Technical Manual for Dam Owners Impact of Plants on Earthen Dams FEMA PDF Free Download

Technical Manual for Dam Owners Impact of Plants on Earthen Dams FEMA 534 Presented by William Bouley, PE Technical Service Center Bureau of Reclamation

Who Developed FEMA 534? North Carolina State University Wright State University University of Tennessee University of Georgia Maricopa County, AZ Stanford University National Performance of Dams Program

Question: Levees are different from Dams. What applicability does FEMA 534 have with Levees?

The general perception is a dam holds a permanent pool and levees have periodic hydraulic loading

What about dry dams, levees with permanent pools, delta levees, and lake dikes. Across our vast inventory of dams and levees, we have Levees that impound a permanent pool on one end of the spectrum to dry dams that only impound water temporarily like a levee.

Homogeneous Rolled-Fill Pervious Zone Impervious Zone

Modified Homogeneous Pervious Zone Rolled-Fill Impervious Zone

Shell Zoned Rolled-Fill Pervious Zone Shell Impervious Zone

Diaphragm Rockfill Impervious Zone Pervious Zone

Central Core Rockfill Pervious Zone Impervious Zone

Technical Manual for Dam Owners Typical Cross Sections of dams and levees from Corps Design Manuals Many similarities exist between dams and levees

Objectives of FEMA 534 1.Advance awareness of the characteristics and seriousness of dam safety problems associated with tree and woody vegetation growth impacts on earthen dams. 2.Provide a higher level of understanding of dam safety issues associated with tree and woody vegetation growth impacts on earthen dams by reviewing current damage control policies. 3.Provide state-of-practice guidance for remediation design considerations associated with damages associated with tree and woody vegetation growth on earthen dams. 4.Provide rationale and state-of-practice techniques and procedures for management of desirable and undesirable vegetation on earthen dams.

Problems with Tree and Woody Vegetation Growth At the time of publishing, there were 48 states with dam safety programs that Responded to the 7 question survey by the team developing the manual All state dam safety officials indicated that they consider trees and plant growth on to be a safety problem The problem most commonly noted by state officials is that trees, woody vegetation, briars, and vines interfere with the effective safety inspections.

Problems with Tree and Woody Vegetation Growth Other dam safety problems caused by woody vegetation growth include: Uprooted trees that produce large voids and reduced freeboard; and/or reduced x-section for maintaining stability Decaying roots that create seepage paths and internal erosion problems. Interfering with effective dam safety monitoring for seepage, cracking, sinkholes, slumping, settlement, deflection, and other signs of stress Hindering desirable vegetative cover and causing embankment erosion Clogging embankment underdrain systems

Root plugging drainage pipe

Dead root shown above a live root

Problems with Tree and Woody Vegetation Growth Other dam safety problems caused by woody vegetation growth include: Inducing local turbulence and scouring around trees in emergency spillways and during overtopping Decaying roots that create seepage paths and internal erosion problems. Provide Cover for burrowing animals Loosening compacted soil Root penetration of conduit joints and joints in concrete structures

Problems with Tree and Woody Vegetation Growth 50% of states reported having formal policies and /or operating procedures for addressing tree and woody plant growth issues. These policies include one, or some combination, of the following: Trees are not allowed to grow on dams or near toe and abutment All trees and stumps must be removed, but roots may be left All trees, stumps, and roots must be removed All trees must be removed, but root systems of small trees may be left; root systems of large trees must be removed Dams are treated on a case-by-case basis -- usually under the direction of a qualified professional engineer

Problems with Tree and Woody Vegetation Growth Several state and federal dam safety officials reported constraints to removing and/or controlling unwanted trees and other vegetation: Financial limitations by owners (13 States) Environmental regulations and/or permits (10 states) Legal Issues (6 States) Aesthetics (5 States) Threatened/endangered species issues (2 States) Media (1 State) Sentimental reasons (several)

Problems with Tree and Woody Vegetation Growth Vegetation- Caused Problems and Failures 29 states indicated documented evidence where vegetation on dams has either caused dam failure or negatively affected their safe operation 16 states had no documented evidence 5 States had no response Several States provided photos and information on tree caused failures or dam safety problems The most recent documented dam failure due to tree root penetration occurred in May 1999 at an Air Force Academy dam near Colorado Springs The dam had not overtopped, and the failure was attributed to internal erosion of the decomposed granite embankment material along the roots. A tree had been located directly over the breach.

Problems with Tree and Woody Vegetation Growth Vegetation- Caused Problems and Failures At the Federal level, USDA/NRCS referred to documented cases where dam failure has been determined to be caused solely by trees, and noted that trees have also masked other more serious seepage problems, which went undetected One recent study for the St. Paul District showed that a hole formed by a Blown-down tree in the downstream toe area can produce a potentially dangerous increase in hydraulic seepage gradient and internal erosion or piping problems in dikes (Duncan, 1999)

Problems with Tree and Woody Vegetation Growth Cost of Removing Trees and Tree Related Remediation General Costs range from about $1,000 to $5,000 per acre for vegetation removal, to include clearing, grubbing, and repair Tree size can greatly influence the cost of repair Embankment slope steepness affects cost of repair Herbicide costs generally range about $60 per acre

Problems with Tree and Woody Vegetation Growth Summary of Problems All dam safety officials agree trees cause problems with dam safety All State and federal agency dam safety officials and experts agree that trees have no place on dams and need to be managed and controlled on both existing and new dams for at least three important reasons: 1. Trees and dense vegetation hinder effective dam inspections; 2. Tree roots can cause serious structural instability or hydraulic problems, which could lead to dam failure and possible loss of life. 3. Trees and brush attract burrowing animals, which can in turn cause serious structural or hydraulic problems. Most dam safety experts agree that research needs to be done on determining the relationship of plant and tree species to root penetration of artificial environments such as embankment dams; interaction between root system and phreatic zone and surface; various types of root control

Tree Growth and Tree Root Development Requirements Common Myths and Misconceptions The tap root are thought to be the primary root system for all ages and types of trees and woody vegetation. As a root ball develops, the tap root becomes less important Tree roots stabilize the soil mass. Tree root systems actually loosen the soil mass Groundwater penetration by tree root system. In general, trees need water and oxygen to survive. If root zones are inundated for significant periods, the tree will die. Soil Moisture Uptake is not significant. It is not uncommon for most species of healthy mature trees to absorb 200-300 gallons of water per day if available. Vegetation Control vs Dam Performance. Tree root penetrations due not stabilize the soil mass. Quite the contrary, tree root penetration loosens the soil of an embankment slope and creates a condition more conducive to surface water penetration and slope failure.

Technical Manual for Dam Owners Tree Growth and Tree Root Development Requirements Tree Root Characteristics and Requirements

Tree Growth and Tree Root Development Requirements Tree Root Characteristics and Requirements Summary: Based on the tabulated summary of typical soil parameters, continual tree root development cannot occur in soils that are well compacted. One of the best remedial measures for controlling growth on new embankments or in rehabilitation is compaction of soils. Compaction of soils reduces the air void content and limits the amount of surface water that can infiltrate into the embankment slope, but still allows for shallow grass root penetration for ground cover.

Dam Safety Inspection and Evaluation Methodology Earthen Dam Configuration The zone of saturation is the zone above the phreatic surface. This partially saturated zone s depth is dependant on the effective particle size and void size In the compacted embankment.

Dam Safety Inspection and Evaluation Methodology Mid-Life Crisis of an Aging Earthen Dam