Assessing the price effects of flood hazard disclosure under the California natural hazard disclosure law (AB 1195)

This study uses hedonic analysis to estimate the effects of flood hazard disclosure under the 1998 California Natural Hazard Disclosure Law (AB 1195) on property values throughout California. It finds that the average floodplain home sold for 4.2% less than a comparable non-floodplain home following AB 1195 while before that law there was no significant price differential. The introduction of interaction terms indicates that the magnitude of the price reduction due to AB 1195 varies positively with Hispanic population share. An average floodplain home in a half-Hispanic neighbourhood saw a $12 324 negative capitalization due to AB 1195, while that amount was only $2191 for a neighbourhood with 10% Hispanic residents. Results suggest that, in particular, homebuyers in Hispanic communities are better disclosed to under AB 1195 than they were under the National Flood Insurance Program (NFIP), which was the primary policy regulating flood disclosure in California prior to passage of AB 1195.     

Assessing Effectiveness of National Flood Policy Through Spatiotemporal Monitoring of Socioeconomic Exposure1

Abstract: After a century of evolving flood policies, there has been a steady increase in flood losses, which has partly been driven by development in flood prone areas. National flood policy was revised in 1994 to focus on limiting and reducing the amount of development inside the 100‐year floodplain, with the goal of decreasing flood losses, which can be measured and quantified in terms of population and property value inside the 100‐year floodplain. Monitoring changes in these measurable indicators can inform where and how effective national floodplain management strategies have been. National flood policies are restricted to the spatial extent of the 100‐year floodplain, thus there are no development regulations to protect against flooding adjacent to this boundary. No consistent monitoring has been undertaken to examine the effect of flood policy on development immediately outside the 100‐year floodplain. We developed a standardized methodology, which leveraged national data to quantify changes in population and building tax value (exposure). We applied this approach to counties in North Carolina to assess (1) temporal changes, before and after the 1994 policy and (2) spatial changes, inside and adjacent to the 100‐year floodplain. Temporal results indicate the Piedmont and Mountain Region had limited success at reducing exposure within the 100‐year floodplain, while the Coastal Plain successfully reduced exposure. Spatially, there was a significant increase in exposure immediately outside the 100‐year floodplain throughout North Carolina. The lack of consistent monitoring has resulted in the continuation of this unintended consequence, which could be a significant driver of increased flood losses as any flood even slightly higher than the 100‐year floodplain will have a disproportionately large impact since development is outside the legal boundary of national flood policy.     

PERCEIVED WATER QUALITY AND THE VALUE OF SEASONAL HOMES1

ABSTRACT: The impact of degraded water quality on the value of seasonal homes adjacent to St. Albans Bay on Lake Champaign in northern Vermont is estimated using hedonic price functions. The Value of properties located adjacent to the bay are depressed by about 20 percent, or $4,500 on average, compared with similar nearby properties on the larger but cleaner lake. Water quality degradation resulted in decressed property values of approximately two million dollars in the area surrounding the Bay.     

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.     

ECONOMIC VALUATION OF RIPARIAN BUFFER AND OPEN SPACE IN A SUBURBAN WATERSHED1

Abstract: This study evaluates the economic value of riparian buffers and open space in a suburban watershed through two nonmarket valuation methods. A contingent valuation survey was implemented in the Dardenne Creek watershed, a suburban watershed of the St. Louis metropolitan area in Missouri, to evaluate the residents' perceptions of and willingness to pay (WTP) for adopting riparian buffers and preserving farmland in a hypothetical real estate market. A hedonic pricing model based on actual sale prices of homes in the watershed was applied to estimate the market value of open space and other environmental conditions such as flood zone and stream proximity in the study area. The results showed that residents' WTP was consistent with the economic values of open space and proximity to streams embedded in existing home prices. Through a better understanding of residents' perceptions and values, riparian buffer and open space programs can be designed and promoted to achieve greater implementation success and environmental benefit.     

A PROPOSED METHOD OF EVALUATING FLOOD DAMAGES TO HISTORIC HOMES - AN EXTERNALITY APPROACH1

ABSTRACT: Traditional procedures for evaluating flood damages to residential dwellings do not reflect intrinsic values when applied to historic homes. Such structures are worth more than that determined by using depth-damage curves provided by insurance companies who assess damage values based upon current labor and material costs. The evaluation of the worth of a historic home and subsequent damages due to inundation can be regarded as a problem of externalities. An assessment technique reflecting historic amenities or what has been termed replication cost is proposed in this paper. Replication costs would have widespread use not only in solving flood dammage problems, but also in any study where historic entities are subject to damages from catastrophies such as hurricanes, soil and beach erosion, and increasing urbanization. If adopted as a technique, it would enhance and preserve the ever-decreasing enclaves of historic homes and neighborhoods.     

Demonstrating Floodplain Uncertainty Using Flood Probability Maps1

Abstract: The U.S. Federal Emergency Management Agency (FEMA) flood maps depict the 100‐year recurrence interval floodplain boundary as a single line. However, because of natural variability and model uncertainty, no floodplain extents can be accurately defined by a single line. This article presents a new approach to floodplain mapping that takes advantage of accepted methodologies in hydrologic and hydraulic analysis while including the effects of uncertainty. In this approach, the extents of computed floodplain boundaries are defined as a continuous map of flood probabilities, rather than as a single line. Engineers and planners can use these flood probability maps for viewing the uncertainty of a floodplain boundary at any recurrence interval. Such a flood probability map is a useful tool for visualizing the uncertainty of a floodplain boundary and represents greater honesty in engineering technologies that are used for flood mapping. While institutional barriers may prevent adoption of such definitions for use in graduated flood insurance rates (as most other insurance industries use to account for relative risks), the methods open the door technically to such a reality.     

Evaluating the effects of local floodplain management policies on property owner behavior

Floodplain management programs have been adopted by more than 85% of local governments in the nation with designated flood hazard areas. Yet, there has been little evaluation of the influence of floodplain policies on private sector decisions. This article examines the degree to which riverine floodplain management affects purchase and mitigation decisions made by owners of developed floodplain property in ten selected cities in the United States. We find that the stringency of such policies does not lessen floodplain property buying because of the overriding importance of site amenity factors. Indeed, flood protection measures incorporated into development projects appear to add to the attractiveness of floodplain location by increasing the perceived safety from the hazard. Property owner responses to the flood hazard after occupancy involve political action more often than individual on-site mitigation. Floodplain programs only minimally encourage on-site mitigation by the owner because most owners have not experienced a flood and many are unaware of the flood threat. It is suggested that floodplain programs will be more effective in meeting their objectives if they are directed at intervention points earlier in the land conversion process.     

Impact of floodplain and Stage 0 stream restoration on flood attenuation and floodplain exchange during small frequent storms

River flooding impacts human life and infrastructure, yet provides habitat and ecosystem services. Traditional flood control (e.g., levees, dams) reduces habitat and ecosystem services, and exacerbates flooding elsewhere. Floodplain restoration (i.e., bankfull floodplain reconnection and Stage 0) can also provide flood management, but has not been sufficiently evaluated for small frequent storms. We used 1D unsteady Hydrologic Engineering Center's River Analysis System to simulate small storms in a 5 km-long, second-order generic stream from the Chesapeake Bay watershed, and varied % channel restored (starting at the upstream end), restoration location, restoration bank height (distinguishes bankfull from Stage 0 restoration), and floodplain width/Manning's n. Stream restoration decreased (attenuated) peak flow up to 37% and increased floodplain exchange by up to 46%. Floodplain width and % channel restored had the largest impact on flood attenuation. The incremental effects of new restoration projects on flood attenuation were greatest when little prior restoration had occurred. By contrast, incremental effects on floodplain exchange were greatest in the presence of substantial prior restoration, setting up a tradeoff. A similar tradeoff was revealed between attenuation and exchange for project location, but not bank height or floodplain width. In particular, attenuation and exchange were always greater for Stage 0 than for bankfull floodplain restoration. Stage 0 thus may counteract human impacts such as urbanization.     

EFFECTS OF DAM IMPOUNDMENT ON THE FLOOD REGIME OF NATURAL FLOODPLAIN COMMUNITIES IN THE UPPER CONNECTICUT RIVER1

ABSTRACT: Understanding the effects of dams on the inundation regime of natural floodplain communities is critical for effective decision making on dam management or dam removal. To test the implications of hydrologic alteration by dams for floodplain natural communities, we conducted a combined field and modeling study along two reaches in the Connecticut River Rapids Macrosite (CRRM), one of the last remaining flowing water sections of the Upper Connecticut River. We surveyed multiple channel cross sections at both locations and concurrently identified and surveyed the elevations of important natural communities, native species of concern, and nonnative invasive species. Using a hydrologic model, HEC‐RAS, we routed estimated pre‐and post‐impoundment discharges of different design recurrence intervals (two year through 100 year floods) through each reach to establish corresponding reductions in elevation and effective wetted perimeter following post‐dam discharge reductions. By comparing (1) the frequency and duration of flooding of these surfaces before and after impoundment and (2) the total area flooded at different recurrence intervals, our goal was to derive a spatially explicit assessment of hydrologic alteration, directly relevant to natural floodplain communities. Post‐impoundment hydrologic alteration profoundly affected the subsequent inundation regime, and this impact was particularly true of higher floodplain terraces. These riparian communities, which were flooded, on average, every 20 to 100 years pre‐impoundment, were predicted to flood at 100 ? 100 year intervals, essentially isolating them completely from riverine influence. At the pre‐dam five to ten year floodplain elevations, we observed smaller differences in predicted flood frequency but substantial differences in the total area flooded and in the average flood duration. For floodplain forests in the Upper Connecticut River, this alteration by impoundment suggests that even if other stresses facing these communities (human development, invasive exotics) were alleviated, this may not be sufficient to restore intact natural communities. More generally, our approach provides a way to combine site specific variables with long term gage records in assessing the restorative potential of dam removal.     

The Impact of Traffic Noise on the Values of Single-family Houses

The objective of this paper is to provide an empirical analysis of the impact traffic noise has on the values of single-family houses. Under the assumption that negative externalities are capitalized into house values, the hedonic price method is used. Issues of asymmetric information and disequilibrium are discussed and tested. Furthermore, the cost-benefit valuation has been corrected for the existence of property tax. Noise pollution was found to have a substantial negative effect on housing values. A single-family house of SEK975 000 would sell for SEK650 000 if located near a road where noise is loud, equivalent to a total discount of 30%.     

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.     

NEW DIRECTIONS IN FLOODPLAIN MANAGEMENT1

ABSTRACT: Over the last 30 years, average annual riverine flood damages have exceed $2 billion. Damages associated with the Mississippi River Flood of 1993 exceeded $12 billion and these costs do not include the non-quantifiable, human impacts of this disaster. In a report submitted to the White House in June 1994, a federal interagency floodplain management review committee proposed better ways to manage the nation's floodplains. The committee indicated that the 1993 Mississippi River flood was the result of a significant hydrometeorological event, that federal flood control efforts in the Mississippi basin had prevented nearly $20 billion in potential damages, and that, in spite of federal flood damage reduction efforts, throughout the nation people and property remain at risk to inevitable future flooding. It recommended that the division of decision and cost-sharing responsibilities among federal, state and local governments be more clearly defined, and that the nation adopt a strategy of, sequentially, avoiding inappropriate use of the flood-plain, minimizing vulnerability to damage through both nonstruc-tural and structural means, and mitigating damages as they occur. The report did not call for abandonment of human use of the flood-plain but argued for full consideration of the economic, social and environmental costs and benefits of all future floodplain activity.     

Assessing flood mitigation,management, and enforcement using insurance data,California and the USA

Previous research found that National Flood Insurance Program (NFIP) premiums collected in some U.S. states, including California, have far exceeded damage payments. However, this finding raises the question of whether such an imbalance represents systematically good flood management or, instead, merely short-term hydrologic good luck. This study investigated patterns in flood losses on structures that pre-date and post-date the first available flood maps (“pre-Flood Insurance Rate Map [FIRM]” vs. “post-FIRM”) in California, several peer states, and nationwide. California has a larger inheritance of pre-FIRM structures than the national average, apparently reflecting development during the latter half of the 20th Century but before most Federal Emergency Management Agency (FEMA) flood maps. Pre-FIRM properties are a disproportionate cost burden on the system, and the number of pre-FIRM policies has declined over time, but only slowly. Local patterns in pre-FIRM claims suggest targeted areas for enhanced mitigation efforts, including buyouts. Conversely, we find that claims on post-FIRM policies are a reasonable metric of good floodplain management and enforcement, and California's 38% of post-FIRM policies generated just 24% of the state's NFIP claims. Local “post-FIRM claim hotspots” suggest areas to examine more closely. California continues to be a net payer into the National Flood Insurance Program, with $102 million in payouts 2009–2018 versus $2.3 billion in premiums collected, or 4.5 cents of premiums collected for every dollar of premiums. In California, its peer states, and nationwide, future management of flood risk depends on: (1) continued investment in flood control and mitigation of existing floodplain structures, and (2) prudent planning and limitations on new floodplain and coastal development.     

A Framework to Develop Nationwide Flooding Extents Using Climate Models and Assess Forecast Potential for Flood Resilience

The methods used to simulate flood inundation extents can be significantly improved by high‐resolution spatial data captured over a large area. This paper presents a hydraulic analysis methodology and framework to estimate national‐level floodplain changes likely to be generated by climate change. The hydraulic analysis was performed using existing published Federal Emergency Management Agency 100‐year floodplains and estimated 100‐ and 10‐year return period peak flow discharges. The discharges were estimated using climate variables from global climate models for two future growth scenarios: Representative Concentration Pathways 2.6 and 8.5. River channel dimensions were developed based on existing regional United States Geological Survey publications relating bankfull discharges with channel characteristics. Mathematic relationships for channel bankfull topwidth, depth, and side slope to contributing drainage area measured at model cross sections were developed. The proposed framework can be utilized at a national level to identify critical areas for flood risk assessment. Existing hydraulic models at these “hot spots” could be repurposed for near–real‐time flood forecasting operations. Revitalizing these models for use in simulating flood scenarios in near–real time through the use of meteorological forecasts could provide useful information for first responders of flood emergencies.     

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.     

A Faster and Economical Approach to Floodplain Mapping Using Soil Information

Flood inundation maps play a key role in assessment and mitigation of potential flood hazards. However, owing to high costs associated with the conventional flood mapping methods, many communities in the United States lack flood inundation maps. The objective of this study is to develop and examine an economical alternative approach to floodplain mapping using widely available soil survey geographic (SSURGO) database. In this study, floodplain maps are developed for the entire state of Indiana, and some counties in Minnesota, Wisconsin, and Washington states by identifying flood‐prone soil map units based on their attributes. For validation, the flood extents obtained from SSURGO database are compared with the extents from other floodplain maps such as the Federal Emergency Management Agency issued flood insurance rate maps (FIRMs), flood extents observed during past floods, and flood maps derived using digital elevation models. In general, SSURGO‐based floodplain maps (SFMs) are largely in agreement with other flood inundation maps. Specifically, the floodplain extents from SFMs cover 78‐95% area compared to FIRMs and observed flood extents. Thus, albeit with a slight loss in accuracy, the SSURGO approach offers an economical and fast alternative for floodplain mapping. In particular, it has potentially high utility in areas where no detailed flood studies have been conducted.     

THE IMPACT OF FLOODPLAIN REGULATIONS ON RESIDENTIAL LAND VALUES IN OREGON1

ABSTRACT: The impact of floodplain regulations on mean appreciation rates of residential land values was tested at six study areas in five counties in western Oregon. The study hypothesis that such regulations significantly depress appreciation rates of regulated lands relative to those of similar unregulated lands was in most cases rejected. When the hypothesis was accepted circumstances would render conclusions tenuous. The problems and issues facing this type of research are presented in case studies of two of the research study areas. The following factors challenge investigators seeking to resolve questions about the relationship between land use regulations and land values: varying degrees of stringency with which regulations are enforced; unequal assessment procedures between counties; influences external to floodplain regulations that may affect appreciation rates, including denial of permits for septic tanks, flood damages, and amenity values associated with waterfront locations; and the uncertain effect that the availability of flood insurance, which accompanies floodplain regulations, has on land values.     

FLOODPLAIN ANALYSIS,SIMPLIFIED VS. COMPLEX METHODS: A CASE STUDY1

ABSTRACT: The accurate and reliable determination of floodplains, floodway boundaries, and flood water elevations are integral requirements of Flood Insurance Studies. These studies are intended to be used for determining the flood insurance rates. Therefore, the accuracy of the water surface profiles are important. To ensure the high degree of accuracy, the HUD Flood Insurance Administration has developed standards which must be met in the analysis of water surface profiles. A somewhat less accurate study is required for the preparation of Flood Emergency Plans. As part of the flood insurance studies of eight locations in the State of North Dakota, various flood hazard and floodplain information reports were reviewed. The hydrologic and hydraulic analyses, especially the computation of the 100-year water surface profiles, were completed using both simplified and complex hydraulic computation methods. Significant differences were found (1 to 3 feet) between the profiles computed by the SCS simplified method and those computed by HEC-2 computer program. However, the floodplain boundaries determined by both methods were found to be similar. Approximate methods are recommended for rapid determination of the floodplain, floodway boundaries, and inundation area mapping, while sophisticated computer programs (HEC-2) are recommended to be used for developing areas where the 100-year flood elevation has a significant impact on the cost of land development.     

SEASONAL WATER TABLE DYNAMICS OF A SOUTHERN APPALACHIAN FLOODPLAIN AND ASSOCIATED FEN1

ABSTRACT: Appalachian mountain alluvial wetlands include floodplain forests interspersed with fens or bogs. This study evaluates the water table dynamics of an Appalachian mountain flood‐plain which includes a depressional fen. Water table wells and piezometers documented seasonal patterns of the water table and the vertical hydraulic gradient (VHG) in the floodplain and fen areas. Additional water table wells determined the potential sources of water from adjacent hillslopes to the fen area. The water table of the floodplain and the fen exhibited distinct regular seasonal fluctuations. The water table remained near the surface of the fen from late winter through late spring and dropped 20 to 80 cm during the summer between precipitation events. The water table of the floodplain fluctuated more but followed similar patterns and was typically within 40 cm of the surface during late winter and early spring months and greater than 60 cm during the summer months. The water table of the floodplain was more often correlated to precipitation than the water table of the fen. The VHG in the floodplain was highly variable although seasonal patterns of upwelling of water in fall and downwelling in winter were common. The VHG of the fen showed a consistent downwelling of water and suggested that the fen serves as a recharge area for an aquifer. Principal sources of water for the fen appeared to be precipitation, inflow from a shallow aquifer on an adjacent slope plus increased interflow associated with precipitation events from another adjacent slope. The influence of soil texture on water dynamics of the fen or floodplain was not fully ascertained but it appeared to influence horizontal flow from hillslopes and the depth of the water table in the fen.