Exploring the Watershed

From the heights of Slide Moun­tain to the Eso­pus Creek val­ley, the Ashokan Water­shed con­tains a diverse array of geo­graph­ic fea­tures. An abun­dance of streams pro­vide habi­tat for a vari­ety of wildlife, many oppor­tu­ni­ties for out­door recre­ation, and drink­ing water for 9 mil­lion New York City and Hud­son Val­ley res­i­dents. The Ashokan Watershed’s social and nat­ur­al his­to­ry make this area an endear­ing and spe­cial place to res­i­dents and vis­i­tors alike.

Social His­to­ry  |  Cre­ation of the Reservoir
Nat­ur­al His­to­ry | Geol­o­gy  |  Phys­i­cal Char­ac­ter­is­tics  |  Cli­mate & Hydrol­o­gy  | Land Use & Land Cover

Map of the Ashokan Watershed

Click to view larg­er image.

Social History of the Ashokan Watershed

The first inhab­i­tants of the Ashokan Water­shed were Native Amer­i­cans of the North­east­ern Wood­land tribes. In the 1600’s, the Lenni Lenape of the Eso­pus Tribe liv­ing in the water­shed by hunt­ing and farm­ing, began encoun­ter­ing Dutch set­tlers mov­ing to the New World. Lat­er, waves of immi­grants seek­ing new oppor­tu­ni­ties joined the Amer­i­can melt­ing pot. These new arrivals slow­ly pushed the Native peo­ples out of their ances­tral land.

Fol­low­ing the Rev­o­lu­tion­ary War and the estab­lish­ment of the Unit­ed States gov­ern­ment, the Ashokan Water­shed area and much of the Catskill Moun­tain region became a cen­ter for resource extrac­tion. Abun­dant hem­lock trees pro­vid­ed tan­nin nec­es­sary for the tan­ning of leather prod­ucts. Tan­ner­ies, char­coal kilns, and quar­ries sprung up along area streams and trade routes. The tan­nin and leather trade was so large that the Catskill Moun­tain region pro­vid­ed most of the leather goods to the Union Army dur­ing the Civ­il War.

In 1870 the rail­road was built to Phoeni­cia, NY, pro­vid­ing a quick and easy way to bring goods to mar­ket, but by the late 19th Cen­tu­ry most of the acces­si­ble hem­locks were cut, oth­er resources had been exhaust­ed and indus­tries began leav­ing the area. With the rail­road, how­ev­er, came a grow­ing sum­mer tourist trade, and in 1904 the estab­lish­ment of the Catskill Park per­ma­nent­ly marked the region as a vaca­tion des­ti­na­tion. For much of the ear­ly 20th cen­tu­ry, City res­i­dents trav­eled north to area board­ing hous­es (many in close prox­im­i­ty to streams) to escape the bru­tal New York City sum­mer heat and enjoy care­free days of fish­ing, hik­ing, camp­ing, and oth­er recre­ation­al activities.

Today, almost the entire water­shed lies with­in the state-des­ig­nat­ed Catskill Park, a checker­board of pub­lic and pri­vate land. As of 2012, the New York City Depart­ment of Envi­ron­men­tal Pro­tec­tion owned about 11% of the land area in the Ashokan Water­shed. Anoth­er 55% of the land area was esti­mat­ed to be in pub­lic own­er­ship, much of it with­in the For­est Pre­serve man­aged by the New York State Depart­ment of Envi­ron­men­tal Con­ser­va­tion. For­est Pre­serve land can­not be sold or trans­ferred with­out amend­ing the state constitution.

The water­shed con­tains sev­er­al ham­lets of rel­a­tive­ly con­cen­trat­ed res­i­den­tial and com­mer­cial devel­op­ment, includ­ing the ham­lets of Boiceville, Mount Trem­per, Phoeni­cia, Shan­dak­en, Big Indi­an, and Pine Hill. The Town of Shan­dak­en has expe­ri­enced a steady increase in pop­u­la­tion since the 1940s, reach­ing pop­u­la­tion lev­els equal to a pre­vi­ous pop­u­la­tion peak in the 1890s with the rail­road and tan­nery indus­try boom.

The Ashokan Reservoir and the Creation of the New York City Watershed

By the late 19th Cen­tu­ry, New York City had become a bustling port city, whose grow­ing pop­u­la­tion had begun to over­whelm the City’s fresh water sup­ply. Major droughts in 1895 and 1896 fur­ther stressed fresh water resources. Although the City had cre­at­ed a sys­tem of reser­voirs in Westch­ester Coun­ty, they were not ade­quate to sup­ply its needs.

In 1905, after care­ful study and analy­sis, plan­ners in New York decid­ed that the Catskill Moun­tain region would be ide­al for a new reser­voir sys­tem. Using emi­nent domain, New York City acquired the prop­er­ties of res­i­dents in the area that would become its new reser­voir sys­tem. Some Catskill fam­i­lies lost their homes and believed that they were not com­pen­sat­ed just­ly. Although hard feel­ings linger to this day, new part­ner­ships are begin­ning to change that dynam­ic toward one of care­ful cooperation.

Work on the Ashokan Reser­voir began in 1908 and was com­plet­ed in 1915. The Eso­pus Creek was now bro­ken into an upper and a low­er part, with the Upper Eso­pus stretch­ing from its head­wa­ters at the top of Slide Moun­tain to the West Basin of the reser­voir. The Schoharie Reser­voir in Greene and Schoharie Coun­ties was built between 1919 and 1928, as was the Shan­dak­en Tun­nel, which brought water from the Schoharie Reser­voir to the Eso­pus Creek near Allaben to be deliv­ered into the Ashokan Reser­voir. The years to come would see the con­struc­tion of addi­tion­al reser­voirs in Ulster, Sul­li­van and Delaware Counties.

The Ashokan is one of the largest reser­voirs in the New York City water sup­ply sys­tem. At the time of its con­struc­tion, it was con­sid­ered one of the won­ders of the mod­ern world — not only for the feat of engi­neer­ing required to build the reser­voir itself, but also the Catskill Aque­duct that brought the drink­ing water from the reser­voir south over 163 miles of ter­rain to the Ken­si­co Reser­voir in Yonkers, NY. Con­sist­ing of two basins sep­a­rat­ed by a con­crete divid­ing weir, the Ashokan Reser­voir holds 122.9 bil­lion gal­lons of water at full capac­i­ty. Includ­ing the water it receives from the Schoharie Reser­voir, the Ashokan sup­plies approx­i­mate­ly 40% of New York City’s dai­ly drink­ing water needs in non-drought peri­ods. The Eso­pus Creek enters the Ashokan’s West Basin and after a peri­od of set­tling flows over a weir or is released into the East Basin. From the East Basin, water is released into the Catskill Aque­duct for drink­ing water use, or dis­charged via a release chan­nel into the low­er Eso­pus Creek. The reservoir’s drainage basin is 255 square miles, the large major­i­ty of which is rep­re­sent­ed by the towns of Olive, Shan­dak­en, Wood­stock, and Hur­ley in Ulster Coun­ty, and Lex­ing­ton and Hunter in Greene Coun­ty.  Back to top

Natural History of the Ashokan Watershed


The entire Catskill Moun­tain region (which includes the Ashokan Water­shed) was cre­at­ed by the inter­ac­tion of water on rock. Much of its phys­i­cal char­ac­ter today is a con­se­quence of the most recent ice ages of 12,000 to 25,000 years ago when the Catskills were most­ly occu­pied by glacial ice or the melt­wa­ter streams and lakes that fol­lowed the ice’s retreat. The moun­tains are com­posed of Devon­ian-aged sed­i­men­ta­ry bedrock (sand­stones, shales and con­glom­er­ate formed in ancient riv­er val­leys). Bro­ken bits of this bedrock are the source of almost all of the stream sed­i­ment seen today — from clay to boul­ders. Cob­bles and boul­ders in the streams have erod­ed from the thick-bed­ded sand­stones that shape the moun­tain cliffs. The red­dish, lay­ered clays exposed in stream­banks are ancient glacial lake sed­i­ments erod­ed from red silt­stones and shales that form many of the moun­tain slopes. The nature of the glacial lake deposits and the dense, clay-rich glacial till that can form some chan­nel bound­aries makes them sus­cep­ti­ble to stream ero­sion. Back to top

Physical Characteristics

The Ashokan Reser­voir Water­shed is 255 square miles in the south-cen­tral Catskill Moun­tain region and con­tains at least 459 miles of streams. The Ashokan Reser­voir is pri­mar­i­ly fed by the 330-mile Eso­pus Creek sys­tem drain­ing about 75% of the water­shed. Addi­tion­al drainages include the Bushkill and small­er trib­u­taries that feed direct­ly into the Ashokan Reser­voir. The Ashokan Water­shed con­tains some of the most rugged ter­rain in the Catskills. Slide Moun­tain is the high­est peak with­in the water­shed at 4,180 ft. above sea lev­el. The Ashokan Reser­voir, by con­trast, is 635 ft. above sea level.

Assess­ments through­out the water­shed have shown that over­all eco­log­i­cal and phys­i­cal con­di­tion of streams is quite good. Closed-Canopy Flood­plain For­est is the most com­mon ripar­i­an cov­er type fol­lowed by Mowed Lawn with Trees (in the Eso­pus Creek water­shed). A major­i­ty of banks along the Eso­pus Creek are bor­dered by more than 100 feet of ripar­i­an buffer. Fish and wildlife are abun­dant through­out the sys­tem, although habi­tat con­di­tions dimin­ish with dis­tance down­stream. Streams of the Ashokan Water­shed are known for their trout fish­ery and sup­port­ing macroin­ver­te­brate com­mu­ni­ties, but you may also find stream sala­man­ders, green frog, snap­ping tur­tle, east­ern paint­ed tur­tle, wood tur­tle, and north­ern water snake in our stream cor­ri­dors. Many bird species use the water­shed’s streams, notably bald eagle, great blue heron, green heron, mal­lard, Amer­i­can black duck, wood duck, spot­ted sand­piper, belt­ed king­fish­er, bank swal­low, and Louisiana waterthrush.

The trout fish­ery is sus­tained in part by cold water seeps in trib­u­taries where spawn­ing occurs. The Eso­pus Creek also receives flows aug­ment­ed by releas­es from the Schoharie reser­voir through an under­ground aque­duct, known as the Shan­dak­en Tun­nel. The Tun­nel emp­ties into the Eso­pus Creek through a por­tal locat­ed in the ham­let of Shan­dak­en just west of Phoeni­cia. New York City is required to obtain a State Pol­lu­tion Dis­charge Elim­i­na­tion Sys­tem per­mit to reg­u­late the allow­able flow, tem­per­a­ture, and tur­bid­i­ty from the tun­nel releas­es to pro­tect trout and oth­er organisms.

Stream con­di­tions in the Eso­pus Creek down­stream from the por­tal are char­ac­ter­ized by cold water tem­per­a­tures and high flow and tur­bid­i­ty dur­ing the sum­mer. Cold water tem­per­a­tures are ben­e­fi­cial to trout, while tur­bid­i­ty can be detri­men­tal to the health of fish and oth­er aquat­ic organ­isms, although lit­tle quan­ti­ta­tive infor­ma­tion exists for the impacts of tur­bid­i­ty on fish pop­u­la­tions in the Esopus.

A study of brown trout response to tem­per­a­ture, tur­bid­i­ty, and flow regimes con­duct­ed dur­ing the sum­mer of 2010 found that trout both above and below the aque­duct were stressed, with some indi­ca­tion of stress-refuge imme­di­ate­ly down­stream from the Shan­dak­en Tunnel’s por­tal (Ross 2012). How­ev­er, the study could not deter­mine whether this refuge would ben­e­fit trout at the pop­u­la­tion level.

A sec­ond study con­duct­ed between 2009 and 2011 com­pared water qual­i­ty, hydrol­o­gy, tem­per­a­ture, and bio­log­i­cal health of Eso­pus Creek (fish, macroin­ver­te­brate and peri­phy­ton) com­mu­ni­ties upstream and down­stream of the por­tal. The study con­clud­ed that though fish com­mu­ni­ties were altered at sites near and down­stream from the por­tal, many changes were pos­i­tive and could be relat­ed to changes in tem­per­a­ture or habi­tat qual­i­ty and quan­ti­ty (Baldigo et al. in prep). The only eco­log­i­cal impair­ment linked direct­ly to the Shan­dak­en Tun­nel was a reduc­tion in pri­ma­ry pro­duc­tiv­i­ty at sites imme­di­ate­ly down­stream from the por­tal. Anoth­er poten­tial adverse effect found was a sig­nif­i­cant­ly low­er den­si­ty of juve­nile brown trout down­stream of the por­tal. The authors not­ed that while these effects could be caused by impaired water qual­i­ty, the aque­duct was only a minor con­trib­u­tor to tur­bid­i­ty and sus­pend­ed sed­i­ment loads in the upper Eso­pus basin dur­ing the study peri­od. In a sep­a­rate study, researchers deter­mined that sev­en trib­u­taries and the last site upstream of the por­tal each con­tribute on aver­age 2–10 times the amount of sus­pend­ed sed­i­ment and tur­bid­i­ty to the upper basin than the por­tal did from 2010-11 (McHale and Siemion in prep).

Japan­ese knotweed, Didy­mo, and oth­er inva­sive species are anoth­er eco­log­i­cal con­cern in the water­shed. Water qual­i­ty is very good in most por­tions of the water­shed, except­ing local­ized issues. Tur­bid­i­ty is the pri­ma­ry water qual­i­ty con­cern, and is tied to the cli­mate, geo­log­ic his­to­ry, and stream man­age­ment regime in the water­shed. Although ero­sion of stream banks is local­ized (and gen­er­al­ly not sys­temic), sec­tions of erod­ing stream are threat­en­ing devel­oped prop­er­ty and infra­struc­ture and require man­age­ment. Flood­ing and ero­sion are close­ly linked in the Ashokan Water­shed. Large floods can ini­ti­ate bank ero­sion. A recent increase in the fre­quen­cy of large flood events and result­ing chan­nel adjust­ments may have exposed more of the sys­tem to ero­sion, at least tem­porar­i­ly. Source reduc­tion efforts are focused on chron­ic sources, such as stream chan­nel and adja­cent hill­s­lope ero­sion into glacial lega­cy sed­i­ments, and should over time reduce tur­bid­i­ty pro­duced dur­ing mod­er­ate and low flows. Back to top

Climate and Hydrology

The south­east­ern Catskills with its high relief and high ele­va­tions cap­tures a lot of water from humid air. When air is lift­ed up over a moun­tain range, the air expands, cool­ing and con­dens­ing into mois­ture, which takes the form of clouds and pre­cip­i­ta­tion. The effect has been observed around Slide Moun­tain with a “bulls eye” of high annu­al rain­fall, the high­est on aver­age in New York Sate. His­tor­i­cal­ly win­ters in the area have left a snow­pack in the moun­tains, and most large floods result­ed from rain on snow melt, usu­al­ly in the spring. How­ev­er, the region is not immune to the destruc­tive path of hur­ri­canes and trop­i­cal storms, which gen­er­al­ly occur in late sum­mer and ear­ly fall. This was seen most recent­ly with Trop­i­cal Storms Irene and Lee, which hit the area in August and Sep­tem­ber 2011. Although glob­al cli­mate fore­casts can be dif­fi­cult to scale down to local regions, it is expect­ed that rain­fall events with greater than one inch of pre­cip­i­ta­tion are like­ly to increase in fre­quen­cy and mag­ni­tude. Drought peri­ods are also expect­ed to become more extreme (in-between seri­ous rain events), while snow­pack amounts and dura­tion are expect­ed to decrease. As the fre­quen­cy and mag­ni­tude of mid-sized storms increas­es, stream chan­nels will like­ly enlarge to accom­mo­date the larg­er flows until a new equi­lib­ri­um is achieved. Chan­nel enlarge­ment could result in increased sed­i­ment loads (until the stream sta­bi­lizes) and more fre­quent shifts in chan­nel align­ments. Back to top

Land Use and Land Cover

Although for­est cov­ers over 95% of the water­shed today, the 1800’s saw sig­nif­i­cant por­tions of the land cleared of for­est by log­ging and bark peel­ing activ­i­ty (for the tan­ning indus­try). Con­se­quent­ly, streams were altered from the increase in erod­ing sed­i­ment and the most­ly defor­est­ed land­scape. Along Route 28 (the watershed’s main thor­ough­fare) devel­op­ment asso­ci­at­ed with roads, res­i­dences, busi­ness­es, and town cen­ters increas­es the amount of imper­vi­ous sur­faces. Farms were once com­mon, but today there are no large-scale agri­cul­tur­al land uses in the water­shed. Most farms and agri­cul­tur­al activ­i­ties tend to be small with rel­a­tive­ly low impacts on the land­scape and environment.

For more infor­ma­tion on these top­ics see the Eso­pus Creek Stream Man­age­ment Plan.

Addi­tion­al Resources:

Galusha, Diane. Liq­uid Assets: A His­to­ry of New York City’s Water Sys­tem. 1999, Pur­ple Moun­tain Press: Fleis­chmanns, NY.
Social His­to­ry  |  Cre­ation of the Reservoir
Nat­ur­al His­to­ry | Geol­o­gy  |  Phys­i­cal Char­ac­ter­is­tics  |  Cli­mate & Hydrol­o­gy  | Land Use & Land Cover

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