Irrigation Practices

8/6/2019 Irrigation Practices

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require irrigation water conservation practices. Rwanda is one of the great lakecountries and hasa lot of water resources. Agriculture employs about 80% of the population and provides over40% of the GDP of the country. Population density of Rwanda is about 305 personsper squarekilometer with a growth rate of about 3.5% ( MINIPLAN, 2002).The area under cult

ivation isabout 1,385,000 hectares, which is 52% of the total surface area of the country(MINAGRI,2003), and the population cultivates even the marginal areas in trying to satisfy their needs infood security. The population is growing but the arable land does not increase.To feed therapidly growing population, there is a need to increase agricultural productivity in the country.

* Corresponding author. Tel.: +250 08678702; fax: +250 530210.E-mail address: [email protected] (D. Nahayo)


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This can be achieved by a change in agricultural practices. Rwanda has about 165,000 hectares ofmarshlands in which only 94,000 hectares are in use (MINAGRI, 2003). In addition, the usedmarshlands are not used wisely or exploited in the appropriate manner. Erosion,lack of

maintenance of irrigation structures and misuse of available water resources inagriculturalactivities impose a problem of food security and water and land conservation inthe country.Migina, one of catchments of the south province of Rwanda, is faced with problems of erosionand flooding in the main rainy season (from mid-February to the end of May ) andwater shortagein the main dry season(from June to mid-September)adding to lack of better maintenance of itscurrent irrigation systems. This study looks at the promotion of irrigation water conservation

opportunities in Nyaligina, Nyamugali, Rwasave and Ndobogo, marshlands of the Miginacatchment. It begins by evaluating the current irrigation practices in these four marshlands andidentifies potentials for improved hydraulic performance. This could help for improvement ofthe standard of living and environmental conditions in the study area so that land and water willbe manageable in a sustainable way.

2. Materials and Methods2.1. Literature ReviewIrrigation practices are the techniques of applying an amount of water to the so

il in the aim ofcontrolling of water application to arable soil, supplying crop water requirements not satisfied byrainfall, providing crop insurance against short duration droughts, etc. Irrigation methods aresummarized into three types which are surface (flooding, furrow and surface dripirrigation),subsurface drip irrigation and overhead irrigation (sprinkler irrigation or hose- end overheadsprinkling). Relative moisture varies the most in furrow irrigation and the least in drip irrigationsystems (Texas Water Development Board, 2002). Irrigation water conservation opportunities aredefined as the structural improvements in the application systems, better maintenance of existingirrigation systems, altered tillage and soil management, changes in the crops grown, waterharvesting to be used in drought season, improved hydraulic performance in the irrigation schemeetc. (Ley, 2003). Efficient agricultural water conservation practices are essential to ensure theviability of water to be used in drought season or in other activities (Texas Water DevelopmentBoard, 2002). Structural improvements in application systems include practices such as

introducing infiltration ditches or replacing open ditches with underground pipe, lining ditches,use of gated pipe, fitting gated pipe systems with surge-flow devices, conversio


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n from furrow tosprinkler irrigation or drip irrigation and installation of tailwater recovery systems. The objectiveof adopting these practices is to increase application efficiency and to apply conflict managementsystem at farm levels (Texas Water Development Board, 2002). In many instances,they also

have the potential of decreasing nonbeneficial consumptive use. Similarly, structural landimprovement such as construction of infiltration ditches, terracing structures,the digging ofboreholes for reducing runoff on high hill slopes and recharging groundwater, afforestation, anti-erosive planting and river beds enlargement and land leveling are designed to improveapplication efficiency, decrease nonbeneficial consumptive use and to reduce thesoil degradationby erosion (Allen, 1991; Boyd at al., 2000). Water conservation and soil management are

practices designed to increase application efficiency at the farm level (Evans,1998). Waterconservation involves techniques that allow growers to schedule irrigation basedon moistureneeds of crops. Specific techniques include monitoring soil moisture and maintaining daily


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records of crop water balance using estimates of consumptive water use from weather data. Useof furrow irrigation and practicing more timely fertilization are examples of altered tillage andsoil management. Water conservation techniques can also be used to schedule strategic deficits in

water availability during periods when crops are relatively insensitive to soilwater deficits. Thisform of water conservation is generally referred to as deficit irrigation, and results in decreasesnonbeneficial consumptive use. Changes in cropping patterns can result in decreasesnonbeneficial consumptive water use. Some conservation measures can be implemented at thesystem level to improve overall application efficiency within a catchment and, in some cases,decrease nonbeneficial consumptive use (Colorado Water Resources Research Institute, 1996).

Rainfall data which are used in irrigation water conservation opportunities aretreated usingOrstm method for large catchments and rational method for small catchment with asurface areanot greater or closed to 5 km2 (Daniill at al., 2005). Using surveys and statistical analysis of allinformation gathered give idea of finding solutions of an improved hydraulic performance(Skogerboe and Merkley, 1996).

2.2 Study area descriptionNyaligina, Nyamugali, Rwasave and Ndobogo marshlands are located upstream of Migina

catchment in south province of Rwanda and situated in the three first subcatchments of Migina:The small subcatchment A of 3.14 km2 which is drained by Rwantarama river and closed byRwasave earth dam; The small subcatchment B of 3.39 km2 which is drained by Kazibaziba andNyamugali rivers; The large subcatchment C of 37.50 km2 which are drained by Ndobogo,Nyagashubi and Kidobogo rivers with Nyakagezi, Nyabitare, Musizi and Kabacuzi astributaries;The climatic rhythm is the followings:

i. A small rainy season from mid-September to mid-December;ii. A small dry season from mid-December to mid- February;iii. A great rainy season from mid-February to the end of May ;iv. A great dry season from June to mid-September.The main agro-climatic parameters which are the temperature, radiation, potential evaporationand hydrous regimes that influence crop production (Hargreaves and Merkley, 2004), as they arederived from the stations of Butare (236' S, 2944'E; 1,768 m) and of Rubona (229' S; 2946' E;1,706 m) for the thermal parameters, are favorable to agricultural activities. The only problemswhich decrease crop production are erosion and flooding in the great rainy seaso

n and watershortage in the great dry season. These could be the results of the topographicconditions with a


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slope which varies between 2 and 3%, rainfall distribution and variation along the year (109 to127mm in the great rainy season and closed to zero in the great dry season 7mm (AHT, 2003)),deforestation and of anti-erosive structures and inadequate irrigation water use.

The rainfall and hydrous patterns are characterized by an annual rainfall of about 1,170 to 1,270mm, the rains are concentrated between September and the end of May. April is the rainiestmonth but the highest amount rain fall during the November to December raining season.November and the period from March to May are sprinkled. The small dry season ofDecember-January, observed relatively well in many other parts of the country, is less clear in Migina,because in the least rainy stations of the zone (Save and Rubona) the average rainfall of

December and January remains closed or ranked even above 100 mm. The annual average of therelative soil moisture, calculated over the 11 last years is 75.7% with minima in June of 59.8%


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and the maximum in April of 86.3%. The annual average of evaporations in the area is 917.2mm.Maximum evaporations are during the months of main dry season (June to September) withmonthly evaporations going from 80 mm to 120.9 mm (August). The winds speed mostly

between 1 to 3m/s and rarely exceed 6 m/s. There is one well marked dry season and animportant hydrous deficit between June and the beginning of September. The firstrains ofSeptember are relatively not very useful for agriculture because of their irregularity and inaddition it fall on a hot and drained surface and get evaporated immediately Itwill be necessaryto envisage irrigations between June to beginning of September to safeguard an optimalagricultural production in that season. The only alternative in the event of lack of water to cover

this deficit is to adapt the farming calendar and to introduce crop that demandless amount ofwater.

2.3. Compilation of existing informationThe first step in this study was to compile existing information about irrigation systems in themarshlands. Some general maps of the project area as well as detailed design maps of thecatchment have been collected. Technical reports, socio-economic studies that have been writtenregarding the project, have been studied. Information regarding difficulties with irrigation

practices has been obtained from different groups of farmers scattered throughout the marshlands.Using questionnaire, much have been learnt from the farmers. Here, information has beengathered primarily by asking people questions either by having interviews ask questions andrecord answers or by having people read or hear questions and record their own answers.Information has been sought from ISAR, RADA, etc, institutions, charged with responsibilitiesover water and land in Rwanda (ISAR, RADA, etc.). All the information gathered in this stepprovide the background of the projects and helps the study of irrigation water conservationpractices in the study area.

2.4. Identification of irrigation structural damagesThe second step in this study was conducting field inspection and surveys in order to identifyproblems related to irrigation structures, its condition, performance and maintenances, for properquantification allow taking appropriate intervention measures. In case of structural damages thecauses are properly assessed for appropriate mitigation.

2.5. Data gathering, handling, analysis and interpretation of the resultsAll the information from the first and the second steps was primarily gathered in packages


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according to the data type and treatment model and secondly handled. As the agricultural use ofthe land of the marshlands is related to the availability of water in the catchment, the hydrologicalor rainfall data were used to estimate the expected maximum amount runoff and base flows, thatare used for the design or redesign of some irrigation structures (e.g. channels

, dams, weirs, etc.)taking into account the topographic conditions for compliance with Laceys regimetheory.Average monthly rainfall and the Orstom and Rational methods were used for dischargeestimation. The determination of irrigation crop water requirements and the irrigation supplyrequirements in comparison with the available water in the stream or in the reservoirs was used tosuggest the method of water delivery and engineering alternatives. The irrigation water demand


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was calculated, by considering all surface areas which are irrigated in the marshlands for allcrops: rice, maize, sorghum, Irish potatoes, suit potatoes, cabbages, beans andothers according tothe available data or by using data from (FAO, 1979). Questionnaire were also analyzed. Data for

this study were collected from smallholder irrigations farmers of, Nyaligina, Rwasave,Nyamugali and Ndobogo, the upstream marshlands of Migina catchment located in the southprovince of Rwanda. A stratified sampling method was employed to the smallholderirrigationfarmers. Taking into account the cost considerations, the deadline of submissionof the study andothers limiting factors, sample of 100 farmers was interviewed using a structured questionnaireset in the local language. In trying to study how to improve irrigation water conservation

practices in the survey area, two methodologies were used to investigate farmersviews on

irrigation water use, their contribution and the intervention of agricultural institutions forimproved hydraulic performance in the marshlands:

Structured interviews on all technical, managerial and irrigation support servicesparticipation issues were carried out;By using Statistical Packages for Social Sciences software (SPSS), descriptive statistics

were developed to describe, the farmers views on irrigation practices, crop productionand water use efficiently in the marshlands.The field visits of structural damages were added to the information from questionnaire analysisto find the normal, catch-up and preventive maintenances in the irrigation scheme. In addition,possible solutions for improved hydraulic performance in the catchment and strategies forattaining irrigation land and water conservation in a manageable and in a sustainable way in allthe marshlands would be established. Finally, all information from data analysiswould besummarized to conclude and make some recommendations to the stakeholders at alllevels.

3. Results, analyses and discussions3.1. Hydrological data analysis( Annex 3-9)The agricultural use of the soil of marshlands is related to the availability ofwater in thecatchment and thus the hydrological regime of the marshlands determines the water resourceswhich can be used in irrigation scheme. This has been explained in the study area description.The hydrological study aims at two things: firstly, the determination of the sto

rm runoff for therequired frequencies and secondly, determination monthly average flow with the level of the


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hydrographic network of the catchment area in which the marshlands is located inorder todetermine whether the water requirements of crops can be met at the various cropping seasons ofthe year. Considering the scarcity of direct measurements, indirect estimation methods were usedto determine certain parameters which are validated by observations on the field

. In the absenceof other hydrological data, rainfall records were used as a basis for the hydrological study. TheButare Airports rainfall records (latitude 0236 - longitude 2944 - altitude 1760 meters) wereused for reference for the study area. In this study, the rational method was used for pick runoffestimation for the small subcatchment (with the surface area not greater than orclosed to 5 km2)and the ORSTOM method of runoff estimation was used for the large subcatchments.In therational method, the Kirpich formula was used to estimate the time of concentrat

ion (the timerequired for the farthest point of the catchment to contribute to runoff), and is given by Eqn. 1.


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0.0195L0.77

tc = , Kirpich formula (Daniill et al., 2005)(1)

0.385

S

Where tc is the time of concentration in minutes, L is the maximum length of theflow in meters,H is the difference of both upstream and downstream altitudes of the catchment in meters and S isthe watershed gradient in meters/meters of the difference in elevation between the outlet and themost remote point divided by the length L (H/L). The formula for peak flow Qp isgiven by Eqn.

2.Qp= 0.278*C *i* A, (Daniill et al., 2005)(2)

Where C is the runoff coefficient, i is the rainfall intensity during the returnperiod tr and A is thecatchment area. The value of i is assumed constant during tc and the peak flow or maximumdischarge continues until the end of the rain. In the ORSTOM method the assumptions remain thesame, but the peak flow or maximum discharge is given by Eqn. 3.

Qp= K*M, (Daniill et al., 2005)

(3)

(Kr *Vp )

M =TB

Vr =Kr *Vp

Vp =a *H*A

Where:

H is the depth of the punctual rain determined by Gumbel adjustment for the raingauge ofreference Butare;Vp is the total volume of rainfall on the catchment;Kr is the runoff coefficient;Vr is the effective volume of runoff;

Tr is the return period in yeas;TB is the effective duration of runoff; and


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K is the independent coefficient determined by experiment and is equal to 2.5 intheORSTOM method.3.2.Irrigation crop water requirement and water use analysisThe irrigation water demand is calculated, by considering all seasonal surface areas which are

irrigated in Migina catchment for all crops: rice, maize, sorghum, Irish potatoes, suit potatoes,cabbages, beans and other.


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The volume of water used in agricultural sector in Migina marshlands is about 80% of the totalsurface water abstraction. The net irrigation is defined as amount of water required to be suppliedto the crop in order to satisfy its consumption use. This was calculated by using Eqn. 4.

Inet= Kc* ETo-Peff, (Michael, 1999) (4)

And the gross irrigation is given by Eqn. 5:

Kc*ETo -Peff

Igros= , (Michael, 1999) (5)

e

f

Where Inet= net irrigation requirement

Kc= crop coefficient

ETo = reference evapotranspiration

Peff = effective rainfall

Pm=monthly precipitation

D=daily interception threshold

-1.76* D

Peff=Pm*Exp ( 0.45 )

Pm

and ef is the global efficiency.

The global efficiency is 80% of water abstraction, and the pan coefficient Kpanis 0.70 (FAO,1979). The daily interception threshold is calculated by using the mean of all the dailyinterception thresholds applied to all crops; D equals to 0.73. Irrigation waterdemand studiesundertaken in Migina marshlands before this study have been generally done well;however, theproblems have been how to implement the recommendations using the required waterforirrigation and save an amount to be used in drought season.

3.3.Irrigation practices and irrigation structures analysis

The surveys and field visits which have been undertaken in the study area have enable us todivide the area into two zones:

The first zone is the marshlands of Nyaligina and Rwasave which are well arranged. This studyshows that Nyaligina marshland has 39ha while Rwasave marshland has 80ha under i


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rrigation.The study shows that the irrigated area uses flooding irrigation for rice crop production whereasother crops like beans, potatoes, sorghum etc. are irrigated naturally by rainfall according to theweather conditions. The most part of these marshlands are arranged. However, there are many

problems with the irrigation structures. Rwasave earth dam with a total reservoir capacity of100,000 m3 and its useful volume of 85,000m3 needs rehabilitation. Two side intakes of Rwasaveearth dam must be rehabilitated by replacing valves and clearing out weeds in all channels andother irrigation structures. The left intake does not function any more and mustbe repaired.Channels, over 86 intakes and about 40 chutes must be completely rehabilitated.Rwasave bridgemust be rehabilitated.The second zone deals with Nyamugali and Ndobogo marshlands which are not arrang

ed at all.The surveys show that Nyamugali marshland has a surface area of 17ha and Ndobogomarshlandhas a surface area of 67ha under irrigation. The surveys have found that there is a need of


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improvement of irrigation and drainage systems. The field visits and discussionswith the farmersby using questionnaire analysis have helped to identify the following major issues for improperwater and land utilization.

Illegal canals cutting

Farmers at the Ndobogo marshland reported that the upstream people divert wateraccording totheir own wishes without consideration to those downstream. The canals are broken at severalpoints and water is being illegally diverted. The farmers at downstream do not receive enoughwater for their crops. Also, they reported that the farms which are far off theriver do not havechannels to feed the crops. Farmers have not any facilitative means of feeding water to the crops,

especially for rice crop production. Illegal canals cutting have been identifiedin Nyaligina andRwasave marshlands. These problems of canals cutting are the source of underdevelopment ofmost irrigated lands. Irregular blockage of water by uncontrolled farmers to keep the irrigationwater supplies confined to their farms is another problem. This practice not only skewed thedistribution of irrigated area but also resulted in wastage of huge investment made on theconstruction of water channels, which remain almost dry, especially in great dryseason. This isattributed to lack of weekly rotational schedule, and insufficient field staff t

o operate thesecorrectly including monitoring for irregular blockage of irrigation water alongcanals. Equity inwater distribution is very important factor for the management of water resources (Ahmad, 1999).Inequity in water distribution results in frustration, lack of interest in farming and maintenance ofwatercourses, distrust among water users and disputes over water rights among the users.Inequity in water distribution is the result of nonfunctional water user associations (Ali andChuddar, 1996; Hussain and Perera, 2004).

Improper maintenance of watercourses, poor field channels and inadequate hill slopes protection

In Ndobogo and Nyamugali marshlands, watercourses are poorly maintained. Channels are filledwith sand and bushes and water overtops the watercourses, especially in rainy season.Watercourses are broken at several places and cleaning of watercourses is not done any more.The designed outlets at several points are broken which reduces the supply of water available tofarmers at the tail end of the canals. The proper repair and maintenance of thes

e watercourses isvery important for getting long-term benefits of the investment made on irrigation structures. Due


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to cheap water availability and lack of knowledge, uncontrolled flood irrigationis commonlyused. The field channels are earthen, not designed and not constructed properlyand are poorlymaintained. As a result, considerable amount of water is wasted in the field channels. Due toundulated fields, huge amount of water is wasted. There is need to level these f

ields, so thatscared water could be used efficiently. For doing so, rehabilitation and reinstallation of theconveyance systems, field adjustments, improvement of circulation roads and bridges,construction of Ndobogo earth dam, which has the following characteristics: 50,000m3 of usefulvolume, 140m of length, 32m and 4m of bottom and top width respectively and maximum heightof 5.5m, for irrigation water storage and flood control; the construction of Nyamugali weir forraising water level upstream of the marshlands in order to construct the main ch

annels on theheight which dominates all the irrigable land of the marshlands and introductionof anti erosivestructures such as the installation of infiltration ditches and terracing structures, the digging ofboreholes for reducing runoff on high hill slopes and recharging groundwater, afforestation, anti-erosive planting and river beds enlargement could contribute to land and water conservation. Byusing Orstom and rational methods of maximum discharge estimations and consideringtopographic condition, we have calculated the main emitters or drains in the marshlands. The


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irrigation water demand was calculated, by considering all seasonal surface areas which areirrigated in Migina catchment for all crops: rice, maize, sorghum, Irish potatoes, suit potatoes,cabbages, beans and others. We have supposed that volume of water used in agriculture sector in

Migina marshlands is about 80% of the total surface water abstraction. The net irrigation wascalculated as amount of water required to be supplied to the crop in order to satisfy itsconsumption use. Proposing two seasons of rice production from September to December andfrom February to May by using flooding boarder irrigation and introducing furrowirrigation forother row crops such as maize, beans and sorghum, and rearranging fields by respecting themaximum slope of 0.5% and introducing chutes where topographic conditions do notpermit that

maximum slope could contribute to water use efficiently and land conservation.

No organized water user associations and incompetent agricultural support services

Water regulation is under established organization in Rwanda, however, water user associationare not organized and do not functioned properly. There is no formal body to look after thewatercourses and irrigation structures in Migina catchment so that there are many problemsamong the farmers on water distribution according to priorities. So, There is therefore the need to

strengthen and empower water users associations to maintain and improve watercourses alongwith more effective use of water through improved water management practices (Skogerboe,1996). In addition competent agricultural support services play a pivotal role in the motivation offarmers towards the formation of water user association, adoption of improved irrigation andwater conservation practices, and introduction of high yield crops, efficient water use and properuse of non-water inputs. However, it was observed that irrigation support services work hardly inthe catchment. Similarly, On-Farm Water Management activities are limited in these marshlands.Improving agronomic and farm water management practices, particularly promotingthe use ofimproved varieties of seeds and enhancing the role of extension services to farmers fordissemination of up-to-date knowledge are very important to improve land and water productivity(Hussain and Perera, 2004). A good coordination and integrated approach by On Farm WaterManagement and Agriculture Extension Department is needed, starting with operation,maintenance of main watercourse and field channels for overcoming inequities tha

t occur alongthe watercourse and assisting farmers with improved irrigation and agronomic practices


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(Skogerboe, 1996; Early et al., 1976). Thereafter, the current agricultural, water resources andenvironmental management institutions which are responsible for of the promotionof irrigationpractices, water and environmental protection have to sit together and study howto increase foodproduction with an acceptable range of land degradation principles.

4. Conclusion and recommendationsIt is a common place to say that rehabilitation and repairing irrigation structures, installations ofnew irrigation structures or improved technologies of water saving and land conservation aresufficient to reach an improved hydraulic performance. As it is said that prevention is better thancure, the proposed solutions for finding an improved hydraulic performance in Miginamarshlands need an additional, systematic and periodic maintenance of all infrastructures in the

catchment. In most cases, farmers are interested in operations, not in maintenance, but may bewilling to pursue an effective maintenance program if they have control over water deliveries.Best operated irrigation systems in the world are managed by farmers, not by theinstitutions incharge of irrigation. However, farmers who are not experienced in the managementof their


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system cannot be effective overnight. They need to go through an evolutionary process ofdeveloping management skills. This is where institutions in charge of irrigationhave to train andequip farmers with skills to manage, operate and maintain irrigation systems. The training should

begin with the heads of water users associations on irrigation maintenance. Themost importantstage in irrigation maintenance is the preventive maintenance. These chiefs would also train otherpeople on how to improve hydraulic performance in the catchment. The institutions in charge ofirrigation have also to work together formally or informally with the water users associations. Inaddition institutions in charge of irrigation could arrange and give on loan basis selected seeds tothe farmers, and allow them to pay after harvesting. Communication skills have also to be

developed between irrigation institutions, staffs of water users associations and farmers for bettermutual understanding in order to maintain a sustainable improved hydraulic performance in thecatchment. Finally, this study has been done in only four marshlands of Migina catchment. Itwould be interesting to see an extension of the study in other marshlands, not only those ofMigina, but also in all Rwandan marshlands. The implementation of the recommendations ofsuch studies could improve the standard of living and environmental conditions in the rural areathrough improved and sustainable water and land management.

5. AcknowledgementsThe study was conducted with the financial assistance from National University of Rwanda inassociation with UNESCO-IHE, the Netherland Institute for Water Education basedin Delft.

6. ReferencesAhmad, S. (1999). Achievements and issues of irrigation in the 20th century. In:Chandio, B.A.(Ed.), Proceedings of The National Workshop on: Water Resources Achievements andIssues in 20th century and challenges for the next millennium, Pakistan Councilof Researchin Water Resources, Islamabad, Pakistan, pp. 188201.

Ali, A., Chaudhary, M.R. (1996). Water conveyance and distribution at watercourse level. In:Khalid, R., Robina, W. (Eds.), Tertiary Sub-System Management. International IrrigationManagement institute, Lahore, Pakistan, pp. 1223.

Boyd Charlotte and Cathryn Turton, January (2000). The Contribution Of Soil AndWater

Conservation To Sustainable Livelihoods In Semi-Arid Areas Of Sub-Saharan Africa.Chanson Hubert (2004). The hydraulics of open channel flow: An introduction


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Colorado Water Resources Research Institute (1996).Irrigation Water Conservation:

Opportunities and Limitations in Colorado A report of the Agricultural Water ConservationTask Force.Daniil E.I., Michas S.N. and Lazaridis L.S. (2005). Hydrologic modeling for the

determination ofdesign discharges in ungauged basins.

Early, A.C., Eckert, J.B., Freeman, D.M., Kemper, W.D., Lowdermilk, M.K., Radosevich, G.E.,Skogerboe, G.V.(1976). Institutional Framework for Improved on-Farm WaterManagement in Pakistan. Colorado State University, Fort Collins, Colorado (SpecialTechnical Report, Water Management Research Project).

Evans O. Robert, Kerry A. Harrison, James E. Hook, Charles V. Privette, WilliamI. Irrigation

Conservation Practices, Appropriate for the Southeastern United States.


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FAO (1789). Water for agriculture.Segars, W. Bryan Smith, Daniel L. Thomas, Anthony W. Tyson,1998. Irrigation Conservation

Practices Appropriate for the Southeastern United States.

Hargreaves and Merkley, 2004.Irrigation Fundamentals.

Hussain, I., Perera, L.R. (2004). Improving Agricultural Productivity for Poverty Alleviationthrough Integrated Service Provision with Public-Private Sector Partnerships:

Examples and Issues. International Water Management Institute, Colombo, Sri Lanka (Workingpaper 66).

MINAGRI (2003). Groupement HYDROPLAN Ingnieur GmbH-S.H.E.R Ingnieur-conseils s.a,

Schma Directeur d'Amnagement des Marais, de Protection des Bassins Versants et delaConservation des Sols.

MINIPLAN (2002). Recensement Gnral de la Population et de lHabitat.Rientjes, 2006. Modeling in Hydrology.Savenije H.H.G and de Laat P.J.M (2002).Lecture notes of Hydrology.Skogerboe V. Gaylord and Merkley P.Gary (1996). Irrigation Maintenanceand Operation. Learning Process.

Smith D.H., Kathleen Klein, Richard Bartholomay, Isreal Broner,G.E. Cardon, W.M.Frasier,

Rod Kuharich, D.C. Lile, Mike Gross, Dan Parker, Hal Simpson, and Eric Wilkinson.Completion (1996). Irrigation Water Conservation: Opportunities And LimitationsInColorado-A Report Of The Agricultural Water Conservation Task Force.

Texas water Development Board (2004). Agricultural Water Conservation Practices.Thomas W. Ley (2003). Surface Irrigation Systems.


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Figures

Figure 1. Location of Migina in Rwanda and the Survey Area in Migina Catchment


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Average rainfall per months calculated in 25 years

Rainfall (mm)

250.0

200.0

150.0

100.0

50.0

0.0

Jan Feb March Apl May June July Aug Sept Oct Nov Dec

Months

Figure 2. Average rainfall of a reference year calculated basing on rainfall records in 25 years

Assesment of Operation of Rwasave Reservoir

9080

Volume (*10^3 m^3)

706050403020100

may jun july aug sept oct nov dec jan feb mar apr may

Months From May To May

Irrigation RequirementsAssessmet of Inflow&Storage in TheReservoirFigure 3. Monthly evolution in Water Storage of Rwasave Reservoir


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Tables

Table 1. Main characteristics of Migina catchment

Catchment

Migina Total Catchment 214,23 79,24 1,52 Long. = 2 30 8-12Trans. > 30Subcatchment a 3,14 6,73 1,06 Long. = 3 30 8-12Trans. > 20Subcatchment b 3,39 7,33 1,11 Long. = 2 30 8-12Trans. > 20Subcatchment c 37,50 27,10 1,24 Long. = 4 30 8-12Trans. > 30Subcatchment d 2,67 7,05 1,21 Long. = 1 30 8-12Trans. > 20Subcatchment e 4,56 9,06 1,19 Long. = 1 30 8-12Trans. > 20

Subcatchment f 44,20 29,73 1,25 Long. = 2 30 8-12Trans. > 30Subcatchment g 4,29 8,92 1,21 Long. = 3 30 8-12Trans. > 30Subcatchment h 3,76 7,89 1,14 Long. = 5 30 8-12Trans. > 30Subcatchment i 5,97 10,48 1,20 Long. = 3 30 8-12Trans. > 30Subcatchment j 37,51 31,74 1,45 Long. = 4 30 8-12Trans. > 30Subcatchment k 11,18 15,14 1,27 Long. = 1 30 8-12Trans. = 20Trans: Transversal slope

Long: Longitudinal slopeTable 2.: Rainfall intensity at Butare rain gauge station

Surface Perimeter Compacity Slopes(%) Flood Meanarea (km2) (km) coefficient Runoff runoffcoefficient coefficient(%) (%)

Duration(min)15By Season56.8By year66.0By 2 years75.215 years87.210 years96.430 45.4 53.4 61.2 71.6 79.445 34.9 41.3 47.7 56.3 62.560 29.2 34.8 40.4 47.8 53.475 23.6 28.2 32.7 38.8 43.4

90 20.2 24.3 28.3 33.5 37.6


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Table 3. Maximum discharges (m3/s) calculated by using ORSTOM method

Subcatchment tc H a A Vp Kr Vr TB M K QmaxMigina 10 0.0797 0.75 214230000 12805598 0.3 3841679 36000 106.7 2.5 266.825 0.0895 0.75 214230000 14380189 0.3 4314057 36000 119.8 2.5 299.6c 10 0.0797 0.82 37500000 2450775 0.3 735233 25200 29.2 2.5 72.9

25 0.0895 0.82 37500000 2752125 0.3 825638 25200 32.8 2.5 81.9f 10 0.0797 0.81 44200000 2853419 0.3 856026 25200 34.0 2.5 84.925 0.0895 0.81 44200000 3204279 0.3 961284 25200 38.1 2.5 95.4j 10 0.0797 0.82 37510000 2451429 0.3 735429 25200 29.2 2.5 73.025 0.0895 0.82 37510000 2752859 0.3 825858 25200 32.8 2.5 81.9k 10 0.0797 0.86 11180000 755300 0.3 226590 14400 15.7 2.5 39.325 0.0895 0.86 11180000 860525 0.3 258158 14400 17.9 2.5 44.8

Table 4. Maximum discharges (m3/s) calculated by using Rational method

Subcatchment Tr(years)

L(m) MeanAlt(m)H(m) S(m/m) Tc(min) S.Area(km2)i(m/hr) C Qdes(m3/s)a 10 1670 1750 50 0.03 23 3.14 87 0.3 22.9b 10 2130 1750 42 0.02 32 3.39 77 0.3 21.8d 10 2340 1675 40 0.02 37 2.67 72 0.3 15.9e 10 3150 1675 45 0.01 49 4.56 60 0.3 22.8g 10 3340 1675 100 0.03 39 4.29 69 0.3 24.8h 10 2430 1700 122 0.05 25 3.76 85 0.3 26.7

i 10 4170 1675 113 0.03 48 5.97 61 0.3 30.2

Table 5: Main emitters or drains designed with trapezoidal cross sections

Sb.C

Sb.C aSb.C bSb.C cSb.C d

S.bC eSb.C fSb.C gQMaxh H B m S P A R n K VDesQDes

(m1/3 (s/m1/3)

(m3/ (m) (m) (m) (n.u) (n.u) (m) (m2) (m) (m/s) (m3/s)s) /s)


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Sb. 26.7 1.00 1.30 2.90 0.33 0.05 4.94 4.33 0.88 0.03 30.03 6.15 26.7C hSb. 30.2 1.15 1.45 3.50 0.33 0.03 5.54 5.78 1.04 0.03 30.03 5.35 30.9C iSb. 73.0 1.50 1.80 4.75 0.33 0.04 6.79 9.63 1.42 0.03 30.03 7.59 73.1C j

Sb. 39.9 1.55 1.85 5.00 0.33 0.01 7.04 10.3 1.48 0.03 30.03 3.90 40.5C k 9

Sb.C i: Subcatchment i;Qmax: Maximum Discharge;

h: Normal water level in the canal;H: Total height of the canal (including the free board of the canal);B: Base of the canal;m: Cotan . = side inclination coefficient of the canal;P: Wetted Perimeter of the canal;

A: Wetted Cross Section Area of the canal;R: Hydraulic Radius;n: Roughness Coefficient of the canal;K: Manning Coefficient;VDes: Designed Velocity;QDes: Designed Discharge.Table 6. Crop water Coefficients (Kc)

Rice 150 Rice120 Maize 125

Kc

Kc ini 1,05 1,05

Kc mid 1,2 1,2Kc end 0,6 0,6

Phase duration (in days)

Init.(Lini) 30 20Dev.(Ldev) 30 20Mid(Lmid) 60 50Late(Llate) 30 30

Cumulative phase duration (in days)

Init.(Lini)

30 20

Dev.(Ldev)

60 40

Mid (Lmid)

120 90

Late (Llate)

150 120


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In: Initial Phase;Mid: Middle Phase;Dev: Development Phase:

0,71,20,35

20354030

205595125

Beans 110 Potatoes13 Sorghu Aubergine0 m 125

0,4 0,5 0,7 1,051,2 1,15 1,1 0,90,35 0,75 0,55 0,720 25 20 3030 30 35 4040 45 40 4020 30 30 2020 25 20 3050 55 55 7090 100 95 110110 130 125 130


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Table 7. Monthly crop water coefficients (Kc)

Month day Rice150Rice120

Maize125Beans110Potatoes130Sorghum125Aubergine1 30 1,05 1,06 0,73 0,45 0,51 0,72 1,052 60 1,13 1,19 1,06 1,03 0,93 0,99 0,993 90 1,20 1,20 1,20 1,20 1,15 1,10 0,91

4 120 1,20 0,89 0,89 0,50 1,06 0,90 0,885 150 0,89 0,07 0,00 0,27 0,10 0,25

Table 8: Composition of mixed-crops

Denomination Crops Proportion Cropping intensityMixed 1 BeansPeppers50 %30 %100 %Cabbages 10 %Groundnut 10 %

Mixed 2 Maize 50 % 100 %Soya 30 %Beans 10 %Cabbages 10 %Mixed 3 Corn Ears 10 % 50 %Irish potatoes 20 %Gren Beans 20 %Total 250 %

Table 9. Farming calendar for double rice crop production

Speculation Area Crop sep oct nov dec ja feb mar april may jun jully aug(ha) t nRice-rice 7.5 Rice1207.5 Rice1207.5 Rice1207.5 Rice120TOTAL 15.0


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Table 10: Farming calendar for mixed-cropping

Speculati

Area crop sept oct nov dec jan feb mar apr may jun july aug

on

(ha)

Mixed

360 Mixed1

crop

360 Mixed2

360 Mixed3TOTAL

360

Table 11. Assessment of operation of Rwasave reservoir

Volume 10 m may jun july aug sept oct nov dec jan feb mar apr mayStorable volume 60 0 0 0 16 67 78 64 58 63 57 94 60Losses by evaporation 3 3 4 4 4 3 3 3 3 3 3 2 3Irrigation water 0 1 15 42 0 0 0 0 0 0 0 0 0RequirementOutflow volume 3 4 19 46 4 3 3 3 3 3 3 2 3

Assessment In/S 85 81 62 16 29 85 85 85 85 85 85 85 85


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Irrigation Practices

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