Objectives: Brushwood checkdams are vegetative measures constructed with vegetative materials, branches, poles/posts and twigs. Plant species which can easily grow vegetatively through shoot cuttings are ideal for this purpose. The objective of BWs is to retain sediments and slowdown runoff, and enhance the revegetation of gully areas. They are constructed either in single or double row. Some of the vegetation can be used for fodder. BWs are also ideal to stabilize conservation structures bunds, SS bunds, check dams, bench terraces, road sides, etc. |
Gully Reshaping, Filling and Revegetation
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Sediment Storage and Overflow Earth Dams (SS Dams) for Productive Gully Control
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Sediment Storage and Overflow Soil Bunds (SS Bunds)
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Agro-forestry, Forage Development and Forestry[1]
Area Closure
Objectives: Strip cropping is a cropping practice where strips of two or more crops are alternately established on the contour or, it is a system of establishing more than one crop in alternate strips following a contour pattern for the purpose of erosion control, crop diversification, and decrease the risks associated to the use of single crops only. This cropping system is designed as a defence mechanism against soil erosion in areas where the cropping system is dominated by row/sparsely growing crops that exposes the ground to erosive forces. For instance, crops like sorghum and maize are susceptible to erosion and need to be grown alternately with soil conserving crops. |
Microbasins (MBs)
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Eyebrow Basins (EBs)
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Herring Bones (HBs)
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Micro-trenches (MTRs)
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Trenches
Objectives: Trenches are large and deep pits constructed along the contours with the main purpose of collecting & storing rainfall water to support the growth of trees, shrubs, cash crops and grass or various combination of those species in moisture stressed areas (350-900 mm rainfall). Trenches can have FLEXIBLE DESIGN, to accommodate the requirements of different species. Therefore they can suit what the farmer want to grow. Trenches collect and store considerable amount of runoff water, thus vegetation grows faster and vigorous. Trenches protect cultivated fields located downstream from flood and erosion. Part of the water captured by the trenches reaches the underground aquifer. Therefore, water tables are recharged and supply springs and wells with good quality water and for a long period of time. |
Improved Pits (IP)
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Multistorey Gardening
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Seed Collection
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Soil Fertility Management and Biological Soil Conservation[1]
Compost Making
Objectives: To promote compost making at household level for cost-effective soil fertility improvement and to support local level compost entrepreneurship linked to natural resources management activities at watershed level. CM will improve soil fertility, increase water storage within the soil profile and reduce surface runoff, thus reduce soil erosion. It is one of the best “hidden” water harvesting methods available (compost absorbs water 4-7 times its own weight). CM can be undertaken at very large scale and linked to area closure management and the upgrading of terraces into “cash crop production belts”. CM can become a business: groups of households (landless, etc.) can decide to become compost makers and provide “fertilization” services to other farmers. |
Fertilization and Manuring
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Live Check Dams
Objectives: Live check-dams are established by planting/seeding or plugging of cuttings in gully bottoms to replace or reinforce physical check-dams. The main objective of the establishment of live check-dams is to reduce the cost of establishing physical check-dams. Live check-dams can be applied by individual farmers and does not need the organization of a large group of people to undertake physical structures. |
Mulching and Crop Residues Management
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Grass Strips along the Contours
Objectives: Grass strips are vegetative barriers made out of grass planted in narrow strips of 0.5 to 1.5 m width laid out along the contour. Grass strips control erosion rather effectively in gentle slopes but above 5-8% slope their effect decreases. While contributing to protect soils against erosion they also provide valuable biomass meant to increase animal feed or used for different purposes (eg. roofing, etc.). Grass strips cause less interference than other measures as they can easily be crossed by oxen and plough. Moreover, grass strips take out little amount of arable land. Cost of construction is much lower than physical structures. |
Stabilization of Physical Structures and Farm Boundaries
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Vegetative Fencing
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Ley Cropping
Objectives: Ley cropping is a cropping system in which legume based pastures are rotated with purely grown crops. Legume based pastures are grown on fallow lands for a few years to improve fertility of the soil and thus the yields of subsequent crops (mainly cereals). The establishment of dense, productive forage crops during the fallow period (1-3 years) provides a thick ground cover, supply forage of good quality after the rainy season, prevent soil erosion, restore soil fertility quicker than bare (and overgrazed) fallow, increase the water holding capacity of the soil and have a beneficial effect on future crop yields. |
Integration of Food/Feed Legumes into Cereal Cropping Systems
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Intercropping
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Crop Rotation
Objectives: Crop rotation is one of the oldest practices known to man for fertility restoration and pest/ disease control and it consists of growing different crops one after the other on the same piece of land. Plants of the same crop develop their roots at the same depth of soil profile and thus the proliferation of the root systems in the same depth results in a strong competition for moisture and nutrients. Therefore, if the same crop is grown on the same land year after year, the soil nutrient in that layer decreases sharply and the crop yield consequently declines. On the other hand, if different crops are rotated, the depletion of soil nutrients and decline of crop yields are not as serious as when the same crop is grown year after year. Different crops have different characteristics that enable them to exploit the soil at different depths. Crops also differ in terms of their effect to the soil. Some crops restore or build fertility while others deplete fertility. |
Strip Cropping
Objectives: Strip cropping is a cropping practice where strips of two or more crops are alternately established on the contour or, it is a system of establishing more than one crop in alternate strips following a contour pattern for the purpose of erosion control, crop diversification, and decrease the risks associated to the use of single crops only. This cropping system is designed as a defence mechanism against soil erosion in areas where the cropping system is dominated by row/sparsely growing crops that exposes the ground to erosive forces. For instance, crops like sorghum and maize are susceptible to erosion and need to be grown alternately with soil conserving crops. |
Flood Control and Improved Drainage[1]
Waterways (Vegetative and Stone Paved)
Objectives: A waterway is a natural or artificial drainage channel constructed along the steepest slope or in a valley to receive/accommodate runoff from cut-off drains and graded terraces/bunds. The waterway carries the run-off to rivers, reservoirs or gullies safely without creating erosion. A vegetative waterway can be constructed in areas without stones. The main advantage is that waterways can be constructed for both very small and large size catchments, thus accommodating individual or communal needs for drainage and evacuation/use of excess run-off. Paved waterways are suitable in steeper terrains and areas with large amount of stones. |
Cut-off Drains
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Graded Soil Bund
Objectives: Graded soil bund is similar in description with level soil bund. However, graded soil bund is upto a maximum of 1% inclined against the contour so that excess runoff is allowed to drain to the adjoining natural or artificial waterways. It is also possible and necessary to include tied ridges smaller in height within the channel of the terrace. The stored water within the ties can infiltrate into the soil while any above that height is drained out. Graded soil bunds can be made to gradually develop in to benched type terraces through careful maintenance. Any integration of other measures such as stabilization and composting can be applied as it can be applied on level bunds. |
Graded Fanya Juu
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Improved Surface Drainage for Increasing Productivity of Vertisols and Soils with Vertic Properties
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Physical Soil and Water Conservation[1]
Level Soil Bunds
Objectives: The bund reduces and stops the velocity of runoff and consequently reduces soil erosion and the steady decline of crop yields. They are impermeable structures, unless provided with spillways, intended to retain all rainfall, and hence, increase the moisture retention capacity of the soil profile and water availability to plants, and increase the efficiency of fertilizer applications if any. Through their water retention effect, the bunds may allow some crop yield even in drought years. Soil bunds are entry points for further stabilisation and application of organic residues or compost (especially if applied in the first meters behind the bund where soil is deeper). |
Stone Bunds
Objectives: The stone bund reduces and stops the velocity of runoff and consequently reduces soil erosion and the steady decline in fertility and crop yields. They are semi-permeable structures unless sealed with soil in their upper side. They increase the moisture retention capacity of the soil profile and water availability to plants, and increase the efficiency of fertilizer applications if any. Through their water retention effect the stone bunds may allow some crop yield even in drought years. Stone bunds are entry points for application of organic residues or compost, especially in the first 2-3 meters behind the bund where soil is deeper. |
Stone Faced Soil Bunds
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Level Fanya Juu
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Bench Terracing
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Conservation Tillage using Maresha and Broad Bed and Farrows Maker (BBM)
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Hillside Terraces
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Hillside Terrace with Trenches
Objectives: HTTs is highly labour intensive - combine both effects of hillsides and trenches constructed immediately above the terrace stone riser, generally suitable for steep slopes (up to 50%) and shallowmedium depth soils (although common in other type of soils). Suitable for tree/shrubs planting and very effective in controlling runoff and erosion. HHTs ensure protection of downstream fields, and play a significant role in replenishing water tables. |
Water Harvesting[1]
Hand-dug Wells
Objectives: Hand dug wells are used to irrigate small plots or to supply drinking water for human and livestock. |
Low Cost Water Lifting
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Low Cost Micro-ponds
Objectives: Supplementary irrigation to high value crops (horticulture, fruit trees, etc.). Water for livestock for a few months. Micro ponds allow to use surface runoff from small catchment areas within and between homesteads (foot paths, small grazing land areas, rocky areas, etc.). Can also collect water from feeder roads, graded bunds, spillways, etc.). Water collected can be used during the rainy season as supplementary irrigation (during dry spells) or after (1-2 months max) for additional support to horticulture crops, fruit trees, compost, small livestock, beekeeping, etc. |
Underground Cisterns
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Percolation Pit
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Percolation Pond
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Farm Pond Construction
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Spring Development
Objectives: Proper spring development helps protect the water supply from contamination. The objective of spring development is to collect the flowing underground water to protect it from surface contamination, store it and avail for use. |
Family Drip Irrigation System
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Roof Water Harvesting System
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Farm Dam Construction
Objectives: Storage farm dams are mainly to store surface runoff water and to use it when required for various uses such as for human and animal consumption, small scale or supplementary irrigation, fish production. |
River-bed or Permeable Rack Dams
Objectives: River bed dams are a floodwater farming techniques where runoff waters are spread in valley bottoms of seasonal riverbeds, large gullies or natural water courses for improved crop and forage producdtion using a long, low structure, made from loose stone (occasionally some gabion baskets may be used). Developing gullies are healed at the same time. Occasionally it is required to raise the riverbed in order to guide spate floods into irrigation canals of spate irrigation schemes, or to accumulate river sediments for riverbed cultivation. In such a case, very strong dams are required that can resist powerful spate floods. It is a relatively low cost structure especially designed to resist heavy flooding. The structures are typically long, low dam walls across valleys. The large amount of work involved means that the technique is labor intensive and needs group approach. |
Small Stone Bunds with Run-on and Run-off Areas
Objectives: The main objective is to considerably increase the biomass production of forage grass and legumes pastures and fodder crops and/or allow the introduction of species having higher water requirements in abandoned, marginal and eroded dry areas. The principle of the system and its application is the same as for runoff/runon systems suggested for the cultivated areas. Rainfall multiplier systems for grazing land can also rehabilitate fertility (decay of grass and increased moisture). In this respect, a few years pasture improvement and soil fertility restoration may allow the area to be cropped again. The main difference between this measure and the one described for the cultivated land is that instead of food crops fodder plants are grown. The system is less demanding in terms of size of structures and management of the plots as fodder species require less water than food crops. |
Narrow Stone Lines Along the Contour
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Stone Faced/Soil or Stone Bunds with Run-off/ Run-on Areas
Objectives: This is a rainfall multiplier system for reclaiming and rehabilitating marginal areas with low productivity, shallow soils, often affected by surface crusts and low water infiltration rates, with slope ranging between 1 to 5%. Both runoff and runon areas are included within the bunds. The runoff area is intended to serve as a micro catchment to supply additional water into a runon area (cultivated area) to increase production levels in one portion of the total area or to introduce crops with higher water requirements that otherwise would not grow without additional moisture. |
Conservation Bench Terraces (s) (CBT(s))
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Tie Ridge (s)
Objectives: Tie ridges are small rectangular series of basins formed withing the furrow of cultivated fields mainly to increase surface storage and to allow more time for rainfall to infiltrate the soil. Making tied ridges manually is time and labor consuming. |
The Zai and Planting Pit System
Objectives: Zai pits are systems of small pits dug along approximate contours allows the cultivation of crops on degraded lands. The zaï pits restore degraded lands (crusted, hard, compacted and poorly structured soils), thus increasing the land available for cultivation. It is a simple technique that, amongst others, landless or oxless can practice because it requires only manual labour. |
Large Half Moons
Objectives: The measure is a rainfall multiplier system that allow cultivation of crops in low rainfall areas. It is applied in areas with sandy and sandy loamy soils affected by low fertility levels and thin surface crusts that inhibit infiltration and increase runoff. Large half moons are suitable structures to enable cultivation of drought resistant crops in areas with very low rainfall. They intercept all runoff and stop erosion. It is also a measure suitable for rangelands and degraded grazing lands in dry areas (forage crops). |
Division Weir Design and Construction
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- For more information see agriwaterpedia.info - Water Harvesting
Education and Training
Income Generating Measures
Participatory Approach
How Interventions Can Improve the Environmental Condition of the Catchment
Box 1: shows three examples of how (rather simple) interventions can improve the environmental condition of the catchment. A more detailed list of mitigation and intervention techniques and the respective application can be found in DESTA, L. ET AL. (2005): Part 1: Community Based Participatory Watershed Development. Addis Ababa: Ministry of Agriculture and Rural Development, pages 69 – 165 and DESTA, L. ET AL. (2005): Part 2: Community Based Participatory Watershed Development: Annex. Addis Ababa: Ministry of Agriculture and Rural Development, pages 43 - 48.
Fenced vs. Unfenced Springs / Wetlands
Springs and wetlands not only guarantee the discharge in dry season, also they have a great retention capacity during and after rains. Springs are sensitive areas that react to disturbances easily. Protection of springs and wetlands is thus crucial for the sustainable use of the MHP projects. Protection measurements might include fencing (to protect the areas from cattle step and thus soil compaction), protection of natural vegetation around the springs, protection of a natural humus layer (in order to sustain sufficient infiltration and thus groundwater recharge). Furthermore fencing can help to improve the water quality, since pollution due to agricultural and pastoral use can be prevented[2].
Buffered vs. Unbuffered Riverbanks / Wetlands
A buffer typically consists of a band of vegetation along a wetland or water body, preferably natural habitat, but including previously altered, stable native or introduced species. A buffer can perform a variety of functions, which can improve the environmental condition of a watershed, such as sediment removal and erosion control, runoff reduction through infiltration, reduction of human impacts by limiting easy access as well as barrier to invasion of exotic species[3]. Thus buffers can benefit the sustainable use of the MHP and should hence be established and/or protected.
Eucalyptus vs. Indigenous Plants
Eucalyptus easily adapts to any soil and water condition, it is characterized by fast growth, high survival, long roots and hard leafs. Those features make it economically very beneficial. When it comes to watershed management, its negatives sides should be considered though: it does not only take a lot of nutrients and water and is hence a high competition to companion plants and decreases biodiversity, also soil erosion can occur which can negatively affect the MHP’s performance. FAO thus recommends that large scale monocultures of eucalyptus plantations be excluded from watersheds, aforestation projects should avoid monocultures and the use of eucalyptus. The only way to include eucalyptus is to adopt it in agroforestry systems, but the proportion of each species should be planned out carefully[4].
Further Information
- Hydro Portal on energypedia
- Environment Assessment Related to Micro-hydro Power (MHP) Projects in Ethiopia
- Environment Assessment and Watershed Action Planning Related to Micro Hydro Power Projects (MHPs)
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 _
- ↑ HELVETAS (2005): Helvetas Wasser Fact Sheet: Quellen und Quellschutz.
- ↑ GALE, J.A. (unknown): Watershedss Wetland Management. http://www.water.ncsu.edu/watershedss/info/wetlands/manage.html#prot
- ↑ SUNGSUMARN, K. (1993): Why Eucalyptus is Not Adopted for Agroforestry. In: Kashio, M. et al. (Hrsg.)(1996): Reports Submitted to the Regional Expert Consultation on Eucalyptus - Volume II. Bangkok: FAO Regional Office for Asia and the Pacific.