Consequences of changing climate and land use to 100-year flooding in the Lamprey River Watershed of New Hampshire

Communities are confronting the effects of rapid development and associated land use transformation, while also dealing with the serious impacts of a changing climate. Both factors influence the frequency and magnitude of flood events. This project presents a method used to assess the flood risk associated with current and projected changes in land use and climate for a 213 square mile coastal New Hampshire watershed. The evaluation includes the use of Low Impact Development (LID) as an adaptation planning tool, and, in particular, as a means for building community resiliency in managing water resources. The hydrologic and hydraulic modeling methods used include the Army Corp of Engineers Hydraulic Engineering Center software Hydrologic Modeling System and River Analysis System, specialty tool kits, in combination with GIS. The rainfall-runoff analysis was consistent with guidance for Federal Emergency Management Agency floodplain analysis. The land use conditions were modeled for historic, current and a future climate change scenarios. Revised precipitation data from the Northeast Regional Climate Center was used with 8.5 inches for the 100-year, 24-hr design rainfall depth, a 26% increase along the seacoast area of New Hampshire as of 2011. LID strategies, including infiltration, pervious pavements, bioretention systems, and undisturbed cover, were modeled as a runoff reduction method using revised curve numbers for the distributed storage. Results of the hydrologic rainfall-runoff analysis, using increased rainfall depth, indicate a 45% increase in the 100-year flood flow at a USGS gaged location on the Lamprey River near Newmarket, NH. The increased flood flows raise the base flood elevations by an average of 2.7 feet along the 36 mile study reach. The conventional build-out scenario indicated an additional 0.3 feet increase in base flood elevation with a 4.3% flood flow increase of 11,109 cfs up from the 2005 flows of 10,649 cfs, and a 2.8% increase with the LID scenario of 10,952 cfs. Differences between conventional and LID build-out scenarios were minimal at the watershed scale because total impervious cover was low (\u3c7.5%); whereas differences were substantial in developed subwatersheds with high impervious cover. Analysis of results from three smaller developed sub basins in urban settings demonstrated that LID had substantial runoff reductions for build-out scenarios and in one instance actually reduced beyond current conditions. Conventional build-out had increases in runoff ranging from 29-36% whereas LID build-out had a range of -2-7%. This last finding is substantial in that it illustrates that LID in a redevelopment scenario can serve to reduce runoff from current conditions. The long-term watershed management implications of LID zoning as a redevelopment strategy are tremendous. It is important to note that the degree of benefit appears to increase with increasing degree of impervious cover

Assessing the Risk of 100-year Freshwater Floods in the Lamprey River Watershed of New Hampshire Resulting from Changes in Climate and Land Use

What is the coastal resource issue the project sought to address? Both the magnitude and frequency of freshwater flooding is on the rise in seacoast NH and around much of New England. In the Great Bay watershed, this is the result of two primary causes: 1) increases in impervious surface stemming from a three-to-four fold increase in developed land since 1962; and 2) changing rainfall patterns in part exemplified by a doubling in the frequency of extreme weather events that drop more than 4 inches of precipitation in less than 48 hours (Wake et al., 2011) over the same time period. Moreover, the size of the 100-year precipitation event in this region has increased 26% from 6.3 inches to 8.5 inches from the mid 1950’s to 2010 (NRCC and NRCS, 2012). One consequence is the occurrence of three 100-year floods measured on the Lamprey River at Packers Falls since 1987, and a fourth if the three days of flooding in March of 2010 had occurred instead in two days (Figure 1). Flooding events are expected to continue to increase in magnitude and frequency as land in the watershed is further developed and climate continues to change in response to anthropogenic forcing (e.g., Hayhoe et el., 2007; IPCC, 2007; Karl et al., 2009). Land use management strategies, in particular low impact development (LID) zoning requirements, are one strategy that communities can employ for increased resiliency to flooding with the greatest influence in urban environments

Assessing the Risk of 100-year Freshwater Floods in the Lamprey River Watershed of New Hampshire Resulting from Changes in Climate and Land Use

What is the coastal resource issue the project sought to address? Both the magnitude and frequency of freshwater flooding is on the rise in seacoast NH and around much of New England. In the Great Bay watershed, this is the result of two primary causes: 1) increases in impervious surface stemming from a three-to-four fold increase in developed land since 1962; and 2) changing rainfall patterns in part exemplified by a doubling in the frequency of extreme weather events that drop more than 4 inches of precipitation in less than 48 hours (Wake et al., 2011) over the same time period. Moreover, the size of the 100-year precipitation event in this region has increased 26% from 6.3 inches to 8.5 inches from the mid 1950’s to 2010 (NRCC and NRCS, 2012). One consequence is the occurrence of three 100-year floods measured on the Lamprey River at Packers Falls since 1987, and a fourth if the three days of flooding in March of 2010 had occurred instead in two days (Figure 1). Flooding events are expected to continue to increase in magnitude and frequency as land in the watershed is further developed and climate continues to change in response to anthropogenic forcing (e.g., Hayhoe et el., 2007; IPCC, 2007; Karl et al., 2009). Land use management strategies, in particular low impact development (LID) zoning requirements, are one strategy that communities can employ for increased resiliency to flooding with the greatest influence in urban environments

Oxygen minimum zone-type biogeochemical cycling in the Cenomanian-Turonian Proto-North Atlantic across Oceanic Anoxic Event 2

Highlights • We present a 5 myr record of biogeochemical cycling in a Cretaceous upwelling area. • A novel quantitative approach for the evaluation of Fe speciation proxies was applied. • Ferruginous proxy signature reflects intense chemical weathering rather than anoxia. • Water column redox conditions evolved from oxic to nitrogenous to euxinic before OAE2. • Smaller seawater nitrate inventory facilitated sedimentary H2S release and euxinia. Abstract Oceanic Anoxic Events (OAEs) in Earth's history are regarded as analogues for current and future ocean deoxygenation, potentially providing information on its pacing and internal dynamics. In order to predict the Earth system's response to changes in greenhouse gas concentrations and radiative forcing, a sound understanding of how biogeochemical cycling differs in modern and ancient marine environments is required. Here, we report proxy records for iron (Fe), sulfur and nitrogen cycling in the Tarfaya upwelling system in the Cretaceous Proto-North Atlantic before, during and after OAE2 (∼93 Ma). We apply a novel quantitative approach to sedimentary Fe speciation, which takes into account the influence of terrigenous weathering and sedimentation as well as authigenic Fe (non-terrigenous, precipitated onsite) rain rates on Fe-based paleo-redox proxies. Generally elevated ratios of reactive Fe (i.e., bound to oxide, carbonate and sulfide minerals) to total Fe (FeHR/FeT) throughout the 5 million year record are attributed to transport-limited chemical weathering under greenhouse climate conditions. Trace metal and nitrogen isotope systematics indicate a step-wise transition from oxic to nitrogenous to euxinic conditions over several million years prior to OAE2. Taking into consideration the low terrigenous sedimentation rates in the Tarfaya Basin, we demonstrate that highly elevated FeHR/FeT from the mid-Cenomanian through OAE2 were generated with a relatively small flux of additional authigenic Fe. Evaluation of mass accumulation rates of reactive Fe in conjunction with the extent of pyritization of reactive Fe reveals that authigenic Fe and sulfide precipitation rates in the Tarfaya Basin were similar to those in modern upwelling systems. Because of a smaller seawater nitrate inventory, however, chemolithoautotrophic sulfide oxidation with nitrate was less efficient in preventing hydrogen sulfide release into the water column. As terrigenous weathering and sediment flux determine how much authigenic Fe is required to generate an anoxic euxinic or ferruginous proxy signature, we emphasize that both have to be taken into account when interpreting Fe-based paleo-redox proxies