Trail Closures Due to Wet Trails and Freeze-Thaw Cycle Explained

 



Trail damage caused by higher than normal wet weather.


Increased numbers of new mountain bike riders, as well as other new outdoor recreational users, are exploring their local, state, and national parks because of the pandemic. For some of these users, this might be their first experience using these public resources and newfound outdoor activities. 


Bicycle shops have experienced a bike boom due to the pandemic, that they probably haven't seen since the bicycle boom of the ’70s. Finding the bike you want might be impossible due to the increased demand. The lack of availability has also created a very strong secondary bicycle market.


In my local area, we have some fantastic trails! Urban trails in downtown Richmond, which are part of the James River Park System, and just 25 minutes south of the city, we have an IMBA bronze level ride center at Pocahontas State Park. Which host over 50 miles of trail.


One of the frustrating issues that we are seeing now is an increased number of riders still riding when the trails have been closed due to wet weather or the freeze-thaw cycle. 


Realizing that many new riders don't understand the "why" behind the trails being closed this time of year due to wet trails and the freeze-thaw cycle. I figured I would share a guest post from Joel, one of our local trail-builders. Joel’s effort to explain the "why" behind trail closures during this time of year was posted to one of the local Facebook pages. At the end of this post, we have provided local resources that communicate the trail status, so you know before you go.


Trail conditions in your region are very subjective, due to the surface soil type, drainage profile, and relative rainfall in a given period. Trails that are located on steep contours may drain better due to the gravitational pull of surface and groundwater downward versus trails that are in a flatter area and have greater retention of groundwater. 

  

Water will seek dry soil if available, but different soil types present different resistance to movement.  Similar to how electricity moves through materials with less resistance, groundwater moves quicker through soils with less resistance than those that are more porous, less dense. In dense and saturated soils, (clay, loam) water will not move as quickly as it will through rocky and sandy soils. In the Metro Richmond Virginia area, the primary soil types are clay and loam-type soils.


This year the Richmond Metro area experienced record rainfall amounts. This has led to higher groundwater concentrations, raising the water table in our area. You can see this in some trail areas where the ground appears to be leaking water via seeps where water has traveled through voids and seams in the soil substrate. Trail builders encounter these “springs” on trails, and we typically address them via “armoring” techniques – using the rock to harden the surface and other techniques to move water off and away from the trail.


Regarding "man-made" trails such as bermed flow style and jump type trails. These trails are fun to ride and are very popular (Park trail counters show this to be true). While not naturally existing on trail surfaces, trail-builders are designing and building jump and berm trails. The trail builder has to build up these features.


Designing and building these features is a bit of art and science within itself. These features usually have shapes and gradients with more surface area than flat ground. The increased surface area and stacked soil lead to more infiltration and moisture retention.  So “built” trails may retain water and moisture while other (natural surface) trails do not.  Heavy precipitation may also result in runoff, leading to erosion and channeling (also not good). 


In the winter, most trees and plants go dormant and don’t provide the added effects of transpiration.  Transpiration- is a process where plants suck up groundwater and hold it or emit it into the atmosphere via humidity expressed from pores in their leaves. Evaporation- from solar radiation is also less impactful during the winter due to colder average temperatures and fewer hours of daylight.  So during the winter, plants are not intercepting as much water, allowing more free water into the soil or surfaces.


What is freeze-thaw? 


When temperature drops at night and the soil is saturated the water freezes.  Ice has more volume than water, so it expands in the same space, heaving up the soil and "unpacking" it, which is referred to as frost heave.  When surface temperatures rise above freezing due to solar radiation and/or air temps rise, that ice thaws and turnback to liquid which is the freeze-thaw situation. 


If you ride or walk on the ground in this state it turns into a slurry (i.e. a "mess") and destroys the shape that it once had.  It’s difficult to predict when trails are safe from freeze-thaw but to avoid damage from freeze-thaw conditions, trail managers will choose to close the trails, and closures may extend well past the last measured precipitation.


Usage of trails when in a fragile state will make areas that are already susceptible to damage even worse and require either longer closures or difficult remediation (fix, re-route, armor, or permanent closure).


As a mountain bike community, we can help keep our trails open and in good shape by being aware of poor trail conditions and respecting trail closures. 


Check local trail conditions here:


Morning trail status text

RVA Trail Report on Facebook  RVA Trail Report and on Instagram rvatrailreport


Friends of Pocahontas website fopsp.org  or text "POCA" to 804-292-2939 to receive an automated daily mountain bike trail conditions and trail closures. This text is normally sent at 6:30 a.m. starting in November and 7:30 a.m. starting in March.


RVA MORE website RVA MORE Trail Status


Now It's Your Turn-


I would like to hear how your local trail systems and trail clubs communicate temporary trail closures due to wet conditions. 


How do they educate new riders about IMBA Rules of the Trail and responsible riding?


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