Flooding on the Hackensack River EarthCache

📋 Logging Requirements

To meet EarthCache guidelines, these tasks require on-site observation. Please answer the following questions based on your visit to Bonnebel Nature Park.  Send answers through geocaching's messaging system.  As this is an Earthcache, there is no physical container to sign.

1. Floodplain Evidence

Walk to the water's edge. 
Do you observe signs of recent flooding?
Describe what you see. Is there a debris line, mud deposit, or staining on tree trunks?
How high above the current water level are these signs?

2. Soil and Ground Conditions

Find a low-lying area near the riverbank and gently press the soil with your fingers or shoe.
Is it dry, moist, muddy, or waterlogged?
How does it compare to the soil on slightly higher ground nearby?

3. Erosion

Walk down the path to Waypoint Two.  What do you see here that indicates a major water event?

4. Photo Task

Please post a photo of yourself or a personal item at the site,  to show you were there.

The Hackensack River: A River Shaped by Ice, Floods, and Time

The Hackensack River begins in the wetlands of Rockland County, NY and flows over 45 miles south through Bergen and Hudson Counties in New Jersey before reaching Newark Bay. Along its course, the river traverses a highly developed suburban landscape—but it also supports critical ecosystems, floodplain forests, and wetlands, particularly in parks and preserved areas like Bonnebel Nature Park.

The Hackensack River Valley was shaped by the melting of the Wisconsin Glacier at the end of the last Ice Age, roughly 18,000–12,000 years ago. As the glacier retreated, it left behind a massive body of water—Glacial Lake Hackensack—which eventually drained, depositing silt, clay, sand, peat, and organic muck into the floodplain below. These sediments, along with ongoing seasonal flooding, continue to define the river's ecology and landscape today.

Today, the river is tidally influenced south of Oradell, but in River Vale it remains non-tidal and primarily shaped by rainfall, runoff, and reservoir discharges from upstream (notably Lake Tappan). This creates a dynamic floodplain environment, where water levels rise and fall dramatically with the seasons or during heavy storms—sometimes leading to overbank flooding and creating temporary wetlands.

Bonnebel Nature Park: A Window Into the Floodplain

Tucked alongside the river in River Vale, Bonnebel Nature Park offers a quiet, accessible space to observe the natural features of a riparian floodplain in action. While small in size, the park is rich in ecological and geological insights, making it an ideal EarthCache site. Visitors can see:

1. Floodplain Forest Vegetation

• Dominant tree species such as red maple, silver maple, and black willow, which are highly tolerant of wet soil conditions.

• Understory plants and grasses that reveal past flooding, including skunk cabbage, sensitive fern, and jewelweed.

• Seasonal variability in plant health and ground cover depending on recent water levels.

2. Flood Indicators

• High water marks on tree trunks from past floods.

• Sediment deposits, organic detritus, and debris lines left behind by receding water.

• Mucky soils underfoot—evidence of poor drainage and saturated ground typical of low-lying floodplain terrain.

3. Soils and Ground Conditions

• Well-drained upland soil and water-retaining floodplain muck.

• In drier weather, cracked mud or dark organic layers may be visible where water once pooled.

• After rainstorms, some paths may be impassable—testifying to how quickly this floodplain can become inundated.

4. Topography and Hydrology

• A slight change in elevation of just a few feet can determine whether an area floods or stays dry.

• The proximity of the river to walking paths allows for direct observation of riverbank erosion, channel movement, and streamside vegetation.

5. Bird and Wildlife Activity

• The floodplain supports diverse wildlife: herons, ducks, frogs, and even the occasional deer.

• These animals rely on periodic flooding to maintain the wetlands and food web dynamics of the area

A floodplain is the low-lying land adjacent to a river that becomes inundated when the river overflows its banks. Floodplains are formed over thousands of years through repeated flooding events that deposit layers of sediment—such as sand, silt, clay, and organic material.

In the case of the Hackensack River floodplain, this process was accelerated and defined by ancient glacial activity. During the last Ice Age, the retreat of the Wisconsin Glacier left behind massive glacial lakes, including Glacial Lake Hackensack. As these lakes drained, they carved out valleys and deposited fine sediments and organic materials across the river basin.

Today, the Hackensack River floodplain in River Vale continues to evolve. During heavy rains or snowmelt, the river often overflows into nearby lowlands—like those found in Bonnebel Nature Park. These overbank events:

• Enrich the soil with nutrients.

• Maintain critical wetland habitat.

• Influence the types of plants and wildlife that can survive here.

However, these floods can also be destructive, especially with modern urban development upstream. As more land is paved and natural absorption is reduced, runoff increases, and flood intensity worsens. 
 

📚 References

1. https://en.wikipedia.org/wiki/Hackensack_River

2. https://www.nodc.noaa.gov/archive/arc0034/0071981/1.1/data/0-data/disc_contents/web_link/text/hm_form.htm

3. https://patch.com/new-jersey/riverdell/bp--the-story-of-our-valley-chapter-two-the-cold-facts

4. https://bplant.org/region/853

5. https://hackensack103.rssing.com/chan-7189576/all_p1.html