An ecosystem in freefall, a shrinking water supply for cities and agriculture, an antiquated network of failure-prone levees—this is the Sacramento-San Joaquin Delta, the major hub of California's ...water system. Written by a team of independent water experts, this analysis of the latest data evaluates proposed solutions to the Delta's myriad problems. Through in-depth economic and ecological analysis, the authors find that the current policy of channeling water exports through the Delta is not sustainable for any interest. Employing a peripheral canal-conveying water around the Delta instead of through it—as part of a larger habitat and water management plan appears to be the best strategy to maintain both a high-quality water supply and at the same time improve conditions for native fish and wildlife. This important assessment includes integrated analysis of long term ecosystem and water management options and demonstrates how issues such as climate change and sustainability will shape the future. Published in cooperation with the Public Policy Institute of California
This is the story of how rural black people struggled against the oppressive sharecropping system of the Arkansas and Mississippi Delta during the first half of the twentieth century. Delta planters, ...aided by local law enforcement, engaged in peonage, murder, theft, and disfranchisement. As individuals and through collective struggle, black men and women fought back, demanding a just return for their crops and laying claim to a democratic vision of citizenship. Nan Woodruff shows how the freedom fighters of the 1960s would draw on this half-century tradition of protest, thus expanding our standard notions of the civil rights movement and illuminating a neglected but significant slice of the American black experience.
Entropy and optimality in river deltas Tejedor, Alejandro; Longjas, Anthony; Edmonds, Douglas A. ...
Proceedings of the National Academy of Sciences,
10/2017, Volume:
114, Issue:
44
Journal Article
Peer reviewed
Open access
The form and function of river deltas is intricately linked to the evolving structure of their channel networks, which controls how effectively deltas are nourished with sediments and nutrients. ...Understanding the coevolution of deltaic channels and their flux organization is crucial for guiding maintenance strategies of these highly stressed systems from a range of anthropogenic activities. To date, however, a unified theory explaining how deltas self-organize to distribute water and sediment up to the shoreline remains elusive. Here, we provide evidence for an optimality principle underlying the self-organized partition of fluxes in delta channel networks. By introducing a suitable nonlocal entropy rate (nER) and by analyzing field and simulated deltas, we suggest that delta networks achieve configurations that maximize the diversity of water and sediment flux delivery to the shoreline. We thus suggest that prograding deltas attain dynamically accessible optima of flux distributions on their channel network topologies, thus effectively decoupling evolutionary time scales of geomorphology and hydrology. When interpreted in terms of delta resilience, high nER configurations reflect an increased ability to withstand perturbations. However, the distributive mechanism responsible for both diversifying flux delivery to the shoreline and dampening possible perturbations might lead to catastrophic events when those perturbations exceed certain intensity thresholds.
In Gilded Voices, Qiliang He focuses on pingtan, a storytelling art using the Suzhou dialect, to explore the role of the cultural market in mediating between the state and artists in the PRC era.
Omolade Adunbi investigates the myths behind competing claims to oil wealth in Nigeria's Niger Delta. Looking at ownership of natural resources, oil extraction practices, government control over oil ...resources, and discourse about oil, Adunbi shows how symbolic claims have created an "oil citizenship." He explores the ways NGOs, militant groups, and community organizers invoke an ancestral promise to defend land disputes, justify disruptive actions, or organize against oil corporations. Policies to control the abundant resources have increased contestations over wealth, transformed the relationship of people to their environment, and produced unique forms of power, governance, and belonging.
Deltas are landforms that deliver water, sediment and nutrient fluxes from upstream rivers to the deltaic surface and eventually to oceans or inland water bodies via multiple pathways. Despite their ...importance, quantitative frameworks for their analysis lack behind those available for tributary networks. In a companion paper, delta channel networks were conceptualized as directed graphs and spectral graph theory was used to design a quantitative framework for exploring delta connectivity and flux dynamics. Here we use this framework to introduce a suite of graph‐theoretic and entropy‐based metrics, to quantify two components of a delta's complexity: (1) Topologic, imposed by the network connectivity and (2) Dynamic, dictated by the flux partitioning and distribution. The metrics are aimed to facilitate comparing, contrasting, and establishing connections between deltaic structure, process, and form. We illustrate the proposed analysis using seven deltas in diverse morphodynamic environments and of various degrees of channel complexity. By projecting deltas into a topo‐dynamic space whose coordinates are given by topologic and dynamic delta complexity metrics, we show that this space provides a basis for delta comparison and physical insight into their dynamic behavior. The examined metrics are demonstrated to relate to the intuitive notion of vulnerability, measured by the impact of upstream flux changes to the shoreline flux, and reveal that complexity and vulnerability are inversely related. Finally, a spatially explicit metric, akin to a delta width function, is introduced to classify shapes of different delta types.
Key Points:
Define metrics that depict the topologic and dynamic complexity of deltas
Study how complexity relates to an intuitive notion of vulnerability
Project deltas for comparison and physical insight in a topo‐dynamic space
Understanding controls on sediment distribution in river deltas is paramount to predicting facies relationships and stratal architecture. Most classifications of deltas have focused on subaerial plan ...morphology as a simplistic function of river, tide, and wave energy. New work, however, is revealing the importance of subaqueous deposits, and in particular shore-parallel sediment redistribution, in the shaping of delta planform. Delta asymmetry has emerged as an important characteristic reflective of patterns of alongshore sediment dispersal. Asymmetry has been described from onshore and offshore environments from several different types of modern deltas, but aspects of asymmetry have not been fully documented and the degree to which these patterns are recorded in deltaic strata is not yet known. This study is a comprehensive literature review of sediment distributions in modern deltas focusing on studies with high resolution geomorphic, geophysical, and geochronological datasets. We reviewed 27 deltas using over 100 papers primarily from the past 15–20years. Morphological, facies, and stratigraphic aspects were analyzed across the entire spectrum of deposits from the delta apex to the most distal muds of the prodelta. We define quantifiable indices of asymmetry describing upcurrent vs. downcurrent distribution of sediment volume, sediment area, sediment caliber, and distributary channels. Most deltas are asymmetrical to some degree with respect to one or more of these parameters. Many deltas are increasingly skewed toward the downcurrent side from proximal to distal sub-environments (i.e. delta plain, delta front, prodelta). Some deltas are skewed toward the upcurrent side in one sub-environment and toward the downcurrent side in another sub-environment. Sand is preferentially deposited on the downcurrent side of most deltas, but distributary channels tend to develop toward the upcurrent side. The highest sand:mud ratios are often on the upcurrent side in the lower delta plain, but in the delta front these ratios are highest on the downcurrent side. These complex patterns of asymmetry reflect different combinations of controls including discharge partitioning, lobe abandonment and localized transgression, plume deflection by coastal currents, dominance of longshore current direction, variable subsidence, and other factors. These processes may result in upcurrent–downcurrent variations in clinoform geometry, rates of progradation, and stratal lapping relationships. Asymmetry has multiple aspects, manifestations, and controls – even within a single delta – but the long-term preservation potential of these patterns likely varies, depending on depositional setting and shoreline trajectory. Studies of ancient deltas will be better-informed by recognizing the wide variety of controls on sediment distribution and avoiding the tendency toward a single model of delta asymmetry.
Deltas are subaerial landforms that cap underlying deposits with subaqueous extensions that result from a river feeding sediment directly into a standing body of water at a rate that overwhelms any ...effective dispersal processes derived from the ambient basin. This definition encapsulates both the terrestrial surface expression and the geological focus on the entire sediment mass. Environmental studies also focus on the ecology of deltaic wetlands, their drowning history, and related sustainability issues including societal considerations, history, and culture. A mean 76 ± 16% drop in hydraulic energy occurs in all subaerial deltas regardless of size, given the break in gradients separating fluvial and deltaic surfaces, driving an ever-decreasing bed-material transport, shallowing of distributary channels and concomitant overbank flooding. A delta's sediment mass grows from the addition of new river loads but can also include aeolian and marine sediment derived from outside the delta domain, growth of peat and other biomass, and inputs from human action. Removal of sediment is via river plumes interacting with marine currents, wave-induced transport, sediment failures and gravity flows, high-tide inundation onto the delta plain, tidal channel widening and deepening, and human action (peat, clay, sand and gravel mining). A delta's trapping efficiency ranges from 0 for small-load rivers that discharge directly into an energetic ocean, to 80% for large deltas, and up to 100% for some semi-enclosed bayhead deltas, including fjords. The global (ensemble) subaerial delta aggradation rate is ∼1.6 mm/y if 70% of the global sediment load exits the river mouth(s), a reminder of how much sediment can be expected to be delivered to the surfaces of global deltas at a time when the 2022 CE sea level rise is ∼4 mm/y.
At the planetary scale, deltas are environmentally complex given Earth's range in climate, hydrodynamics, tectonic settings, relative sea-level provinces, sediment input, redistribution processes, and human actions. Under natural conditions, the subaerial portion of deltas adapt to change by advancing, retreating, switching, aggrading, and/or drowning, whereas many modern deltas are structurally constrained by societal needs. The 89 large and mud-rich coastal marine deltas (i.e. subaerial area > 1000 km2) account for 84.3% of Earth's total deltaic area that hosts >89% of all humans occupying deltas, many living within megacities. The 885 medium-size deltas (i.e. subaerial areas 10–1000 km2) account for 15.5% of the global delta area and 10.5% of humans living on deltas, with characteristics that fall between the small and large delta categories. The 1460 small and essentially sandy deltas (1–10 km2), including all fjord deltas, are impacted less from human action (with exceptions) and most are better able to withstand climate change. Recognizing the limits of big data in capturing delta complexity, field data remains a necessary gold standard for site investigators.
•295 out of ∼2400 deltas comprise 95% of Earth's marine deltaic area of ∼855,000 km2.•The ensemble-average delta aggradation rate is ∼1.6 ± 0.4 mm/y, if 70% of the global sediment load exits river mouths.•Many Late Holocene deltas have moved from a growth phase to a sinking phase during the Anthropocene.•A mean 76 ± 16% drop in hydraulic energy occurs in all deltas and drives an ever-decreasing bed-material transport.
Background. Coastal river deltas provide multiple ecosystem services. Many deltas serve as major centers of agriculture, industry and commerce. The annual economic benefits derived from major deltas ...are often a substantial fraction of a country's GDP. Yet, many deltas are losing land due to erosion, subsidence and subsequent flooding. Such vulnerabilities are often increased due to local land and water management decisions, relative sea-level rise, and increases in climate extremes. Aim of this review. Considerable literature exists addressing the formation of deltas and the effects of increasing urbanization, industrialization and crop and fish production, increases in relative sea level rise, and decreasing sediment deposition. This leads to the question: are the economic, environmental, ecological and social benefits derived from developed river deltas sustainable? This review focuses on this question. Methods/Design. Over 180 published documents were identified and reviewed using various search engines and key words. These key words included river deltas; delta sustainability, vulnerability, resilience, coasts, ecology, hazards, erosion, water management, urbanization, reclamation, agriculture, governance, pollution, geomorphology, economic development, socio-economic changes, and delta wetlands; relative sea level change; sediment trapping; sand mining; salinity intrusion; coastal restoration; estuarine engineering; shoreline evolution; estuarine processes; and the names of specific river basin deltas. Review Results/Synthesis and Discussion. Deltas provide humans important resources and ecosystem services leading to their intensive development. The impacts of this development, together with sea-level rise, threatens the sustainability of many river deltas. Various management and governance measures are available to help sustain deltas. Controls on land use, improved farming and transport technology, wetland habitat protection, and d improved governance are some that might help sustain the economic and ecological services provided by deltas. However, increased population growth and the impacts of climate change will put increased pressure on deltas and the benefits derived from them.
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