Recurrence Interval Flood Research Articles

Conservation Reserve Program effects on floodplain land cover management

Growing populations and industrialized agriculture practices have eradicated much of the United States wetlands along river floodplains. One program available for the restoration of floodplains is the Conservation Reserve Program (CRP). The current research explores the effects CRP land change has on flooding zones, utilizing Flood Modeller and HEC-RAS. Flood Modeller is proven a viable tool for flood modeling within the United States when compared to HEC-RAS. Application of the software is used in the Nodaway River system located in the western halves of Iowa and Missouri to model effects of introducing new forest areas within the region. Flood stage during the conversion first decreases in the early years, before rising to produce greater heights. Flow velocities where CRP land is present are reduced for long-term scopes. Velocity reduction occurs as the Manning's roughness increases due to tree diameter and brush density. Flood zones become more widespread with the implementation of CRP. Future model implementations are recommended to witness the effects of smaller flood recurrence intervals.

Assessment of flood hazard in a riverine tract between Damodar and Dwarkeswar River, Hugli District, West Bengal, India

Flood is mainly a natural hazard which causes heavy destruction to society. A part of Arambag Sub-Division mainly Arambag, Pursurah, Khanakul-I and II Blocks of Hugli District belongs to the Damodar–Dwarkeswar interfluvial region which is one of the flood prone areas of West Bengal. A huge area of these Blocks goes under water every year during the monsoon season. The Recurrence interval of floods for this region is very low. The frequency of extreme floods is increasing in recent times. Out of 38 years of observed data, moderate to heavy floods have occurred in 21 times and the Extreme Danger Level (EDL) has crossed 17 times. Gumbel’s extreme value distribution (EV-I) method is applied to identify the recurrence interval with the magnitude of events. It is one of the best suitable methods for analyzing extreme events. It has been observed that flood happens in this region when discharge crosses 2,000 cumecs (m3 s−1). It has been figured out from the Gumbel’s extreme value that discharge of 2,175.3 cumec at Horinkhola Gauge station has a return period of 2.03 years and its probability of occurrence is 49.26%. So there is 50% chance of a flood in every year. Population density of this region is very high (1,381 persons/km2) and economic activity mainly depends upon agriculture. Most of the people of this region are affected by floods which brings negative impact on the economy and food security. 327.8 km2 of land (47% of total area) was inundated during the floods of 2015. If this trend continues, future flooding will be very disastrous. Structural as well as non-structural measures should have to be taken for managing the overall situation.

English

Several hydromorphological and soil factors may be the cause of variations in the total organic carbon (TOC%) and total nitrogen (TN%) content of riparian soils. Despite the importance of these two essential components in soil-forming processes, few studies have focused on the variability of carbon and nitrogen content for soils subjected to frequent flooding. Successive floods may in fact result in soil depletion. Measurements of TOC% and TN% content as well as of other physico-chemical soil properties (e.g. litter thickness, texture, pH, Fe and Al concentrations, C/N ratio, bulk density, colour) were performed in various flood zones (recurrence intervals of 0-20 and 20-100 years) and in no-flood zones (outside of floodplains). To do so, soil samples were systematically collected along transects perpendicular to the riverbank which cross through the various flood zones. The results show that TOC% and TN% content varies significantly from one zone to another. The concentrations of these two components are significantly lower in the flood zone with a recurrence interval of 0-20 years (29% ±0.80 TOC and 0.17% ±0.05 TN) compared to the other two zones, name 3.45% ±1.56 TOC and 0.26% ±0.10 TN (recurrence interval of 20-100 years), and 3.52% ±1.57 TOC and 0.27% ±0.11 TN (no-flood zone). There is often no soil biomass (litter) in flood zones with a flood recurrence interval of 0-20 years (72% of sites without litter), whereas litter is almost always present in the flood zone with a recurrence interval of 20-100 years and in the no-flood zone, with average thicknesses of 2.84 and 3.65 cm, respectively. The absence or virtual absence of litter in the frequent-flood zones progressively results in soil depletion in terms of CO and N, which over time could adversely affect forest stand regeneration and deeply alter current river ecosystems. Key words: Alluvial soils, total organic carbon (TOC), total nitrogen (TN), soil biomass, floodplain, flood, recurrence intervals.

Development and Application of Improved Long-Term Datasets of Surface Hydrology for Texas

Freshwater availability and agricultural production are key factors for sustaining the fast growing population and economy in the state of Texas, which is the third largest state in terms of agricultural production in the United States. This paper describes a long-term (1918–2011) grid-based (1/8°) surface hydrological dataset for Texas at a daily time step based on simulations from the Variable Infiltration Capacity (VIC) hydrological model. The model was calibrated and validated against observed streamflow over 10 Texas river basins. The simulated soil moisture was also evaluated using in situ observations. Results suggest that there is a decreasing trend in precipitation and an increasing trend in temperature in most of the basins. Droughts and floods were reconstructed and analyzed. In particular, the spatially distributed severity and duration of major Texas droughts were compared to identify new characteristics. The modeled flood recurrence interval and the return period were also compared with observations. Results suggest the performance of extreme flood simulations needs further improvement. This dataset is expected to serve as a benchmark which may contribute to water resources management and to mitigating agricultural drought, especially in the context of understanding the effects of climate change on crop yield in Texas.

Wood export varies among decadal, annual, seasonal, and daily scale hydrologic regimes in a large, Mediterranean climate, mountain river watershed

The dynamics that move wood through and out of watersheds are complex and not yet fully understood. In this study, climatic conditions, hydrologic responses, and watershed processes were explored to better understand variations in wood export using aerial imagery, event-based video monitoring, and field measurements from the 1097km2 mountainous Mediterranean climate North Yuba River, California, watershed and its reservoir near the downstream outlet. Over a 30-year study period, 198\\5–2014, volumetric estimates of annual wood export into the reservoir, available for a subset of years, were used to investigate watershed-scale wood export dynamics. Variations in annual peak discharge explained 79% of the variance in interannual wood export, with 84% of total observed wood export (ca. >10,000m3 of wood per event) delivered by three discharge events of 19-year, 21.5-year, and 60-year flood recurrence intervals. Continuous video monitoring conducted during snowmelt season periods in 2010 and 2011 yielded wood discharge observations at minima 15% of statistical bankfull flow, while maximum daily discharge explained 55% of observed daily wood piece variation. No statistically significant wood discharge differences were found in snowmelt season observations, likely because of domination of the hydrograph by diurnal pulses within the seasonal cycle. A conceptual model and functional framework are introduced in support of a watershed-scale explanation of wood export, transport, and storage processes applicable to large, Mediterranean-climate, mountain watershed settings.

Featured Collection Introduction: Open Water Data Initiative

Featured Collection Introduction: Open Water Data Initiative

An assessment of engineered log jam structures in response to a flood event in an upland gravel‐bed river

AbstractEngineered log jams (ELJs) are employed to address river restoration goals and a range of river management problems including coarse sediment movement. In the Bowmont Water, a dynamic wandering gravel‐bed river in the Scottish Borders, 33 previously untested ELJs primarily designed to capture and store coarse sediment, were installed on a trial basis. Using repeated topographical surveys and field observations, the performance of the ELJs in response to a 5–10 year recurrence interval flood that occurred on the 25 September 2012 was evaluated at two reaches with catchment areas of 28 km2 and 57 km2. Three of the structures were damaged due to scour of surrounding material that exposed the pile anchors and all the timbers of one structure were completely displaced downstream. Sixteen structures induced geomorphic responses and only four induced significant deposition (>0.3 m) above that which would occur naturally within the adjacent active gravel bar deposition zones. The placement in gravel bars, minor channel blockage ratio created by the structures and their porous nature limited the hydraulic interference and in turn geomorphic responses. Therefore the ELJ placement goal of increasing sediment storage was not fully met. This study contributes to the empirical evidence base for ELJ performance evaluation of different designs in a range of physiographic settings needed to validate performance and refine design. Using these initial findings and knowledge gained from other studies, recommendations for improving the design and placement strategy are proposed. Copyright © 2016 John Wiley & Sons, Ltd.

Dependence of mean and peak streamflow on basin area in the conterminous United States

Basin area is the primary control on both mean and peak streamflows, but relationships vary with regional meteorological conditions. Rich historical data sets permit deduction of these relationships for most areas of the United States, revealing both expected and unexpected correlations. On log-log plots, mean flows for most basins with >75 cm/y rainfall have unit slopes, with the y-intercept approximating the mean annual runoff. Lower slopes characterize regions where runoff is greatest at high topographic elevations, or where significant withdrawals for irrigation occur at lower elevations. Peak flows also correlate strongly with basin area, but the regressions for most regions have slopes ranging from 0.4 to 0.9, and y-intercepts that increase with increasing flood recurrence interval. The slopes on these log-log plots for peak flows are highest in cool regions with low sunshine and low evapotranspiration, and lowest where sunshine is abundant, evapotranspiration is high, and small convective storm cells are common. Effects of relief are small and inconsistent. Peak flows of small watersheds are huge compared to their mean flows, commonly being several thousand times greater, particularly in the USA midcontinent where the slopes for peak flows are low.

Effects of a ‘natural’ flood event on the riparian ecosystem of a regulated large‐river system: the 2011 flood on the Missouri River, USA

AbstractFlow regulation has significantly altered hydrological, geomorphic, and ecological processes on the Missouri River. Cumulative effects are evident in declines in cottonwood (Populus deltoides) recruitment and in altered forest age structure and composition. Record runoff in 2011 exceeded reservoir capacity on the Upper and Middle Missouri, leading to a 500‐year recurrence interval flood in terms of volume, with the highest peak discharge in 59 years and flood durations of up to 3 months. We assessed the effects of this ‘large infrequent disturbance’ by comparing pre‐flood (2006–2009) to post‐flood (2012) changes in riparian forests along two unchannelized segments of the Missouri River. Live shrub and tree density declined sharply within young forest stands (<30 years). Higher proportions of non‐native (Elaeagnus angustifolia) and upland (Juniperus virginiana) trees showed evidence of recent mortality than did the native cottonwood. Sandbar area increased sharply from 2006 to 2012 and area of young forests declined, with particularly sharp declines in sapling stands that had established following the previous post‐dam record flow releases in 1997. Cottonwood recruitment was widespread in 2012, but nearly all seedling patches occurred on sandbars in the active channel rather than on overbank sites, with moderately high (61–77%) seedling mortality over 2012–2013. Physical and operational constraints within the regulated Missouri River limited the restorative effects of the 2011 flood and will likely limit future forest recovery. Process‐based riparian restoration would require restoring flow and sediment regimes that more closely mimic historical conditions, as well as overcoming the physical legacies of decades of flow regulation. Copyright © 2015 John Wiley & Sons, Ltd.

Coupling channel evolution monitoring and RFID tracking in a large, wandering, gravel-bed river: Insights into sediment routing on geomorphic continuity through a riffle–pool sequence

Bedload transport and bedform mobility in large gravel-bed rivers are not easily monitored, especially during floods. Large reaches present difficulties in bed access during flows for flow measurements. Because of these logistical issues, the current knowledge about bedload transport processes and bedform mobility lacks field-based information, while this missing information would precisely match river management needs. The lack of information linking channel evolution and particle displacements is even more striking in wandering reaches. The Durance River is a large, wandering, gravel-bed river (catchment area: 14,280km2; mean width: 240m), located in the southern French Alps and highly impacted by flow diversion and gravel mining. In order to improve current understanding of the link between sediment transport processes and river bed morphodynamics, we set up a sediment particle survey in the channel using Radio Frequency Identification (RFID) tracking and topographic surveys (GPS RTK and scour chains) for a 4-year recurrence interval flood. By combining topographic changes before and after a flood, intraflood erosion/deposition patterns from scour chains, differential routing of tracer particles, and spatial distribution of bed shear stress through a complex reach, this paper aims to define the critical shear stress for significant sediment mobility in this setting. Gravel tracking highlights displacement patterns in agreement with bar downstream migration and transport of particles across the riffle within this single flood event. Because no velocity measurements were possible during flood, a Telemac three-dimensional model helped interpret particle displacements by estimating spatial distribution of shear stresses and flow directions at peak flow. Although RFID tracking in a large, wandering, gravel-bed river does have some technical limitations (burial, recovery process time-consuming), it provides useful information on sediment routing through a riffle–pool sequence.

An Evaluation of the Stream Simulation Culvert Design Method in Washington State

AbstractStream simulation has become an increasingly common culvert design method around the world. It is based on the assumption that geologic and hydraulic conditions in natural channels define passage characteristics for migrating fish and that water crossing structures that imitate these conditions can then achieve those same passage characteristics. This study expands on an initial evaluation of 19 culverts in 2003 to 50 culverts and includes methods and analyses comparing hydraulic characteristics based on cross sections, profile variation, and bed texture between each culvert and its paired reference reach situated in an adjacent section of the natural channel of each stream. Taken as a group, these culverts simulate bed texture, 100‐year recurrence interval flood velocity and 2‐year flood width but did not simulate thalweg complexity or other hydraulic metrics. Culvert span, relative to the bankfull width of the stream, does not by itself determine whether the culvert simulates the reference reach. Of the 50 culverts, many of which experienced record floods, only one showed significant bed degradation. Copyright © 2014 John Wiley & Sons, Ltd.

Quantifying flooding regime in floodplain forests to guide river restoration

Determining the flooding regime needed to support distinctive floodplain forests is essential for effective river conservation under the ubiquitous human alteration of river flows characteristic of the Anthropocene Era. At over 100 sites throughout the Connecticut River basin, the largest river system in New England, we characterized species composition, valley and channel morphology, and hydrologic regime to define conditions promoting distinct floodplain forest assemblages. Species assemblages were dominated by floodplain-associated trees on surfaces experiencing flood durations between 4.5 and 91 days/year, which were generally well below the stage of the two-year recurrence interval flood, a widely-used benchmark for floodplain restoration. These tree species rarely occurred on surfaces that flooded less than 1 day/year. By contrast abundance of most woody invasive species decreased with flooding. Such flood-prone surfaces were jointly determined by characteristics of the hydrograph (high discharges of long duration) and topography (low gradient and reduced valley constraint), resulting in increased availability of floodplain habitat with increasing watershed area and/or decreasing stream gradient. Downstream mainstem reaches provided the most floodplain habitat, largely associated with low-energy features such as back swamps and point bars, and were dominated by silver maple (Acer saccharinum). However, we were able to identify a number of suitable sites in the upper part of the basin and in large tributaries, often associated with in-channel islands and bars and frequently dominated by sycamore (Platanus occidentalis) and flood disturbance-dependent species. Our results imply that restoring flows by modifying dam operations to benefit floodplain forests on existing surfaces need not conflict with flood protection in some regional settings. These results underscore the need to understand how flow, geomorphology, and species traits interact to produce characteristic patterns of floodplain vegetation, and that these interactions should form the basis of effective river restoration and conservation.

The efficacy of stream power and flow duration on geomorphic responses to catastrophic flooding

Geomorphologists have long studied the impacts of extreme floods, yet the association between the magnitude of flow parameters (discharge, velocity, shear stress, or stream power) and resulting geomorphic effectiveness remains vague and non-deterministic. Attempts have been made to include flow duration and total expenditure of stream power, in combination with peak unit stream power, as important variables, but there has been minimal exploration of this hydraulic combination. Taking advantage of Tropical Storm Irene's rapid track through eastern Vermont (USA) in late summer 2011, this paper presents the array of geomorphic responses to a short duration (time to peak of <8h) but high magnitude flood that was the twentieth century flood of record for numerous watersheds. We present herein the geomorphic imprint of Tropical Storm Irene flooding within a larger context of fluvial theory concerning the role of, and trade-off between, the magnitude of energy expenditure during a flood and its duration. Focusing on a detailed field effort within the 187-km2 Saxtons River basin in southeastern VT, augmented by select sites along the adjacent lower gradient Williams River (291-km2), we elucidate (1) the geomorphic effects of a short duration flood in a humid, well-vegetated landscape; (2) the relationship between geomorphic response and (a) peak stream power, (b) total stream power, and (c) flow duration of stream power above a critical threshold; and (3) the spatial variation of geomorphic effects relative to reach-scale geologic and geomorphic controls. Flooding associated with Tropical Storm Irene ranged from the 1000year recurrence interval (RI) flood (based on Weibull flood frequency analysis) to the 300year RI flood (log Pearson Type III). Discharges spawned a peak unit stream power of 712W/m2 (Saxtons River) and 361W/m2 (Williams River), with total energy expenditure throughout the event of ~16,000×103 and 15,000×103J, respectively. For the Saxtons River, channel widening was spatially infrequent and limited in magnitude; however, other geomorphic effects were profound (1) the entrainment, transport, and deposition of extremely coarse material; (2) stripping of floodplain surfaces; (3) channel avulsions and incision into Pleistocene-aged material; and (4) deposition of coarse material across floodplains. Based on our extensive field data and hydrologic/hydraulic analyses, we contend that short duration, high energy flows can have profound sedimentological effects but have limited erosive, channel widening impacts. Gravel entrainment and deposition of a catastrophic nature can certainly occur under these flow regimes, but the impacts of these extreme flows on channel geometry may have limited expression.

Short-term geomorphic analysis in a disturbed fluvial environment by fusion of LiDAR, colour bathymetry and dGPS surveys

ObjectiveEstimating river's underwater bed elevations is a necessary but challenging task. The objective of this study is to develop a revised approach to generate accurate and detailed Digital Terrain Models (DTMs) of a river reach by merging LiDAR data for the dry area, with water depth indirectly derived from aerial imagery for wet areas. MethodsThis approach was applied along three sub-reaches of the Brenta River (Italy) before and after two major flood events. A regression model relating water depth and intensity of the three colour bands derived from aerial photos, was implemented. More than 2400 in-channel depth calibration points were taken using a differential Global Positioning System (dGPS) along a wide range of underwater bed forms. ResultsThe resulting DTMs closely matched the field-surveyed bed surface, and allowed to assess that a 10-year recurrence interval flood generated a predominance of erosion processes. Erosion dominated in the upper part of the study segment (−104,082m3), whereas a near-equilibrium is featured on the lower reach (−45,232m3). The DTMs allowed the detection of processes such as riffle–pool downstream migration, and the progressive scour of a pool located near a rip-rap. ConclusionThe presented approach provides an adequate topographical description of the river bed to explore channel adjustments due to flood events. PracticeCombining colour bathymetry and dGPS surveys proved to represent a useful tool for many fluvial engineering, ecology, and management purposes. ImplicationsThe proposed approach represents a valuable tool for river topography description, river management, ecology and restoration purposes, when bathymetric data are not available.

Sensitivity of a hydraulic model to channel erosion uncertainty during extreme flooding

Recent research into flood modelling has primarily concentrated on the simulation of inundation flow without considering the influences of channel morphology. River channels are often represented by a simplified geometry that is implicitly assumed to remain unchanged during flood simulations. However, field evidence demonstrates that significant morphological changes can occur during floods to mobilize the boundary sediments. Despite this, the effect of channel morphology on model results has been largely unexplored. To address this issue, the impact of channel cross-section geometry and channel long-profile variability on flood dynamics is examined using an ensemble of a 1D–2D hydraulic model (LISFLOOD-FP) of the ~1 : 2000 year recurrence interval floods in Cockermouth, UK, within an uncertainty framework. A series of simulated scenarios of channel erosional changes were constructed on the basis of a simple velocity-based model of critical entrainment. A Monte-Carlo simulation framework was used to quantify the effects of this channel morphology together with variations in the channel and floodplain roughness coefficients, grain size characteristics and critical shear stress on measures of flood inundation. The results showed that the bed elevation modifications generated by the simplistic equations reflected an approximation of the observed patterns of spatial erosion that enveloped observed erosion depths. The effect of uncertainty on channel long-profile variability only affected the local flood dynamics and did not significantly affect the friction sensitivity and flood inundation mapping. The results imply that hydraulic models generally do not need to account for within event morphodynamic changes of the type and magnitude of event modelled, as these have a negligible impact that is smaller than other uncertainties, e.g. boundary conditions. Instead, morphodynamic change needs to happen over a series of events to become large enough to change the hydrodynamics of floods in supply limited gravel-bed rivers such as the one used in this research.

Variability of soil properties in different flood-risk zones and link with hydroclimatic changes (Southern Québec, Canada)

We have analyzed and compared concentrations of soil organic carbon (SOC), soil total nitrogen (STN) and other soil properties in different inundated areas based on governmental flood risk maps (recurrence intervals of 0–20years and 20–100years). In this case study, a paired-site approach was used to determine the impact of periodic floods on soil properties (organic carbon, total nitrogen, pH, cation exchange capacity (CEC), phosphorus, potassium and grain size particles) in riverine areas located in the mid section of the Saint-François River (southern Québec). Two specific flood-risk zones, i.e. Frequent flood zones (FFz) and Moderate flood zones (MFz), in connection with the flood recurrence intervals (20-year vs 100-year flood) were considered to evaluate the variability of different soil properties. Sampling sites located outside (NFz: No-flood zones) of the two flood-risk zones were also selected for a cross-comparison. In this study area of the Saint-François river catchment, an increase in the flood rate was noted over the last few decades, especially from 1970 to 2000, which has the effect of modifying the hydrogeomorphic conditions and pedogenetic processes. The results show that alluvial soils subject to frequent flooding (FFz) have a lower concentration in soil organic carbon (SOC%) and soil total nitrogen (STN%) than soils in non-inundated zones. The average values obtained for surface horizons (0–20cm depth) range from 1.79±0.83 to 2.16±1.28 (SOC%) and from 0.14±0.05 to 0.17±0.07 (STN%) for soils in frequent flood zones (FFz), while for soils in no-flood zones (NFz), the values range from 5.17±2.99 and 3.82±1.88 (SOC%), and from 0.30±0.28 to 0.24±0.10 (STN%). The t-student tests conducted among the various zones confirm this trend of depletion in soil organic carbon and soil total nitrogen for the soils found in the Frequent Flood Zones (FFz). A lower concentration of nutrients was also noted for the soils affected by floods. Soil acidity is higher in the no-flood zones, which could be attributed to the acidifying input of the litter, which is more abundant and better formed (LFH layers) in the no-flood forest zones. The soil textural matrices are relatively similar among the three zones under study, although the textures are generally coarser for the soils outside the flood zones. Lastly, if the current hydrological conditions are maintained (i.e. an increase in the flood rate), one can expect a nutrient storage depletion that could restrict the regeneration of forest stands and the vitality of riverside ecosystems.

Spatial patterns and temporal changes of heavy metal distributions in river sediments in a region with multiple pollution sources

The main purpose of this study was to evaluate temporal and regional variability of contamination by heavy metals (HMs) in river sediments using their enrichment factors (EFs) and benchmarking according to sediment quality guidelines (SQGs). The Zlin region in the Czech Republic (Morava and Drevnice River basins) represents a model area where several regionally specific ecological risk assessment studies have recently been conducted with a focus on organic pollution, eco-toxicity, geological, and geochemical characteristics. Four consecutive sediment sampling campaigns were undertaken in spring and autumn 2005–2006. Aqua-regia leachable content of Cd, Co, Cr, Cu, Ni, Pb, Sb, V, and Zn in surface sediments from 14 sites was analyzed using ICP-MS, and Hg content was analyzed using AMA-254 analyzer. EFs were calculated to identify the human impact on pollution in the area. Comparisons to SGQs were conducted to identify the areas and HMs of greatest risk. Calculation of EFs contributed to the effective clustering of HMs. Median EFs of Co, Ni, and V ranged from 0.9 to 1.4 at all sites indicating concentrations very close to natural geological background levels. There was greater enrichment at locally polluted sites, the highest in the cases of Cd, Sb, Hg, and Cr. Widespread influence of diffuse HM sources (traffic, agriculture, and urban wastes) was apparent from elevated concentrations of Pb, Cu, and Zn at all sites. EF values also helped to identify the greatest temporal changes and shifts in HMs contamination between adjacent sites caused by 50-year recurrence interval floods in early spring 2006. The impact was most apparent in downstream sites; namely directly below the confluence of the two major rivers. The overall contamination of HMs in the region was classified as low-to-moderate with significantly contaminated sub-areas. The study showed relatively stable spatial distributions of HMs, indicating potential sources of pollution. Cu was identified as the HM of greatest risk. The study emphasizes the necessity of considering both environmental circumstances and background HM occurrence to prevent misinterpretation of the pollution situation. The use of EFs which include grain size proxy normalization and HM background levels, along with the comparison of the detected concentrations to SQGs, proved an efficient way to identify hazardous contamination from anthropogenic sources.

Implications of Environmental Considerations for Floods in Pakistan

World is making significant progress in different fields meanwhile facing plethora of natural and manmade disasters. Disasters provide opportunity in positive realm meanwhile disasters setback advances. Developing countries are more prone to disasters because of more physical, social, economic and environmental vulnerabilities. Pakistan is facing different natural and man-made disasters since few decades. World major disasters comprises of Pakistan's 2005 earthquake and 2010 floods as well. Lesson learnt from these major disasters clearly depicts that many factors like lack of institutional framework, preparedness plan and other shortcomings leads to disaster which have adverse impact on society. Past profile of major disasters also indicated that these disasters have adverse impact on country economic conditions like fiscal deficit affected, GDP falls so it is clear that environmental issues has direct linkage with economic vulnerability. Disasters like floods not only affect people but environment too. The relationship between environment and disaster is interdependent, Manmade hostile environmental activities like pollution, deforestation, water erosion, salinity, industrial wastes leads to disastrous conditions and disaster has adverse impact on environment like environmental degradation, diseases outbreak, poor sanitation conditions and ecological disturbance. The purpose of this study is to identify recurrence interval of floods in Pakistan with subsequent environmental problems leads to degradation and also resilience of environmental considerations in response to floods in Pakistan.

FLOOD INUNDATION MAPPING FOR INTEGRATED FLOODPLAIN MANAGEMENT: UPPER MISSISSIPPI RIVER SYSTEM

ABSTRACTNatural hydrogeomorphic characteristics and hydrologic alterations are important ecological drivers, and hydrology is also a common ecological, flood control and navigation system indicator. Hydrologic characteristics change dramatically from one end of the Upper Mississippi River System to the other, and hydraulic characteristics also differ spatially across the river channels and floodplain in response to dams, levees and diversions. Low flow surface water spatial change in response to navigation and flood control has been well known for many years, but little information was available on the spatial distribution of frequent floods. The flow frequency data presented here were developed to better estimate contemporary floods after historic flooding in 1993. Flood stage estimates are enhanced in GIS to help quantify and map potential floodplain inundation for more than 1000 river miles on the Upper Mississippi and Illinois Rivers. Potential flood inundation is mapped for the 50% to 0.2% annual exceedance probability flood stage (i.e. 2‐ to 500‐year expected recurrence interval flood) and also for alternative floodplain management scenarios within the existing flood protection infrastructure. Our analysis documents: (i) impoundment effects, (ii) a hydrologic gradient within the navigation pools that creates repeating patterns of riverine, backwater and impounded aquatic habitat conditions, (iii) potential floodplain inundation patterns for over 2 million acres and (iv) several integrated floodplain management scenarios. Extreme flood events are more common in recent decades, and they are expected to continue to occur at greater frequency in response to climate change. Floodplain managers can use the results presented here to help optimize land management and flood damage reduction on the Upper Mississippi River System. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

The influence of paleofloods on archaeological settlement patterns during A.D. 1050–1170 along the Colorado River in the Grand Canyon, Arizona, USA

Abstract Excavations at four archaeological sites consisting of the material remains of A.D. 1050–1170 era farmers along the Colorado River in Grand Canyon National Park, yield geomorphic information used to address questions related to settlement patterns. Archaeological excavation units, test pits, feature fill, and natural exposures contain sediments used to interpret geomorphic history that can, in turn, shed light on archaeological site selection in a challenging environment. The Grand Canyon experiences dramatic geomorphic events such as catastrophic floods and destructive debris flows that are preserved in the stratigraphic record, and can be used to understand cultural/landscape interactions. By combining new geomorphic, stratigraphic, and archaeological data collected during recent excavations with results from previous geomorphic and sediment transport studies, observed trends can be interpreted regarding the possible influence of paleofloods on past settlement patterns. For example, at each of the four sites, reconstructed paleoflood elevations (from existing HEC-RAS virtual shorelines), flood recurrence intervals, site layout, and site stratigraphy/geomorphic setting suggests a temporal trend in site location. The two early sites (Early Pueblo II period: A.D. 1050–1080) contain habitation features located above the approximately 6–8 year high flood (3500 cubic meters per second [cms]) recurrence interval; larger floods (4800 to 5900 cms) of a longer recurrence interval between 40 and 80 years inundate these features. The two later sites in the sample (Late Pueblo II; A.D. 1080–1170) contain habitation features located well above the 40–80 year recurrence high flows. We suggest that early farmers (Early Pueblo II period: A.D. 1050–1080) may not have had adequate experience with flood magnitudes and frequencies and therefore their habitation structures were located in risk-prone areas relatively close to the river. Later habitations (Late Pueblo II; A.D. 1080–1170) were positioned in more protected areas further from the river, perhaps reflecting an acquired knowledge of river dynamics. These trends, although currently based on a limited data set, provide insights into site selection decisions and settlement patterns of early farmers along the Colorado River through Grand Canyon.