Sloff K.,Technical University of Delft |
Van Spijk A.,Water Management |
Stouthamer E.,University Utrecht |
Sieben A.,Rijkswaterstaat Center for Water Management
International Journal of Sediment Research | Year: 2013
In the Rhine-Meuse delta in the south-western part of the Netherlands, the morphology of the river branches is highly dependent on the erodibility of the subsoil. Erosion processes that were initiated after closure of the Haringvliet estuary branch by a dam (in 1970), caused a strong incision of several connecting branches. Due to the geological evolution of this area the lithology of the subsoil shows large variations in highly erodible sand and poorly erodible peat and clay layers. This study shows how the geological information can be used to create 3D maps of the erodibility of the sub-soil, and how this information can be used to schematize the sub-soil in computational models for morphological simulations. Local incisement of sand patches between areas with poorly erodible bed causes deep scour holes, hence increasing the risk on river-bank instability (flow slides) and damage to constructions such as groynes, quays, tunnels, and pipelines. Various types of mathematical models, ranging from 1D (SOBEK) to quasi-3D (Delft3D) have been applied to study the future development of the river bed and possible management options. The results of these approaches demonstrate that models require inclusion of a layer-bookkeeping approach for sub-soil schematization, non-uniform sediment fractions (sand-mud), tidal and river-discharge boundary conditions, and capacity-reduction transport modeling. For risk-reducing river management it has been shown how the development of the river bed can be addressed on a large scale and small scale. For instance, the use of sediment feeding and fixation of bed can be proposed for large-scale management, while monitoring and interventions at initiation of erosion can be proposed as response to small-scale developments that exceed predefined intervention levels. © 2013 International Research and Training Centre on Erosion and Sedimentation and the World Association for Sedimentation and Erosion Research.
Panigrahi P.,Water Management |
Sharma R.K.,Indian Agricultural Research Institute |
Hasan M.,Indian Agricultural Research Institute |
Parihar S.S.,Indian Agricultural Research Institute
Agricultural Water Management | Year: 2014
Scarcity of irrigation water in critical growth stages of the crop is one of the major causes of low productivity and decline of citrus orchards. Regulated deficit irrigation (RDI) is a recently proposed water saving technique in irrigated agriculture. The present study was planned with a hypothesis that the optimal RDI scheduling at early fruit growth period (EFGP), which coincides with summer months could save substantial amount of water, without significantly affecting the yield of 'Kinnow' mandarin (Citrus reticulata Blanco) plants. Two DI strategies: (a) withholding irrigation at EFGP (RDI0) and (b) irrigation at 50% crop evapotranspiration (ETc) at EFGP (RDI50) were compared with full irrigation (FI, 100% ETc) in relation to gas exchange, water relation and nutrient composition of leaves along with growth and yield of the plants. The greater plant growth with maximum fruit yield (61.9-63.2tha-1) was recorded with fully-irrigated plants. However, the yield under RDI50 was statistically (p>0.05) at par with that under FI. The reduction in water application of around 24% with RDI50 resulted in 30% improvement in irrigation water use efficiency with this treatment over that with FI. The maximum rate of net-photosynthesis, stomatal conductance and transpiration of leaves was recorded with fully-irrigated plants. However, the plants under RDI50 exhibited the highest leaf water use efficiency. The leaf nutrients (N, P, K, Fe, Mn, Cu and Zn) analysis revealed that RDI0 produced significantly (p<0.05) lower concentration of all the nutrients except P and Cu than that in other treatments. Relative leaf water content (RLWC), leaf water concentration (LWC) and mid-day stem water potential (Ψ) showed a decreasing trend, whereas water stress integral (SΨ) and plant canopy reflectance indices (water band index, WBI; normalised difference water index, NDWI; and moisture stress index, MSI) showed the reverse trend of RLWC with water stress. The prediction model formulated based on midday stem water stress integral, leaf N, leaf K, stomatal conductance and water stress index using Principal component regression technique during EFGP performed well with reasonably accuracy (R2=0.85) to forecast annual fruit yield of the citrus plants. Overall, these results reveal that irrigation at 50% ETc during EFGP could impose desirable water stress on 'Kinnow' mandarin plants, improving their water use efficiency, without significantly affecting the fruit yield under water scarce condition. © 2014.
Dun R.W.,Water Management |
Wicks J.M.,CH2M HILL
Proceedings of the Institution of Civil Engineers: Water Management | Year: 2014
Advances in inundation modelling software, computer hardware and national data sets mean that it is now practical to use full solutions of the two-dimensional (2D) shallow water equations (SWE) to undertake national-scale modelling of breach inundation. Such modelling enables much improved asset management activities, which lead to reduced risk to life, lower risk of damage to properties and a much better targeting of investment by asset owners. This paper describes how a 2D SWE inundation modelling system was designed and applied to the UK Canal and River Trust canal system as part of a quantitative high-level risk assessment framework. The framework includes a new approach for estimating breach probability and hydrographs in the canal system for potential embankment and culvert failures. An innovative automated model build-and-run process using Isis 2D software was applied to model inundation in urban areas. Predicted likely loss of life and property damage outputs were used to generate a risk chart to prioritise asset inspection and maintenance.
Seifert D.,Water Management |
Sonnenborg T.O.,Geological Survey of Denmark |
Refsgaard J.C.,Geological Survey of Denmark |
Hojberg A.L.,Geological Survey of Denmark |
Troldborg L.,Geological Survey of Denmark
Water Resources Research | Year: 2012
In this study six hydrological models that only differ with respect to their conceptual geological models are established for a 465 km2 area. The performances of the six models are evaluated in differential split-sample tests against a unique data set with well documented groundwater head and discharge data for different periods with different groundwater abstractions. The calibration results of the six models are comparable, with no model being superior to the others. Though, the six models make very different predictions of changes in groundwater head and discharges as a response to changes in groundwater abstraction. This confirms the utmost importance of the conceptual geological model for making predictions of variables and conditions beyond the calibration situation. In most cases the observed changes in hydraulic head and discharge are within the range of the changes predicted by the six models implying that a multiple modeling approach can be useful in obtaining more robust assessments of likely prediction errors. We conclude that the use of multiple models appear to be a good alternative to traditional differential split-sample schemes. A model averaging analysis shows that model weights estimated from model performance in the calibration or validation situation in many cases are not optimal for making other predictions. Hence, the critical assumption that is always made in model averaging, namely that the model weights derived from the calibration situation are also optimal for model predictions, cannot be assumed to be generally valid. © 2012. American Geophysical Union. All Rights Reserved.
But now, seagrass is dying at a rate unseen since the late 1980s in the Florida Bay, off the southern tip of Florida between the Atlantic Ocean and the Gulf of Mexico. "It is like a desert," said fishing guide Xavier Figueredo, peering into the water, where only an occasional needle fish or ray could be seen scooting along a bottom clustered with matted, dead underwater grasses. Seagrass provides shelter for small fish, which are eaten by bigger fish, and serves as the foundation for the marine food chain. In Florida, where recreational saltwater fishing is a $7.6 billion industry, experts consider seagrass a key indicator of the ecosystem's health. "This has historically been a wonderful spotted seatrout fishery. This year it was non-existent, literally," said Figueredo, one of a group of fishing guides who cater to tourists visiting the string of islands known as the Florida Keys. Ecologists say the problem is mainly due to the way humans have for decades diverted the natural flow of fresh water from central Florida southward to the Everglades wetlands, protecting sugar cane farms and other property. A massive die-off that began in 1987 and lasted for years helped spark ambitious plans to protect the area, but fishermen say progress has been too slow. Now, they see the death cycle happening again, as increasingly warm and salty water smothers the underwater grass. First the grass detaches from the bottom. It floats to the surface during the day and sinks again at night, earning it the nickname "zombie grass," said Steve Davis, a wetland ecologist with the Everglades Foundation, as he inspected a once-popular fishing area called Whipray Basin. "It's dead, it just doesn't know it yet," he explained. Eventually, the grass bleaches, and the blades amass into smelly islands. The die-off makes an algae bloom quite likely, sucking oxygen out of the water and making it a hostile environment for marine life. "It is dramatic. It looks like a disaster area," said Davis. Heavy rain led to record freshwater inflows coming into the bay in January and February, Davis said, but it is not enough. The die-off is gathering steam. "We just have to now ride it out, and we know it is going to take years to recover," he said. State wildlife officials say the affected area covers about 25,000 acres (110,000 hectares) of dead sea grass—about the size of Paris. But Davis said fishermen who have seen it firsthand say it's twice that big—on the order of 50,000 acres. "It is a massive area in Florida Bay where the entire habitat has been decimated," said Davis. The crisis has prompted some fishing guides to press for government action. Some have formed advocacy groups like Captains for Clean Water, which has more than 9,000 followers on Facebook. The solution, they say, is to acquire a patch of land south of the state's largest freshwater lake, Lake Okeechobee, to act as a reservoir for fresh water that can flow south to the Everglades and the Florida Bay. But the land in that area belongs to sugar cane farms, a powerful industry known as "Big Sugar" that has resisted giving up any territory. "When times were tough, the industry was anxious to sell, and then times got better and the economics changed," Congressman Carlos Curbelo told a gathering of fishermen and concerned citizens in Islamorada this month. "We need to find a partner that is willing to engage." The lead government agencies involved—the US Department of the Interior and the South Florida Water Management District—did not respond to AFP requests for comment. The Everglades Foundation said money is not an issue, with some $200 million a year for the next 20 years earmarked to pay for the state's share of restoration, and federal funds to match. "The only other thing that is lacking is the political will to get the land that we need," said Davis. "Without that land, without that reservoir, we can't solve the problem in the Florida Bay." The Florida Bay did bounce back on its own after the 1987 die-off, but the rejuvenation process took nearly a decade. John Guastavino, who has been taking tourists out to fish from the Florida Keys for 26 years, remembers a time, not so long ago, when the catch was bountiful. "I've had days when I could go catch 65 redfish in a day, and days when I've caught 30 or 40 snook," he said. Now, "if you are having a good day, you might catch five or six snook," he added. "I can't remember the last time I had someone catch more than one or two redfish." He also has to travel farther than ever to find a good fishing spot. "It is probably one of the most frequently asked questions that I get," said Guastavino. "'Aren't there any fish back there, the 30 miles we just traveled?' It is sad to tell them, 'No, not really.'" Explore further: Restrictions on boaters proposed to protect Everglades seagrass