10.3: Flood Management - Geosciences
A flood is a high water level that overflows the natural (or artificial) banks or levees along any portion of a stream. This flooding keeps the land around the Nile fertile.
The fertility of frequently flooded land is what draws people to cluster near rivers. Worldwide, many people live within the 50 or 100 year flood plain of rivers. Flood plains are rated statistically based on how often they flood. For example, a 50 year flood plain floods, on average, every 50 years. People who live near rivers often build levees or artificially high banks around the river to contain it and try to avoid periodic flooding events. However, while levees keep one area from flooding, they heighten the flood risk for areas further down stream by constraining the water and 'pushing' more of it downstream.
Describing adaptation tipping points in coastal flood risk management
GIS software, open source data and programming languages can support coastal flood risk management activities.
Scenario discovery helps simplify complex environmental changes for use in vulnerability assessment and adaptation planning.
Scenario discovery can be used to describe conditions leading to adaptation tipping points.
The timing of adaptation responses can be better informed by knowledge of key sensitivities in existing management controls.
Insights from scenario discovery can facilitate targeted data collection and coastal monitoring activities.
Two Views of the Coconino Sandstone: Wind or Water Deposit?
Figure 2a: Wind Deposit in a Desert?
Modern deserts blow piles of sand grains into large sand dunes. As the sand bangs around, it gets a frosted appearance and is sorted by size. The piles of sand eventually collapse, forming steep deposits called cross-beds. The sharp angle is usually around 32°.
Figure 2b: Water Deposit During the Flood?
Under the ocean, avalanches leave piles of sand grains in large dunes. But because the water is gentler than air, the grains don’t get frosted, and different sizes are jumbled together. The piles of sand eventually collapse, forming gentler cross-beds.
A Guide to Ordinary High Water Mark (OHWM) Delineation for Non-Perennial Streams in the Western Mountains, Valleys, and Coast Region of the United States
A Guide to Ordinary High Water Mark (OHWM) Delineation for Non-Perennial Streams in the Western Mountains, Valleys, and Coast Region of the United States
Federal regulations define the ordinary high water mark (OHWM) as “that line on the shore established by the fluctuations of water and indicated.
Federal regulations define the ordinary high water mark (OHWM) as “that line on the shore established by the fluctuations of water and indicated by physical characteristics such as a clear, natural line impressed on the bank, shelving, changes in the character of soil, destruction of terrestrial vegetation, the presence of litter and debris, or other appropriate means that consider the characteristics of the surrounding areas” (U.S. Congress 1986). Under Section 404 of the Clean Water Act (CWA), the OHWM defines the lateral extent of federal jurisdiction in non-tidal waters of the United States (WoUS) in the absence of adjacent wetlands (U.S. Congress 1977). Thus, accurate and consistent OHWM delineation practices are essential for proper implementation of the CWA.
The dynamic nature of stream systems and fluvial processes presents challenges for OHWM delineation. Natural sources of variability in river and stream systems (e.g., climate, sediment supply, landscape position, etc.) are compounded by direct and indirect anthropogenic sources of variability (e.g., watershed alteration, dam emplacement and removal, climate change, etc.). Thus, it is challenging to impose a consistent measure of “ordinary” high flow conditions across systems in which the hydrology and geomorphology can vary greatly in both space and time.
OHWM delineation in non-perennial (i.e., intermittent and ephemeral) streams can be especially challenging. The U.S. Army Corps of Engineers (USACE) defines intermittent streams as having “flowing water during certain times of the year, when groundwater provides water for stream flow. During dry periods, intermittent streams may not have flowing water. Runoff from rainfall is a supplemental source of water for stream flow” (USACE 2012). Ephemeral streams have “flowing water only during, and for a short duration after, precipitation events in a typical year. Ephemeral stream beds are located above the water table year-round. Groundwater is not a source of water for the stream,” and “[r]unoff from rainfall is the primary source of water for stream flow” (USACE 2012). In contrast to both intermittent and ephemeral streams, perennial streams have “flowing water year-round during a typical year. The water table is located above the stream bed for most of the year,” and “[g]roundwater is the primary source of water for stream flow” (USACE 2012).
Given the less persistent streamflow regimes characteristic of non- perennial streams, particularly ephemeral systems, the characterization of ordinary high water flows is perhaps more challenging than in perennially flowing systems. Moreover, depending on climate, vegetation, and other related factors, the appearance of some OHWM indicators may vary greatly between wet and dry seasons or between relatively infrequent flow events, more so than in many perennial streams. Mountainous terrain can present additional challenges to OHWM delineation. For instance, the relatively steep and confined valleys in which mountain streams commonly flow can restrict the development of some alluvial features (e.g., flood-plains, bankfull benches, etc.) that are typical of low-gradient systems and that may help to identify the OHWM. Thus, in non-perennial mountain streams, it is often difficult to determine what constitutes ordinary high water and to interpret the physical and biological indicators established and maintained by ordinary high water flows.
Challenges and inconsistencies pertaining to OHWM delineation practices are becoming increasingly relevant in mountainous parts of the western U.S. in light of expanding development. This increased pressure on fluvial systems highlights the need for accurate, consistent, and repeatable OHWM delineation practices in this region. These factors, combined with the particular challenges of OHWM delineation in non-perennial mountain streams, provided the impetus for developing this delineation guide.
This guide presents the concepts, field indicators, and methods for assessing, delineating, and documenting the OHWM in non-perennial streams in the Western Mountains, Valleys, and Coast (WMVC) Region of the United States (Figure 1). The information presented here is based on the findings of Mersel et al. (2014) (discussed in Section 1.5) and on years of field observations and data gathering in the WMVC Region and in other regions of the U.S. by the authors and other contributing experts. The remainder of Section 1 provides background information regarding the concept of the OHWM and pertaining to stream hydrology and geomorphology in general. Section 2 discusses and provides examples of the specific field indicators used to identify the OHWM in non-perennial streams in the WMVC Region. Section 3 discusses field methods for delineating the OHWM and addresses additional techniques and lines of evidence that may help in problematic delineation scenarios.
The information presented here is technical guidance and does not define, amend, or replace any existing regulations, laws, or legal guidance related to the OHWM or to the regulation of WoUS. Furthermore, determining whether any stream is a jurisdictional WoUS is beyond the scope of this document and involves further assessment in accordance with regulations, case law, and clarifying guidance. This guide pertains to non-perennial streams in the WMVC Region of the U.S., and while the information presented here may have a wider applicability to other regions or to perennial rivers within the WMVC Region, this has not been tested or validated. This manual serves as a companion to A Field Guide to the Identification of the Ordinary High Water Mark (OHWM) in the Arid West Region of the Western United States (Lichvar and McColley 2008) as these two regions—the WMVC and the Arid West—are interspersed with one another. Best professional judgment is required to determine which manual is most appropriate for any given location within these two regions.
The technical guidance presented here aims to provide an informed and consistent approach to OHWM delineation within the WMVC Region however, OHWM delineation is not a precise practice. The OHWM can take on a variety of appearances and characteristics and may change over time due to natural or anthropogenic causes. Best professional judgment and consideration of the unique characteristics of each project site are always required.
10.3: Flood Management - Geosciences
The effectiveness of alert systems for civil protection purposes, defined as the ability to minimize the level of risk in a region subjected to an imminent flood event, strongly depends on availability and exploitability of information. It also depends on technical expertise and the ability to easily manage the civil protection actions through the organization into standardized procedures. Hydro-geologic and hydraulic risk estimation, based on the combination of different technical issues (in this case meteorological, hydro-geological, hydraulic matters), but also socio-economic ones, requires the integration between quasi-static and time-varying information within the same operative platform. Beside the real-time data exchange, a Decision Support System must provide tools which enable knowledge sharing among the civil protection centres. Moreover, due to the amount and heterogeneity of information, quality procedures become necessary to handle all forecasting and monitoring routines within operative centres, according to the latest national directive. In Italy procedures on the civil protection matter have been condensed into the Prime Minister's Directive (27 February 2004. STORM 3 , an innovative management and monitoring System for real-time flood forecasting and warning, takes in the Directive, supporting the operator step by step within the different phases of civil protection activities.
We are, unfortunately, aware of the significant socio-economic impacts associated with floods. According to the International Disaster Database (EM-DAT), floods represent the most frequent and most impacting, in terms of the number of people affected, among the weather-related disasters: nearly 0.8 billion people were affected by inundations in the last decade (2006&ndash2015), while the overall economic damage is estimated to be more than $300 billion. Despite this evidence, and the awareness of the environmental role of rivers and their inundation, our knowledge and modelling capacity of flood dynamics remain poor, mainly related to the availability of measurements and ancillary data.
In this context, remote sensing represents a value source of data and observations that may alleviate the decline in field surveys and gauging stations, especially in remote areas and developing countries. The implementation of remotely-sensed variables (such as digital elevation model, river width, flood extent, water level, land cover, etc.) in hydraulic modelling promises to considerably improve our process understanding and prediction and during the last decades, an increasing amount of research has been undertaken to better exploit the potential of current and future satellite observations. In particular, in recent years, the scientific community has shown how remotely sensed variables have the potential to play a key role in the calibration and validation of hydraulic models, as well as provide a breakthrough in real-time flood monitoring applications. However, except for a few pioneering studies, the potential of remotely sensed data to enhance flood modelling has not yet been fully enough explored, and the use of such data for operational flood mapping is far away from being consolidated. In this scenario, the forthcoming satellite missions dedicated to global water surfaces monitoring will enhance the quality, as well as the spatial and temporal coverage, of remotely sensed data, thus offering new frontiers and opportunities to enhance the understanding of flood dynamics and our capability to map their extents.
This Special Issue aims to collect studies and experiences aimed at aiding and advancing flood monitoring and mapping through remotely sensed data. The list below provides a general (but not exhaustive) overview of the topics that are solicited for this Special Issue:
- Remote sensing data for flood hazard and risk mapping
- Remote sensing techniques to monitor flood dynamics
- The use of remotely sensed data for the calibration, or validation, of hydrological or hydraulic models
- Data assimilation (DA) of remotely sensed data into hydrological and hydraulic models
- Improvement of river discretization and monitoring by means of satellite based observations
- River flows estimation by means of remote sensed observations.
- River and flood dynamics estimation from satellite (especially time lag, flow velocity, etc.)
Dr. Alessio Domeneghetti
Dr. Guy J.-P. Schumann
Dr. Angelica Tarpanelli
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An algorithm for rapid flood inundation mapping from optical data using a reflectance differencing technique
This paper presents an algorithm for flood inundation mapping in the context of emergency response. Rapid satellite-based flood inundation mapping and delivery of flood inundation maps during a flood event can provide crucial information for decision-makers to put relief measures in place. With the development of remote sensing techniques, flood mapping for large areas can be done easily. The algorithm discussed here involves the use of shortwave infrared, near-infrared and green spectral bands to develop a suitable band rationing technique for detecting surface water changes. This technique is referred to as Normalized Difference Surface Water Index (NDSWI). The NDSWI-based approach produces the best results for mapping of flood-inundated areas when verified with actual satellite data. Analysis of results reveals that NDSWI has the potential to detect floodwater turbidity, which was verified using principal component analysis. The application of the technique is informative about flood damages, which are illustrated using the floods in Pakistan in 2010 as an example.
Constructed wetland management in urban catchments for mitigating floods
Wetlands in urban ecosystems provide significant environmental benefits. In the present study, the concept of urban constructed wetland development is studied from the viewpoint of urban planning with dynamic water level orifice setting controller. A two-step modelling procedure is carried out: (1) development of a hybrid model, by coupling a well-established two-dimensional hydrodynamic model (International River Interface Cooperative, iRIC) with a one-dimensional physically-based, distributed-parameter model (Storm Water Management Model, SWMM), to compute and map flood scenarios and to identify the flood-prone areas and (2) use of SWMM to simulate the water inflow to the proposed constructed wetland, which acts as a cushion for storing excess flood water. The proposed methodology is implemented on the Jahangirpuri drain catchment located in Delhi, India. Results show that the hybrid model is effective, and the simulations are observed to be in good agreement with the recorded data, which assist in detecting the flood-prone areas. Further, an estimation of the impact of the proposed constructed wetland on catchment hydrology indicates an overall reduction of 23% in flooding adjacent to the channel with a significant reduction in backflow as well as water depth in the drain. The flapgate at the outlet of the wetland helps in maintaining the desired water depth in the wetland. The outcomes of this study will assist the hydrologists and administrators in urban stormwater management and planning to mitigate the impact of floods in urban watersheds.
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Bicol River Basin Management Committee convenes for flood mitigation measures
NEDA USec Adoracion M. Navarro, Chairperson of the Technical Board of the National Land Use Committee and the Technical Management Group for Rehabilitation and Recovery of the National Disaster Risk Reduction and Management Council, oversaw the re-convening of the Bicol River Basin Management Committee (BRBMC) on January 22, 2019 at the National Economic and Development Authority (NEDA) Regional Office 5, Arimbay, Legazpi City, after the Committee’s three-year hiatus. Chaired by the DENR-Region 5 and co-chaired by the DILG-Region 5, the BRBMC is mandated to: formulate a Bicol River Strategic Management Plan review and monitor the strategic action plans of the local government units (LGUs) facilitate the implementation of the management strategies and action plans and resolve implementation issues coordinate the implementation of activities between the different agencies and LGUs and enhance the capacity of stakeholders in promoting good practices in river basin and watershed management.
NEDA USec Adoracion Navarro (third from left) joins the BRBMC in discussing flood control and mitigation measures during its meeting on January 22, 2019 at NEDA Region 5, Arimbay, Legazpi City.
The regional offices of the Department of Public Works and Highways, National Irrigation Authority, Philippine Atmospheric, Geophysical and Astronomical Services Administration, Mines and Geosciences Bureau and Environmental Management Bureau presented ongoing and proposed programs, activities and projects in the Bicol River Basin area. These include: (1) consulting services for the feasibility study and
detailed engineering design for proposed flood control projects in the Bicol River Basin (2) habitation protection at the upper and central basin (3) Lake Buhi and Lake Bato flood control structures (4) Bula embankment (5) Rinconada Integrated Irrigation System (6) Sagip-Ilog Program (7) Geohazard Map Distribution and Seminar, and (8) Strengthening of Flood Forecasting and Warning System in Bicol River Basin.
The BRBMC agreed that a holistic approach should be applied rather than fragmented solutions in dealing with problems related to flooding. Dir. Antonio M. Daño of the DENR-River Basin Control Office encouraged the agencies to shift from flood mitigation approach to flood risk management. The same recommendation was raised by the NIA representative as it referred to the siltation in the canal structures of irrigation projects.
As part of her guidance, USec Navarro said that in the succeeding meetings of the BRBMC, agencies should not only report the accomplishments but also monitor the remaining gaps in the context of the 2015 Bicol River Basin Management and Development Master Plan. “To ensure that the secretariat support to this body will be sustained, the next step is to reconstitute the secretariat created in 2012, that is, the Bicol River Basin Coordinating Office, into a Bicol River Basin coordinating unit that shall be manned by existing positions in the DENR-Region 5. The interim secretariat can be NEDA-Region 5, which can hand-hold the DENR secretariat. The proposed governance structure in the 2015 Bicol River Basin master plan of having eight sub-basin management councils is not an immediate priority but can be considered in the work plan,” said USec Navarro
She reiterated to the agencies some of the proposed interventions in the immediate term, such as: minimize incidences of flooding through improved storage capacity of rivers and lakes by constructing flood control structures in strategic locations provide sufficient irrigation facilities through rehabilitation and upgrading of existing irrigation facilities rehabilitate at least 18,000 hectares of degraded forest lands improve waste disposal by developing sanitary landfill facilities in different LGUs resettle at least 6,000 families in high disaster risk areas particularly the informal settlements in river easements and comprehensively identify vulnerabilities and corresponding adaptation actions for communities.
The inventory of projects included in the master plan but not yet funded shall be reviewed for possible funding and implementation. The next meeting of the body is set in July, after the national election to get commitments from newly elected local government leaders.
Cities and Flooding
Urban flooding is a significant challenge which today increasingly confronts the residents of the expanding cities and towns of developing countries, as well as policymakers and national, regional and local government officials. The Global Handbook presents the state-of-the art in urban flood risk management in a thorough and user-friendly way. It serves as a primer in integrated urban flood risk management for technical specialists, decision-makers and other concerned stakeholders in the private and community sectors. It covers the causes, probability and impacts of floods the measures that can be used to manage flood risk, balancing structural and non-structural solutions in an integrated fashion and the means by which these measures can be financed and implemented, and their progress monitored and evaluated. The Handbook provides an operational guide on how most effectively to manage the risk of floods in rapidly urbanizing settings ? and within the context of a changing climate.