TIDAL HUDSON RIVER ICE COVER CLIMATOLOGY Prepared for: The Hudson River Sustainable Shorelines Project NYSDEC Hudson River National Estuarine Research Reserve Prepared by: Nickitas Georgas, Jon Miller, Yifan Wang, Yu Jiang, and David DAgostinoDavidson Laboratory, Stevens Institute of Technology June 2015 ACKNOWLEDGEMENTS This report was prepared by the Davidson Laboratory at Stevens Institute of Technology for the Hudson River Sustainable Shorelines Project. TheauthorswouldliketothanktheiceofficersandicebreakerpersonneloftheUnitedStatesCoast Guard Sector New York, without whom the present effort would not have been accomplished. We would especiallyliketothankLCDRAnneMorrissey(formerSectorNYcommander),LCDREdwardMunoz (former Chief, Waterways Management Division, Sector NY), and CWO Kary Moss (former Sector NY ice officer) for their assistance and provision of the ice report data and for useful correspondence throughout multipleiceseasons.TheauthorwouldalsoliketoacknowledgethemembersoftheHudsonRiver Sustainable Shorelines Project for their guidance and support, especially Emilie Hauser and Ben Ganon of theHudsonRiverNationalEstuarineResearchReserve(HRNERR),alsothankyoutoJohnLaddofthe NYSDEC Hudson River Estuary Program for making the data publically available.About the Hudson River Sustainable Shorelines Project The Hudson River Sustainable Shorelines Project is a multi-year effort lead by theNewYorkStateDepartmentofEnvironmentalConservationHudsonRiverNationalEstuarine Research Reserve, in cooperation with the Greenway Conservancy for the Hudson River Valley. Partners in the Project include Cary Institute for Ecosystem Studies, NYSDEC Hudson River Estuary Program and Stevens Institute of Technology. The Project is facilitated by The Consensus Building Institute. The Project fulfills aspects of Goal 2 of the Action Agenda of the Hudson River Estuary Program.TheProjectissupportedbytheNationalEstuarineResearchReserveSystem(NERRS)Science Collaborative, a partnership of the National Oceanic and Atmospheric Administration and the University ofNewHampshire.TheScienceCollaborativeputsReserve-basedsciencetoworkforcoastal communitiescopingwiththeimpactsoflandusechange,pollution,andhabitatdegradationinthe context of a changing climate.Disclaimer The opinions expressed in this report are thoseof theauthorsand do not necessarily reflectthose of the New York State Department of Environmental Conservation,the Greenway Conservancy for the Hudson RiverValleyorourfunders.Referencetoanyspecificproduct,service,process,ormethoddoesnot constitute an implied or expressed recommendation or endorsement of it.Suggested Citation Georgas,N.,Miller,J.K.,Wang,Y.,Jiang,Y.andD.DAgostino(2015).TidalHudsonRiverIceCover Climatology. Stevens Institute of Technology, TR- 2949; in association with and published by the Hudson River Sustainable Shorelines Project, Staatsburg, NY 12580, http://hrnerr.org. Tidal Hudson River Ice Cover ClimatologyPage 1 TABLE OF CONTENTS SECTIONPAGE Executive Summary .................................................................................................................................................... 2 Introduction ................................................................................................................................................................. 3 Importance of This Study .......................................................................................................................................... 3 Data Source and Profile ..................................................................................................................................... 4 Methods ....................................................................................................................................................................... 6 Statistical Analysis .............................................................................................................................................. 6 Climatology Analysis ......................................................................................................................................... 6 Results .......................................................................................................................................................................... 9 Discussion .................................................................................................................................................................. 10 References .................................................................................................................................................................. 17 Appendix AMethodology ................................................................................................................................... 18 Statistics and Confidence Intervals ................................................................................................................ 18 Appendix BStatistics and Tables ........................................................................................................................ 21 Region ID and Name ........................................................................................................................................ 21 Ice Occurrence ................................................................................................................................................... 22 Ice Types for Every River Region ................................................................................................................... 22 CDF Analysis results ........................................................................................................................................ 24 Spatial Variation of Cumulative Probability ................................................................................................. 25 Color of Different Ice Type .............................................................................................................................. 26 Appendix CPlots ................................................................................................................................................... 27 Statistical analysis Plots ................................................................................................................................... 27 Climatology Analysis Plots ............................................................................................................................. 44 Appendix DIce Types, definitions and photographs...................................................................................... 60 Tidal Hudson River Ice Cover ClimatologyPage 2 EXECUTIVE SUMMARY The winter ice season (mid-December to late March each year) brings many significant changes to the water circulation and tides in the Hudson River Estuary. Ice cover thickness is also an important engineering and design parameter for Hudson River Sustainable Shorelines. To describe ice conditions in the Hudson, Stevens Institute of Technology has collected and processed US Coast Guard (USCG) daily ice reports from the tidal Hudson River for the past 11 winter seasons [2004-2015] at 16 different stretches and ice choke points spanning some 140 miles along the river from the George Washington Bridge in Manhattan on the south, to Troy, NY on the north.In association with the NERRS Science Collaborative, this report describes the methodology and results of climatological and statistical analyses for ice distributions along the Hudson, based on the USCG dataset. Given the scarcity of ice data in the tidal Hudson, the statistical distributions of ice thickness and ice cover area (in the form of cumulative probability density functions when ice is present) as well as ice type information, are meant to provide some guidance on engineering planning studies along the Hudson River. The tabulated climatological conditions, although based only on 11 years of USCG observations from the decks of the ice breakers that maintain traffic flow of the Hudson during winter, can form the beginning of an understanding of how ice grows and finally rots in the tidal Hudsons regions during a season, and provide a baseline to compare future years by. It is found for example that the latest ice season, 2014-2015 broke ice thickness records for the months of February and March for most regions of the tidal Hudson. The statistics that are presented in this report have been published as georeferenced datasets in the NYS GIS clearinghouse: http://gis.ny.gov/gisdata/metadata/nysdec.hudson_ice_meta.xml. Use Limitation This dataset is based on a compilation of USCG ice reports, which have a limited scope and are empirical. The scope of the presented datasets are therefore to provide a general picture of the regional ice climatology in the Tidal Hudson River, and is by no means an accurate description of ice conditions at any given year. Use at your own risk. Tidal Hudson River Ice Cover ClimatologyPage 3 INTRODUCTION Importance of This Study The United States Coast Guard defines the winter ice season in Sector New Yorks tidal waters as the period beginning December 15 to the end of March each year. During winter ice seasons, a seasonal ice field grows on the surface waters of the Hudson River Estuary, which, during colder years, can cover the Hudsons surface from bank to bank. Though the ice cover may vary significantly in extent and thickness from year to year, Georgas (2012), showed that it can bring many significant changes to the water circulation and water levels along the Tidal Hudson River and Estuary. When the ice concentration increases and the cover becomes fast from shore to shore, under-keel ice friction can greatly reduce tidal currents under the ice cover through frictional dumping, leading to much smaller current magnitudes and tidal circulation than during warmer winters that ice concentration is more limited. Near Troy, New York, the reduced tidal flows become smaller relative to the rivers stream flow discharge coming over the Federal Dam, leading to increased ebb predominance and constantly-downstream flows down to the port of Albany, NY; In other words, as tides can slow down due to ice friction when ice is fast to the shore, the geographic extent of the river that flows both ways Mahicantuck in the local Native American language decreases, and the non-tidal Hudson River may push downstream past Albany. The frictional tidal dumping from the ice cover can also raise low waters by a couple of feet and reduce tidal ranges (the difference between tidal high and low waters) by as much as 50% in the northern parts of the tidal river near Albany and Troy. On the contrary, tidal ranges increase near the southern edge of the ice field and on Manhattans western shores, currents increase because of tidal wave reflection from the shore-fast ice cover upstream. These amplified currents can also create stronger vertical mixing leading to a less stratified lower Estuary and decreasing salt front intrusion.These ice effects on hydrodynamics, water circulation, salinity intrusion, and local residence times, increase with ice concentration and ice thickness (Georgas 2012) and can have significant implications to life and trade within the Hudsons waters and along the Hudsons shores. Commercial navigation and route scheduling rely on careful timing for the passage of cargo-carriers through tidal waters so that ships have enough under-keel clearance not to run aground and enough over-head clearance to pass under the Hudsons bridges, while maximizing tonnage to ensure profitability. The dynamic variations in water levels caused by the ice explained above and in Georgas (2012) are uncertainty factors that need to be considered for safe navigation. Habitat and fish (especially through early life stages) can be affected by hydrodynamics, thus they may be affected by the seasonal ice effects on hydrodynamics, especially in view of ongoing climate change and predictions for a much warmer climate by the end of this century. Shoreline engineers planning either hard or soft engineering projects need to also consider the effect seasonal ice has on exposed structures. Usually, the most critical types of dynamic forces imposed by ice are horizontal loads on vertical and sloping structures. The magnitude of this type of loading is dependent on the point where the ice fails by crushing or splitting, which is dependent on its thickness (USACE 2011). This type of horizontal loading is typically experienced on vertical structures, such as walls, because their vertical face and height prevent ice from overtopping the structure before breaking apart. The force imposed by ice riding up over a structure, such as a revetment, is therefore much less than direct horizontal loading on the face of the revetment.Vertical ice forces include the weight of ice piling Tidal Hudson River Ice Cover ClimatologyPage 4 up on a structure and the cyclic stresses of the freeze and thaw cycles; they have small impact on established vegetated shorelines. Adfreeze loads are pressure forces applied to a structure that has become encased and frozen in ice (Miller and Georgas 2015). Ice jams (resulting when ice passage in a river section is blocked and the ice piles up upstream) are an important consideration for in-stream structures in the Hudson River; the USACE ice jam database (USACE, 2009) lists ice jams having occurred in the tidal Hudson River as recently as 2007 and 1996 at Catskill, NY and Troy, NY, respectively.Total ice loads are site-specific and very little general guidance exists for its impacts on sustainable shoreline treatments; however, a good rule of thumb to prevent the movement of individual stones in stone structures impacted by horizontal ice loads is to size the median stone diameter (Dn50) to be two to three times greater than the expected maximum winter ice thickness (Tuthill, 2008). Once a shoreline stabilization project is designed, it is suggested that a maintenance plan be included to ensure that it maintains stability after significant ice events in the Hudson. However, quantifiable information on the thickness, distribution, type and the growth-rot cycle of ice on the Hudson is extremely limited. It was the present studys objective to work on filling in this knowledge gap, based on statistical and climatological analyses of observations collected from United States Coast Guard / Sector NY ice reports. Data Source and Profile To describe ice conditions on the Hudson, we collected and processed US Coast Guard daily ice reports from the tidal Hudson River for the past 11 winter ice seasons (datasets a and b below). The ice season starts on December 15th and ends on March 31st of each year. Out of these 11 ice seasons, only the last 8 winter seasons (dataset b) include data from USCG for the 7 listed ice choke points (areas of river-ice congestion) in the Hudson (Figure 1). a) 2004-2005 2005-2006 2006-2007 b) 2007-2008 2008-2009 2009-2010 2010-2011 2011-20122012-2013 2013-2014 2014-2015 Stevens Institute of Technology obtained the USCG daily ice reports either directly from USCG/Sector NY by mail in print form, for the period December 15 2009 to February 10 2011, post-marked February 11 2011; by downloading daily from the USCG Sector NY ice portal: https://homeport.uscg.mil, for the rest of February 2011 to March 2015 and; by downloading from the Moran Shipping online archives of daily USCG port of New York and New Jersey updates: http://nynj.ports.moranshipping.com, for dates prior to April 2009.The daily USCG reports divide the Tidal Hudson River into 16 regions (Figure 1). The reports record the ICE TYPE, ICE THICKNESS RANGE, and PERCENT COVERAGE for each region and day. The ICE TYPE report entry denotes the type(s) of ice that was present on that river region on that day. Pictures and definition for each ice type can be found in Appendix D. Based on the USCG definition (USCG, 2015), ICE THICKNESS is measured in inches as accurately as possible, and in as many places as the varying thickness warrants. This variation is then tabulated for each region as an ice thickness RANGE. PERCENT COVERAGE is defined by USCG as the percentage of water surface covered by ice to the total surface area at a specific location or over a defined area. Tidal Hudson River Ice Cover ClimatologyPage 5 Figure 1: The sketch map of 16 Hudson River ice regions based on the USCG Sector NY definitions. Tidal Hudson River Ice Cover ClimatologyPage 6 METHODS InordertodescribeiceconditionontheHudson,twoapproacheswereused:a)statisticalanalysisthat focusedontheuseofanextremevaluedistributiontoprobabilisticallydescribetheobservedice thickness and ice concentration during times that ice is present on the river, with the coastal engineer in mind, and b) ice climatology analysis, for a more general audience. In this section, we briefly explain our methodologyandprovideanexample.Detailsonthestatisticalapproach,especiallyforicethickness ranges, can be found in Appendix A. Statistical Analysis For each of the 16 Hudson River regions defined by USCG (Figure 1) we computed the number of days that ice was present in the Hudson within each winter ice season. We report the number of days with ice as a percent of all winter ice season days with USCG observations, and call this recorded ice occurrence. We then created empirical cumulative probability density functions (CDF) based on all daily ice thickness and %-ice-cover data from the days that had ice on that region. A Generalized Extreme Value Distribution (GEV) was then used to fit the empirical CDF for both ice thickness and percent ice cover, and provide tabulated probability percentiles at 50%, 75%, 90%, and 95% probabilities. Statistical confidence intervals were also calculated for each percentile, as well as the corresponding actual regional daily variations for these percentiles, which were then plotted. Finally, the occurrence of each ice type reported during ice days was summarized and plotted as a bar chart. An example for Region 1 (River Stretch from George Washington Bridge to Tappan Zee Bridge) is seen in Figure 2.Climatology Analysis A climatology analysis was carried out for both thickness range and coverage.The winter ice season was divided into 7 stages by splitting each month in half: Stages: 1) Late December2) Early January 3) Late January 4) Early February 5) Late February 6) Early March 7) Late March Daily values within each stage were then considered, and averaged across all 8 (for choke points) to 11 (for river stretches) winter ice seasons. In this case, all observations were considered in the averages, including days with no ice reported. For ice thickness range, the lows and highs of the daily ranges were considered independently, creating a climatology low and climatology high range estimate for each stage. The means for each stage were tabulated, and plots comparing each of the past 11 ice seasons to the average climatology were created. Figure 3 is an example of the climatology analysis for Region 1. Tidal Hudson River Ice Cover ClimatologyPage 7 Figure 2:Top panel: Reported ice thickness (inches) and percent ice cover (%) from 2005-2015. Middle panel: CDF (Cumulative Distribution Function; empirical and GEV-fit) for ice thickness and percent cover. For ice thickness, dotted lines show the 50% and 95% percentile ice thickness calculated for that region during days with ice, while horizontal bars show the expected ice thickness ranges for these percentiles. Bottom panel: Bar chart shows the probability of occurrence, in percent form, for each kind of ice type, based on the reports when ice was present. Tidal Hudson River Ice Cover ClimatologyPage 8 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.00.10.50.40.20.20.0 MeanHigh (in)0.0 0.2 0.9 0.8 0.5 0.4 0.0Record High (in) Year record occurred 3.0(2010) 3.0(2014)8.0(2009)6.0(2005/2015)6.0 (2015)6.0 (2015)0.0 a Mean Coverage (%)0.1 2.8 11.1 10.7 6.3 2.1 0.0 Figure 3: Top panel: Climatology analysis for Thickness. Light green bars show the climatological Records per stage: The maximum ice thickness recorded over the whole 11 year period for each stage. Actual recorded maximum thicknesses observed within each stage and year are also shown (yellow thick bars). The black lines show the climatologically Average Ice Thickness Range while the red lines show the Actual Mean Range recorded during that stage and ice season. Bottom panel: Climatology analysis for Coverage. The heights of the thick light green bars represent the Climatologically Average Coverage. The heights of the narrower bars show the Actual Average Coverage recorded during that stage and ice season. The color of bar represent the prevalent ice type recorded during that stage and ice season (the type that had the higher percent occurrence during that stage and season). Tables shows the values of the climatological averages and the record highs. Tidal Hudson River Ice Cover ClimatologyPage 9 RESULTS An important parameter we wanted to quantify with this work is the 95% cumulative probability for ice thickness, which can inform an engineer on the thickness of ice cover that would be expected to be surpassed only 5 out of 100 ice days. Using the statistical analysis described in the Methods section and, in more detail, in Appendix A, we were able to calculate both the 95th percentile cumulative probability of the representative ice thickness for a given region, as well as a representative ice thickness range for that percentile across that region. For example, for region 1 (River Stretch: George Washington Bridge to Tappan Zee), the 95% region-wide representative ice thickness is around 5.7 inches and, within that region, the 95% thickness is expected to vary between 4.2 inches and 7.2 inches (Figure 4). Ice thickness in that southern-most Region 1 is the least one of all 16 river regions, which is to be expected.There are 12 regions where the 95-percent region-wide representative ice thickness is greater than 10 inches. At region 9 (Choke Point: Esopus Meadows), the 95th percentile representative ice thickness reaches a maximum of 12.1 inches, with an expected within-region variation from 11.1 inches to 13.1 inches. Figure 4: 95% Cumulative Probability of regional ice thickness and its within-region expected variation. See Figure 1 for location of regions.With regard to Ice Type, the most prevalent in the southern regions 1 to 7 is Drift Ice, in regions 8 to 15 is Brash Ice, and for the last northernmost region of the Tidal Hudson River it is Fast Ice (Table 3).All statistical analysis results are shown in Appendix-B. The results of the climatology analysis are included in Appendix-C. Tidal Hudson River Ice Cover ClimatologyPage 10 DISCUSSION Figure 5: Ice Occurrence (% of winter ice season days during which ice was present in the river) for each of the 16 USCG River Regions. See Figure 1 for location of regions. Figure 5 shows the distribution of ice occurrence in the 16 regions based on the 11 past ice seasons (8 past ice seasons at choke points). It shows the regional variation for the presence of ice on the river. There is a general increase of ice occurrence from the southern-most regions of the Hudson to the north where ice occurs more days in the season. The most ice appear in region 12 (River Stretch: Kingston to Catskill). Interestingly, in the northernmost regions from Catskill (region 14) to Troy (region 16) ice occurs slightly less, except at the Stuyvesant anchorage choke point (region 15). Figure 6: Ice thickness percentiles in the 16 regions, in inches. See Figure 1 for location of regions. Figure 6 shows that the Cumulative Probability of Ice Thickness varies with location too, especially at the boundaries of the estuarine and freshwater regions of the tidal Hudson, and especially near West Point where the rivers width decreases dramatically and its sinuosity increases (see region 3, Jones Point to West Point, and regions 4 and 5, at and north of West Point; Figure 6). Region 4 (Choke Point: West Point), region 5 (River Stretch: West Point to Newburgh), and region 9 (Choke Point: Esopus Meadows) tend to have thicker ice compared to other regions. A drop in thickness occurs at region 6 which includes the Tidal Hudson River Ice Cover ClimatologyPage 11 wider Newburgh Bay. Except for the first three regions and region 6, the 95% Cumulative Probability for the rest of the 12 regions are all above 10 inches. Figure 7: Ice Coverage Distribution within each of the 16 Regions. See Figure 1 for location of regions. Figure 7 shows that, generally, ice coverage within a given region increases from south to north, which is reasonable because not only the temperature is decreasing but also the salinity is decreasing. The figure shows that from region 4 (Choke Point: West Point) and upstream, 70% or more of each regions area is expected to be covered for at least half of the winter ice seasons duration. On the contrary, shore to shore ice cover is extremely unlikely in the southern, wider and saltier regions; Only 5 out of 100 days are expected to have over 80-90% areal ice coverage there. The above-mentioned spatial patterns are also visible in the maps shown on Figure 8. Figures 9 and 10 show maps of the progression of regional ice coverage within each stage of the winter season based on the climatological averages calculated here. Figures 11 and 12 show the same progression for thickness growth and rot/break-up. As time goes by, results show that ice typically grows until sometime in February when it starts breaking up. Tidal Hudson River Ice Cover ClimatologyPage 12 Figure 8: This figure shows maps from the tidal Hudson River ice statistics GIS layer. It shows the spatial variation of statistically-derived ice quantities. Generally, ice occurrence at the northern part is larger than that at the southern part of the river. However, both occurrence and ice thickness peak at the central part of the river. Downstream, the most prevalent ice type tends to be Drift Ice while upstream it is Brash Ice and finally Fast Ice near Troy. In terms of areal ice coverage, the narrower northern parts can fill with ice from shore to shore more days than the wider southern parts of the river. Tidal Hudson River Ice Cover ClimatologyPage 13 Figure 9: This figure shows maps from the tidal Hudson River Ice Climatology GIS layer on Ice Coverage %. Shown from left to right are the seven stages of the winter ice season (late Dec, early Jan, late Jan, early Feb, late Feb, early Mar, late Mar). Here, different colors represent the ice coverage of each region: the whiter the more ice coverage; dark blue is open waters. The upstream regions within the red box can be better seen in Figure 10. Tidal Hudson River Ice Cover ClimatologyPage 14 Figure 10: This figure shows maps from the upstream regions mentioned in Figure 9 from the tidal Hudson River Ice Climatology GIS layer on Ice Coverage %. Shown from left to right are the seven stages of the winter ice season (late Dec, early Jan, late Jan, early Feb, late Feb, early Mar, late Mar). Comparison of the later stages between Figures 9 and 10 reveals that these northern tidal Hudson Regions have less ice coverage during March than the southern part. It is likely that river flow pushes the broken ice from these regions down to the south. Tidal Hudson River Ice Cover ClimatologyPage 15 Figure 11: This figure shows maps from the tidal Hudson River Ice Climatology GIS layer on Ice Thickness (inches). It shows ice thickness (values increase from blue to white color) during each of the seven stages of the winter ice season (late Dec, Early Jan, Late Jan, Early Feb, Late Feb, Early Mar, Late Mar), from left to right. Ice thickness typically increases from Late Dec to Late Jan and then decreases. Some regions in center part of tidal Hudson River have ice thickness that is still growing, but most decrease, and this decrease shows up with a time lag as a decrease in spatial ice coverage (Figure 9). The upstream regions within the red box can be better seen in Figure 12. Tidal Hudson River Ice Cover ClimatologyPage 16 Figure 12: This figure shows maps from the upstream regions mentioned in Figure 11 from the tidal Hudson River Ice Climatology GIS layer on Ice Thickness (inches). It shows ice thickness (values increase from blue to white color) during each of the seven stages of the winter ice season (late Dec, Early Jan, Late Jan, Early Feb, Late Feb, Early Mar, Late Mar), from left to right. Tidal Hudson River Ice Cover ClimatologyPage 17 REFERENCES Georgas, N., 2012. Large Seasonal Modulation of Tides due to Ice Cover Friction in a Mid-Latitude Estuary, Journal of Physical Oceanography. 42(3), 352-369. Miller, J.K., and N. Georgas, 2015. Hudson River Physical Forces Analysis: Data Sources and Methods. Stevens Institute of Technology, TR- 2946; in association with and published by the Hudson River Sustainable Shorelines Project, Staatsburg, NY 12580, http://hrnerr.org Rubin, D., 1978. Multiple Imputations in Sample Surveys A phenomenological Bayesian approach to nonresponse. Educational Testing Service, 28pp. Tuthill, A., 2008. Ice Considerations in the Design of River Restoration Structures, ERDC/CRREL TR-08-2. US Army Corps of Engineers, 2009.CRREL Ice Jam Database, CRREL TR-99-2. US Army Corps of Engineers, 2011. Coastal Engineering Manual: Fundamentals of Design, EM 1110-2-1100.US Coast Guard, 2015. Ice Definitions. Homeport NY Icebreaking Operations. Accessed online, 2015: https://homeport.uscg.mil/mycg/portal/ep/portDirectory.do?tabId=1&cotpId=2 Tidal Hudson River Ice Cover ClimatologyPage 18 APPENDIX A--METHODOLOGY Statistics and Confidence Intervals The goal of CDF analysis is to figure out the likelihood of how thick the ice in one river region will be. In this aspect, we have to face two problems. One is the limited number of samples from 11 ice seasons and the second is that we do not have enough information about what the daily thickness ranges in the USCG reports really say about the distribution of ice within a given region that day. We addressed both problems simultaneously using a non-parametric statistical imputation approach (Rubin 1978). We first generated 50 random numbers inside of each daily thickness range in each region to expand the number of samples [500 were also tested and the results were nearly identical]. Without knowledge of a statistical distribution within each range, we considered these 50 random numbers as 50 independent thickness samples within that different region. This random imputation technique is more reasonable in terms of sampling the distribution of ice thickness than using, say, the mid-point of each daily range. Next, we performed CDF analysis of all these ice thickness samples (50 samples per observation day for all ice seasons) in order to find the 50%, 75%, 90% and 95% percentiles, among which the 95% percentile can be a really useful parameter for engineering planning. We then calculated the 95% confidence intervals of the GEV fit for each of these four percentiles using Rubins formula (Rubin 1978, equation 1-1). In Eq. 1-1, the first term represents the mean level of the variate and the second term represents the variation of variate within each imputation. Here, the variate is the confidence interval. )5011 (501501 biasbb rubinCI ci CI (1-1) In which, 5012501)501(b bb b biasci ci CI(1-2) For instance, in one river region, say we had a thickness range in one day which was 2-4 inches. We generated 50 random numbers (thicknesses) in the range of 2-4 inches. We did the same thing for each thickness range we had for that region. If we choose the first random thickness sample of every range, and do CDF analysis for these chosen thicknesses, we can get a confidence interval. This confidence interval is cib in Equation 1-1, while b=1. And so on, for the rest of the 50 random drawings. After using Rubins formula we get a variational confidence interval for all samples (Figure 13). Tidal Hudson River Ice Cover ClimatologyPage 19 Figure 13: The difference between two Confidence Intervals (C.I.) for the Generalized Extreme Value (GEV) distribution fit can be seen in this figure. The blue C.I. is the variation confidence interval after using Rubins equation to account for the variation of each imputations C.I. compared to the overall grand mean C.I. (which considers all imputations together). By doing the CDF analysis based on imputation we calculated robust confidence intervals through Rubins non-parametric formula for the GEV fit of the four percentiles of representative region-wide ice thickness. Within each region however, we also want to consider the possible spatial variation of ice thickness. To do that, sub-sampled CDF analyses were completed for each ice sample within each percentiles confidence interval. For example, if a days range was 2-4 inches, the length of within-region spatial range for that day was 2 inches.For the subsampled CDFs, we chose those daily thickness ranges whose mid-points were located within Rubins confidence interval for a specific percentile. We then retrieved the median of the length of those thickness ranges for that percentile; and so on for the other percentiles. We regard this median as a representative range for the spatial variation of ice thickness for each percentile (Table 5).For instance, after doing the imputed CDF, we get a result that there are 95% possibility that thickness will be less than 10 inches, and Rubins 95% variational confidence interval for that percentile is from 9 in to 11 in. Then we find those thickness range whose mid-point was located between 9-11 inches and find out the length of these thickness ranges. They may be, for example, [2 in, 4 in, 4 in, 5 in, 9 in]. The median Variational C.I. from Rubin Grand Mean C.I. Tidal Hudson River Ice Cover ClimatologyPage 20 is 4 in. I.e., we have 95% confidence that the representative thickness for that region as a whole will not exceed 11 inches (the upper limit of the confidence interval) more than 5 winter days in 100. Since this thickness however may further vary spatially within that region an extra 4 inches, one could say with 95% confidence that ice thickness will not exceed 15 inches more than 5 winter days in 100 anywhere within that region. In other words, a conservative value for the 95% percentile would be:[Upper-95%-C.I. of the 95-percentile] + median 95-percentile range. Tidal Hudson River Ice Cover ClimatologyPage 21 APPENDIX B--STATISTICS AND TABLES Region ID and NameTable 1: Region ID information. This table lists the stretch of the river corresponding to the Region ID. This information is displayed in a map in Figure 1.REGIONIDNAME 1 River Stretch: George Washington Bridge to Tappan Zee Bridge 2River Stretch: Tappan Zee Bridge to Jones Point 3River Stretch: Jones Point to West Point 4Choke Point: West Point 5River Stretch: West Point to Newburgh 6River Stretch: Newburgh to Poughkeepsie 7Choke Point: Crum Elbow 8Choke Point: Hyde Park Anchorage 9Choke Point: Esopus Meadows 10River Stretch: Poughkeepsie to Kingston 11Choke Point: Silver Point 12River Stretch: Kingston to Catskill 13Choke Point: Hudson Anchorage 14Choke Point: Stuyvesant Anchorage 15River Stretch: Catskill to Albany 16River Stretch: Albany to Troy Tidal Hudson River Ice Cover ClimatologyPage 22 Ice Occurrence Table 2:The ice occurrence of different river region. The occurrence based on ice data of 11 ice seasons.REGION IDOCCURENCE(%) 114.5 234.5 334.9 453.7 554.8 660.9 763.9 863.6 966.3 1069.2 1163.7 1270.8 1361.5 1453.7 1563.8 1649.6 Tidal Hudson River Ice Cover ClimatologyPage 23 Ice Types for Every River Region Table 3: Ice Types of every river region with their respective percent occurrence. REGION Drift (%) Brash (%) Fast (%)Plate (%)Floe (%) Grease (%)Frazil (%) Slush (%)Pancake (%)Hummocked(%)Rafted (%) Skim (%) 192.077.46.511.33.21.61.600000 286.272.515.08.51.32.02.02.02.6000 388.472.912.98.41.91.91.91.90.6000 480.273.719.414.22.800.42.00.8000.4 577.476.023.710.82.800.42.500.70.40 682.780.818.98.73.3001.6000.70.3 779.075.419.011.82.00.32.01.30.7002.0 872.173.724.613.82.00.301.00.7001.0 964.472.829.017.31.200.31.20.3000.9 1073.673.925.013.62.600.31.40.30.30.30 1163.967.939.418.11.100.41.10001.1 1265.374.136.912.73.3000.81.100.30.6 1358.571.343.815.12.3001.10.40.400 1458.073.242.415.61.0001.00.50.500.5 1561.669.939.413.01.40.300.30.300.70.3 1642.044.961.424.40.61.1000.600.60 Tidal Hudson River Ice Cover ClimatologyPage 24 Cumulative Distribution Function (CDF) Analysis Result Table 4: CDF Analysis result for both ice thickness and coverage. REGION_ID THICK_50P (inches) THICK_75P (inches) THICK_90P (inches) THICK_95P (inches) AREA_50P (%) AREA_75P (%) AREA_90P (%) AREA_95P (%) 12.13.14.55.732.548.565.878.6 22.63.75.36.53552.872.486.8 32.53.75.26.535.453.473.288.6 44.06.08.811.171.394.8100100 54.16.39.411.970.786.5100100 63.75.57.89.870.084.293.5100 73.55.58.411.178.192.1100100 83.85.98.711.174.192.5100100 94.16.39.412.182.6100100100 104.16.39.111.581.592.3100100 114.36.38.710.487.6100100100 124.36.48.910.780.9100100100 134.97.19.511.287.8100100100 144.16.08.310.087.0100100100 154.36.48.810.678.394.8100100 164.56.68.810.4100100100100 Tidal Hudson River Ice Cover ClimatologyPage 25 Spatial Variation of Cumulative Probability Table 5: Spatial (Within-Region) Variation of Each Cumulative Probability. REGION ID RANGE_50 (inches) RANGE_75 (inches) RANGE_90 (inches) RANGE_95 (inches) 11.02.03.03.0 21.02.03.02.0 31.02.03.52.5 42.04.04.02.0 52.54.04.02.0 61.04.04.04.0 71.04.02.01.0 82.04.02.02.0 93.03.52.02.0 103.04.04.02.0 113.04.02.04.0 123.03.02.04.0 133.02.02.54.0 143.03.53.02.0 153.03.02.04.0 163.02.02.54.0 Tidal Hudson River Ice Cover ClimatologyPage 26 Color of Different Ice Type Table 6:Color of different ice Type. Ice TypeColor DriftDark Green BrashBrown FastOrange PlateRed FloePurple Tidal Hudson River Ice Cover ClimatologyPage 27 APPENDIX C--PLOTS Statistical Analysis Plots Brief explanation of the plots that follow per Hudson Region is given below:Top panels: Reported ice thickness (inches) and percent ice cover (%) from 2005-2015. Medium panels: CDF (Cumulative Distribution Function; empirical and GEV-fit) for ice thickness and percent cover. For ice thickness, dotted lines show the 50% and 95% percentile ice thickness calculated for that region during days with ice, while horizontal bars show the expected ice thickness ranges for these percentiles. Bottom panel: Bar chart shows the probability of occurrence for each kind of ice type, based on the reports when ice was present. Tidal Hudson River Ice Cover ClimatologyPage 28 Figure 14:Statistical Analysis for Region 1, George Washington Bridge to Tappan Zee Bridge. In this region, ice has historically occurred 14.5% of days during the analyzed winter ice seasons. The most prevalent ice type for this region has been Drift. Based on the statistical analysis described in this report, conditions with ice thicker than 5.7 (4.2 to 7.2 at the 95% confidence level), and areal ice coverage greater than 78.6%, are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 1 day of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 29 Figure 15:Statistical Analysis for Region 2, Tappan Zee-Jones Point. In this region, ice has historically occurred 34.5% of days during the analyzed winter ice seasons. The most prevalent ice type for this region has been Drift. Based on the statistical analysis described in this report, conditions with ice thicker than 6.5 (5.5 to 7.5 at the 95% confidence level), and areal ice coverage greater than 86.8%, are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 2 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 30 Figure 16: Statistical Analysis for Region 3, Jones Point-West Point. In this region, ice has historically occurred 34.9% of days during the analyzed winter ice seasons. The most prevalent ice type for this region has been Drift. Based on the statistical analysis described in this report, conditions with ice thicker than 6.5 (5.25 to 7.75 at the 95% confidence level), and areal ice coverage greater than 88.6%, are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 2 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 31 Figure 17: Statistical Analysis for Region 4, Choke Point: West Point. In this region, ice has historically occurred 53.7% of days during the analyzed winter ice seasons (Note: data were only available after December 2007). The most prevalent ice type for this region has been Drift, though Brash ice has also occurred with similar frequency. Based on the statistical analysis described in this report, conditions with ice thicker than 11.1 (10.1 to 12.1 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 3 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 23.5% of the time on average, or, equivalently, during 14 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 32 Figure 18: Statistical Analysis for Region 5, West Point-Newburgh. In this region, ice has historically occurred 54.8% of days during the analyzed winter ice seasons. The most prevalent ice type for this region has been Drift, though Brash ice has also occurred with similar frequency. Based on the statistical analysis described in this report, conditions with ice thicker than 11.9 (10.9 to 12.9 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 3 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 13% of the time on average, or, equivalently, during 8 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 33 Figure 19: Statistical Analysis for Region 6, Newburgh-Poughkeepsie. In this region, ice has historically occurred 60.9% of days during the analyzed winter ice seasons. The most prevalent ice type for this region has been Drift, though Brash ice has also occurred with similar frequency. Based on the statistical analysis described in this report, conditions with ice thicker than 9.8 (7.8 to 11.8 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 3 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 8% of the time on average, or, equivalently, during 5 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 34 Figure 20:Statistical Analysis for Region 7, Choke Point: Crum Elbow. In this region, ice has historically occurred 63.9% of days during the analyzed winter ice seasons (Note: data were only available after December 2005). The most prevalent ice type for this region has been Drift, though Brash ice has also occurred with similar frequency. Based on the statistical analysis described in this report, conditions with ice thicker than 11.1 (10.6 to 11.6 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 3 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 19% of the time on average, or, equivalently, during 13 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 35 Figure 21: Statistical Analysis for Region 8, Choke Point: Hyde Park Anchorage. In this region, ice has historically occurred 63.6% of days during the analyzed winter ice seasons (Note: data were only available after December 2005). The most prevalent ice type for this region has been Brash, though Drift ice has also occurred with similar frequency. Based on the statistical analysis described in this report, conditions with ice thicker than 11.1 (10.1 to 12.1 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 3 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 20% of the time on average, or, equivalently, during 14 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 36 Figure 22: Statistical Analysis for Region 9, Choke Point: Esopus Meadows. In this region, ice has historically occurred 66.3% of days during the analyzed winter ice seasons (Note: data were only available after December 2005). The most prevalent ice type for this region has been Brash, though Drift ice has also occurred with similar frequency. Based on the statistical analysis described in this report, conditions with ice thicker than 12.1 (11.1 to 13.1 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 4 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 26% of the time on average, or, equivalently, during 18 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 37 Figure 23: Statistical Analysis for Region 10, Poughkeepsie-Kingston. In this region, ice has historically occurred 69.2% of days during the analyzed winter ice seasons. The most prevalent ice type for this region has been Brash, though Drift ice has also occurred with similar frequency. Based on the statistical analysis described in this report, conditions with ice thicker than 11.5 (10.5 to 12.5 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 4 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 17% of the time on average, or, equivalently, during 13 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 38 Figure 24: Statistical Analysis for Region 11, Choke Point: Silver Point. In this region, ice has historically occurred 63.7% of days during the analyzed winter ice seasons (Note: data were only available after December 2005). The most prevalent ice type for this region has been Brash, though Drift ice has also occurred with similar frequency. Based on the statistical analysis described in this report, conditions with ice thicker than 10.4 (8.4 to 12.4 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 3 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 35% of the time on average, or, equivalently, during 24 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 39 Figure 25:Statistical Analysis for Region 12, Kingston-Catskill. In this region, ice has historically occurred 70.8% of days during the analyzed winter ice seasons. The most prevalent ice type for this region has been Brash. Based on the statistical analysis described in this report, conditions with ice thicker than 10.7 (8.7 to 12.7 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 4 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 28% of the time on average, or, equivalently, during 21 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 40 Figure 26: Statistical Analysis for Region 13, Choke Point: Hudson Anchorage. In this region, ice has historically occurred 61.5% of days during the analyzed winter ice seasons (Note: data were only available after December 2005). The most prevalent ice type for this region has been Brash. Based on the statistical analysis described in this report, conditions with ice thicker than 11.2 (9.2 to 13.2 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 3 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 40% of the time on average, or, equivalently, during 26 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 41 Figure 27:Statistical Analysis for Region 14, Choke Point: Stuyvesant Anchorage. In this region, ice has historically occurred 53.7% of days during the analyzed winter ice seasons (Note: data were only available after December 2005). The most prevalent ice type for this region has been Brash. Based on the statistical analysis described in this report, conditions with ice thicker than 10.0 (9.0 to 11.0 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 3 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 31% of the time on average, or, equivalently, during 18 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 42 Figure 28: Statistical Analysis for Region 15, Catskill-Albany. In this region, ice has historically occurred 63.8% of days during the analyzed winter ice seasons. The most prevalent ice type for this region has been Brash, though Drift ice has also occurred with similar frequency. Based on the statistical analysis described in this report, conditions with ice thicker than 10.6 (8.6 to 12.6 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 3 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 23% of the time on average, or, equivalently, during 16 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 43 Figure 29: Statistical Analysis for Region 16, Albany-Troy. In this region, ice has historically occurred 49.6% of days during the analyzed winter ice seasons. The most prevalent ice type for this region has been Fast Ice. Based on the statistical analysis described in this report, conditions with ice thicker than 10.4 (8.4 to 12.4 at the 95% confidence level), are only expected during 5% of days with ice on that river stretch during the winter ice season, or, equivalently, during only 3 days of an ice season. When ice is present, it may fill that region from bank to bank, (100% ice cover), 50% of the time on average, or, equivalently, during 27 days of an ice season. Tidal Hudson River Ice Cover ClimatologyPage 44 Climatology Analysis Plots ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.00.10.50.40.20.20.0 MeanHigh (in)0.0 0.2 0.9 0.8 0.5 0.4 0.0Record High (in) Year record occurred 3.0(2010) 3.0(2014)8.0(2009)6.0(2005/2015)6.0 (2015)6.0 (2015)0.0 Mean Coverage (%)0.1 2.8 11.1 10.7 6.3 2.1 0.0 Figure 30: Region 1 in general has the lowest ice thickness and coverage of any of the 16 analyzed Tidal Hudson River regions, as it is further south near the New York / New Jersey Harbor and has saline estuarine waters. Tidal Hudson River Ice Cover ClimatologyPage 45 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.1 0.8 1.0 1.1 0.6 0.5 0.2 MeanHigh (in)0.1 1.2 2.0 2.2 1.1 1.0 0.3 Record High (in) Year record occurred 3.0 (2010) 18.0(2010) 8.0(2011) 8.0 (2011) 8.0 (2005/2015) 8.0(2015) 2.0(2014) Mean Coverage (%)0.3 19.3 25.1 22.1 7.9 6.4 1.6 Figure 31: For region 2, the thickest ice appears in Early January. On average, the ice has been thicker in Late January and Early February. In terms of coverage, the most ice coverage appears in Late January. Mean ice prevalent types are Drift and Brash. Tidal Hudson River Ice Cover ClimatologyPage 46 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.1 0.9 1.1 1.0 0.6 0.5 0.2MeanHigh (in)0.1 1.3 2.1 2.1 1.0 1.0 0.3Record High (in) Year record occurred 3.0 (2010)18.0 (2010)8.0 (2009)8.0 (2011)8.0 (2005 /2015)8.0 (2015)2.0 (2014)Mean Coverage (%)0.3 20.6 25.0 22.7 8.3 6.4 1.6 Figure 32: For region 3, the thickest ice appears in Early January. On average, the ice has been thicker in Late January and Early February. In terms of coverage, the most ice coverage appears in Late January. Mean ice prevalent types are Drift and Brash. Tidal Hudson River Ice Cover ClimatologyPage 47 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.1 1.7 2.3 3.2 1.8 2.1 0.6MeanHigh (in)0.2 2.5 3.8 4.9 3.3 3.7 1.0Record High (in) Year record occurred 5.0 (2010)12.0 (2010/2011)12.0 (09/11 /15)24.0 (2015)12.0 (2011 /2015)14.0 (2015)4.0 (2014)Mean Coverage (%)2.7 39.9 48.3 52.8 36.1 32.3 11.8 Figure 33: For region 4, the thickest ice appears in Early February. On average, the ice has been thicker in Early February. In terms of coverage, the most ice coverage appears in Early February. Mean ice prevalent types are Drift and Brash. Tidal Hudson River Ice Cover ClimatologyPage 48 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.1 1.4 2.7 3.3 2.2 2.1 0.9MeanHigh (in)0.2 2.1 5.0 5.4 3.4 3.4 1.4Record High (in) Year record occurred 5.0 (2010)10.0 (2009 /2010)30.0 (2005)24.0 (2015)18.0 (2015)18.0 (2015)5.0 (2015)Mean Coverage (%)1.8 34.1 52.4 55.7 37.6 28.5 14.7 Figure 34: For region 5, the thickest ice appears in Late January. On average, the ice has been thicker in Late January and Early February. In terms of coverage, the most ice coverage appears in Early February. Mean ice prevalent types are Drift, Brash, and Fast. Tidal Hudson River Ice Cover ClimatologyPage 49 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.3 1.2 2.8 2.8 2.3 2.5 1.2MeanHigh (in)0.5 2.0 4.9 4.5 3.8 4.2 2.1Record High (in) Year record occurred 5.0 (2010)10.0 (2009)18.0 (2011)12.0 (2011 /2015)12.0 (2015)24.0 (2015)6.0 (2015)Mean Coverage (%)7.3 33.8 55.1 56.7 51.2 34.5 25.0 Figure 35: For region 6, the thickest ice appears in Early March. On average, the ice has been thicker in Late January. In terms of coverage, the most ice coverage appears in Early February. Mean ice prevalent types are Drift and Brash. Tidal Hudson River Ice Cover ClimatologyPage 50 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.5 2.0 3.0 2.5 2.3 3.5 1.7MeanHigh (in)0.7 2.8 4.9 3.8 3.6 4.8 3.1Record High (in) Year record occurred 5.0(2009) 12.0 (2010 /2011)18.0 (2011)12.0 (2009 /2015)12.0 (2009 /2015)24.0 (2015)6.0 (2014 /2015)Mean Coverage (%)19.4 42.5 64.8 51.1 45.6 43.0 34.0 Figure 36: For region 7, the thickest ice appears in Early March. On average, the ice has been thicker in Late January. In terms of coverage, the most ice coverage appears in Late January. Mean ice prevalent types are Drift, Brash, and Fast. Tidal Hudson River Ice Cover ClimatologyPage 51 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.4 1.9 3.0 3.3 2.2 3.2 1.5MeanHigh (in)0.6 2.7 4.8 5.0 3.7 4.4 3.1Record High (in) Year record occurred 5.0 (2009/2010)12.0 (2011)12.0 (2011)18.0 (2015)12.0 (2015)24.0 (2015)6.0 (2015)Mean Coverage (%)17.4 37.0 64.2 62.6 43.9 39.1 32.4 Figure 37: For region 8, the thickest ice appears in Early March. On average, the ice has been thicker in Early February. In terms of coverage, the most ice coverage appears in Late January. Mean ice prevalent types are Drift, Brash, and Fast. Tidal Hudson River Ice Cover ClimatologyPage 52 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.6 2.0 3.4 3.9 2.5 3.6 1.9MeanHigh (in)0.8 2.9 5.2 5.8 3.9 4.8 3.7Record High (in) Year record occurred 8.0 (2009)12.0 (2010 /2011)18.0 (2010 /2011)24.0 (2013)14.0 (2009)20.0 (2015)6.0 (2015)Mean Coverage (%)21.5 45.6 68.5 69.3 52.5 45.5 46.1 Figure 38: For region 9, the thickest ice appears in Early February. On average, the ice has been thicker in Early February. In terms of coverage, the most ice coverage appears in Early February. Mean ice prevalent types are Drift, Brash, Fast, and Plate. Tidal Hudson River Ice Cover ClimatologyPage 53 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.6 2.1 3.1 3.8 2.6 3.5 1.8MeanHigh (in)0.9 3.2 5.4 5.6 4.4 5.5 3.8Record High (in) Year record occurred 8.0 (2009)16.0 (2010)13.0 (2010)12.0 (09/11/15)12.0 (2009/2015)24.0 (2015)6.0 (2015)Mean Coverage (%)20.0 43.8 68.6 66.2 57.3 49.6 40.2 Figure 39: For region 10, the thickest ice appears in Early March. On average, the ice has been thicker in Early February. In terms of coverage, the most ice coverage appears in Late January. Mean ice prevalent types are Drift, Brash, and Fast. Tidal Hudson River Ice Cover ClimatologyPage 54 ClimatologyLate DecEarly JanLate JanEarly Feb Late Feb Early MarLate Mar Mean Low (in)0.5 1.7 2.7 3.5 2.8 3.1 1.8MeanHigh (in)0.8 2.4 4.5 5.0 4.4 5.0 3.7Record High (in) Year record occurred 4.0 (2010)10.0 (2010)10.0 (09/10/11/15)12.0 (10/11/15)12.0 (2015)16.0 (2015)6.0 (2015)Mean Coverage (%)22.1 43.8 61.7 63.4 53.8 52.1 50.0 Figure 40: For region 11, the thickest ice appears in Early March. On average, the ice has been thicker in Early February and Early March. In terms of coverage, the most ice coverage appears in Early February. Mean ice prevalent types are Drift, Brash, and Fast. Tidal Hudson River Ice Cover ClimatologyPage 55 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.5 1.8 3.2 4.0 3.3 2.6 1.7MeanHigh (in)0.9 2.8 5.4 5.8 5.4 4.8 4.3Record High (in) Year record occurred 5.0 (2010)10.0 (2010)24.0 (2011)12.0 (09/11/15)18.0 (2011/2015)16.0 (2015)8.0 (2015)Mean Coverage (%)22.8 49.2 65.3 69.6 60.7 51.8 52.3 Figure 41: For region 12, the thickest ice appears in Late January. On average, the ice has been thicker in Early February. In terms of coverage, the most ice coverage appears in Early February. Mean ice prevalent types are Drift, Brash, Fast, and Plate. Tidal Hudson River Ice Cover ClimatologyPage 56 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.5 1.7 2.8 4.1 3.8 2.9 1.7MeanHigh (in)0.6 2.4 4.6 5.9 5.5 4.7 3.0Record High (in) Year record occurred 4.0 (2010)10.0 (2010)13.0 (2010)16.0 (2010)12.0 (2009/2015)16.0 (2015)7.0 (2014)Mean Coverage (%)23.0 39.4 62.4 62.6 57.7 46.6 42.5 Figure 42: For region 13, the thickest ice appears in Early February and Early March. On average, the ice has been thicker in Early February. In terms of coverage, the most ice coverage appears in Late January and Early February. Mean ice prevalent types are Drift, Brash, and Fast. Tidal Hudson River Ice Cover ClimatologyPage 57 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.5 1.3 1.8 3.3 2.7 2.0 0.8MeanHigh (in)0.5 1.9 3.4 4.7 4.6 3.3 1.4Record High (in) Year record occurred 3.0 (2010/2013)8.0 (2009 /2015)8.0 (09/14/15)12.0 (10/11/15)12.0 (2014 /2015)10.0 (2015)4.0 (2014 /2015)Mean Coverage (%)19.2 36.5 55.1 60.0 47.8 36.4 25.6 Figure 43: For region 14, the thickest ice appears in February. On average, the ice has been thicker in Early February. In terms of coverage, the most ice coverage appears in Early February. Mean ice prevalent types are Drift, Brash, Fast, and Plate. Tidal Hudson River Ice Cover ClimatologyPage 58 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.5 1.6 2.6 3.7 2.8 2.3 1.2MeanHigh (in)0.6 2.5 5.1 5.5 4.7 4.4 2.6Record High (in) Year record occurred 4.0 (2010)18.0 (2009)16.0 (2009)12.0 (2011 /2015)18.0 (2015)16.0 (2015)8.0 (2014)Mean Coverage (%)20.7 38.5 60.5 63.3 50.1 38.9 34.3 Figure 44: For region 15, the thickest ice appears in Early January and Late February. On average, the ice has been thicker in Early February. In terms of coverage, the most ice coverage appears in Early February. Mean ice prevalent types are Drift, Brash, and Fast. Tidal Hudson River Ice Cover ClimatologyPage 59 ClimatologyLate DecEarly JanLate JanEarly FebLate FebEarly MarLate Mar Mean Low (in)0.2 1.4 1.9 2.5 2.8 1.6 0.6MeanHigh (in)0.4 2.1 3.4 3.9 3.6 2.2 0.8Record High (in) Year record occurred 4.0 (2010)18.0 (2009)16.0 (2009)12.0 (2015)10.0 (2005/2009)12.0 (2015)6.0 (2014)Mean Coverage (%)15.6 46.7 51.1 60.8 46.5 31.8 2.7 Figure 45: For region 16, the thickest ice appears in Early January. On average, the ice has been thicker in Early February. In terms of coverage, the most ice coverage appears in Early February. Mean ice prevalent types are Drift, Brash, Fast, and Plate. Tidal Hudson River Ice Cover ClimatologyPage 60 APPENDIX D. USCG ICE TYPES, DEFINITIONS AND PHOTOGRAPHS (PROVIDED BY USCG) BRASHICE - Conglomerates of small ice cakes and chunks that have been broken off from other ice formations. These conglomerations coalesce an