Posts Tagged ‘flood’

5-Year Flood Event in Oliverea

Posted on: November 1st, 2021 by Tim Koch

The Esopus Creek headwaters and Birch Creek both experienced a 5-year flood event as a result of heavy rains on October 25th and 26th. The McKinley Hollow bridge was briefly overtopped due to downed trees blocking the inlet. Oliverea Road (County Route 47) was closed for a number of hours due to flooding in a low lying area where the road and stream are at the same elevation. Ulster County DPW promptly responded to reopen the bridge and road.

McKinley Hollow bridge after large trees were removed from the inlet and placed on the downstream side of the bridge.
Ulster County DPW crews at work reopening a low-lying section of Olivera Road.

A 5-year flood event is the discharge that has a 20% chance of occurring in any given year, based on statistical analysis of at least 10 years of continuous flow data from a USGS stream gage. The “100-year flood” has a 1% chance of occurring in any given year.

The longer the period of record at the gage, the more accurate the probabilities will be for a flood of a given magnitude. The Ashokan Reservoir watershed is one of the most heavily monitored watersheds in New York State, both in terms of the number of gages and the length of time.

The Esopus Creek gage at Allaben has continuous flow data since 1968 (53 years) and the Birch Creek at Big Indian gage has been in operation since 1998 (23 years). The Esopus Creek at Coldbrook gage has been continuously monitoring flow since 1931 (90 years), with monthly flow data dating back to 1914, when the Olivebridge dam and the Ashokan Reservoir were still being constructed.

USGS stream gage on the Esopus Creek at Coldbook, in continuous operation for 90 years. Photo courtesy of USGS.

The Ashokan Watershed Stream Management Program is continuing to assess this flood event and assisting local highway departments with emergency stream repairs as requested. If you need advise on how to manage flooding or erosion on your property in the Ashokan Reservoir watershed, call the stream program office at (845) 688-3047.

How Antecedent Moisture Conditions Impact Flooding

Posted on: August 4th, 2020 by Tim Koch

The amount of precipitation that falls during a storm obviously has an impact on the flood dynamics of rivers and streams. When it rains a lot, rivers and streams can flood dramatically. Flooding from Tropical Storm Irene in 2011 is an all too familiar example.

Flooding in Boiceville as a results of Tropical Storm Irene

Flooding in Boiceville as a results of Tropical Storm Irene

Another important but less well known influence on flooding is the antecedent moisture condition.

To understand what antecedent moisture condition is and how it impacts floods we need to briefly discuss the water balance:

     P = RO + ET + ΔS


     P = precipitation,
     RO = runoff,
     ET = evapotranspiration, and
     ΔS = change in groundwater or soil storage.

This generalized equation is saying that all the water that falls as rain either (1) runs off the surface and becomes flow in a stream, (2) is evaporated or transpired (i.e., used by plants), or (3) is stored in the ground, often in the pore spaces between soil particles.

Soil can be thought of as a giant sponge that can absorb large amounts of water. Antecedent moisture condition is how wet or dry that soil storage sponge is when it starts to rain.

If the soil storage sponge is already saturated before the storm hits, only a small percentage of the rainfall can be absorbed, meaning a large portion of the rainfall total will become runoff. For example, prior to TS Irene in 2011 the antecedent moisture condition was relatively high, as can be seen in the stream gage hydrograph at Allaben (below). The orange triangles represent the average flow for that day (approx 20-30cfs). In the week leading up to Irene, flow in the Esopus Creek was well above average (blue line, 100-200 cfs), indicating that soil moisture levels were already high when the storm hit.

Hydrograph of Esopus Creek at Allaben prior to TS Irene in 2011.

Hydrograph of Esopus Creek at Allaben prior to TS Irene in 2011.

Conversely, if the soil storage sponge is mostly dry when the storm hits a larger percentage of the precipitation can potentially be absorbed, or stored in the soil sponge rather that becoming runoff.  Less runoff can sometimes mean less dramatic flooding.

Today, as we await the arrival of Tropical Storm Isaias, antecedent moisture conditions are relatively low, with flow in the Esopus at Allaben hovering near the approximate average value for early August (20-30 cfs), far less than what it was prior to Irene. There is more room for water in the sponge.

Antecedent moisture conditions prior to the arrival of TS Isaias.

Antecedent moisture conditions prior to the arrival of TS Isaias.

This does not mean that flooding can’t happen when antecedent moisture conditions are low. Even with a dry soil storage sponge, the rate of precipitation is also an incredibly important component of flood dynamics. If rain falls faster than it can infiltrate into the soil, water will run off regardless of antecedent moisture conditions, which can cause damaging flash floods.

The soil storage sponge also has a limited capacity and can become saturated quickly.

Please refer to our recent post on the Flash Flood Watch issued for the Ashokan Watershed for information on how to prepare for a flood.

Flash Flood Watch in Effect for Ashokan Watershed

Posted on: August 4th, 2020 by Leslie_Zucker

High flows on the Esopus Creek in September 2018.

High flows on the Esopus Creek in September 2018.


The National Weather Service has currently issued a flash flood watch for the Ashokan Watershed and much of the rest of the region. Tropical Storm Isaias is currently tracking up the eastern seaboard and bringing heavy rains and damaging winds in its path. While the region has been abnormally dry this summer and the rain itself is welcome, the potential intensity of the downpours could cause localized flooding.

Our Watershed is no stranger to floods but it is still a good idea to be prepared. Throughout the day today, monitor the National Oceanic and Atmospheric Administration’s (NOAA) weather radio and/or local weather stations to get updated information about conditions. You can also monitor local stream gages by going to the United States Geological Survey (USGS) website. The Allaben and Coldbrook stream gages are two major gages on the Esopus Creek.

If possible, please stay home. High winds could topple trees and power lines making roads impassible. In addition, flood waters across roadways are particularly dangerous and lead to a high number of injuries and fatalities each year because water depths are often deceiving. Remember, it only takes one foot of moving water to move most passenger cars and six inches of moving water to knock a person over. If you come across a flooded roadway always Turn Around Don’t Drown!

If your locality issues evacuation orders please evacuate to your nearest emergency shelter immediately and follow all instructions from local officials and emergency responders.

For more information on flood preparedness and what to do in an emergency you can view the AWSMP Flood Emergency Preparedness Guide. Also be sure to check out resources from FEMA’s website and the NY Extension Disaster Education Network (NY EDEN) website.


What is a Stream Feature Inventory (SFI)?

Posted on: July 7th, 2020 by Tim Koch

Hold on tight for a bit of reverse engineering:

The Ashokan Watershed Stream Management Program (AWSMP) is a collaboration between Cornell Cooperative Extension of Ulster County, the Ulster County Soil & Water Conservation District, and the New York City Department of Environmental Protection.

All of the AWSMP’s stream management activities are undertaken in coordination with a local Stakeholder Council. The Stakeholder Council uses recommendations from Stream Management Plans to guide their decision making. Management plans contain a comprehensive review of stream characteristics, data, maps, and recommended management strategies.

The large amount of data and observations required to write a management plan for a stream come from a Stream Feature Inventory (SFI). This is where the rubber meets the road, or, where the wading boots meet the stream bed.

During a SFI, AWSMP staff from the Ulster County Soil & Water Conservation District walk a stream from top to bottom, collecting data on eroding stream banks, logjams, and infrastructure. These data are then analyzed and ultimately used to write a stream management plan.

Join AWSMP Stream Educator Tim Koch as he joins the assessment crew on a SFI of the Elk Bushkill Creek in the Town of Shandaken. This SFI is part of a larger effort by AWSMP to assess multiple headwater tributaries of the Esopus Creek, including McKinley Hollow Creek and Little Peck Hollow Creek. These tributaries may be contributing excessive sediment loads to the upper Esopus  Creek in the Oliverea valley. Excess sediment supply leads to aggradation, or sediment “filling in” the stream, which can subsequently trigger bank erosion and raise flood elevations.  SFI’s of the Esopus Creek headwaters may help to locate and prioritize restoration project sites aimed at reducing the sediment supply reaching the valley.

Stay tuned in the coming months for a SFI report on the Esopus Creek Headwaters and for a new stream management plan for the Little Beaver Kill in the Town of Woodstock.


Mount Tremper Route 28 Bridge Replacement Project Takes Shape

Posted on: April 30th, 2020 by Leslie_Zucker

Land clearing for the new Route 28 Bridge in Mount Tremper begins. Photo by A. Bennett.

Land clearing for the new Route 28 Bridge in Mount Tremper begins. Photo by A. Bennett.


If you’ve been through Mount Tremper recently you may have noticed some major changes including a lot of land clearing and grading. The reason for this is that the New York State Department of Transportation (NYSDOT) is preparing to replace the Route 28 Bridge across the Esopus Creek. The new bridge will be constructed just downstream of the current bridge and will have a higher and much longer span. This will allow more water to pass beneath it during a flood and help prevent a backup of water from flooding the nearby area. During Tropical Storm Irene in 2011, flood waters temporarily prevented traffic from crossing the bridge as well as adjacent State Route 212. Route 28 will also be slightly realigned to match the approach to the new bridge.

There will be even more changes in Mount Tremper. Since 2011, several properties there have been acquired through federal, state, and city acquisition programs. NYSDOT will be using portions of these bought-out properties to realign and raise Route 212. In addition, the existing berm, which is no longer needed to help protect homes, is being removed and the material from it will be used to elevate the road. Without the berm, floodwaters will now be able to better access the floodplain, and when coupled with the larger bridge, flood elevations during the 100-Year Flood are expected to decrease by 6.8 feet at the bridge. Later this year, the Mount Pleasant Bridge, which has been closed to traffic for decades, will be removed which will further reduce flood risk for the area. During the construction of all these projects, Mount Tremper residents will be temporarily getting their mail from the Boiceville Post Office.

We’ll be covering the progress of this project throughout the year so check back regularly for more updates. Be sure to check out our Facebook, Twitter, and Instagram pages for more photos.

Land is being cleared to prepare for the new Route 28 Bridge in Mount Tremper. Photo by A. Bennett.

Land is being cleared to prepare for the new Route 28 Bridge in Mount Tremper. Photo by A. Bennett.

HEC-RAS Workshop a Success!

Posted on: August 16th, 2019 by Tim Koch

The Ashokan Watershed Stream Management Program recently hosted a three-day workshop on how to use HEC-RAS, a powerful computer program used to model flow in stream channels. HEC-RAS is an acronym for the Hydrologic Engineering Center’s River Analysis System. First released in 1995, its capabilities have grown significantly over time. HEC-RAS is now on its fifth version. It is often used to delineate the extent of the 1% annual chance floodplain (aka, the 100-year floodplain) among other regulatory, technical, and environmental uses.

Workshop participants use digital models of the terrain to help model how rivers behave during flood events.

Workshop participants use digital models of the terrain to help model how rivers behave during flood events.

This 3-day workshop focused on using HEC-RAS to aid in the assessment and design of bridges and culverts. Milone and MacBroom, Inc. (MMI) were contracted to conduct the hands-on workshop to an audience of twenty people. Participants included staff and managers from County Departments of Public Works and Town Highway Departments within the West of Hudson Water Supply watersheds. Others in attendance included flood hazard mitigation personnel from NYC DEP, Stream Management Program staff, DEC hydrologists, and folks from Riverkeeper.

HEC-RAS requires site-specific input data to accurately model flows and floods. Thus, the workshop had a field component where people were taught where to place stream cross sections in relation to the bridge, how to conduct pebble counts to determine size distribution of sediment particles on the stream bed, and how to measure specific components of bridges and culverts required to build a HEC-RAS model. Only local data were used, and the workshop centered around modeling existing conditions and proposed alternatives for an under-sized bridge in the Ashokan Reservoir watershed.

Workshop participants investigate the Fox Hollow Road bridge over the Esopus Creek. Measurements taken on site were used to model different bridge replacement scenarios in order to increase community resilience during floods.

Workshop participants investigate the Fox Hollow Road bridge over the Esopus Creek. Measurements taken on site were used to model different bridge replacement scenarios in order to increase community resilience during floods.

It is important that bridges and culverts are sized properly to pass flows that the structure is likely to see over the course of its life. Undersized bridges and culverts not only worsen flooding, but also fragment aquatic ecosystems and can create instability in the stream channel that can propagate significant distances upstream and downstream from the structure and lead to other damage.

This workshop was aimed at empowering local engineers and highway department staff to make informed decisions when managing road-stream crossings (i.e., bridges and culverts.) Properly sized crossings help to increase community resilience to climate change, improve aquatic habitat, and help to maintain water quality in the Esopus Creek and its tributaries.

Elevation and Floodproofing Workshop Advances Flood Mitigation

Posted on: April 12th, 2019 by Leslie_Zucker

A workshop participant observes an engineered flood vent at the Elevation and Floodproofing Workshop held on March 26 and 27, 2019. Photo by Tim Koch.

A workshop participant observes an engineered flood vent at the Elevation and Floodproofing Workshop held on March 26 and 27, 2019. Photo by Tim Koch.


Potentially thousands of structures across the NYC West of Hudson Watershed are located within mapped FEMA floodplains. Many are located in downtown hamlet areas and are vital to the local economy. More intense flood events and rising flood insurance rates are threatening these structures and the communities that rely on them for tax base, habitation, economic activity, and sense of place.

Property owners in flood zones are advised to reduce their flood risks and take action. A range of risk reduction measures are being tested and implemented across the country. The Ashokan Watershed Stream Management Program brought speakers with national expertise to the region on March 26 and 27 to deliver a workshop for local officials to learn more about elevation and floodproofing of structures. The workshop was held at the Emerson Inn in Mount Tremper and attended by nearly 50 building department and other officials from Ulster, Greene, Sullivan, and Delaware counties.

The workshop featured presenters from Ducky Johnson Home Elevations out of Harahan, LA, and consultants recently retired from the NYS Dept. of Environmental Conservation and the U.S. Army Corps of Engineers.

“Every dollar spent on mitigation saves six dollars in recovery costs,” said Rod Scott of Ducky Johnson. “Elevation and dry flood proofing are proven flood hazard mitigation techniques used to reduce flood risk and flood insurance premiums,” he said.

In the 2018 hurricane season alone, U.S. territories experienced 15 storms and 8 hurricanes responsible for $50 billion in damage. In response to this “new normal” of billions in annual losses due to property damage, Congress has mandated flood insurance rate hikes for structures with mortgages in the FEMA floodplain.

“Elevating or floodproofing structures provides a way for communities to keep their building stock, and their tax base stable while also decreasing flood insurance premiums for the owners and lessening their risk of flood-related damage,” said Brent Gotsch, Resource Educator for Cornell Cooperative Extension of Ulster County and organizer of the workshop. “With increasing precipitation patterns and more damaging flood events, it’s vital that communities consider using these methods to adapt and become more resilient,” he added.

Elevation and Floodprooging Workshop participants view an elevated home in Mount Tremper, NY. Photo by Brent Gotsch

Elevation and Floodproofing Workshop participants view an elevated home in Mount Tremper, NY. Photo by Brent Gotsch


During the workshop, local code officials learned the differences between wet and dry floodproofing and effective elevation methods for structures. They learned how these practices change flood insurance premiums and how simple measures such as filling-in a basement can reduce premiums by hundreds or even thousands of dollars.

A bus tour showed participants local examples of structures retrofitted with elevation and floodproofing measures. At one property, watertight shields were installed to prevent water from flowing into the living area. Another stop featured a residence with engineered “smart vents” that allow water to safely flow underneath the structure’s first floor and equalize potentially dangerous pressures that could buckle the foundation.

At the end of the workshop, local officials left with increased knowledge about how to properly retrofit floodprone structures. Going forward, county partners plan to work with local municipalities to identify and access funding for elevation and floodproofing projects and minimize costs to property owners.

Additional presentations by the Catskill Watershed Corporation, the NYS Division of Homeland Security and Emergency Services, and FEMA informed participants about potential funding opportunities for elevation and floodproofing projects. Presenters walked through the application process and gave advice on how to create a strong application.

Funding for the workshop was provided by the New York City Department of Environmental Protection.

A manager of a local bank branch shows Elevation and Floodproofing Workshop participants how they install the floodproofing barriers. Photo by Tim Koch.

The manager of a local bank branch shows Elevation and Floodproofing Workshop participants how they install floodproofing barriers. Photo by Tim Koch.

Olive Engineering Consultant Talks Flooding and Requests Resident Assistance

Posted on: July 15th, 2015 by Leslie_Zucker

On July 14, the Town of Olive Flood Advisory Committee (FAC) held a  meeting with town residents and Woidt Engineering and Consulting to review initial findings for the Local Flood Analysis (LFA)  in the hamlets of Boiceville and West Shokan. George Fowler, an engineer with Woidt and the project lead for the LFAs, described what he and his team have discovered. Woidt Engineering and the Olive FAC will work together over the next few months to analyze the possible mitigation options for the hamlets. Once these options are identified they will be run through the Benefit-Cost Analysis (BCA) process to determine eligibility for multiple funding sources. You can help with this process by filling out a questionnaire to report damages to your home or business. This information will used during the BCA process. The more information we receive the better! It will be used to develop the most accurate results possible. The form can be downloaded here or picked up at the Olive Town Hall.

Not surprisingly, inundation of the business district in Boiceville is a major concern. George and his team showed how the high and tight valley wall forces the Esopus Creek to flood areas in that district during high flows. More analysis is needed but initial findings show  there may be potential to reconnect the stream with its floodplain just upstream of the Five Arch Bridge. Building a floodplain here may help keep water out of the business district or lessen the amount of water there. That project would likely require relocating the fire department building and other structures in order to make room for water storage.

In West Shokan, the major problems are associated with debris jams and sediment buildup. One of the major concerns for residents and Town officials is the gravel bar just upstream of the Bushkill Bridge. The concern is that if the gravel bar grows it could cause an obstruction that damages or destroys the Bridge, cutting residents off from emergency services. George explained that we are living with the legacy of historical human management of the stream, namely the deforestation of the landscape that occurred in the 19th Century that caused large pulses of sediment to enter the stream corridors, and more recently dredging and berming of material on stream banks that creates unstable stream corridors. As with Boiceville, more analysis is needed, but one idea to explore is restoring appropriate stream channel dimensions to help move sediment and debris through that area without undue buildup.


Olive Residents: Flooding Problems?

Posted on: April 16th, 2015 by Leslie_Zucker

If you are a resident of the Town of Olive and want to either view or add to flood maps you are welcome to stop by the AWSMP office between 8:00 am and 4:30 pm, Monday through Friday.  Recently, the Town of Olive Town Board heard a presentation from Woidt Engineering and Consulting on the Local Flood Analysis (LFA) process and how it will benefit the Town. Part of the presentation focused on Woidt’s desire to learn more from Olive residents about hazardous flood areas. Woidt created a set of maps where residents can mark  locations of concern or known flooding and erosion hazards. Woidt will use the information to examine flooding solutions.  The maps are posted at the AWSMP office at 3130 State Route 28 in Shokan, NY (located between Ashokan Turf and Timber and the Shokan Square plaza, across from the Citgo gas station). The maps will be available for approximately three more weeks before they are returned to Woidt. For more information on the LFA process in Olive please visit our office or view the Town of Olive website.

Living by the Waterfront class offered March 21

Posted on: February 18th, 2015 by Leslie_Zucker

Are you a prospective homeowner thinking of buying waterfront property? Do you already own waterfront property but are confused about flood insurance or how to limit flood damages? If so, you should attend the class “Living by the Waterfront—Keeping Dry When the Waters Rise”  at Cornell Cooperative Extension of Ulster County, 232 Plaza Road in Kingston, NY on March 21, 2015 from 9:00am to Noon. Cost to attend is $10 per person or $15 per couple. Watershed Educator Brent Gotsch will teach the class on what prospective property owners should think about before purchasing waterfront property. Register online by March 15. Contact Heather Eckardt at or call 845-688-3047 for questions about registration.