DESIGN FOR A STABLE CHANNEL IN COARSE ALLUVIUM FOR RIPARIAN ZONE RESTORATION1

Geomorphic, hydraulic and hydrologic principles are applied in the design of a stable stream channel for a badly disturbed portion of Badger Creek, Colorado, and its associated riparian and meadow complexes. The objective is to shorten the period of time required for a channel in coarse alluvium to recover from an impacted morphologic state to a regime condition representative of current watershed conditions. Channel geometry measurements describe the stream channel and the normal bankfull stage in relatively stable reaches. Critical shear stress equations were used to design a stable channel in noncohesive materials with dimensions which approximate those of less disturbed reaches. Gabion controls, spaced at approximately 300 m intervals, are recommended to help reduce the chance of lateral migration of the newly constructed channel. Controls are designed to allow for some vertical adjustment of the channel bed following increased bank stability due to revegetation. The flood plain is designed to dissipate flood flow energy and discourage multiple flood channels. The channel has approximately a 90 percent chance of remaining stable the first two years following construction, the time estimated for increased stability to occur due to revegetation.     

ANALYSIS OF UNCERTAINTY IN FLOOD PLAIN MAPPING1

ABSTRACT: Components contributing to uncertainty in the location of the flood plain fringe of a mapped flood plain are identified and examined to determine their relative importance. First-order uncertainty analysis is used to provide a procedure for quantifying the magnitude of uncertainty in the location of the flood plain fringe. Application of the procedure indicated that one standard deviation of uncertainty in flood plain inundation width was about one third of the mean computed inundation width for several flood population-flood geometry combinations. Suggested mapping criteria, which directly incorporate uncertainty estimates, are given. While these criteria are more suitable for use in developing areas than in flood plains that have had extensive development, the analysis procedure can be used to accommodate property owners who challenge the validity of estimated flood fringe boundaries. Use of uncertainty analysis in flood plain mapping should enhance the credibility of the final plan.     

COMPREHENSIVE FLOOD PLAIN MANAGEMENT1

Flooding and the susceptibility to flood damage inherent in all land uses constitute the flood hazard. Resolution of the hazard while properly recognizing flood plain environmental attributes within the context of overall community or area needs is the essence of comprehensive flood plain management. The traditional approach–flood control–has effected modification of only the flooding component of the hazard whether it be coastal or inland. Until recently Federal programs have overlooked the possibilities of modifying the susceptibility component, for which the major responsibility lies with non-Federal interests. Beginning with actions in the TVA area, the latter is now being strongly encouraged through Federal programs and actions notably the Flood Plain Management Services and Survey Programs of the Corps of Engineers, those stemming from Executive Order 11296, and those required for eligibility under the National Flood Insurance Act of 1968. Flood plain management objectives must be stated in planning, e.g., economic efficiency, reduction in threat to life and health, environmental improvement, and regional development, to permit proper evaluation of the optional means and approaches for achieving them.     

FLOOD DAMAGES IN CHANGING FLOOD PLAINS: A FORENSIC‐HYDROLOGIC CASE STUDY1

ABSTRACT: Hydraulic modification of flood plains by human activity is the primary cause of rising flood damages throughout the world. As flood‐plain hydraulic roughness increases, so does the water level for a fixed flow rate. This raises the flood damage associated with a flood of given return period, and thus, magnifies the flood risk. This article presents an approach that integrates climatic, hydrologic, and hydraulic principles and presents models to discern the probable causes of flood damage in a basin that undergoes flood‐plain development. The article documents key factors that govern flood damage and presents a case study that illustrates the principles of forensic hydrology in an impacted flood plain. The study demonstrates flood level rise caused by hydraulic alteration of a flood plain between 1969 and 1995 and apportioned the increased water level among agricultural and structural factors located in the study area.     

Rehabilitation and Flood Management Planning in a Steep,Boulder-Bedded Stream

This study demonstrates the integration of rehabilitation and flood management planning in a steep, boulder-bedded stream in a coastal urban catchment on the South Island of New Zealand. The Water of Leith, the primary stream flowing through the city of Dunedin, is used as a case study. The catchment is steep, with a short time of concentration and rapid hydrologic response, and the lower stream reaches are highly channelized with floodplain encroachment, a high potential for debris flows, significant flood risks, and severely degraded aquatic habitat. Because the objectives for rehabilitation and flood management in urban catchments are often conflicting, a number of types of analyses at both the catchment and the reach scales and careful planning with stakeholder consultation were needed for successful rehabilitation efforts. This included modeling and analysis of catchment hydrology, fluvial geomorphologic assessment, analysis of water quality and aquatic ecology, hydraulic modeling and flood risk evaluation, detailed feasibility studies, and preliminary design to optimize multiple rehabilitation and flood management objectives. The study showed that all of these analyses were needed for integrated rehabilitation and flood management and that some incremental improvements in stream ecological health, aesthetics, and public recreational opportunities could be achieved in this challenging environment. These methods should be considered in a range of types of stream rehabilitation projects.     

DETERMINANTS OF LANDOWNER'S WILLINGNESS TO PAY FOR FLOOD HAZARD REDUCTION1

ABSTRACT: Estimated benefits of flood control projects are typically limited to avoided property damages. However, the possibility that there are (1) benefits from reduced psychological stress among flood plain occupants, and (2) benefits to the community has long been recognized. A survey of landowners residing in a flood plain in Roanoke, Virginia, found that nonproperty considerations did help explain their expressed willingness to pay for flood control. Of particular importance was the respondents' concern for disruption of the community caused by possible flooding.     

Development and Operational Testing of a Super‐Ensemble Artificial Intelligence Flood‐Forecast Model for a Pacific Northwest River

Coastal catchments in British Columbia, Canada, experience a complex mixture of rainfall‐ and snowmelt‐driven contributions to flood events. Few operational flood‐forecast models are available in the region. Here, we integrated a number of proven technologies in a novel way to produce a super‐ensemble forecast system for the Englishman River, a flood‐prone stream on Vancouver Island. This three‐day‐ahead modeling system utilizes up to 42 numerical weather prediction model outputs from the North American Ensemble Forecast System, combined with six artificial neural network‐based streamflow models representing various slightly different system conceptualizations, all of which were trained exclusively on historical high‐flow data. As such, the system combines relatively low model development times and costs with the generation of fully probabilistic forecasts reflecting uncertainty in the simulation of both atmospheric and terrestrial hydrologic dynamics. Results from operational testing by British Columbia's flood forecasting agency during the 2013‐2014 storm season suggest that the prediction system is operationally useful and robust.     

EVALUATION OF URBAN STREAM CORRIDOR RESTORATION DESIGN ALTERNATIVES USING HEC-21

ABSTRACT: The rehabilitation of urban stream channels and riparian areas involves a potentially large number of design alternatives. When substantial modifications are planned, water surface profile models (e.g., HEC-2) provide a means for a thorough and efficient evaluation of many design variations. The rehabilitation of a reach of Paradise Creek, Idaho, utilized the REC-2 model to verify the appropriateness of a new channel geometry and explore the consequences of variable floodplain geometries and excavation depths. The desirability of habitat diversity, coupled with the constraints of minimized earthwork costs and adequate flow capacity, framed the floodplain design question. The final design geometry was iteratively approached using the HEC-2 model to mimic the existing channel capacity. This modeling framework produces as output computed water surface elevations for the design channel and floodplain under any discharge. Hence, the method provides the means for demonstrating that rehabilitation designs will (or will not) cause increases in flood elevations, an assessment that is generally required for project approval.     

THE EFFECT OF FLOOD PLAIN LOCATION ON PROPERTY VALUES: THREE TOWNS IN NORTHEASTERN NEW JERSEY1

ABSTRACT: The persistence of development and settlement in flood plains and continued damages from flooding, raises the question of how property owners respond to flood plain location and whether property values reflect this response. Existing studies disagree on the significance of flood hazard for property values. This study evaluates the effect of flood plain location on assessed valuation and home value in three towns in New Jersey. A t-test on mean assessed value and value of owner-occupied units at block levels showed no statistically significant variation for flood prone and nonflood prone lands. Possible explanations are that homeowners do not know or perceive the risk of living in flood plains, assessors do not incorporate flooding into assessment criteria, and the National Flood Insurance Program subsidies and broadened financial markets may equalize property values.     

DUAL PURPOSE DETENTION BASINS IN STORM WATER MANAGEMENT1

Storm water management contributes to flood hazard mitigation; but new approaches now being developed consider also the reduction in particulate pollution and stream erosion. Such approaches involve retardation of storm runoff, or detention programs of some kind, and detention basins are usually required if large storms are to be controlled. The usual concept is that future storms occurring after development should have no more adverse effect than similar storms would have had before development; but a number of different criteria are being used. If control of storms of different sizes is required, only a small amount of additional capacity is required to obtain retention of particulate pollution in the same basin. In at least three different parts of the country, such dual purpose detention basins are being required of developers. In such programs the developers bear the cost, the governmental contributions are not involved.     

MATHEMATICAL MODELING OF VEGETATIVE IMPACTS FROM FLUCTUATING FLOOD POOLS1

ABSTRACT: A flood control reservoir protects valuable developments on the downstream flood plain by storing flood waters and releasing them at a rate that will reduce the downstream damage. The water surface level of the flood pool behind the dam can fluctuate considerably during the occurrence of a large magnitude flood causing severe impacts on shoreline vegetation and water based recreation facilities located in the flood pool. A mathematical simulation model describing shoreline vegetative succession in response to flooding is presented. Plant species are grouped into ecologically similar compartments. Differential equations describing compartment intrinsic growth, intraspecies competition, interspecies competition, and other growth limiting factors are solved numerically. The model is used to evaluate the impacts of various operating policies on plant succession for a new reservoir in Central Iowa.     

FLOOD CONTROL RESERVOIR OPERATIONS UNDER ENVIRONMENTAL RESTRAINTS1

ABSTRACT: A flood control reservoir protects valuable developments on the downstream flood plain by storing flood waters and releasing them at a rate that will reduce the downstream damage. The water surface level of the flood pool behind the dam can fluctuate considerably during the occurrence of a large magnitude flood causing the inundation of trees, low vegetation, and water based recreation facilities located in those areas of the flood pool area that are normally well above the water level. The amount of damage that will occur in the upper levels of the flood storage area will depend on the depth and duration of the inundation that occurs. This, in turn, is directly related to the operating policy for the reservoir. A dynamic programming optimization model of flood control reservoir operation is presented. This model determines the reservoir operating schedule that minimizes downstream flood damages. Various constraints are added to the model to account for the environmental impacts of long periods of flood storage.     

Recovery of the Benthic Macroinvertebrate Community in a Small Stream After Long-Term Discharges of Fly Ash

Recovery of the benthic macroinvertebrate community in a small east Tennessee stream impacted by fly ash discharges from a power plant was investigated over a period of 6.5 years. The rate of recovery was greatest in the first 2 years after an initial 75% reduction in coal use led to a similar reduction in ash discharges and associated contaminants; further recovery followed after all fly ash discharges ceased. Recovery of the stream progressed through two phases. In the first phase, which lasted for approximately the first 2 years, most density and richness metrics increased considerably. In the second phase of recovery, the increases in metric values were followed by declines before fluctuating in and out of the lower reference ranges for the metrics. Detrended correspondence analyses and indicator species analyses showed that changes in species composition and community structure were ongoing throughout the second phase. Thus, the first phase was characterized by species additions, while the second phase involved species replacements and shifts in community dominants. Further recovery of the macroinvertebrate community will probably depend on additional flushing of fly ash deposits from the streambed and flood plain, because their continued presence reduces habitat quality in the stream and serves as a potential source of contaminants. Further recovery also may be limited by the availability of vagile species in nearby watersheds.     

ESTIMATING RESIDENTIAL FLOOD CONTROL BENEFITS USING IMPLICIT PRICE EQUATIONS1

ABSTRACT: An implicit price model relating residential lot value to price determining characteristics of land is developed to measure the benefits of a structural flood control project. Special attention is given to the selection of relevant price determining characteristics of residential lots. An implicit price equation is estimated for both the with and without project conditions. Flood damages are quantified through the use of a dummy variable indicating a flood plain location. The analysis shows that annual flood damages were reduced by $15,275.     

DEVELOPMENT OF A GIS‐BASED FLOOD INFORMATION SYSTEM FOR FLOODPLAIN MODELING AND DAMAGE CALCULATION1

ABSTRACT: This work presents a flexible system called GIS‐based Flood Information System (GFIS) for floodplain modeling, flood damages calculation, and flood information support. It includes two major components, namely floodplain modeling and custom designed modules. Model parameters and input data are gathered, reviewed, and compiled using custom designed modules. Through these modules, it is possible for GFIS to control the process of flood‐plain modeling, presentation of simulation results, and calculation of flood damages. Empirical stage‐damage curves are used to calculate the flood damages. These curves were generated from stage‐damage surveys of anthropogenic structures, crops, etc., in the coastal region of a frequently flooded area in Chia‐I County, Taiwan. The average annual flood damages are calculated with exceedance probability and flood damages for the designed rainfalls of 2, 5, 10, 25, 50, 100, and 200 year recurrence intervals with a duration of 24 hours. The average annual flood depth in this study area can also be calculated using the same method. The primary advantages of GFIS are its ability to accurately predict the locations of flood area, depth, and duration; calculate flood damages in the floodplain; and compare the reduction of flood damages for flood mitigation plans.     

Conceptual Framework for the National Flood Interoperability Experiment

The National Flood Interoperability Experiment is a research collaboration among academia, National Oceanic and Atmospheric Administration National Weather Service, and government and commercial partners to advance the application of the National Water Model for flood forecasting. In preparation for a Summer Institute at the National Water Center in June‐July 2015, a demonstration version of a near real‐time, high spatial resolution flood forecasting model was developed for the continental United States. The river and stream network was divided into 2.7 million reaches using the National Hydrography Dataset Plus geospatial dataset and it was demonstrated that the runoff into these stream reaches and the discharge within them could be computed in 10 min at the Texas Advanced Computing Center. This study presents a conceptual framework to connect information from high‐resolution flood forecasting with real‐time observations and flood inundation mapping and planning for local flood emergency response.     

Flood Effects on an Alaskan Stream Restoration Project: The Value of Long‐Term Monitoring1

Densmore, Roseann V. and Kenneth F. Karle, 2009. Flood Effects on an Alaskan Stream Restoration Project: The Value of Long‐Term Monitoring. Journal of the American Water Resources Association (JAWRA) 45(6):1424‐1433. Abstract: On a nationwide basis, few stream restoration projects have long‐term programs in place to monitor the effects of floods on channel and floodplain configuration and floodplain vegetation, but long‐term and event‐based monitoring is required to measure the effects of these stochastic events and to use the knowledge for adaptive management and the design of future projects. This paper describes a long‐term monitoring effort (15 years) on a stream restoration project in Glen Creek in Denali National Park and Preserve in Alaska. The stream channel and floodplain of Glen Creek had been severely degraded over a period of 80 years by placer mining for gold, which left many reaches with unstable and incised streambeds without functioning vegetated floodplains. The objectives of the original project, initiated in 1991, were to develop and test methods for the hydraulic design of channel and floodplain morphology and for floodplain stabilization and riparian habitat recovery, and to conduct research and monitoring to provide information for future projects in similar degraded watersheds. Monitoring methods included surveyed stream cross‐sections, vegetation plots, and aerial, ground, and satellite photos. In this paper we address the immediate and outlying effects of a 25‐year flood on the stream and floodplain geometry and riparian vegetation. The long‐term monitoring revealed that significant channel widening occurred following the flood, likely caused by excessive upstream sediment loading and the fairly slow development of floodplain vegetation in this climate. Our results illustrated design flaws, particularly in regard to identification and analysis of sediment sources and the dominant processes of channel adjustment.     

Application of Index Procedures to Flood Frequency Analysis in Turkey1

Abstract: This study investigates the regional analysis of annual maximum flood series of 48 stream gauging stations in the basins of the West Mediterranean Region in Turkey. The region is divided into three homogeneous subregions according to both Student‐t test and Dalrymple homogeneity test. The regional relationships of mean annual flood per unit area‐drainage area and coefficient of skew‐coefficient of variation are obtained. Two statistically meaningful relationships of the mean flood per unit area‐drainage area and a unique relationship between skewness and variation coefficients exist. Results show that the index‐flood method may be applicable to each homogenous subregion to estimate flood quantiles in the study area.     

FLOOD PLAIN MODELING1

Computer simulation of river basin hydrology has rapidly progressed from an interesting academic exercise to a practical engineering procedure of increasing utility. Mathematical models of the many interrelated processes which occur in a basin have been developed along with efficient numerical procedures for their solution. The present paper is concerned with a particular model which has been used to describe the transformation of a temporally and spatially varying rainfall into a time history of stage and discharge on a flood plain. Although developed principally as a model of the physical processes involved, it is envisioned that the model can serve as one component of an information system for flood plain planning and management. The model consists of the following elements: (i) a rainfall simulation which generates stochastic inputs to the model according to specified rainfall statistics, (ii) a catchment-runoff model which converts the rainfall to surface runoff, (iii) a flood stage model which converts the surface runoff to time histories of flood stage and discharge. The model has been used to investigate the effect of various structural flood control measures in a basin and, in particular, to establish frequency-stage information for each of these. Of particular interest in development of the model have been recurring and partially unanswered questions relative to the proper balance among availability of data for use in the model, data requirements of the model and the objectives of the outputs produced by the model.     

Does Wetland Location Matter When Managing Wetlands for Watershed‐Scale Flood and Drought Resilience?

Wetland protection and restoration strategies that are designed to promote hydrologic resilience do not incorporate the location of wetlands relative to the main stream network. This is primarily attributed to the lack of knowledge on the effects of wetland location on wetland hydrologic function (e.g., flood and drought mitigation). Here, we combined a watershed‐scale, surface–subsurface, fully distributed, physically based hydrologic model with historical, existing, and lost (drained) wetland maps in the Nose Creek watershed in the Prairie Pothole Region of North America to (1) estimate the hydrologic functions of lost wetlands and (2) estimate the hydrologic functions of wetlands located at different distances from the main stream network. Modeling results showed wetland loss altered streamflow, decreasing baseflow and increasing stream peakflow during the period of the precipitation events that led to major flooding in the watershed and downstream cities. In addition, we found that wetlands closer to the main stream network played a disproportionately important role in attenuating peakflow, while wetland location was not important for regulating baseflow. The findings of this study provide information for watershed managers that can help to prioritize wetland restoration efforts for flood or drought risk mitigation.