By Thembi Borras
Stream crossings exist where roads intersect watercourses, they include bridges, culverts, fords and rock armored fill crossings. One of the fundamentals of road management is that stream crossings be designed for large storm events. The currently accepted standard is for stream crossings to be designed for 100-year flood flows.
Stream crossings deserve considerable attention in road management because if a crossing fails the fill associated with the crossing will almost certainly enter the watercourse. Bridges with inadequately sized abutments, fords with steep dirt approaches and rock armored fill crossings with inadequately sized rock contribute sediment. However, in my experience, the highest risk of direct sediment delivery to a watercourse is from undersized, poorly designed and installed culverted stream crossings.
Culverted stream crossings have appropriately been described as a dam with a hole in it and are prone to plugging. The most common reason why culverts fail is the inlet becomes plugged with woody debris. The following design considerations will lower the risk of failure: 1) size the culvert to pass the 100-year flood flow and the wood and debris associated with that event, 2) align the culvert with the natural stream channel, 3) install the culvert at the grade of the original stream channel, 4) place the culvert in the bottom of the fill and compact the fill well, 5) install a trash rack and 6) install a diversion proof dip. The purpose of a diversion proof dip is, if the culvert should plug, the watercourse is directed back into the channel so that diversion is avoided. Finally, realize there are alternatives to culverted stream crossings that require less maintenance. For example, a rock armored fill crossing or a ford is a good alternative to a culverted stream crossing, where drivability allows.
There are a number of resources to aid you in stream crossing design and implementation. They include the Handbook for Forest and Ranch Roads by Pacific Watershed Associates and the February 2004 publication entitled Designing Watercourse Crossings for Passage of 100-year Flood Flows, Wood, and Sediment available through the California Department of Forestry and Fire Protection website. Click on Resource Management then click on Forest Practice or go directly to (http://www.fire.ca.gov/php/rsrc-mgt_forestpractice_pubsmemos.php).
August 28, 2005
August 21, 2005
Roads
By Thembi Borras
Roads facilitate travel to our homes and places of work. In fact, nearly every activity in a rural community requires getting in a car and traveling on a road somewhere. In a logging operation roads influence aesthetics, logging costs and environmental mitigation. I often find myself asking the question, can an existing problem road, located near a watercourse, be relocated to a ridge and diminish the environmental consequences at the same time facilitate logging method and be financially feasible? During my forestry fieldwork, second only to deciding what trees will be left and cut, is managing roads for improvement and aesthetics. I have yet to meet a road that did not need improvement. Why should you be concerned about roads? Because poorly constructed roads accelerate erosion, which increases stream sedimentation, and can be maintenance nightmares.
According to Danny Hagans of Pacific Watershed Associates the three goals of road improvement are to reduce the chance of sediment delivery as a result of episodic events, reduce chronic delivery of sediment and reduce maintenance. There are many ways to accomplish these goals. Addressing the following points in your road management decisions will insure the ultimate goal, of making roads as invisible on the landscape as possible, is met. Drain roads well and frequently onto stable surfaces, diversion proof crossings, design crossings to pass fish and design crossings for the large episodic event.
There are resources to aid you in road management decision making. A widely used publication is the Handbook for Forest and Ranch Roads by Pacific Watershed Associates. The concepts in the Handbook have been adapted into a "Roads" video. Both are available through the Mendocino County Resource Conservation District (707-468-9223) and the Navarro River Resource Center (707-895-3230). Also check out the website of the Navarro Watershed Working Group (http://www.nwwg.org/) and click on workshops. There you will find a comprehensive write-up from a 2003 Roads workshop.
Roads facilitate travel to our homes and places of work. In fact, nearly every activity in a rural community requires getting in a car and traveling on a road somewhere. In a logging operation roads influence aesthetics, logging costs and environmental mitigation. I often find myself asking the question, can an existing problem road, located near a watercourse, be relocated to a ridge and diminish the environmental consequences at the same time facilitate logging method and be financially feasible? During my forestry fieldwork, second only to deciding what trees will be left and cut, is managing roads for improvement and aesthetics. I have yet to meet a road that did not need improvement. Why should you be concerned about roads? Because poorly constructed roads accelerate erosion, which increases stream sedimentation, and can be maintenance nightmares.
According to Danny Hagans of Pacific Watershed Associates the three goals of road improvement are to reduce the chance of sediment delivery as a result of episodic events, reduce chronic delivery of sediment and reduce maintenance. There are many ways to accomplish these goals. Addressing the following points in your road management decisions will insure the ultimate goal, of making roads as invisible on the landscape as possible, is met. Drain roads well and frequently onto stable surfaces, diversion proof crossings, design crossings to pass fish and design crossings for the large episodic event.
There are resources to aid you in road management decision making. A widely used publication is the Handbook for Forest and Ranch Roads by Pacific Watershed Associates. The concepts in the Handbook have been adapted into a "Roads" video. Both are available through the Mendocino County Resource Conservation District (707-468-9223) and the Navarro River Resource Center (707-895-3230). Also check out the website of the Navarro Watershed Working Group (http://www.nwwg.org/) and click on workshops. There you will find a comprehensive write-up from a 2003 Roads workshop.
August 7, 2005
Sudden Oak Death
By Thembi Borras
Sudden Oak Death (SOD) is a forest disease caused by a water mold fungus (Phytophthora ramorum). This fungus will cause SOD in hosts including tanoak, coast live oak and California black oak and a foliar/twig disease in other hosts including California bay laurel.
The most useful diagnostic symptom for Phytophthora ramorum in mature oaks and tanoak is cankers on the trunk from which dark black to red or amber sap exudes. Diagnosis of the disease is not always easy, for example, a tanoak tree may be infected but the symptoms do not show. The sudden browning of the tree crown, for which the "sudden" part of "sudden oak death" was derived, may occur several years after the onset of infection and not all trees end in a sudden browning, some have gradual leaf loss. Black charcoal bubbles, a fungus know as Hypoxylon decays sapwood and may move into a tree weakened by Phytophthora ramorum, but presence of Hypoxylon does not mean the tree has Phytophthora ramorum.
A common diagnostic symptom of Phytophthora ramorum in California bay laurel is dead areas on the leaves, where water collects. No bay laurel trees have reportedly died from this fungus. However, bay laurels are thought to be very important in spreading the disease as the fungus readily produces spores on moist bay leaves. The vectors of Phytophthora ramorum are wind and water.
By answering the following questions you can get an idea if a tree you suspect, is infected with Phytophthora ramorum: Is the tree a host species? Is it located in an infected area? Does it have the symptoms? The only way to be certain that a plant has Phytophthora ramorum is to have a tissue sample laboratory-tested. If you determine a tree is infected, what should you do? It depends, see " A Homeowner's Guide to Sudden Oak Death" at the website http://www.suddenoakdeath.org/. The fungus can be killed by burning infected wood or composting it very well. Moving infected wood can spread the fungus especially if conditions are wet. Remember, when leaving an infected area; disinfect your shoes or other wet muddy transport mechanisms.
The website http://www.suddenoakdeath.org/ is an excellent resource as are the County Agricultural Departments.
Sudden Oak Death (SOD) is a forest disease caused by a water mold fungus (Phytophthora ramorum). This fungus will cause SOD in hosts including tanoak, coast live oak and California black oak and a foliar/twig disease in other hosts including California bay laurel.
The most useful diagnostic symptom for Phytophthora ramorum in mature oaks and tanoak is cankers on the trunk from which dark black to red or amber sap exudes. Diagnosis of the disease is not always easy, for example, a tanoak tree may be infected but the symptoms do not show. The sudden browning of the tree crown, for which the "sudden" part of "sudden oak death" was derived, may occur several years after the onset of infection and not all trees end in a sudden browning, some have gradual leaf loss. Black charcoal bubbles, a fungus know as Hypoxylon decays sapwood and may move into a tree weakened by Phytophthora ramorum, but presence of Hypoxylon does not mean the tree has Phytophthora ramorum.
A common diagnostic symptom of Phytophthora ramorum in California bay laurel is dead areas on the leaves, where water collects. No bay laurel trees have reportedly died from this fungus. However, bay laurels are thought to be very important in spreading the disease as the fungus readily produces spores on moist bay leaves. The vectors of Phytophthora ramorum are wind and water.
By answering the following questions you can get an idea if a tree you suspect, is infected with Phytophthora ramorum: Is the tree a host species? Is it located in an infected area? Does it have the symptoms? The only way to be certain that a plant has Phytophthora ramorum is to have a tissue sample laboratory-tested. If you determine a tree is infected, what should you do? It depends, see " A Homeowner's Guide to Sudden Oak Death" at the website http://www.suddenoakdeath.org/. The fungus can be killed by burning infected wood or composting it very well. Moving infected wood can spread the fungus especially if conditions are wet. Remember, when leaving an infected area; disinfect your shoes or other wet muddy transport mechanisms.
The website http://www.suddenoakdeath.org/ is an excellent resource as are the County Agricultural Departments.
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