A statistical analysis of all available continuous hourly and 15‐minute duration rainfall records for Pennsylvania was performed to develop an updated procedure to estimate design storms. As a resuit of this study, Pennsylvania was divided into five homogeneous rainfall regions and a set of rainfall intensity‐duration curves developed for each region, for return periods of 1 to 100 years and durations ranging from 5 minutes to 24 hours. The PDT‐IDF curves were judged to be a better representation of Pennsylvania rainfall than the nationwide TP‐40 maps, particularly for storm events of 10‐years and lower return periods. The average time distribution of 24‐hour storms in Pennsylvania was found to be well represented by the SCS Type II distribution. The Corps of Engineers SPS 24‐hour distribution was found to differ appreciably from both the SCS Type H and the Pennsylvania 24‐hour storm distribution. For storm durations between 15 and 90 minutes the standard Yarnell intensity‐duration curves closely resemble Pennsylvania storm distributions.

Tonnage (T), Simmonds (S) avocado trees, and TxS crosses were evaluated for differences in chlorophyll content and maximal quantum yield of photosystem II in sun and shade-type leaves. Total chlorophyll content by area (Chl a+b ar ) ranged from 984 mg m -2 in TxS240 to 4320 mg m -2 in Simmonds. Chlorophyll a/b ratio (Chl a/b) ranged from 9.8 to 5.5 in TxS238 and TxS243, respectively. Tonnage and Simmonds had similar Chl a/b with a wide range in values found among the avocado trees tested. Shade leaves contained more Chl a, Chl b and Chl a+b wt than sun leaves. Differences in Chl a/b were insignificant or greater in shade adapted leaves for all trees except TxS238; this did not follow the expected sun/shade pattern. A low chlorophyll a/b ratio indicates more light harvesting proteins and higher stacking of thylakoids. Chl a+b ar indicates Simmonds, Tonnage and to a lesser extent TxS238 had dense packing of chloroplasts in both sun and shade adapted leaves. Shade leaves had more efficient Fv/Fm values than those adapted to sun for all varieties except TxS240. Tonnage had the largest range of total chlorophyll content between shade and sun adapted leaves and likely has the largest genetic variation in its ability to acclimate to changing light intensities. The range in efficiency of photosystem 11 found between the avocado trees tested indicates a potential for improvements through selective breeding. More research is needed to evaluate the entire USDA avocado germplasm collection for traits associated with photosynthetic efficiency and to determine their heritability.

Since arbuscular–mycorrhizal (AM) fungi are aerobic, symbiosis was not considered significant under flooded conditions. However, AM colonization of wetland plants is now believed more common than previously thought. In the humid tropics, storms that result in standing water for 24 hours or less are common. Short-term floods, especially on sandy soils, may leach banded fertilizer, reducing uptake efficiency. Crops planted in flood prone areas are not normally enhanced with mycorrhizal mixes. However, mycorrhizal associations tolerant to wet conditions may improve nutrient uptake as plants recover from short-term flooding. Greenhouse studies were initiated to determine the effects of frequent short-term floods (two to four events) on mycorrhizal colonization and subsequent development in snap bean (Phaseolus vulgaris Phaseolus vulgaris L.) plants. Flooding produced no obvious long-term physical effects on plant shoots. In the first study, flooding did not affect survival of colonies established before the first flood event. Percent root colonization in flooded vs. nonflooded treatments was not significantly different at either 31 or 50 days after planting (DAP). As root length increased there was a concomitant increase in colonization so that percent colonization remained approximately the same in both flooded and nonflooded treatments. In the second study, three weekly floods beginning 13 DAP (cotyledon leaf open only) did not inhibit initial mycorrhizal colonization. Mycorrhizal associations should form with snap bean under conditions subject to short-term flooding. Additional research is needed to determine the efficacy of different mycorrhizal mixes under short-term flooded conditions in the field.

Abstract. United States Army Corps of Engineers (USACE) policystates that USACE will analyze water resources projects, including flood risk management projects, using a risk framework that incorporates watershed, systems and life-cycle approaches. However, software to directly support these requirements has not been available. The current software used within USACE to perform these types of analyses, HEC-FDA (Flood Damage Reduction Analysis), has a number of limitations. For this reason and others, USACE's Hydrologic Engineering Center (CEIWR-HEC) developed the Watershed Analysis Tool (HEC-WAT). HEC-WAT was initially developed to assist USACE personnel conduct water resources studies of complex riverine systems with an integrated, comprehensive and systems based approach. However, since USACE also requires a life-cycle analysis, CEIWR-HEC added capability through the Flood Risk Analysis (FRA) compute option that allows risk analysis computations while incorporating a life-cycle approach. HEC-WAT/FRA includes systems and life-cycle approaches, event-based sampling, parameter sampling, and the ability to do scenario and alternative analyses. Applications of the FRA compute include levee certification studies, dam and levee safety studies, and planning and design studies. This paper will introduce HEC-WAT/FRA, describe scientific advancements included within it and provide applications to demonstrate how it will advance USACE modeling approaches.

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