Bringing in the floods : a comparative study on controlled flooding in the Dutch, Bangladesh and Vietnamese deltas
Staveren, Martijn F. van - \ 2017
Wageningen University. Promotor(en): J.P.M. Tatenhove, co-promotor(en): J.F. Warner; P. Wester. - Wageningen : Wageningen University - ISBN 9789463437035 - 174
water management - flooding - deltas - hydraulic engineering - rivers - environmental management - environmental policy - environmental control - netherlands - vietnam - bangladesh - waterbeheer - inundatie - delta's - waterbouwkunde - rivieren - milieubeheer - milieubeleid - milieubeheersing - nederland - vietnam - bangladesh
This thesis investigates contested initiatives to restore controlled flooding in the deltas of the Dutch, Bangladesh and Vietnamese (Mekong) deltas. Restoring controlled flooding is a seemingly contradictory measure in densely populated delta areas, where approaches based on full flood prevention has been typically dominant for decades. This has instigated the question how the emergence of restored controlled flooding initiatives can be explained. Related, this study reflects on how controlled flooding could contribute to long-term flood risk management and sustainable development in deltas, which are simultaneously attractive and vulnerable places for humans to live in. In order to answer this question, a case study approach has been used to investigate social, environmental and technological factors that have shaped controlled flooding initiatives. Cases have been identified that materialized under different conditions: from very dynamic delta environments to relatively stable ones, and from interventions driven by “top-down” policies to “bottom-up” action to modify or remove embankments. This thesis has an article-based structure, which means that individual chapters (2-5) have been designed for publication with peer reviewed academic journals. Chapter 1 provides the general background information, problem definition, and objectives. Chapter 6 ties together the findings of the individual case study chapters and presents the conclusions.
Chapter 2 conceptualizes deltas as interacting social-ecological-technological systems. It argues that a better understanding of how hydraulic infrastructure influences social processes and environmental dynamics in deltas is critical to understand how deltas evolve over time. By means of the delta trajectories concept, the chapter presents a way to understand this interaction. It also presents a way to understand the sustainability of a delta trajectory, and discusses how new flood management concepts might contribute to “realigning” the development trajectory towards more sustainable system states.
In Chapter 3, the first controlled flooding case is investigated. The Noordwaard is an agricultural polder, located at the junction of tides and riverine discharge in the Netherlands. As part of the Room for the River programme, the northern embankments were lowered which enables the inflow of water during high water levels in the river Merwede. This reduces peak water levels in the river, supports the adjacent freshwater Biesbosch wetland by means of restored water dynamics, but also affects the possibilities for agricultural production. The chapter highlights that a strong coupling can be observed between the domains of water safety and nature development objectives, and that a top-down decision concluded a long stakeholder negotiation processes. From the perspective of “subsiding polder lands,” controlled flooding is not regarded for its strategic importance, as excessive sedimentation would hamper the intended design discharge of the area.
Chapter 4 explores the Tidal River Management concept. In the coastal zone of Bangladesh, community-enforced embankment breaches have opened up some of the polders or low-lying areas called “beels,” and exposed them to tidal influence again. Besides stimulating agricultural production and providing safer places to live in, the extensive network of polder embankments also caused increased sedimentation in the region’s rivers, and water logging in enclosed areas due to insufficient drainage possibilities. The chapter highlights that policy debates in Bangladesh have revolved around adopting “open” or “closed” approaches, where TRM represents a hybrid form. The case showed that TRM involves water management and sediment management, and that it represented a “social opening up” for local communities and NGOs to get involved with water projects and embankment removal.
Plans to restore seasonal flooding in the Mekong delta are center stage in Chapter 5. The Mekong delta system is very dynamic and dealing with the delta’s water resources, in connection with intensive rice production, have been heavily debated by Vietnamese and international policy makers. This chapter investigates a number of older and more recent long-term development plans for the Mekong delta. This analysis highlights how ideas about controlled flooding and flood control have gradually evolved over time. The most recent delta management plan suggests to restore seasonal flooding in some parts of the delta, as a way to safeguard downstream urban areas from peak flows, and as a way to improve the conditions for agricultural production.
Chapter 6 summarizes the findings of the case study chapters one by one, and concisely answers the research questions. It highlights key similarities and differences when it comes to social, environmental and technological dimensions, and discusses these findings with the literature on flood risk management policy, complex adaptive systems research, and delta studies. The findings demonstrate that environmental dynamics have been critical to emphasize the potential of restoring controlled flooding, but that social and technological factors have been important enablers or constrainers for controlled flooding initiatives to take shape. In itself, controlled flooding reconciles ecosystem-based ideas about flood management with more mainstream policies based on flood control. For this reason controlled flooding can be seen as a “niche-development” with limited influence on how flood management policies, and environmental delta systems, evolve. At the same time, controlled flooding has been acknowledged for its strategic opportunities, for example when it comes to diverting peak water discharges, land heightening by means of capturing suspended sediment, and by providing nutrient for agricultural. This offers opportunities for further thinking about and conceptual development of controlled flooding.
Bringing in the tides. From closing down to opening up delta polders via Tidal River Management in the southwest delta of Bangladesh
Staveren, M.F. van; Warner, J.F. ; Shah Alam Khan, M. - \ 2017
Water Policy 19 (2017)1. - ISSN 1366-7017 - p. 147 - 164.
Bangladesh - controlled flooding - delta management - hydraulic engineering - policy pendulum swing - Tidal River Management - water policy
The southwest coastal delta of Bangladesh is not only geographically home to a dynamic interplay between land and water, and between fresh surface water and saline tides, but also to contentious debates on flood management policy and hydraulic engineering works. It has been argued that dealing with delta floods in this region boils down to adopting either open or closed approaches. This paper longitudinally structures the open-or-closed debate based on a number of emblematic water management projects in the region. Departing from a typical open wetland history, river and polder embankments increasingly started to constrain flood dynamics. Upheaval among rural populations in response to the negative impacts of hydraulic engineering plans and works coalesced in efforts to restore open approaches, synthesized in the Tidal River Management concept. Its resemblance to historic overflow irrigation is often used politically as a yardstick to challenge the dominant hydraulic engineering paradigm. This paper argues that dealing with floods in Bangladesh requires plans, policies and projects formulated against the historic background of complex interactions among social processes, environmental dynamics and technological interventions: a lesson to be incorporated in on-going policy-making processes and long-term delta management plans.
Volksdijk; de adaptieve dijk, studielocatie Grebbedijk
Blokland, J. ; Ziegler, P. ; Aben, R. ; Vries, R. de; Broekhuizen, R.E. van; Agricola, H. ; Kuiper, E. - \ 2016
In: De adaptieve dijk; strategieën voor dijktransitie in de komende 100 jaar BNA Onderzoek Amsterdam - p. 32 - 41.
dijken - veiligheid - hoogwaterbeheersing - waterbouwkunde - innovaties - ruimtelijke ordening - gebiedsontwikkeling - dykes - safety - flood control - hydraulic engineering - innovations - physical planning - area development
Hoe kan de dijk weer volwaardig onderdeel worden van de maatschappij, zonder daarbij de veiligheid aan te tasten? Kunnen we onze democratie –die een oorsprong heeft in de waterschappen- herijken en waarde geven? Hoe maken van de dijk als technisch kunstwerk ook een democratisch kunstwerk dat past bij 21ste eeuw? Hoe transformeren we de verkrampte en functioneel eenzijdige dijk in een adaptieve en veelzijdige dijk?
Hydraulic engineering in the social-ecological delta: understanding the interplay between social, ecological, and technological systems in the Dutch delta by means of “delta trajectories”
Staveren, M.F. van; Tatenhove, J.P.M. van - \ 2016
Ecology and Society 21 (2016)1. - ISSN 1708-3087 - 11 p.
adaptive delta management - delta trajectory - flood management - hydraulic engineering - path dependency - social-ecological systems - technological lock-in
Several of the world's largest deltas have recently been conceptualized as social-ecological delta systems. Although such conceptualizations are valuable in emphasizing complex interaction between social actors and ecological processes in deltas, they do not go into specific dynamics that surround technological developments in the hydraulic domain. By drawing from concepts originating
in socio-technical systems research, we stress the importance of technology, particularly the domain of hydraulic engineering, in shaping a delta’s future. Based on two geographically distinct cases of flood management infrastructure in the Dutch delta, we demonstrate the influence of existing hydraulic works, in mutual interaction with social responses and environmental processes, on the development of the congregated delta system over time. The delta trajectory concept is introduced as a way to understand the interplay between social, ecological, and technological systems in deltas. We discuss options to realign unsustainable pathways with more desirable ones. Adaptive delta management presents a policy environment where these messages may be picked up.
Investigation of Desso GrassMaster® as application in hydraulic engineering
Steeg, P. van der; Paulissen, M.P.C.P. ; Roex, E. ; Mommer, L. - \ 2015
Deltares - 42
Grass dike - Dessa GrassMaster - grass reinforcement - dykes - grasses - cladding - hydraulic engineering - reinforcement - revetments - flood control - sports grounds - dijken - grassen - bekleding, bouw - waterbouwkunde - versterking - steunmuren - hoogwaterbeheersing - sportterreinen
Dessa GrassMaster® is a reinforced grass system which is applied successfully on sports fields and enables to use a sports field more intensively than a normal grass field. In this report the possibility of an application of Dessa GrassMaster®in hydraulic conditions, with a focus on grass dikes, is discussed.
A description of several aspects of grass dikes is given as well as other known reinforcement grass systems. A comparison between grass on sports fields and grass of grass dikes is made. Based on state-of-the art literature, requirements for Dessa GrassMaster® as a revetment under hydraulic loading are provided. Potential applications are identified and knowledge gaps are given. From the point of view of hydraulic engineering and based on theoretical and existing
knowledge, it is concluded that Dessa GrassMaster® may potentially be used as a dike revetment but more insight in the strength of this system is required/before it will be applied as a revetment. It is currently not clear what effect Dessa-Grasslvlaster'" will have on root volume and distribution in dike grasslands and how this influences overall strength of the grass cover. The strength of Dessa GrassMaster®can be determined by performing physical hydraulic experiments.
Several knowledge gaps concerning ecological, toxicological and environmental issues have been identified that may hamper the implementation of Dessa Grasslvlaster". It is recommended to perform tests to quantify these potential impacts on the environment in order to find solutions to mitigate potential negative effects. This will lead to increased societal acceptability of application of the product on dikes. For comprehensive conclusions, langerterm full-scale tests (2-4 years) are recommended.
Laboratory spectroscopy experiment : Spectral reflectance of beach sand as function of surface moisture content with sample of beach sand collected from the Sand Motor, the Netherlands
Nolet, C. ; Roosjen, P.P.J. - \ 2015
Spectral reflectance of beach sand (350-2500 nm) under different moisture conditions at 1 nm interval, obtained by a laboratory spectroscopy experiment. Optical remote sensing has the potential to measure surface moisture at a high spatio-temporal resolution. It is based on the principle that wet sand appears darker than dry sand: it is less reflective. The goals of this study are (1) to measure and model reflectance under controlled laboratory conditions as function of wavelength ( ) and surface moisture ( ) over the optical domain of 350–2500 nm, and (2) to explore the implications of our laboratory findings for accurately mapping the distribution of surface moisture under natural conditions. A laboratory spectroscopy experiment was conducted to measure spectral reflectance (1 nm interval) under different surface moisture conditions using beach sand. A non-linear increase of reflectance upon drying was observed over the full range of wavelengths. Two models were developed and tested. The first model is grounded in optics and describes the proportional contribution of scattering and absorption of light by pore water in an unsaturated sand matrix. The second model is grounded in soil physics and links the hydraulic behaviour of pore water in an unsaturated sand matrix to its optical properties.
De Zandmotor - Gepassioneerde Wetenschap
Baptist, M.J. - \ 2014
kustbeheer - zandsuppletie - natuurontwikkeling - openluchtrecreatie - duinen - kustgebieden - waterbouwkunde - zuid-holland - coastal management - sand suppletion - nature development - outdoor recreation - dunes - coastal areas - hydraulic engineering
De Zandmotor is een groot pilotproject voor natuurlijke kustbescherming, waarmee tegelijk ruimte voor natuur en recreatie ontststaat. Onderzoekers van verschillende universiteiten volgen de ontwikkelingen op de voet. De Zandmotor ontwikkelt zich zoals verwacht; de kust wordt versterkt,voor kitesurfers is de Zandmotor één van de beste plekken in Nederland en de natuur ontwikkelt zich op verschillende fronten. In deze korte documentaire zie je hoe dat werkt. Selecteer HD bij instellingen voor optimale weergave)
Gebruik vispassage gemaal Maelstede door schieraal: DIDSON meting
Keeken, O.A. van; Griffioen, A.B. - \ 2013
IJmuiden : IMARES (Rapport / IMARES Wageningen UR C025/13) - 27
european eels - palingen - vismigratie - waterbouwkunde - proefprojecten - evaluatie - nadelige gevolgen - zeeuwse eilanden - dierenwelzijn - eels - fish migration - hydraulic engineering - pilot projects - evaluation - adverse effects - animal welfare
Door Waterschap Scheldestromen is bij gemaal Maelstede nabij ’s Gravenpolder in de provincie Zeeland een nieuwe vispassage aangelegd ter bevordering van de vismigratie voor zowel de intrek als uittrek van migrerende vissen. De vispassage bestaat uit een buizensysteem, waarbij vissen vanuit de polder tegen een waterstroom in via een buis een opvangbak inzwemmen. Elke twee uur sluit een afsluiter aan de polderzijde en wordt het water in de opvangbak naar de Westerschelde gepompt, zodat vissen met de stroom mee kunnen zwemmen naar de Westerschelde. Op basis van de resultaten concluderen wij dat geen aanwijzingen zijn gevonden dat de vispassage werkt zoals bedoeld is.
Natuurlijk IJsselmeer: ecodynamisch visie IJsselmeer 2100
Groot, A.M.E. ; Lenselink, G. ; Slobbe, E.J.J. van; Meurs, G.A. ; Noordhuis, R. ; Wiersma, A. ; Bos, M. ; Pasmans, I. ; Dankers, P. ; Wilms, T. - \ 2012
Wageningen : Ecoshape - 56
landschapsecologie - natuurtechniek - biodiversiteit - waterbouwkunde - dijken - openbare veiligheid - infrastructuur - recreatie - zoet water - ijsselmeer - noordoostpolder - landscape ecology - ecological engineering - biodiversity - hydraulic engineering - dykes - public safety - infrastructure - recreation - fresh water - lake ijssel
Deze ecodynamische visie laat een palet van potentiële ontwikkelingen voor het IJsselmeer zien: ecodynamische ontwikkelingen, die bijdragen aan meerdere functies en ambities waaronder natuur, waterveiligheid, visserij, recreatie en infrastructuur, en waarbij optimaal gebruik wordt gemaakt van de in het gebied aanwezige natuurlijke factoren als wind, water, sediment en vegetatie. Deze visie laat zien dat er kansen liggen voor nieuwe vormen van waterbouw, die de veiligheid van de Houtribdijk en de Afsluitdijk vergroten. Ook worden de kansen in kaart gebracht om met moerassen zowel de waterveiligheid als de biodiversiteit langs dijken bij de Noordoostpolder te verbeteren.
Pilotstudie innovatieve dijken Lauwersoog : ervaringen meerwaardebepaling innovatieve waterkeringen voor de pilotlocatie Lauwersoog
Loon-Steensma, J.M. van; Schelfhout, H.A. ; Eernink, N.M.L. ; Paulissen, M.P.C.P. ; Tangelder, M. - \ 2012
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2384) - 56
dijken - hoogwaterbeheersing - veiligheid - regionale planning - landgebruik - waterbouwkunde - gebiedsgericht beleid - innovaties - lauwersmeergebied - groningen - waddenzee - dykes - flood control - safety - regional planning - land use - hydraulic engineering - integrated spatial planning policy - innovations - lauwersmeergebied - groningen - wadden sea
Bij Lauwersoog komen een aantal functies bij elkaar: haven, visserij, toerisme, natuur, maar ook waterveiligheid. De waterkering vormt een belangrijk element in het gebied. In dit rapport worden de ervaringen met het bepalen van de meerwaarde van innovatieve waterkeringen voor de pilotlocatie Lauwersoog beschreven. Het Deltaprogramma Waddengebied wil de ervaringen in de pilotstudie gebruiken in brede gebiedsbijeenkomsten, waarin samen met lokale stakeholders wordt gezocht naar geschikte waterveiligheidsstrategieën in het Waddengebied die zich naast waterveiligheid ook richten op doelstellingen voor natuur en voor de ruimtelijke kwaliteit. Uit de pilotstudie Lauwersoog kwam naar voren dat het belangrijk is dat afwegingscriteria locatiespecifiek zijn en afgestemd zijn op de kenmerken en randvoorwaarden en de opgaven, plannen en wensen voor het gebied. Op basis van de ervaringen is de werkwijze voor het bepalen van meerwaarde geschematiseerd. Het is belangrijk dat zowel stakeholders als experts worden betrokken in het proces.
Ecodynamische visie IJsselmeer 2100
Groot, Annemarie - \ 2012
ecological engineering - morphology - ecology - hydraulic engineering - coastal management - lake ijssel - sand suppletion - friesland
Voordelig bouwen met de natuur
Baptist, M.J. - \ 2012
Kennis Online 9 (2012)juni. - p. 8 - 9.
waterbouwkunde - kustbeheer - natuurontwikkeling - hydraulic engineering - coastal management - nature development
Bouwen mét de natuur, het zou iedereen winst op kunnen leveren. Met de zandmotor voor de kust en met kunstmatige oesterriffen die zandplaten in de Oosterschelde beschermen, en wellicht met nieuwe kwelders in het Waddengebied. Profijtelijk voor de natuur, de staatskas en het bedrijfsleven dat het natuurlijke waterwerk kan exporteren. IMARES Wageningen UR telt vissen, vogels en andere dieren om te kijken of de grote beloften echt uitkomen.
The importance of the surf zone for fish and brown shrimp in The Netherlands
Teal, L.R. ; Keeken, O.A. van - \ 2011
IJmuiden : IMARES (Report / IMARES Wageningen UR C054/11) - 80
waterbouwkunde - vissen - nadelige gevolgen - kustgebieden - hydraulic engineering - fishes - adverse effects - coastal areas
Human activity in the North Sea is increasing, invloving more motorised cargo shipping, and rapidly expanding construction and operation of oil platforms and wind farms. In recent years underwater sand levees or sand suppletion near shore has been performed for coastal protection. The aim of this literature review was to provide the necessary information required for the design of a survey, investigating the role of the shallow coastal area and the potential newly created areas.
Morfologische, ecologische en governance principes voor ecodynamisch ontwerpen: toegespitst op de 'Bouwen met Natuur' pilots Friese IJsselmeerkust : building with nature, case Markermeer IJsselmeer, MIJ 4.2, Deliverable 1.6
Groot, A.M.E. ; Lenselink, G. ; Vlieger, B. de; Janssen, S. - \ 2011
S.l. : Ecoshape - 165
natuurtechniek - morfologie - ecologie - waterbouwkunde - natuur - bescherming - sediment - kusten - ijsselmeer - ecological engineering - morphology - ecology - hydraulic engineering - nature - protection - sediment - coasts - lake ijssel
Het concept ‘Bouwen met Natuur’ richt zich op gebiedsgerichte ontwerpprocessen langs kusten met het doel om de interactie tussen menselijke ingrepen en ecosysteem processen te vergroten. Het concept maakt maximaal gebruik van dynamiek van natuurlijke processen en van de inzet van bio@engineers bij de ontwikkeling van nieuwe kustlandschappen. De uitdaging bij ‘Bouwen met Natuur’ projecten is om een menselijke ambitie m.b.t. waterbouw te realiseren op een wijze die maximaal gebruik maakt van het ecosysteem en tevens dit ecosysteem versterkt. Het zoeken naar een win@win situatie voor zowel de menselijke waterbouwambitie als voor de natuurwaarden is dus iets anders dan natuur behouden die er is of nieuwe natuur ontwikkelen. Ook is het concept fundamenteel anders dan het compenseren van natuur die elders verloren gaat.
Role of sediment in the design and management of irrigation canals : Sunsari Morang Irrigation Scheme, Nepal
Paudel, K. - \ 2010
Wageningen University. Promotor(en): E. Schultz, co-promotor(en): N.M. Shakya. - [S.l. : S.n. - ISBN 9789085858515 - 271
irrigatie - irrigatiesystemen - irrigatiekanalen - waterbouwkunde - ontwerp - bedrijfsvoering - sediment - waterstroming - nepal - irrigation - irrigation systems - irrigation channels - hydraulic engineering - design - management - sediment - water flow - nepal
Sediment transport in irrigation canals
The sediment transport aspect is a major factor in irrigation development as it determines to a large extent the sustainability of an irrigation scheme, particularly in case of unlined canals in alluvial soils. Investigations in this respect started since Kennedy published his channel-forming discharge theory in 1895. Subsequently different theories have been developed and are used around the world. All of them assume uniform and steady flow conditions and try to find the canal dimensions that are stable for a given discharge and sediment load. In the past irrigation schemes were designed for protective purposes with very little flow control, hence steady and uniform flow conditions could be realised to some extent.
Modern irrigation schemes are increasingly demand based, which means that the water flow in a canal is determined by the crop water requirements. Accordingly the flow in the canal network is not constant as the crop water requirement changes with the climate and the growing stages of the crops. Also the inflow of the sediment is not constant throughout the irrigation season in most schemes. The situation is even worse for run-of-the-river schemes where fluctuations in the river discharge have a direct effect on the inflow of water and sediment.
The conventional design methods are not able to predict accurately the sediment transport behaviour in a canal, firstly due to the unsteady and non-uniform water flow conditions and secondly due to the changing nature of the sediment inflow. Hence, the actual behaviour of a canal widely diverges from the design assumptions and in many cases immense maintenance costs have to be met with to tackle the sediment problems.
An irrigation scheme should not only be able to deliver water in the required amount, time and level to the crops on the field, but also should recover at least its operation and maintenance cost. Cost recovery is, to some extent, related to the level of service provided by the irrigation organization and the expenditure for operation and maintenance of the scheme. Past experiences in Nepal have shown that modernization of existing irrigation schemes to improve the level of service has also increased the operation and maintenance costs. These costs are, in some cases, high compared to the generally low level of ability of the water users and farmers to pay these costs. The search of making schemes more equitable, reliable and flexible has resulted in the introduction of new flow control systems and water delivery schedules that may, if not carefully designed, adversely affect the sediment transport behaviour of a canal. In quite some schemes unpredicted deposition and/or erosion in canals have not only increased the operation and maintenance costs but also reduced the reliability of the services delivered.
Irrigation development in Nepal and the study area
Nepal is a landlocked country in South Asia lying between China and India. It is situated between 26º22' N to 30º27' N latitude and 80º4' E to 88º12' E longitude of the prime meridian. Roughly rectangular in shape, the country has an area of 147,181 km2. It is 885 km in length but its width is uneven and increases towards the West. The mean North-South width is 193 km. Nepal is a predominantly mountainous country, with elevations ranging from 64 m+MSL (Mean Sea Level) at Kechana, Jhapa to 8,848 m+MSL at the peak of the world highest mountain, Everest, within a span of 200 km. Nepal has a cultivated area of 2.64 million ha, of which two third (1.77 million ha) is potentially irrigable. At present 42% of the cultivated area has some sort of irrigation, out of which only 41% is receiving year round irrigation water. The existing irrigation schemes contribute approximately 65% of the country’s current agriculture production.
Nepal has a long history of irrigated agriculture. Most of the existing large-scale irrigation schemes are located in the southern alluvial plain (Terai). The canals are unlined and the sediment load forms an integral part of the supplied irrigation water. The schemes are predominantly supply based and have a very low duty for intensive cropping. In view of the increased competition among the different water using sectors and low performance of these schemes, many of them are undergoing modernization. For example, the Sunsari Morang Irrigation Scheme (SMIS) is one of the schemes under modernization, and it has been taken as a study case for this research. A better understanding of the sediment transport process under changing flow and sediment load conditions, a shifting management environment and different maintenance scenarios will be very useful in pulling out the schemes from the present vicious cycle of construction-deterioration-rehabilitation.
The Sunsari Morang Irrigation Scheme (SMIS) is located in the eastern Terai. The Koshi River is the source of water. A side intake for the water diversion, an around 50 km long main canal of capacity 45.3 m3/s for water conveyance and 10 secondary canals and other minor canals of various capacities for water distribution were constructed to irrigate a command area of 68,000 ha. The system was put into the operation in 1975, but faced a serious problem of water diversion and sediment deposition in the canal network. Hence from 1978, after 3 years of operation, rehabilitation and modernization work of the scheme has been started. During modernization the intake has been relocated to increase the water diversion and reduce the sediment entry. Besides, a settling basin with dredgers for continuous removal of sediment has been provided near the head of the main canal. Apart from that the command area development and modernization of existing canal network is in progress and till third phase (1997-2002), around 41,000 ha area has been developed.
Sediment transport research
The aim of this research is to understand the relevant aspects of sediment transport in irrigation canals and to formulate a design and management approach for irrigation schemes in Nepal in view of sediment transport. In the process, the design methods used in the design of irrigation schemes in Nepal and their effectiveness on sediment transport have been studied. The impact of operation and maintenance on sediment movement has been analysed taking the case study of SMIS. An improved design approach for sediment transport in irrigation canals has been proposed. A mathematical model SETRIC has been used to study the interrelationship of sediment movement with the design and management and to evaluate the proposed design approach for irrigation canal based on the data of the SMIS.
The mathematical formulation of sediment transport process in an irrigation canal is based on the previous works in this field, most notably the work of Mendez on the formulation of the mathematical model SETRIC. Subsequent analysis, improvement and verification works by Paudel, Ghimire, Orellana V., Via Giglio and Sherpa have been used. The model SETRIC has been verified and improved where found necessary and has been used to analyse the irrigation scheme and to propose an improvement in the design and management from sediment transport point of view.
Assessment of design parameters
The methods of selecting the design discharge and sizing of canals for modern irrigation schemes based upon the present concept of crop based irrigation demand, water delivery schedules and water allocation to the tertiary units have been analysed. The selection of a crop depends upon the soil type, water availability, socio-economic setting and climatic conditions. The type of crop together with the soil type determines the irrigation method and irrigation schedules, while the type of crop and climatic condition determines the irrigation water requirement. The required flow in a canal is then derived based on the water delivery schedule from that canal to the lower order canals or to the field to meet the water requirement.
The factors that influence the roughness of an irrigation canal have been analysed and a proposal for a more rational roughness determination process has been formulated based on the available knowledge. The roughness in the sides depends upon the shape and size of material, vegetation and surface irregularities, while the roughness in the bed is a function of shape and size of material and the surface irregularities (bed form in case of alluvial canals). For the prediction of roughness in the bed mostly two approaches are in use – methods based on hydraulic parameters (water depth, flow velocity and bed material size) and the methods based on bed forms and the grain related parameters. In this research, the method based on the bed form and grain related parameters, as suggested by van Rijn, has been used. Similarly, for the determination of roughness in the sides, the influence of surface irregularities have been included by dividing the maintenance condition as ideal, good, fair and poor and accordingly applying the correction to the standard roughness value for the type of material. The influence of vegetation has been accounted based on the concept of V.T. Chow. The various methods of computing the equivalent roughness have been compared and the method proposed by Mendez has been found to be better when tested with the Kruger data.
Most of the sediment transport predictors consider the canal with an infinite width without taking into account the effects of the side walls on the water flow and the sediment transport. The effect of the side wall on the velocity distribution in lateral direction is neglected and therefore the velocity distribution and the sediment transport are considered to be constant in any point of the cross section. Under that assumption a uniformly distributed shear stress on the bottom and an identical velocity distribution and sediment transport is considered. Majority of the irrigation canals are non-wide and trapezoidal in shape with the exception of small and lined canals that may be rectangular. In a trapezoidal section the water depth changes from point to point in the section and hence the shear stress. The effect would be more pronounced if the bed width to water depth ratio (B-h ratio) is small. The change in velocity distribution in a canal in view of the change in boundary shear and water depth along the cross section has been analysed and evaluated with the field measurements. The change in velocity and shear stress in a canal section has been used to evaluate the influence of B-h ratio and side slope in the prediction of sediment transport capacity by selected predictors (Brownlie, Engelund-Hansen and Ackers-White). The evaluation with the available data set showed that the proposed correction improved the predictability for non-wide irrigation canals.
Canal design approaches for sediment transport in Nepal
For the design of canals having erodible boundary and carrying sediment loads two approaches are in practice, namely the regime method and the rational method. The regime design methods are sets of empirical equations based on observations of canals and rivers that have achieved dynamic stability. The rational methods are more analytical in which three equations, an alluvial resistance relation, a sediment transport equation and a width-depth relationship, are used to determine the slope, depth and width of an alluvial canal when the water and sediment discharges as well as the bed material size are specified.
In Nepal, the design manuals of the Department of Irrigation recommend Lacey’s regime equations and White-Bettess-Paris tables with the tractive force equations for the design of earthen canals carrying sediment. But in practice, there is no consistency in the design approaches that has been found to vary from canal to canal even within the same irrigation scheme. The use of Lacey’s equation for computing the B-h ratio has generally resulted in wider canals. This is so, because flatter side slopes than predicted by the Lacey’s equations are used from soil stability considerations.
The White-Bettess-Paris tables are derived from alluvial friction equations of White, Bettess and Paris (1980) and sediment transport equations of Ackers and White (1973). No records regarding the use of this method for the design of canals was found and hence its performance in terms of sediment transport could not be verified. However, the Ackers and White sediment transport equations over-predicted the sediment transport capacity of a canal when tested with the SMIS data. The sediment load entering into the canals of SMIS is mostly fine (d50 < 0.2 mm) and most of the large scale irrigation schemes in Nepal have similar geo-morphological settings. That means that the White-Bettess-Paris tables will result in a canal with a flatter slope than actually required to carry the type of sediment prevailing in SMIS and other similar irrigation schemes of Nepal. Analysis showed that the Brownlie and Engelund and Hansen equations are more suitable for the type of sediment that has been found in SMIS.
During the modernization, the secondary canals (S9 and S14) of SMIS have been designed by two different approaches. Secondary Canal S9 has been designed using Lacey’s regime concept while Secondary Canal S14 has been designed using an energy approach. In the energy approach the erosion is controlled by limiting the tractive force and the deposition is controlled by ensuring equal or non-decreasing energy of the flow in the downstream direction. Both the canals have been evaluated for their sediment transport capacity for the prevailing sediment characteristics. The carrying capacities of both canals (~ 230 ppm) have been found to be less than the expected sediment load (~ 300 – 500 ppm) in the canal. The energy concept assumes that the sediment transport is proportional to the product of velocity and bed slope. The carrying capacity of the canal designed by this principle has been found to be variable along its length. It means that the sediment transport capacity is not only a function of bed slope and water depth as assumed in the energy concept.
An improved approach for the design and management of irrigation canals
In general the reliability of sediment transport predictors is low and at best they can provide only estimates. As per Vito A Vanoni (1975) a probable error in the range of 50-100% can be expected even under the most favourable circumstances. There is no universally accepted formula for the prediction of sediment transport. Most of them are based upon laboratory data of limited sediment and water flow ranges. Hence they should be adjusted to make them compatible to specific purposes, otherwise the predicted results will be unrealistic. An improved rational approach has been proposed for the design of alluvial canals carrying sediment loads. To find the bed width, bed slope and water depth of a canal for a given discharge and sediment characteristics three equations, namely a sediment transport predictor (total load), resistance equation (Chézy) and a B-h ratio predictor are used.
A canal design program DOCSET (Design Of Canal for SEdiment Transport) has been prepared for the improved approach including the above mentioned improvements. The program can also be used to evaluate the existing design for a given water flow and sediment characteristics. Basic features of the new approach are:
concept of dominant concentration. Instead of using the maximum concentration, the approach suggests to look for a concentration that results in net minimum erosion/deposition in one crop calendar year;
determination of roughness. The proposed method makes use of the elaborated and more realistically determined roughness value in the design process. The roughness of the cross section is adjusted as per the hydraulic condition and sediment characteristics. Moreover the influences of the side slopes and the B-h ratio are included while computing the equivalent roughness of the section. This should result in a more accurate prediction of hydraulic and sediment transport characteristics of the canal and hence, a better design;
explicit use of sediment parameters. The sediment concentration and representative size (dm) is explicitly used in the design. That will make the design process more flexible as different canals might have to divert and convey sediment loads of different sizes (dm) and amounts;
Use of an adjustment parameter. An adjustment parameter has been used that includes the influence of non-wide canals, sloping side walls and exponent of velocity in the sediment transport predictor. This adjustment should increase the accuracy of the predictors when they are used in irrigation canals, an environment for which they were not derived;
holistic design concept. This approach uses one canal system as a single unit. The canal system may have different canals of different levels, but the water and sediment management plans are prepared for the whole system. Then the hydraulic design of the individual canal can be made to meet the design management plan for that canal;
Selection of B-h ratio. A B-h ratio selection criterion has been proposed considering the side slope selection practices in Nepal as well as the sediment transport aspects.
Since, the sediment transport process is influenced by the management of the irrigation scheme, the design should focus to have a canal that is flexible enough to meet the demand and still have a minimum deposition/erosion. The provision of sufficient carrying capacity up to the desired location (conveyance), providing controlled deposition options if the water delivery plans limit the transport capacity (provisions of settling pockets) and preparation of maintenance plans (desilting works) are some of the aspects that would have to be analysed and included in the design to reduce the sediment transport problems.
The canal design methods can give the best possible canal geometry for a given water flow and sediment concentration only. For water flows and sediment concentrations other than the design values, there may be either erosion or deposition. The aim of the design would have to be to balance the total erosion and deposition in one crop calendar year. So, a design may not be based on the maximum sediment concentration expected during the irrigation season, but on a value that results in the minimum net erosion/deposition. The best way to evaluate a canal under such scenario is to use a suitable sediment transport model. Besides, the roughness of the canal depends upon the hydraulic conditions, sediment characteristics and the maintenance plans that are constantly changing throughout the irrigation season. The canals are designed assuming a uniform flow and sediment transport under equilibrium condition. However, such conditions are seldom found in irrigation canals due to the control in flow to meet the variation in water demand. Hence, the design of a canal would have to be evaluated using a sediment transport model for the selection of proper design parameters and to evaluate the design for the proposed water operation plans.
The mathematical model SETRIC
The mathematical model SETRIC is a one-dimensional model, where the water flow in the canal has been schematised as a quasi-steady and gradually varied flow. This one dimensional flow equation is solved by the predictor-corrector method. Gallappatti’s depth integrated model for sediment transport has been used to predict the actual sediment concentration at any point under non-equilibrium conditions. Galappatti’s model is based on the 2-D convection-diffusion equation. The mass balance equation for the total sediment transport is solved using the modified Lax’s method, assuming a steady condition of the sediment concentration. For the prediction of the equilibrium concentration one of the three total load predictors: Brownlie, Engelund and Hansen or Ackers and White methods can be used.
The model SETRIC was evaluated using other hydrodynamic and sediment transport models (DUFLOW and SOBEK-RIVER) and was validated by the field data of SMIS. Predictability of different predictors has been compared. The Brownlie and Engulund and Hansen methods predicted reasonably for the sediment size of 0.1 mm (d50), while predictability of Ackers and White for the sediment size was found to be poor. The sensitivity of Brownlie’s method was more uniform than the other two methods for a sediment size range of 0.05 to 0.5 mm.
Field data collection
For the field measurements of the sediment transport process, one of the secondary canals of SMIS (S9) was selected. Since, the objective of field data was to test the design approach for sediment transport; preference was given for a canal that was recently designed and constructed. The field measurement of water and sediment flow was carried out in 2004 and 2005. During field measurements the water inflow rate into Secondary Canal S9 system was measured. A broad crested weir immediately downstream of the intake for Secondary Canal S9 was calibrated and used for discharge measurement. For sediment concentration measurements, dip samples just downstream of the hydraulic jump were taken on a daily basis. The samples were then analysed in the laboratory and the sediment concentration was determined. Point sampling across the section using pump samplers were also taken and the calculation results showed that the dip samples underestimated pump samples by around 8% in case of the total load and by around 35% for the sediment of size > 63 μm. At the end of the irrigation season, the deposited sediment samples along the canal were taken to determine the representative sediment size and other properties.
The irrigating water delivered to the sub-secondary canals, delivery schedules and the set-points upstream of water level regulators were also measured. For morphological change, the pre-season and post-season canal geometry was measured. The velocity distribution in the trapezoidal earthen canal section was measured. Besides, field measurement roughness (indirect measurement) was also made in the beginning, mid and end of the seasons to determine the change in roughness in time.
The model SETRIC was used to study the effect on the sediment transport process due to system management activities namely, change in water demand and supply, water delivery modes based on the available water and the change in sediment load due to the variation in sediment inflow from the river or problems in proper operation of the settling basin. For the design water inflow into Secondary Canal S9, a water delivery schedule has been designed and has been evaluated for sediment transport efficiency under changing sediment inflow conditions. The improved canal design approach was evaluated comparing the results with the existing design of Secondary Canal S9. Some of the findings of the modelling results are:
water delivery schedules can be designed and implemented to reduce the erosion/deposition problems of a certain reach even after the system is constructed and put into operation;
the design operation plans and assumptions have not been followed in Secondary Canal S9 of SMIS. From sediment transport perspective, the existing water management practice results more sedimentation in the sub-secondary and tertiary canals than Secondary Canal S9;
the periodic change in the demand and the corresponding change in sediment transport capacity of the canal can be manipulated to arrive at the seasonal balance in the sediment deposition. In one period, there may be deposition but that can be eroded in the next period;
the proposed water delivery plan is based on the existing canal and its control structures and covers discharge fluctuation from around 46% to 114%. Hence, it can be implemented with the present infrastructure and can handle all possible flow situations in the canal;
the proposed delivery schedule ensures either full supply or no supply to the sub-secondary canals which have been designed for the same principle. This could reduce the existing deposition problem faced by these canals;
proper operation of the settling basin is crucial for the sustainability of the SMIS;
the secondary canals need to be operated in rotation when there is less demand or less available water in the main canal. This will ensure design flow in the secondary canals and reduce the sedimentation problem. The main canal would have to be analysed for the best mode of rotation from sediment transport and water delivery perspective.
Major contributions of this research
Apart from the recommendations made in the design, management and operation of Secondary Canal S9 from sediment transport perspective, the following contributions are made by this research:
an elaborate analysis of the velocity and shear stress distribution across the trapezoidal canal is made to derive the correction factor for the sediment transport predictor. This will help to increase the predictability when the predictors are used for the analysis of sediment transport in irrigation canals;
an explicit method of including roughness parameters in the calculation of the equivalent roughness for the mathematical model has been proposed;
the sediment transport model SETRIC has been updated and its functionality has been improved. The model can now be used as a design as well as research tool for analyzing the sediment transport process for different water delivery schedules and control systems;
an improved approach for the design and management of irrigation canals has been proposed. A computer program DOCSET has also been prepared based on the approach. The program is interactive, easy to use and can be used by designers with limited modelling know-how;
a water delivery plan has been designed and tested for the changing water and sediment inflow condition that can be implemented with the existing canal infrastructure;
the causes of sedimentation in the sub-secondary canals of Secondary Canal S9 have been identified.
Conclusions and outlook for the future
Canal design is an iterative process where the starting point is the preparation of management plans. Then the design parameters need to be selected and the preliminary hydraulic design of the canal can be made. The design results can then be used in the model to simulate and evaluate the proposed management plans and the sediment transport process in the system. Necessary adjustment can be made either in the design parameters or in the management plans, if needed. Then the canal need to be redesigned and the process would have to be continued till a satisfactory condition is reached.
The coarser fraction of the sediment is mostly controlled at the headwork and settling basin of an irrigation scheme. The sediment that is encountered in main and secondary canals is generally fine sand. Most of the silt fraction (sediment < 63 μm) is transported to the lower order canals and fields where it gets deposited. In the sub-secondary and tertiary canals, it has been observed that the fine sediment does not roll down to the bed as normally assumed in the case of sand and gets deposited on the slope also. Thus the canal section becomes narrower and the side slope becomes steeper. This phenomenon can not be analysed with the present sediment transport assumptions and an investigation in this aspect to address the transport process of fine sediment would be beneficial for improving the design and management of irrigation canals.
Flexibility of operation and sediment transport aspects restrict each other. A canal without any control can be designed and operated with higher degree of reliability in terms of sediment transport. Once the flow is controlled the sediment transport pattern of the canal is changed and the designed canal will behave differently. Hence, both flexibility and efficient sediment management are difficult to achieve at the same time. A compromise has to be made and this needs to be reflected in the design.
All the methods to transport, exclude or extract the sediment are temporary measures and just transfer the problem from one place to the other. They are not the complete solutions of the sediment problem. A better understanding on sediment movement helps to identify the problems beforehand and look for the best possible solutions.
Trekgedrag van schieraal rondom het Zaangemaal in Zaandam. DIDSON metingen
Keeken, O.A. van; Winter, H.V. - \ 2010
IJmuiden : IMARES (Rapport / IMARES Wageningen UR no. C018/10) - 16
waterbouwkunde - palingen - european eels - vismigratie - pompstations - waterschappen - noord-holland - hydraulic engineering - eels - fish migration - pumping stations - polder boards
Het Zaangemaal is één van de twee gemalen, die het belangrijkste boezemsysteem van Hollands Noorderkwartier, de Schermerboezem, bemalen. Parallel aan het gemaal ligt een historisch sluisje, welke mogelijk gebruikt kan worden om aal voor het gemaal op te vangen en door het sluisje langs het gemaal te sturen, om op deze manier schade aan vis te voorkomen. Dit onderzoek maakt onderdeel uit van een proef van het Hoogheemraadschap om te onderzoeken of vismigratie via deze historische sluis kan worden omgeleid langs het gemaal. Met behulp van de akoestische camera DIDSON is tijdens twee dagen gemeten of schieraal intrekt in dit historische sluisje in Zaandam.
TO monitoring vooroeververdediging Oosterschelde: cluster 1 - 2009
Heuvel-Greve, M.J. van den - \ 2009
Yerseke : IMARES (Rapport / IMARES Wageningen UR C137/09) - 35
kustbeheer - dijken - bescherming - marien milieu - flora - fauna - waterbouwkunde - mariene biologie - mariene ecologie - oosterschelde - coastal management - dykes - protection - marine environment - flora - fauna - hydraulic engineering - marine biology - marine ecology - eastern scheldt
De stromingen in de Ooster- en Westerschelde zorgen lokaal voor erosie van de oevers en geulwanden. Om dat proces tegen te gaan, worden op die locaties waar deze erosie de stabiliteit van de waterkering in gevaar brengt of de reeds bestaande oeverwerken ondermijnt, ‘bestortingen’ uitgevoerd om de oevers te beschermen. In 2009 zijn oeververdedigingswerken gepland en vanaf de zomer reeds gedeeltelijk uitgevoerd op drie locaties in de Oosterschelde en twee locaties in de Westerschelde. Rijkswaterstaat maakt voor dijkversterkingen in de Oosterschelde gebruik van breuksteen en staalslakken. Door de ‘bestortingen’ zal de bestaande lokale fauna en flora in ieder geval tijdelijk verdwijnen. Daarnaast kunnen er door het gebruik van staalslakken en breukstenen effecten optreden op de aanwezige flora en fauna, zoals bijvoorbeeld door uitloging van stoffen (waaronder zware metalen) uit staalslakken. Met name over uitloging van stoffen uit staalslakken in het mariene milieu is weinig bekend, evenals eventuele effecten hiervan op de flora en fauna. Voorafgaand aan geplande werkzaamheden op de locaties in de Oosterschelde is een zogenaamd T0-onderzoek (T nul) uitgevoerd. De uitkomsten zullen als referentie gebruikt worden voor een later op te starten monitoringsprogramma. Dit rapport beschrijft deze T0-situatie en is gebaseerd op drie onderliggende datarapportages.
Climatology of extreme rainfall from rain gauges and weather radar
Overeem, A. - \ 2009
Wageningen University. Promotor(en): Remko Uijlenhoet, co-promotor(en): I. Holleman; T.A. Buishand. - [S.l. : S.n. - ISBN 9789085855170 - 131
neerslag - klimatologie - klimaatfactoren - weersgegevens - meteorologische waarnemingen - regenmeters - inundatie - overstromingen - weersvoorspelling - waterbouwkunde - hydraulische systemen - nederland - precipitation - climatology - climatic factors - weather data - meteorological observations - rain gauges - flooding - floods - weather forecasting - hydraulic engineering - hydraulic structures - netherlands
Extreme neerslaggebeurtenissen hebben een grote invloed op de maatschappij en kunnen leiden tot materi¨ele schade en slachtoffers. Daarom is een betrouwbare klimatologie van extreme neerslag belangrijk, bijvoorbeeld voor het ontwerp van afvoersystemen. Een dergelijke klimatologie kan worden verkregen door jaarmaxima te selecteren uit lange neerslagreeksen. Vervolgens wordt een kansverdeling aangepast aan de geselecteerde jaarmaxima, zodat neerslaghoeveelheden kunnen worden geschat voor een gekozen herhalingstijd, die langer kan zijn dan de neerslagreeks. In dit proefschrift worden jaarmaxima gemodelleerd met de Gegeneraliseerde ExtremeWaarden (GEV) verdeling.
Voorkomen en gedrag van trekvissen nabij kunstwerken en consequenties voor de vangkans met vistuigen
Winter, H.V. - \ 2009
IJmuiden : IMARES (Rapport / IMARES Wageningen UR no. C076/09) - 57
waterbouwkunde - dammen - sluizen - barrières - vismigratie - diergedrag - natuurbescherming - hydraulic engineering - dams - sluices - barriers - fish migration - animal behaviour - nature conservation
Het Ministerie van Landbouw, Natuur en Voedselkwaliteit heeft IMARES opdracht verleend te onderzoeken of “het instellen van een visserijvrije zone rond kunstwerken (inclusief zoet/zout overgangen) kan bijdragen aan de bescherming van zalm, zeeforel en andere trekvissen zoals paling”. Hiertoe heeft IMARES literatuuronderzoek verricht en een analyse uitgevoerd van reeds beschikbare gegevens.
Dispersie van macrofauna door duikers : resultaten van een veldmeting
Didderen, K. - \ 2009
Wageningen : Alterra (Alterra-rapport 1834) - 54
zoetwaterecologie - distributie - waterdieren - verspreiding - barrières - waterbouwkunde - nederland - macrofauna - freshwater ecology - distribution - aquatic animals - dispersal - barriers - hydraulic engineering - netherlands
Binnen het project ‘Dispersie van aquatische organismen’ is onderzoek gedaan naar het dispersievermogen van macrofauna doelsoorten, ten behoeve van het voorspellen van de kans op terugkeer na het uitvoeren van herstelmaatregelen. In petgaten in een Natura 2000 gebied is gemeten of duikers een barrière opleveren voor de dispersie van verschillende groepen van aquatische macrofauna bij het bereiken van een nieuw habitat. Uit het onderzoek blijkt dat duikers een barrière vormen voor verschillende families van aquatische organismen. Verder komt ook duidelijk naar voren dat er meer passieve dan actieve dispersie door duikers plaatsvindt en dat stroming zowel in richting als kwantiteit zelfs in stilstaande wateren zeer belangrijk is als sturende factor bij de dispersie van aquatische organismen.