“Respect your local trail builders and be a good steward of the physical environment. Keep singletrack single by staying on the trail. Practice Leave No Trace principles. Do not ride muddy trails because it causes rutting, widening and maintenance headaches. Ride through standing water, not around it. Ride (or walk) technical features, not around them.” https://www.imba.com/ride/imba-rules-of-the-trail
So many great articles have been written about why it is important to “Respect the landscape”. In some places like the Pacific Northwest or the UK you can ride the trail just after a rain because the soil types drain fast and when ridden in wet conditions does not stick to the tires and create ruts. You have heard this term many times and may not be familiar with why “ruts” are so damaging. To understand this, we need to become familiar with the soil types that make up our local trails in Bexar county. The Bexar County region is made up of three soil types: Edwards Plateau in Northern Bexar County, Blackland Prairie in Central Bexar County, and Post Oak/Claypan in the Southern region of Bexar County.
Post Oak/Claypan Area Soils
“Upland soils commonly have a thin, light-colored, acid sandy loam surface layer over dense, mottled red, yellow, and gray claypan subsoils. Some deep, sandy soils with less clayey subsoils exist. Bottomlands are deep, highly fertile, reddish-brown to dark-gray loamy to clayey soils.”
“Water erosion is a serious problem on the highly erosive claypan soils, especially where they are overgrazed.” https://texasalmanac.com/topics/environment/soils-texas
South of Highway 90 and 87 East – Parks and greenways such as the Medina River Natural Area, Mission Reach, Pearsall Park, Southside Lions Park, and the Howard W. Peak Greenway.
Blackland Prairie Soils
“Both upland and bottomland soils are deep, dark-gray to black alkaline clays. Some soils in the western part are shallow to moderately deep over chalk. Some soils on the eastern edge are neutral to slightly acid, grayish clays and loams over mottled clay subsoils (sometimes called graylands). Blackland soils are known as “cracking clays” because of the large, deep cracks that form in dry weather. This high shrink-swell property can cause serious damage to foundations, highways, and other structures and is a safety hazard in pits and trenches.”
“Water erosion, cotton root rot, soil tilth, and brush control are the major management problems.” https://texasalmanac.com/topics/environment/soils-texas
On the East Side of Bexar County between I-35 and Highway 87 and on the West Side between FM471 and Highway 90 – Parks and greenways such as Culebra Creek Park, Leon Creek Greenway trails south of O.P. Schnabel Park to include Devil’s Den, McAllister Park, Olmos Basin Park, Brackenridge Park, Martin Luther King Jr. Park, John James Park, and the Salado Creek Greenway.
Edwards Plateau Soils
“Upland soils are mostly shallow, stony, or gravelly, dark alkaline clays and clay loams underlain by limestone. Lighter-colored soils are on steep sideslopes and deep, less-stony soils are in the valleys. Bottomland soils are mostly deep, dark-gray or brown, alkaline loams and clays.”
“The major soil-management concerns are brush control, large stones, low fertility, excess lime, and limited soil moisture.” https://texasalmanac.com/topics/environment/soils-texas
North of FM 471 and I-35 North/East – Government Canyon State Natural Area, Eisenhower Park, Panther Springs Park, Stone Oak Park, and the soon to come Classen-Steubing Park (sometime in late 2021).
“Soils are more erodible as you move north to south (Medina and South Salado are the softest and we have the greatest problems with erosion on these trails)….SA is prone to flash flooding, which washes out unsustainable dirt trails and is prone to suddenly deposit large amounts of sediment in our waterways.” – Brandon Ross, AICP, San Antonio Parks and Recreation
None of these soils are particularly conducive to riding when wet for all the reason stated above. Some of them do, however drain faster than the others. Because of the soil types described above we also encounter many damaging erosion conditions such as ruts, cracks, and ditches. If your mud is sticking to your tire or clumping up and not allowing you to advance, then you should turn around immediately. You are not only damaging the dirt trail and speeding up the effects of erosion, but your bikes drivetrain is not too happy with you either.
Riding local trails when wet leads to the formation of ruts which are created when the mud sticks to your bike tire or shoes and is carried away or when you create a depression in the soil. When mud is carried off and deposited somewhere else, it leaves a depression for more water to collect in the future. Multiply that by however many other users decided it was a good idea to ride or run on the muddy trails and now you have a problem. Depending on the soil type the rut can become rock solid when dry and create an extremely unpleasant experience for other trail users that can cause them to go around that area widening the trail to avoid twisting/breaking an ankle or going over the bars (OTB) and risking a serious injury. This trail widening, or lensing, can transform singletrack trails into dirt trail superhighways. This is not good for the vegetation or wildlife, leading to the edge effect and habitat fragmentation.
What can also happen is the formation of trenches when water runs down the trail instead of being shed off the trail. Instead of people going around the rut and widening the trail you then have these repetitive cycles that remove the dirt/mud from its current location and over time becomes a ditch, trench, or gully when the erosive effects of water continue to remove soil over time. The same can happen with dirt features such as berms or jumps if you do not wait for these areas to dry completely before riding them. This is probably a low-lying spot that remains wet longer than other parts of the trail. It can easily be fixed by contacting your local mountain biking organization and helping them elevate that section of trail and or create grade reversals to shed water off the trail.
If the problems are not identified and addressed immediately, these ditches will continue to erode until they become deeper (sometimes several feet deep) and extremely dangerous for all tail users. Just like with previous issues, trail users will create a reroute and abandon the eroded trail. These issues can be fixed, but with all the trail maintenance your local organization must do throughout the city it would be best to stave off these terrible results and intensive trail maintenance efforts by staying off the wet trail. As the old saying goes, “An ounce of prevention is worth a pound of cure”. If the dirt is sticking to your tires turn back and ride the pavement. If all sections of the trail are dry except for that area, avoid riding that trail or turn around and back track to another trail that is not holding water.