The Hudson: An Illustrated Guide to the Living River

By Stephen P. Stanne, Roger G. Panetta, Brian E. Forist and Maija Liisa Niemisto

Since 1996, The Hudson: An Illustrated Guide to the Living River has been an essential resource for understanding the full sweep of the great river's natural history and human heritage. This updated third edition includes the latest information about the ongoing fight against pollution and environmental damage to the river, plus vibrant new full-color illustrations showing the plants and wildlife that make this ecosystem so special.
 
This volume gives a detailed account of the Hudson River’s history, including the geological forces that created it, the various peoples who have lived on its banks, and the great works of art it has inspired. It also showcases the many species making a home on this waterway, including the Atlantic sturgeon, the bald eagle, the invasive zebra mussel, and the herons of New York Harbor. Combining both scientific and historical perspectives, this book demonstrates why the Hudson and its valley have been so central to the environmental movement. 
 
As it charts the progress made towards restoring the river ecosystem and the effects of emerging threats like climate change, The Hudson identifies concrete ways that readers can help. To that end, royalties from the sale of this book will go to the non-profit environmental advocacy group Hudson River Sloop Clearwater, Inc.

• Language: English
• Publisher: Rutgers University Press
• Release date: Jan 15, 2021
• ISBN: 9781978814073

Book preview

THE HUDSON

THE HUDSON

An Illustrated Guide to the Living River

THIRD EDITION

STEPHEN P. STANNE, ROGER G. PANETTA, BRIAN E. FORIST, and MAIJA LIISA NIEMISTÖ

A Project of Hudson River Sloop Clearwater, Inc.

RUTGERS UNIVERSITY PRESS

New Brunswick, Camden, and Newark, New Jersey, and London

Library of Congress Cataloging-in-Publication Data

Names: Stanne, Stephen P., 1950- author. | Panetta, Roger G., 1939- author. | Forist, Brian E., 1956- author. | Niemistö, Maija, 1982- author. | Hudson River Sloop Clearwater, Inc., sponsoring body.

Title: The Hudson: an illustrated guide to the living river / Stephen P. Stanne, Roger G. Panetta, Brian E. Forist, Maija Liisa Niemistö.

Description: Third edition. | New Brunswick, New Jersey: Rutgers University Press, 2021. | A Project of Hudson River Sloop Clearwater, Inc. | Includes bibliographical references and index.

Identifiers: LCCN 2020019314 | ISBN 9781978814059 (paperback) | ISBN 9781978814066 (cloth) | ISBN 9781978814073 (epub) | ISBN 9781978814080 (mobi) | ISBN 9781978814097 (pdf)

Subjects: LCSH: Natural history—Hudson River (N.Y. and N.J.) | Stream ecology—Hudson River (N.Y. and N.J.) | Hudson River (N.Y. and N.J.)—History. | Hudson River (N.Y. and N.J.)—Environmental conditions.

Classification: LCC QH104.5.H83 S74 2020 | DDC 508.747/3—dc23

LC record available at https://lccn.loc.gov/2020019314

A British Cataloging-in-Publication record for this book is available from the British Library.

Copyright © 2021 by Hudson River Sloop Clearwater, Inc.

All rights reserved

No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, or by any information storage and retrieval system, without written permission from the publisher. Please contact Rutgers University Press, 106 Somerset Street, New Brunswick, NJ 08901. The only exception to this prohibition is fair use as defined by U.S. copyright law.

The paper used in this publication meets the requirements of the American National Standard for Information Sciences—Permanence of Paper for Printed Library Materials, ANSI Z39.48-1992.

www.rutgersuniversitypress.org

Manufactured in the United States of America

To Pete and Toshi Seeger, who set us to sailing on our golden river

CONTENTS

Preface to the Third Edition

1|  A Physical Overview of the Hudson

2|Energy Flow and Nutrient Cycles in the Hudson

3|The Hudson’s Habitats and Plant Communities

4|The Hudson’s Invertebrate Animals

5|The Hudson’s Fishes

6|The Hudson’s Birds and Beasts

7|Exploration, Colonization, and Revolution

8|The Romantic River

9|Industrialization and the Transformation of the Landscape

10|Conservation and Environmentalism

11|Resolving River Conflicts

12|Is the Hudson Getting Cleaner?

13|Climate Change and the Hudson

Acknowledgments

Glossary

Notes

Suggested Readings and Sources

Text and Illustration Credits

Index

Preface to the Third Edition

WHEN WORK BEGAN ON THE first edition of The Hudson: An Illustrated Guide to the Living River a quarter century ago, we intended to create an introduction to the river that combined environmental science and history in a manner useful to teachers and students, a mission reflected in the original working title: A Hudson River Primer. Over the years, we have found that this book fulfills a larger role, providing information to anyone inclined to be a student of the river, whether or not the inquiry takes place in a formal classroom.

Given the opportunity to reimagine those goals with this third edition, we were tempted to greatly expand its coverage. After all, the Hudson has become even more prominent in the public eye. Some of that recognition has been the result of newsworthy events: the Miracle on the Hudson, U.S. Airways Flight 1549’s successful emergency landing in 2009, and the humpback whale that swam up to the George Washington Bridge in 2016. More attention has come to the Hudson as opportunities to enjoy the river have expanded, from the rebuilt piers at the Hudson River Park in Manhattan that bring 17 million people to the waterfront each year, to the Walkway Across the Hudson, attracting half a million visitors annually since its 2009 opening, and the growing number of small businesses offering kayak tours for more intimate experiences on the water.

Then there are events that have sounded warnings about the damage humans are doing to our environment. Tropical Storm Irene’s devastating flooding in 2011 and Superstorm Sandy’s disastrous storm surge in 2012 were previews of the likely impacts of intensifying climate change. Dead and dying ash trees, victims of the emerald ash borer that arrived in the Hudson Valley in 2010, bear witness to the impacts of the invasive species we are inadvertently ferrying from one continent to another.

There have been promising developments that confirm our ability to undertake actions benefiting the river. The uproar over a 2016 proposal to expand the number of anchorages for oil barges, many carrying Bakken crude oil, provided evidence—10,000 comments, most in opposition—that Hudson Valley residents are paying attention to and want a voice in making decisions that potentially endanger decades of improvements in the river’s health. Additional thousands, young and old, are participating in river cleanups and citizen science projects that improve both the state of the Hudson and our understanding of it.

Hand in hand with all this attention, research and scholarship has generated a wealth of new data and interpretation of the Hudson, providing a corresponding trove of fresh material to include in a revised book.

In response, this new edition is longer, but not by much. We are standing by our original intent to provide a broad overview, and to re-emphasize the importance of interdisciplinary examination of the river. The Hudson Valley is a unique and special place, and integrated knowledge of its ecology, natural and human history, and culture is essential to understanding its distinctiveness.

Thus, The Hudson remains a book of elementary principles, focused on the portion of the river between the head of tidewater at Troy and the briny ocean at its mouth. It could not possibly cover all the basic tenets of sciences that have application to studying the Hudson—from astronomy, botany, and chemistry all the way to zoology—nor could it serve as a field guide for identifying the river’s multitudinous life-forms. Rather, we attempt to convey a sense of the rich tapestry of the Hudson’s natural and human communities as we weave descriptions of representative organisms into discussions of the ecological ties that bind them together or look at how historical themes are restated over the years. That said, those interested in specific fields of inquiry will find examples from the Hudson to illustrate the workings of important phenomena, theories, laws, and principles from many disciplines.

The Hudson’s content draws on the research and writing of—among others—historians, naturalists, scientists, and government officials. However, it is not intended to be an academic or scientific work; thus we have not cited the source of every fact or observation that originated in earlier works. Key references are acknowledged in the Sources and Suggested Readings section.

Any book dealing with science must confront the challenge of complex terminology. Scientists sort out phenomena, particles, organisms—whatever it is they study—and assign names to the categories they create. In his authoritative Freshwater Invertebrates of the United States, Robert W. Pennak quotes Lewis Carroll’s Alice in Wonderland:

What’s the use of their having names, the Gnat said, if they won’t answer to them?

No use to them, said Alice; but it’s useful to the people that name them, I suppose.

The terminology created may seem daunting, but it is a necessity for scientists who must be very precise in their descriptions.

We have made an effort to limit terminology, but there are scientific terms that are very useful in discussing the Hudson River in any detail. Most will be defined where and when they first appear in the text, as well as in the appended glossary. In studying history, a major obstacle is the memorization of dates, the names of people and places, or similar facts. Like scientific terms, they have their place in discussions of the Hudson. But pay attention to them as you pay attention to minutes passing on a clock, reference points against which major themes of American history play out on the stage provided by the Hudson. Just as species descriptions illustrate biological diversity and junctures in the network of ecological relationships, so do accounts of specific events of the Hudson’s history, with their associated dates, people, and sites, illuminate the interplay of far-reaching social, political, and cultural ideas and movements.

Scientific information in the book has been updated, as has the status of the various environmental battles centered on the river. Revisions in this edition also include a new chapter on climate change and highlight the many ways in which Hudson Valley residents can engage with the river through joining citizen science projects, visiting relevant historic sites, and using online resources.

In years of leading Hudson River workshops for teachers, we have learned that educators attend them not only—or even mainly—because they expect the practical reward of being able to enrich their curricula or programs. Most participate because they are fascinated by the Hudson and feel that it is a vital part of their lives and communities. For all those who dwell along the river, it is our hope that this book will reinforce that fascination and strengthen that sense of the Hudson’s vitality and importance.

Stephen P. Stanne

Roger G. Panetta

Brian E. Forist

Maija Liisa Niemistö

THE HUDSON

Lake Tear of the Clouds nestles high on the southwest shoulder of Mt. Marcy, New York State’s highest peak. (Photo by Kim Cuppett.)

Chapter 1

A PHYSICAL OVERVIEW OF THE HUDSON

The Chapter in Brief

The Hudson River flows 315 miles—507 kilometers (km)—from Lake Tear of the Clouds in the Adirondacks to the Battery in New York City. Its course and shoreline topography result from erosion by water and glacial ice over the past sixty-five to seventy-five million years. The river is influenced by ocean tides to Troy, 153 miles (246 km) north of the Battery. Diluted seawater typically ranges upriver to a point between the Tappan Zee and Newburgh, depending on the volume of runoff from the Hudson’s watershed. The lower Hudson is an estuary, a type of ecosystem that ranks among the most productive on the planet.

The Hudson’s Origins

To begin a study of the Hudson River at its source, lay out a map of eastern New York State and trace the blue line north from New York Harbor along the cliffs of the Palisades, under the ramparts at West Point, through the sunset shadows of the Catskill Mountains, past the capital city of Albany, and on into the Adirondack Mountains. There, at the confluence of two creeks near Henderson Lake, the name Hudson River disappears; the map offers the option of following Calamity Brook northeastward or the outlet from Henderson Lake westward.

Looking for the highest body of water feeding the Hudson, turn northeast and face the heart of the High Peaks region. Continue upward along Calamity Brook, the Opalescent River, and little Feldspar Brook to find, as Verplanck Colvin did in 1872, a tiny lake perched 4,322 feet—1,317 meters (m)—up on the southwest side of Mt. Marcy, New York State’s highest peak at 5,344 feet (1,629 m). Colvin, an indefatigable explorer and surveyor of the Adirondacks, described his discovery as a minute, unpretending tear-of-the-clouds—as it were—a lonely pool shivering in the breezes of the mountains. Thus the Hudson’s source was named—Lake Tear of the Clouds.

THE WATER CYCLE

The clouds that so often cap the Adirondacks, the snow that falls on Mt. Marcy’s shoulder, the raindrops that dimple the surface of Lake Tear, the fog that condenses in tiny droplets on spruces lining Feldspar Brook, and their union in the runoff that eventually becomes the Hudson—all are manifestations of a much larger stream of water. These visible forms are linked to water hidden in the ground and pulled up in the stems of plants to their leaves, from which it is transpired into the atmosphere. There it joins water vapor invisibly rising from great oceans and tiny puddles, moving with weather systems from continent to continent or from a valley to its bordering hills, and once more taking forms that we can see—clouds and precipitation. This unending movement of water, seen and unseen, constitutes the water cycle.

In this simplified illustration of the water cycle, rain falls to earth (1) and runs off into streams flowing seaward (2) or enters the ground (3). As groundwater moves toward the ocean, it feeds streams and lakes and is taken up by plants (4), from which it is transpired into the atmosphere as water vapor. Evaporation from the sea (5) and other surface waters also supplies water vapor to the atmosphere. There, the vapor condenses to form clouds (6) and eventually falls to earth again as precipitation.

The water cycle is a circulatory system supporting life on earth much as arteries and veins support human existence. Like blood, water transports substances needed by living organisms in the Hudson and its valley. In our bodies, the heart is the pump that circulates blood through the system. In the water cycle, the sun’s energy evaporates water and moves it from place to place in the atmosphere, while gravity causes precipitation to flow as runoff across the land and as groundwater under the land’s surface.

THE HUDSON’S WATERSHED

From Lake Tear of the Clouds to the Battery at the southern tip of Manhattan, the Hudson follows a course 315 miles (507 km) long. Joining it along the way are many tributaries, the largest being the Mohawk River, which flows in from the west at Cohoes. The area of land drained by the Hudson and its tributaries—the Hudson’s watershed—totals 13,390 square miles (34,680 km²), mostly in eastern and northern New York State. Small portions of this area reach into Vermont, Massachusetts, Connecticut, and New Jersey.

Besides gathering rivulets into creeks and creeks into a river, the watershed sustains the Hudson ecosystem with essential nutrients that fertilize aquatic plants and with autumn’s faded leaves and other organic matter to be recycled in food chains. The watershed’s contributions are greatly influenced by human land use, sometimes with less desirable outcomes. These include pollution from—among many sources—factory pipes, parking lots, farm fields, malfunctioning septic systems, and suburban lawns.

The watershed, particularly the portion drained by the Mohawk, is also the major source of clay, silt, sand, and other sediment entering the Hudson. Some settles out in the river, becoming a foundation for the establishment of plant and animal communities, and some remains suspended in the water, giving the Hudson a muddy appearance. This turbidity is especially noticeable after major rainstorms, when the river resembles café au lait due to the volume of sediment in runoff. Particles of sediment settle and fill in certain stretches of the river, notably at Haverstraw Bay and from Kingston north to Albany. In these areas, the ship channel must be maintained by dredging—digging out bottom mud—since under federal law, the channel between New York and Albany must be kept at least 32 feet (9.8 m) deep. This allows large barges and ocean-going ships to reach the Port of Albany.

AN ARM OF THE SEA

In length and watershed area the Hudson does not rank highly among American rivers. Yet numbers do not tell the full story, as one can appreciate when gazing across wide bays at Newburgh, the Tappan Zee, and Haverstraw, the latter being where the Hudson is widest—about 3.5 miles (5.6 km) east to west.

Such expansive grandeur results from the fact that for nearly half its length, the Hudson is an arm of the sea. In plunging over a dam at Troy, the river falls to a level only a few feet above that of the Atlantic Ocean, entering a long narrow trough in which its flow is governed less by the pull of earth’s gravity than by the pulse of ocean tides responding to the gravity of the moon.

Gathering waters from Adirondack tributaries, the Hudson rushes through its gorge at Blue Ledge, near the village of North Creek.

The lowest portions of the Hudson’s valley south of Troy were drowned when the sea level rose at the end of the most recent ice age. The deepest spot known is at World’s End near West Point, where the most recent riverbed mapping found bottom 177 feet (54 m) down.¹ The Hudson’s gorge through the Highlands is its deepest stretch, with many charted depths greater than 100 feet (30.5 m).

Bordered on the west by the northern portion of the Palisades, Haverstraw Bay is the widest spot on the Hudson.

THE HUDSON FJORD

With its great depths and cliffs slanting steeply into the river, the Hudson’s route through the Highlands reminds many observers of the scenic fjords of Norway. Fjords are troughs eroded below sea level, often to great depths, by glacial ice. They are deepest not at their mouths but upstream, where the ice was thickest and its erosive power greatest. A shallower, less eroded sill of bedrock is usually present at their mouths.

The bedrock underlying the lower Hudson is largely buried below layers of sediments, some deposited by the river, others dropped by the ice sheets or their meltwaters. These deposits fill a much deeper gorge scoured out by the glaciers. Drilling during construction of aqueducts and bridges across the river found that the deepest portions of this gorge lie at least 750 feet (229 m) below sea level at the northern entrance to the Highlands, and 740 feet (226 m) down at the Tappan Zee. Nearer the ocean, geologists have found a shallower sill: bedrock is less than 200 feet (61 m) down at the Verrazzano Bridge. Thus, this portion of the Hudson qualifies as a fjord.

OF TIME AND RIVER FLOWING

The handiwork of water and ice over millions of years created a waterway that offered immense advantages to the humans who eventually settled in the Hudson Valley. In a time before railroads and interstate highways, water-based transportation was the fastest, most comfortable, and most capacious way of moving goods and people long distances. The river’s surface is unbroken by rapids or waterfalls for more than 150 miles (241 km) inland. Its gorge through the Highlands is the only sea-level passage through the Appalachian Mountain range. This fact figured prominently in DeWitt Clinton’s vision for a water route linking America’s expanding west to its Atlantic coast, a vision realized in the Erie Canal.

The Troy Dam marks the upriver limit of tidal influence on the Hudson. A lock here allows boat passage via the river to and from the New York State Barge Canal (successor to the famed Erie Canal) and the Champlain Canal.

The river’s general course was probably set starting sixty-five to seventy-five million years ago, long before the great glaciers’ advance. The region’s landscape at the time was very flat, similar to that seen today near the coasts of the southeastern states. The rocks that would later be sculpted into the Highlands and Palisades were buried under coastal plain sediments, over which the ancestral Hudson made its way to the ocean.

Over many millennia the river wore away those sediments, exposing and cutting into bedrock. Gaps carved into the ridges of the Palisades and New Jersey’s Watchung Mountains suggest that the lower Hudson followed a course different from its present route between the Tappan Zee and the Atlantic. It crossed the Palisades at the Sparkill Gap, located a few miles south of the Mario M. Cuomo Bridge, and continued southwest across the Watchungs near Paterson, New Jersey. The river then paralleled the Watchungs south for about 15 miles (24 km) before turning eastward and re-crossing them on its way to the ocean at what is today Delaware Bay.

The Hudson’s established channel through the Highlands was gouged to greater depths by glacial ice, which also steepened the slopes plunging down to the river.

The Sparkill Creek now flows through the low-lying Sparkill Gap, where the Hudson once flowed westward through the Palisades and on to the sea past the site of present-day Paterson, New Jersey, instead of Manhattan.

During the early part of the Ice Age some 2.5 million years ago the Hudson was diverted and flowed south across Queens to reach the Atlantic. Its present course east of the Palisades was eroded by the last southward push of the Pleistocene’s continental glaciers.

SHAPED BY THE ICE SHEETS

At the peak of the final episode of glaciation, the metropolitan New York area was buried under as much as 3,000 feet (914 m) of ice. So much water was frozen in ice sheets worldwide that the Atlantic Ocean was about 400 feet (122 m) lower than it is today.

Debris eroded by the ice sheets was piled up at the limit of their southward advance. At this terminus, the rate of melting equaled the speed of advance; like Cinderella, left without conveyance as her carriage turned back into a pumpkin, the debris was dropped, forming rows of low hills, as ice turned to water. A ridge of such deposits, called a terminal moraine, constitutes the backbone of Long Island and Brooklyn. This ridge extended to Staten Island, damming meltwater from the ice sheets to form Glacial Lake Albany.² Its outlet to the sea went through Hell Gate and Long Island Sound until about sixteen thousand years ago, when huge volumes of water flooded into Lake Albany from another glacial lake in the Wallkill River valley. This event breached the moraine to create the Narrows between Brooklyn and Staten Island.

With sea level much lower at that time, the Hudson flowed an additional 120 miles (193 km) across a wide coastal plain to the Atlantic Ocean. A submerged valley running across the continental shelf—a feature not seen off other East Coast rivers—marks its route. It was deepened by torrential flows of glacial meltwaters from the prehistoric Great Lakes and Lake Champlain, their St. Lawrence River outlet blocked by the ice sheets. These flows carried great loads of sediment—the remains of rock and soil pulverized by the moving ice. Reaching the edge of the continental shelf, these surges of meltwater and accompanying turbidity currents (underwater landslides generated by the buildup of sediment deposits) carved an even deeper gorge—the Hudson Submarine Canyon—southeast of New York Harbor.

Further north, rivers swollen by meltwater carried gravel and sand into Lake Albany and other glacial lakes that pooled behind moraines, glacial debris, and melting ice masses in the region’s valleys. As they entered the lakes and their currents slowed, the rivers dropped this material to form deltas. Much of Croton Point is such a delta, built up by the ancestral Croton River.³ In the still waters of the lake, tiny particles of rock flour—soil and rock ground up by the glaciers—gradually settled to the bottom, forming deep beds of clay. These beds later supplied the raw material for the brick industry that flourished along the Hudson.

As the post-glacial thaw continued, sea level rose. About twelve thousand years ago, the ocean reached the Narrows and seawater pushed into the Hudson. Sea level rise tapered off globally some six thousand years ago and over most of the last two thousand years remained fairly stable. However, it started upward again in the late 1800s, an increase linked to climate change.

RISING SEAS, RISING RIVER

Today’s rising sea levels are mainly the result of global warming due to surging levels of atmospheric carbon dioxide (CO2) from burning fossil fuels. Carbon dioxide traps heat generated by sunlight, keeping it from radiating back into space. This phenomenon, known as the greenhouse effect, has elevated sea level in two ways. Oceans have warmed, and as water warms it expands. This thermal expansion accounts for about one-third of sea level rise over the last century. Meltwater from shrinking land-based glaciers accounts for the other two-thirds.

Globally, sea level has risen 8 inches since 1880, and more along the U.S. Atlantic coast. Data from the National Oceanic and Atmospheric Administration’s (NOAA) tide gauge at the Battery reveal that rising sea level has pushed the Hudson up 12 inches over the last hundred years, and since the start of this century the rate of rise has been increasing. New York State predicts that water levels in the lower Hudson may be 2 to 6 feet (0.6 to 1.8 m) higher by 2100, depending on what happens to CO2 emissions and the rate of melting in the world’s two largest reservoirs of land-based ice, Greenland and Antarctica.

A River That Flows Two Ways

The breach of the terminal moraine at the Narrows and rising sea levels opened the Hudson to the ocean’s influence. The most visible evidence of the Atlantic Ocean’s sway over the river are high and low tides and their accompanying tidal currents.

Tides occur in patterns set by a celestial dance involving the earth, the moon, and, to a lesser extent, the sun. The most obvious of these patterns is the daily tidal cycle along the Atlantic coast, in which two high tides and two low tides occur over roughly twenty-four hours. A simple overview of how tides work will be helpful in understanding the Hudson.

THE PULL OF THE MOON …

The moon is large enough and near enough to exert considerable gravitational pull on the earth. In the oceans, this attraction literally causes water to bulge out toward the moon. This bulge remains positioned under the moon (slightly behind it due to inertia and friction) as the earth spins on its axis. Thus, while beachcombers on the Atlantic coast watch the moon rise, they are being inexorably carried into a mound of water, evident in the rising tide lapping around their feet.

[high tide]

[low tide] The effects of ocean tides in the Hudson are evident at Poughkeepsie, where the average high tide is 3 feet (0.9 m) higher than the average low tide.

The water in this bulge is also pulled horizontally as the earth rotates under the moon. As the tidal bulge moves into New York Harbor and past the Battery on Manhattan’s southern tip, strollers gazing out at the Statue of Liberty might notice not only that the water is rising along pilings lining the shore but that the Hudson’s current is pushing northward, in from the sea toward the mountains.

Hours later, after the beachcombers and strollers have gone to bed, the Atlantic coast has passed under the moon and reached the backside of the bulge. The tide is now falling, and the current at the Battery reverses and starts flowing toward the sea once more. The native peoples of the valley have a descriptive name for the river: Muhheakantuck, often loosely translated as river that flows two ways.⁴

A second tidal bulge forms at a point on the earth opposite the moon. Between the two bulges ocean levels are lower, resulting in low tides. Thus, in the twenty-four hours it takes the earth to spin around its axis, a given point on the Atlantic coast will usually experience two high tides and two low tides, one following the other roughly every six hours.⁵

… AND OF THE SUN

In addition to this daily rhythm, tides vary cyclically over the twenty-eight-day lunar month—the time the moon takes to circle once around the earth. The lunar month is marked by the phases of the moon. More extreme tides (higher highs and lower lows) occur when the moon is in its new or full phase; these are the spring tides. During the moon’s first and last quarter, the range between high and low tide heights is minimal; these are the neap tides.

Spring and neap tides reflect the interaction of the sun’s gravitational attraction with the moon’s. One might expect the sun to have greater tidal influence because it is so much bigger than the moon. However, gravitational attraction decreases with distance. Since the sun is much further away from the earth, its effect in raising tides is only about half that of the moon’s.

Spring tides occur when the moon is new or full. The sun, moon, and earth are all in line, so that the sun’s gravity works with the moon’s to create a more extreme tidal bulge evident in higher high tides and lower low tides.

UP AND DOWN, BACK AND FORTH

The rise and fall of ocean tides affects the river all the way to the dam at Troy, 153 river miles (246 km) north of the Battery. In fact, the Hudson’s maximum tidal range (the difference in level between average high and low tides) of 4.7 feet (1.4 m) is observed at Troy, caused by the crest of the tidal wave being forced upward as it reaches this shallow and narrow section of the river. Tidal range is least along the mid-Hudson, averaging only 2.7 feet (0.8 m) at West Point.

Like high and low tides, reversals in current direction follow roughly a six-hour schedule. The current draining the river south toward the ocean is called the ebb; that pushing north from the ocean is called the flood.

The velocity of the Hudson’s currents varies depending on the strength of tidal forces at a given time, location along the river, the volume of runoff entering the estuary, and weather conditions. Currents are swiftest near the George Washington Bridge (average flood 1.9 mph; ebb 2.6 mph) and further north around Catskill (flood 1.9 mph; ebb 2.4 mph).

An adventure like Huckleberry Finn’s raft trip down the Mississippi would be quite a different experience on the Hudson below Troy. Instead of progressing steadily downstream, a rafter on the Hudson might admire the scenery while drifting southward on an ebb current for about six hours, then view the same scenery again as the flood current pushed the raft back upstream for the next six hours, and endure it yet again as the ebb current took over once more. The ebb current is generally stronger than the flood; thus our Hudson River rafter would eventually reach New York Harbor.

How long would the trip take? That depends on the flushing rate—the time it takes water entering the estuary at Troy to reach the harbor. The rate varies greatly, depending on freshwater runoff. In very dry summers with minimal runoff, the raft’s net movement downriver might only be 1.5 miles (2.4 km) per day. At that rate, it would take 102 days to float from the head of tide at Troy to New York Harbor. On the other hand, a major rainstorm can cause heavy runoff that presses against and shortens the duration of the flood current while strengthening the ebb. This speeds up the flushing rate, perhaps to 5 miles (8 km) per day, reducing the rafter’s trip to about 30 days.

Neap tides occur at the moon’s first and last quarters, when sun and moon are at right angles relative to earth. The moon raises the high tides alone, without help from the sun; thus these highs are lower than normal. However, the sun’s pull does act on the low tide area of the bulge, causing higher low tides.

At any given time different parts of the river will be experiencing different tides. Since the Hudson’s tides are generated in the ocean, there is an increasing lag in the timing of a specific event as one moves away from the sea. The crest of a high tide which occurs at the Battery at 12:00 noon will not reach Poughkeepsie until about 4:30 P.M., and Albany around 9:00 P.M. The accompanying table shows lag times based on high and low tides at the Battery. Tide predictions are available for numerous locations along the river.

STORM SURGE AND BLOWOUT TIDES

These published tide predictions take into account the relative positions of the earth, moon, and sun, coupled to knowledge of how geography influences water levels and currents in a particular waterbody. These predictions cannot account for the effects of daily weather as they are made years in advance. For example, extreme rain and accompanying runoff will sometimes suppress the flood current in northern reaches of the estuary.⁶

Data from National Ocean Survey Tide Tables.

Winds can have major impacts on currents and water levels. Strong easterly winds off the Atlantic, associated with nor’easters and hurricanes, can create storm surge—a bulge of ocean water pushing toward the coast and into the estuary.