FLOOD PROTECTION HANDBOOK

(designed for homeowners and businesses in the City of Arvada, Colorado)

Mayor's Letter

July 6, 1994

Dear Arvada Resident:

You have this handbook because you may have a flood problem. Flooding affects many residents of our town. Some face fast-moving floodwaters when creeks or irrigation canals overflow. Others have frequent but slow-moving water problems in their streets or yards during local storms. Some people have had repeated floods, while others have yet to be hit.

Regardless of what you have seen, the next flood could be worse. Floods can wash people and cars away. They can cause thousands of dollars in damage to your home and its contents. Floods can cost you in lost work, lost sleep, lost valuables and heirlooms, and lost money and time repairing and replacing things that could be flooded again. They can be devastating emotionally to you and your family both while they are happening and later when you have to deal with their aftermath.

We cannot ignore our flood risk. The City of Arvada is working to reduce the threat of stream and street flooding by building and maintaining flood protection works. We have a flood monitoring and warning program to provide advance notice of the hazard. We regulate new construction to prevent things from getting worse. However, flood control projects are very expensive, will take years to complete, and will not offer 100% protection to everyone.

While we are doing what we can, there are things that you can do, too. You can prevent future damage by floodproofing your own building and making a flood preparedness plan for your own household. You can learn important flood safety rules and health precautions. And, you can minimize your losses during flood recovery. This handbook was specially designed to help you do all those things. If you follow the guidelines in here, you will go a long way toward protecting your family and your home from the next flood.

A short handbook like this cannot provide all the answers. If you have questions or would like to know more about what the City is doing, please feel free to call the Department of Public Works' Engineering Division at 421-2550.

Sincerely,

Robert Frie
Mayor

Acknowledgements

Numerous people contributed to the creation of this handbook. It was produced by French and Associates, Ltd., of Park Forest, Illinois, with funding from the City of Arvada and the Urban Drainage and Flood Control District of Denver, Colorado. It was researched and written by French Wetmore, with technical advice from Clancy Philipsborn of The Mitigation Assistance Corporation, Eve C. Gruntfest of the University of Colorado at Colorado Springs, Shirley Laska of the University of New Orleans, Jacquelyn L. Monday of Lakewood, Colorado, and John Williams of John Williams and Associates, Denver, Colorado.

Additional contributions and specialized insights were provided by Bill DeGroot and Kevin Stewart, Urban Drainage and Flood Control District, Denver, Colorado; Patrick Dougherty, Debbie Muenchow, Chris Proper, Jim Root, Fred Ross, Ed Talbot, G. Noel Vargo, and Merle Westling, all with the City of Arvada.

The draft was carefully reviewed and commented upon by the project's Advisory Committee: A. Mark Peyton, American Red Cross; Larry Stern, Boulder City and County Office of Emergency Management; Bob Smith, Colorado Association of Stormwater and Floodplain Managers; Robert Kistner, Colorado Office of Emergency Management; Brian Hyde and Larry Lang, Colorado Water Conservation Board; Virginia Motoyama, Federal Emergency Management Agency Region VIII; John Pflaum, McLaughlin Water Engineers, Ltd.; and Larry Buss, U.S. Army Corps of Engineers.

HOW TO USE THIS HANDBOOK

This handbook was prepared for the Arvada Department of Public Works, Engineering Division, by French & Associates, Ltd., Park Forest, Illinois. Funding support was provided by the Urban Drainage and Flood Control District, Denver, Colorado.

Printed copies are available free at the Arvada City Hall Information Desk in the main lobby.

All page numbers reference in this web document pertain to the printed version of this handbook.

Record your Important Phone Numbers by printing copy of this linked-page.

Photo credits

Cover and page 1: Photo courtesy of Urban Drainage and Flood Control District. Pages 4 and 5: Photos reprinted with permission of the Roanoke Times & World-News. Page 8: Photos courtesy of Arvada Department of Public Works (top) and French & Associates (bottom).

Disclaimer

The information provided in this handbook is based on careful research and input from experienced professionals. The reader must assume responsibility for adapting this information to fit his or her conditions. This handbook is not intended to replace the advice and guidance of an experienced professional who is able to examine a building and assess the needs of the particular situation. The reader is advised to seek professional assistance if he or she is not experienced and competent in handling technical matters such as building construction or electrical components.

Table of Contents

FOOTNOTE:  The above page numbers and all page references that follow pertain to the hard copy version of this Flood Protection Handbook which is available free of charge at the information kiosk or information desk located in the Arvada City Hall main lobby.  You may also obtain a free copy by calling the City's Engineering Office at 303-421-2550 or the Urban Drainage and Flood Control District at 303-455-6277.

Chapter 1:  Arvada's Flood Hazards

Many folks think that if they haven't been flooded yet, they never will be. But it's just not so. Arvada has really been lucky so far. The City has not had a major flood in recent history. This chapter reviews the types of flood hazards faced by Arvada's residents and how you could be affected by a flood worse than any you may have already experienced.

The Causes of Flooding in Arvada

Arvada's floods are caused by heavy rains, usually during summer storms. Sometimes, snowmelt adds to the amount of water running off during a storm. Creeks, ditches, and storm sewers can only carry so much water. Even in natural settings, creeks overflow every year or two when rains overload the channel. This can be aggravated if debris blocks the waterway.

Urban development has changed the natural setting of the Arvada area. Pavements and rooftops mean that less rainwater can soak into the ground. Gutters and storm sewers speed the runoff to the channels. Our pattern of streets and buildings has interrupted some of the natural drainageways and reduced the size of some channels. As a result, more water runs off and it runs off faster. In some areas, floodwaters can't go where they used to go and in many places, the drainage system gets overloaded more often.

This combination of storms and an overloaded drainage system results in three sources of flooding in Arvada:

1. overbank flooding,
2. irrigation canals, and
3. streets.

Each source causes a different type of flood problem with somewhat different hazards.

            (1) Overbank flooding. The most hazardous kind of flooding in Arvada happens when the creeks flow over their banks. This can occur on Little Dry Creek in the north part of the City and on Leyden, Ralston, and Van Bibber creeks in the south during heavy storms or if an upstream dam fails. Floodwaters are usually fast-moving and can be several feet deep. The combination of velocity and depth makes overbank flooding the most destructive and the hardest to protect against.

Overbank flooding occurs in Arvada every year. Fairly severe floods happened in 1965, 1973, and 1991. On July 22, 1991, Van Bibber and Ralston creeks flooded several blocks on each side of their banks. Businesses in Arvada Plaza were flooded and the Valley Mobile Manor trailer park had to be evacuated. The 1991 flood was estimated to be about a 5-year flood. A flood that size has one chance in five of occurring again every year. More serious floods can and do occur. The 1976 Big Thompson flood, for example, exceeded the 100-year level, killed over 130 people, and caused millions of dollars in property damage.

Most flood construction projects and regulations try to protect people and property from the 100-year flood (one chance out of 100 or a 1% chance of occurring every year). The areas affected by the 100-year flood have been mapped for the National Flood Insurance Program and the Urban Drainage and Flood Control District. These maps are available for review at the Arvada Public Library and City Hall.

On the next page is a summary map of the 100-year floodplain in Arvada. You should not use it to determine whether buildings are in or out of the floodplain, but it does give a general idea of what areas could be affected by overbank flooding. Check to see if your property is close to the mapped floodplain. If so, take a look at the larger map in the library, or contact the City's Engineering Division (303-421-2550) to get more information on the expected flood depths and velocities in your area.

Although overbank flooding is the most hazardous of the three sources of flooding, its danger is reduced somewhat by a flood warning system. The Urban Drainage and Flood Control District and the National Weather Service monitor rain and stream gages and report to the Arvada Police Department and the Jefferson County Emergency Operations Center. With the help of this system, flood watches and warnings can be issued, but they cannot provide more than a few minutes advance notice of a flash flood. This amount of time should be enough to get people to safety and, in many cases, take some emergency steps to protect property, if you know where to go and what to do. (See the section about making a Flood Response Plan on page 12.)

        (2) Irrigation canals. Arvada has three irrigation canals (or ditches) going through it, the Farmers Highline, Church, and Croke canals. They carry water collected in the mountains to users downstream. They travel along hillsides, following the contours. As a result, they cut across the natural drainage pattern, which carries water down hillsides.

The summary map on the next page shows that the canals cross the creeks. Overbank flooding, heavy local rains, or burrowing animals can break the canal banks, causing them to flood nearby properties. A few years ago, the bank of the Highline Canal was weakened by muskrats near 75th and Carr. Luckily, the water flowed into the Croke Canal and there was little damage. However, the experience shows that there is little or no warning for this type of flooding.

        (3) Street flooding. Stormwater runs across yards and into the streets on its way to the City's storm sewers, canals, and creeks. The streets are part of the human-built drainage system and they carry water away from buildings. In some areas the land is very flat or has depressions. In other areas streets, buildings, or other construction projects have blocked the old routes that the runoff used to follow. As a result, water may collect or "pond" in low or flat areas.

Except at underpasses, street flooding and yard ponding usually do not get deeper than a foot or two. There can be high-velocity flows on streets going downhill. There is no special warning system for this problem.

Street flooding and yard ponding is often viewed more as a nuisance than a major hazard. It obstructs traffic and may mean that some streets have to be closed for a while. However, ponding next to a house can cause the same water damage as other types of flooding.

Impact of Flooding

If you haven't been through a flood, it is hard to envision the kinds of damage and how severe it can be. Flooding affects people and their property in four ways:

        Damage to the building and yard.    Standing water can seep through building walls, soak wood, dissolve wallboard, and contaminate insulation. Water and electricity don't mix-electrical components may short, creating a fire or safety hazard. If dried the wrong way, wet wood will warp and plywood will split, requiring replacement of stairs and flooring.

As the water gets deeper, it puts more and more pressure on the walls and floor. Basement walls and floors face the greatest pressures because they are subject to the deepest water. A flood that is over three feet deep will crack or break a standard house wall. Even very shallow flooding on the surface will put over seven feet of water pressure on a basement wall or floor, causing cracks, leaks, or even buckling.

Moving water causes more problems than standing water. It may carry debris that batters building walls. It scours the ground, removing grass and plants and eroding channel banks. Anything that floats, like toys, firewood, propane tanks, and landscaping timbers, will be carried away.

        Damage to contents.    Wet wooden furniture may get so badly warped that it can't be used. Other furnishings, like upholstery, carpeting, mattresses, and books, are usually not worth the cost of drying them out and restoring them. Electrical appliances and gasoline engines won't work safely until they are professionally dried and cleaned.

        Safety hazards.    As noted above, floodwaters and electricity are a bad combination. Floods may damage gas lines, floors, and stairs and create secondary hazards. Certain animals, especially snakes, like to move into flooded homes.

Tests at Colorado State University have shown that as depth or velocity increase, a person is less able to stand up in a flood. They showed that a person six feet tall will be knocked over in four feet of water that is moving at a velocity of only one foot per second, or in one foot of water that is moving at four feet per second. Smaller people will have trouble in even shallower, slower flooding.

Being in an automobile is not much safer. Cars can float in one or two feet of water. More people are killed trying to drive on flooded streets or bridges than in any other single flood situation.

        Health hazards.    Floodwaters are not clean. They carry mud, silt, road oil, and whatever else was on the ground. Sometimes they even carry sewage. Food, cosmetics, medicines, stuffed animals, baby toys, and any other items that would come in close contact with people must be thrown out. Clothes and dishes need to be washed thoroughly. Even clean water causes a problem if it sits around too long. Mold, mildew, and bacteria grow in damp, flooded areas. If the water system lost pressure, a boil order may be issued to protect people and animals from contaminated water.

Floods also take a toll on people's mental health. Stress comes from not knowing how badly your family, home, and contents were hit. This is aggravated by fatigue during cleanup and anxiety over lost income, health risks, and damage to irreplaceable items. Children and the elderly are especially susceptible to stress from the disruption of their daily routines. How to deal with these problems is discussed on page 35.

Chapter 2:  Government Flood Programs

There are many programs underway to prevent or reduce flood damage. Most are implemented by the City, the County, and the Urban Drainage and Flood Control District. This chapter reviews these programs so you can see that you're not tackling your flood problem by yourself.

Public Information Programs

This handbook is only one of several ways to get flood protection advice. There is flood information at the Arvada Public Library. People purchasing flood-prone property are required by law to be advised of the flood hazard. Each year the Urban Drainage and Flood Control District sends notices to all of the City's floodplain residents reminding them of the hazard and suggesting ways they can protect themselves.

Flood Warnings

The City participates in a flood warning program in cooperation with the Urban Drainage and Flood Control District, Jefferson County, and the National Weather Service. Automated rain and stream-level gages have been installed along Ralston, Van Bibber, and Leyden creeks. They give officials the ability to continuously monitor storm and flood conditions. A private meteorologist, hired by the District, has access to this gaging network and to other weather-related information. Early flood predictions and warnings are provided directly to the Arvada Police Department. The police then pass this information on to other key City agencies and the fire department, so they can prepare for a possible flood emergency. When flood danger is imminent, a flood warning is issued to the public.

Emergency Operations

When the warning system indicates that a flood is expected, the Emergency Operations Center (EOC) is activated. Arvada uses the Incident Command System to respond to emergencies. Each City department has one or more representatives in the EOC, ready to react quickly to meet the needs that are reported. Periodic drills and experiences with real emergencies help keep City crews ready to respond to floods.

Flood Control Projects

No city will ever have enough money to stop flooding completely, and Arvada is no exception. For example, a 1986 study estimated that it would cost $33 million to keep the 10-year flood in the banks of the Ralston Creek watershed. Instead of trying to stop flooding, the City has undertaken smaller projects to reduce flood damage. Since 1982, the Department of Public Works has spent nearly $600,000 each year on bridge and culvert improvements, installing larger storm drains, protecting stream and canal banks, and building small walls along curbs to redirect street flooding away from buildings.

Stream Maintenance

Each spring the Streets Division inspects all the City's creeks and canals. Accumulated debris and low tree limbs are removed to keep the channels clear so water can flow more readily along its drainage path. The Department also repairs banks and pipes before the summer storm season. Banks are mowed and cleaned during the summer to maintain the channels' flood carrying capacity. If you see debris or other problems in the channels, you should call the Streets Division (303-431-3041).

The Urban Drainage and Flood Control District also funds annual maintenance programs to preserve floodplains. Its program includes routine maintenance, such as mowing and debris cleaning, tree thinning and channel stabilization, and replacement of culverts, retaining walls, and other structures that have deteriorated over time.

Floodplain Parks

One of the best ways to prevent flood damage is to keep the floodplain open. If there are no buildings, there will be little damage. Oak, Davis Lane, Danny Kendricks, Leyden Creek, Ralston Valley, North Jeffco, Woodrun, and Lake Arbor parks are all examples of floodplain areas that have been acquired and kept open. Not only do they provide recreational opportunities, but they also will be good, safe places for water to flow or stand temporarily during the next flood.

Building Regulations

The City Council has adopted several regulations to help ensure that new construction will not make our flooding problem worse. Only certain low-damage developments are allowed in the floodway-that portion of the floodplain including and closest to the channel-that is needed to carry floodwaters. These areas are limited to agricultural, parking, recreation, and similar open space uses. In other places in Arvada, new residential buildings and substantial improvements to existing residential buildings in the floodplain must be built two feet above the 100-year flood level.

All development projects in the 100-year floodplain need a City permit. This includes new buildings, garages, sheds, walls, or fences, as well as improvements to existing properties. If you see construction near a creek or canal without a City permit sign, call the Building Inspection Division (303-431-3032). Improperly constructed development of any kind can obstruct water flows, causing damage to property nearby or at other places in the floodplain.

There are additional regulations for areas outside the floodplain. New developments must provide storm drainage plans. The plans are designed so that the development's stormwater runoff during the 100-year storm does not overload the drainage system downstream.

Flood Insurance

Arvada's building regulations allow the federal government to make flood insurance available in the City. Arvada is one of the few Colorado communities that participates in the National Flood Insurance Program's Community Rating System. Because the City and the other agencies are doing so much to reduce flood problems, Arvada residents receive a reduction in their flood insurance rates. Flood insurance is described on pages 13-14.

Other Programs

There are numerous other programs administered by state, federal, and private agencies. These include technical assistance for reducing flood damages, planning assistance, and construction programs (U.S. Army Corps of Engineers), disaster response and assistance (Colorado Office of Emergency Management, the Federal Emergency Management Agency (FEMA), and the American Red Cross), floodplain development regulations and flood insurance (Colorado Water Conservation Board and FEMA), and dam safety (Office of the State Engineer and the Colorado Office of Emergency Management). When these agencies do work in Arvada, it is usually coordinated by City offices. A large collection of information about floods and emergency preparedness is maintained at the Natural Hazards Research and Applications Information Center at the University of Colorado in Boulder.

Chapter 3:  Before the Flood

The time to protect yourself from flooding is before the flood. This chapter covers three ways to do that: flood preparedness, flood response planning, and insurance. A fourth way--and one of the best and more dependable--is floodproofing, which is covered in Chapter 4.

Flood Preparedness

There are many things that can be done to get ready for the next flood. Doing them in the logical order presented below and using this as a checklist will help you prepare properly.

Flood Response Plan

Preparing a flood response plan will help you think through all the details that demand attention after a flood watch or warning is issued. Walk through your house with this handbook, and make notes of how to adjust these instructions to your own situation. Writing it down will help you remember everything, which is especially important when everyone is in a hurry and excited because a flood is coming. Be sure to include important phone numbers in your plan.

The flood response plan needs to be based on your own property's flood risk and how much lead time you will have after a flood watch or warning. For example, if you are subject to a life-threatening flash flood, you should get out of the area immediately without worrying about the backup power supply to your sump pump. Your plan should be a checklist of steps to take before floodwaters reach your house. If you have only a few minutes, the following things might be on your plan:

If you have 10-15 minutes warning time, include items like these:

While you're working on a flood plan, think about the other types of emergencies you face, such as fires and tornadoes. The City's Risk Management Office (303-431-3004) and the American Red Cross (303-722-7474) can also help you with ideas for a flood or disaster response plan. Disaster kits and planning materials are available in the Arvada Public Library, the City Hall, and the Red Cross office at 10030 W. 27th Avenue.

Insurance

Insurance is highly recommended, especially if you don't floodproof. If you did floodproof, it is still recommended in case the flood exceeds your floodproofing design. An advantage of insurance is that your property is covered as long as the policy is in force, even when you're not home to implement your flood response plan. Most standard homeowner's insurance policies do not cover a property for flood damage. However, there are three ways you can get the house and contents insured.

        National flood insurance.    The City of Arvada participates in the National Flood Insurance Program (NFIP). Local insurance agents can sell a separate insurance policy under rules and rates set by the Federal Insurance Administration. Any agent can sell a policy and all agents must charge the same rates. If your agent does not know about flood insurance, ask him or her to call the NFIP Denver office (303-740-6629). Your rates will not change just because you file a damage claim; they are set on a national basis.

        Coverage--Any walled and roofed structure can be covered by a flood insurance policy. Detached garages and accessory buildings are covered under the policy for the lot's main building. Separate coverage can be obtained for the building's structure and for its contents (except for money, valuable papers, and the like). Renters may purchase contents coverage. The structure generally includes everything that stays with a house when it is sold, including the furnace, cabinets, built-in appliances, and wall-to-wall carpeting. There is no coverage for things outside the house, like the driveway and landscaping.

        Basements--The NFIP considers any floor below grade as a basement. For example, the lower level of a split level house is considered a basement. A National Flood Insurance policy does not cover damage to contents in a basement. Structural coverage only covers the structural parts of basement walls and floor (not finishings like wallpaper or paneling) and selected items such as the furnace, water heater, washer, and sump pump. The NFIP does not insure buildings for subsurface flooding, including seepage and sewer backup.

        Mandatory purchase--If you are located in a "Special Flood Hazard Area" identified on a Flood Insurance Rate Map, you must buy flood insurance coverage as a condition of having a federally-backed mortgage, home improvement loan, or disaster assistance. Arvada's "Special Flood Hazard Area" is shown on the rough map on page 3. In some cases, a private insurance policy will satisfy this requirement, but usually the lender or granting agency will ask to see an NFIP policy.

        Waiting period--There is a five-day waiting period before NFIP flood coverage takes effect. Don't wait for the next flood to buy insurance protection. Contact your insurance agent for more information on rates and coverage.

        Cost--The cost of a flood insurance policy for a building built before January 1975 depends on the amount of coverage and the location of the house. Buildings built since then should be above the 100-year flood level and will be subject to lower rates. As shown in the following table, premiums are lower for buildings outside the floodplain. There is a $750 deductible on the structure and a separate similar deductible on the contents for most buildings. Higher deductibles are available, and they will result in a reduced premium.

In the following examples, the insurance costs are based on a single-family house with a basement, and on one without a basement. The sample annual premiums are those for $80,000 of structural coverage for a $100,000 house. This amount of coverage (80% of the building's replacement cost) provides replacement cost coverage. The example for $10,000 in structural coverage is only recommended for a building subject to shallow, slow-moving water. It would only provide actual cash value coverage.

        Basement backup insurance.    Several insurance companies have sump pump failure or sewer backup coverage that can be added to a homeowner's insurance policy. Each company has different amounts of coverage, exclusions, deductibles, and arrangements. Most are riders that cost extra. Most exclude damage from surface flooding that would be covered by an NFIP policy.

Each company has its own deductibles and exclusions. Some may cancel the coverage or increase the premium if the policy holder collects on a claim. The cost varies from nothing to up to about $75 for a rider on the homeowner's insurance premium.

        Private flood insurance.    A few private insurance companies sell their own flood insurance policies, although the coverage and rates are different from the NFIP's. Some mobile home insurance covers flood losses. Unlike the NFIP, private insurance will vary from company to company so check several for their coverage and rates. Make sure that your coverage won't be cancelled if you submit a claim for damage.

Chapter 4:  Floodproofing

This chapter covers floodproofing, i.e., changes that you can make to your building or lot to prevent or reduce damage by floodwaters. This handbook can only introduce the topic. Before you invest much money in floodproofing, talk to an engineer, architect, or experienced contractor. The measures are explained in more detail in several books and a video that are available in the Arvada Public Library (see the box).

Different floodproofing techniques are appropriate for different types of buildings and different flood hazards. See the box on page 11 for what you need to know about your flood hazard. Use the following as a guideline:

Basement Cracks

Groundwater can seep into your basement around pipes or if there are cracks in the walls or floor. This may be difficult to determine if the walls have been covered with paneling or other finishing. The best way to deal with a groundwater problem is to waterproof the walls and relieve the water pressure through a footing drain system and sump (see next section).

Cracks can be repaired and the walls can be waterproofed from inside or outside. Waterproofing on the outside is more effective because groundwater pressure forces the sealer into the foundation. The best technique is to dig a ditch around the basement wall so that you can apply a commercial sealant to the exterior walls. This can be done by the handyperson (many home maintenance manuals have instructions for this) or a commercial waterproofing company.

        Precautions.    Waterproofing alone is only recommended for groundwater problems. Surface water will put much more pressure on the building's walls and can even break them. If the building is affected by surface flooding, the owner should also install a barrier as explained on page 24.

Because the work is hidden and sloppy work may not show up for several years, there have been many instances of disreputable contractors doing basement waterproofing. Therefore, ask the waterproofing supplier or company to provide references of buildings in your area that have used their material or technique.

        Cost.    $10-$10,000. A homeowner can seal up cracks from the inside with a tube of sealant. Using a commercial waterproofing company to completely seal the exterior of all the basement walls will cost more.

Sump Flooding

Basement flooding caused by saturated ground can be corrected by installing a footing drain around the foundation (see illustration). The drain collects groundwater and directs it to a sump. When the sump fills, water is pumped out, usually onto the ground away from the building. Depending on local conditions, the drain and pumping system may have to handle large volumes of water.

If the pump is blocked with debris, gets overloaded, or there is a loss of power, the system designed to keep groundwater out of your basement can act as a conduit to bring water in. You can prevent sump flooding by doing one or more of these floodproofing projects:

       Precautions.   When the basement is full of water, it is hard to tell how it got in. It's a good idea to check for cracks in the walls and install sewer backup protection, too. If your backup source of electricity is a generator, be sure it is set up outside or vented to the outside to direct deadly carbon monoxide exhaust fumes outdoors.

        Cost.   0-$500. A homeowner can redirect the downspouts and discharge in a few minutes at no cost. Another sump pump will cost around $65, a battery backup system is $150-$250, and a standby generator can run up to $350.

Sewer Backup

The illustration above shows the sewer arrangements for a typical house with a basement. The sanitary sewer line drains toilet waste, laundry tubs, and the basement floor drain to the sanitary sewer main in the street. Clean stormwater and groundwater is handled by downspouts, footing drains, and sump pumps.

Often basement flooding is caused by these two sewer systems being interconnected. Some houses have the downspouts, footing drain, and/or the sump pump connected to the sanitary sewer service. During a heavy rain, excessive amounts of stormwater enter the sanitary sewers, causing backups into one house and overloading the main lines, contributing to backups in other houses.

Sewer backups can also be caused by events not related to storms or flooding. Individual service lines can be plugged by grease, waste, tree roots, breaks in the pipe, or saturated ground. The City's main lines can also be plugged by the same causes as well as vandalism or illegal placement of items in manholes. These problems can be fixed by the owner or the City, depending on where the stoppage occurs. Proper maintenance, like pouring tree root killer down the toilet each year, can prevent most of these problems.

This section focuses on protection measures that deal with sanitary sewer backup that occurs when the sewer main is overloaded and backs up through the sanitary service line into the house. There are four ways to stop sewer backup: a floor drain plug, a floor drain standpipe, an overhead sewer, and a backup valve. Each of these measures will work for buildings with basements or below-grade floors.

        Floor drain plug.    The simplest way to stop sewer backup is to plug the opening where it first occurs. This is at the floor drain, the sanitary sewer system's lowest opening in the house. Commercial plugs are available that can be placed in the floor drain below the grate. Bolts on metal end pieces are tightened, causing a rubber gasket to expand and seal the plug in the pipe.

A plug stops water from flowing in either direction. Therefore, if the laundry tub overflows or other spillage occurs, it will stay in the basement unless the plug is removed. Because of this, it may be best to leave the plug out under normal circumstances and put it in place only during heavy rains.

One variation is a plug with a float. It allows water to drain out of the basement (see illustration, left). When the sewer backs up, the float rises and plugs the drain (see illustration, right). A float plug permanently installed will not interfere with the floor drain's normal operation.

        Precautions--A plug left in the floor drain may contribute to a wet basement if spillage cannot drain out. Float plugs are known to have been jammed open by a small amount of debris. A floor drain plug does not stop backup from coming out of the next lower opening, like a laundry tub or basement toilet. Sealing the base of the toilet to the floor will protect you until the water backs up higher than the top of the bowl.

A plug does not tell you if there is a problem in your sewer service line. If the plug is not tight enough, pressure can eject it. In older houses, the sewer lines under the basement floor may be clay tile. A buildup of pressure can break them. In newer houses, they are cast iron and unlikely to break.

        Cost--$5-$10. The great advantage of a plug is its low cost and ease of installation. A standard floor drain plug can be purchased at most local hardware stores for $5-10. A float plug costs about $10, and is sold at local plumbing suppliers.

        Standpipe.   A standpipe is an inexpensive alternative to a floor drain plug. A "donut" with metal end pieces and a rubber gasket in the middle is placed in the floor drain. A length of pipe is placed in the "donut hole." Bolts are tightened and the metal end pieces squeeze the gasket to make a tight seal on both the floor drain and the pipe.

When the sewer backs up, the water stays in the pipe. Water pressure cannot build up to blow a standpipe (if properly installed) out of the floor drain. The system works unless the backup is so deep that it goes over the top of the pipe.

One advantage of the standpipe over the floor drain plug is that the overflow acts as a safety valve. A flooded basement equalizes water pressure on the walls and floor, minimizing the chance of a cracked floor from broken pipes underneath.

        Precautions--A standpipe left in the floor drain may contribute to a wet basement if spillage cannot drain out. A standpipe only protects up to its height, normally three feet. Deeper flooding will flow over the top. A standpipe does not stop backup from coming out of the next lower opening, such as a laundry tub or toilet in the basement. Sealing the base of the toilet to the floor will protect you until the water backs up higher than the top of the bowl.

Because water pressure depends on the height of water in the pipes, a standpipe does not reduce the pressure in the pipes. Because the pressure in the pipes is the same with a standpipe or a plug, standpipes and plugs are only recommended for buildings with cast iron sewer lines underneath the floor.

        Cost--$15. A standpipe is almost as inexpensive as a floor drain plug. The "donut" can be purchased for about $10. A three-foot length of pipe costs less than $5.

        Overhead sewer.   An overhead sewer acts like a standpipe but without the problems. A sump is installed under the basement floor to intercept sewage flowing from basement fixtures and the basement floor drain. An ejector pump in the sump pumps sewage up above the flood level. From there it can drain by gravity into the sewer service line. Plumbing fixtures on the first floor are not affected. They continue to drain by gravity to the sewer service line.

It is unlikely that the sewers will back up above ground level. If water does go higher, a check valve in the pipe from the ejector pump keeps it in the pipes. Backed up sewage is enclosed in the sewer pipes so there is no worry about overflowing laundry tubs or basement toilets.

Another advantage is that you don't have to be home during the storm because an overhead sewer is a permanent alteration to the plumbing. The only concern is that during a power outage, the ejector pump won't work. But this only limits the use of the facilities in the basement that need the pump. The upstairs plumbing still works and the sewer is still prevented from backing up.

        Precautions--The ejector pump requires maintenance and electricity to work properly. The basement is disrupted during construction. The contractor may have to run the overhead pipes through one or more basement rooms, although often they can be camouflaged. This work requires a licensed plumber and a permit from the City's Building Inspection Division (303-431-3032).

In older houses, the sewer lines under the basement floor may be clay tile, and a buildup of pressure can break them. Sometimes this can be accounted for by running the overhead line through the basement wall. (In newer houses, the sewer line under the floor is cast iron, and probably won't break.)

        Cost--$2,000-$5,000. Although more dependable than a standpipe, an overhead sewer is more expensive. A plumbing contractor must reconstruct the pipes in the basement and install the ejector pump.

        Backup valve.   A backup valve stops the water in the sewer pipes. Older versions of this approach were located in the basement and relied on gravity to close the valve. If debris got caught in the flapper, the valve did not close tight. Because of its unreliability, valves were discouraged and even prohibited in some communities.

A newer "balanced valve" has corrected these design shortcomings. A system of counterweights keeps it open all the time so debris won't catch and clog it. When the sewer backs up, instead of relying on gravity, floats force the valve closed. It is usually installed in a manhole in the yard so there is less disruption during construction and no concerns over breaking the pipes under the basement floor.

As with overhead sewers, a valve is fully automatic. It can even work when there is surface flooding. The installation is outdoors, so there is minimal disruption of the basement during construction. The owner can still use the sanitary sewers during flooding as long as there is power to run the ejector pump, which forces wastewater into the sewer line when the valve is closed.

        Precautions--The ejector pump and the valve require maintenance. This work requires a licensed plumber and a permit from the City's Building Inspection Division (303-431-3032).

        Cost-- $3,500-$4,500.

Barriers

Barriers keep surface floodwaters from reaching a building. There are three types: large engineered earthen levees, smaller earthen berms, and concrete or steel floodwalls. Barriers can surround the building ("ring levee") or connect to high ground.

Most earthen barriers are made from locally available fill. Their strength comes from their mass, so they need a lot of room. The standard design is three horizontal feet for each vertical foot (3:1 slope). As a result, you should plan on six feet of ground for each foot in height.

Concrete floodwalls are used where there is not enough room for a berm or levee. They should be built with internal reinforcing bars for strength and to resist cracking and settling over time. They must be properly anchored to withstand lateral hydrostatic pressure and care must be taken to ensure that they are watertight.

Depending on how porous your ground is, if floodwaters will stay up for more than an hour or two, your barrier will need to handle leaks, seepage of water underneath, and rainwater that falls inside the perimeter. You will need a sump and/or drain to collect the internal groundwater and surface water. A pump and pipe is also needed to pump the internal drainage over the barrier.

Barriers are safest if they are no more than three feet high. Any type of building can be protected, although buildings with basements will be more susceptible to underseepage. A levee or floodwall should be as far from the building as possible to reduce the threat of seepage and hydrostatic pressure.

Basements

Basements and the lower floors of split levels can also be protected by construction of low walls around stairwells or using backfill (see illustration on the next page). A waterproofing compound is applied to the walls. Walls are built up around the window wells (don't block basement windows that are needed for emergency exits). An earthen berm is filled against the side of the house. A subsurface drain and one or two sump pumps are a must. The drains and pumps can keep up with the seepage before it gets through the berm and reaches your house.

The secret is to not let floodwaters touch the house. If water on the surface of the ground gets up against the house, it probably will seep down the gap between the basement walls and the surrounding soil. This will greatly increase the amount of water pressure against the basement walls. Sump pumps cannot keep up with surface water. If you have sandy or permeable soil, you should consult an engineer or soil scientist to ensure that the berm will extend far enough away from the walls.

        Precautions.    Barriers can only be built so high. They can be overtopped by a flood higher than expected. Earthen barriers are susceptible to erosion from rain and floodwaters if they are not properly sloped and covered with grass. Levees, berms, and floodwalls can settle over time, lowering their protection levels. Walls can crack, weaken, and lose their watertight seal.

Some barriers have openings for driveways and sidewalks. Closing these openings is dependent on someone being available and strong enough to put the closure in place. You also need to account for water in the sewer lines that may back up under the barrier and flood inside your house. See the section on sewer backup (page 19).

Constructing a barrier may require a permit from the City. A berm or wall must be set back from the property line so that drainage problems are not diverted to neighboring properties. Barriers are not allowed in a floodway or in drainage easements. Check with the Building Inspection Division (303-431-3032) to be sure that your project does not violate these code requirements.

       Cost.   The cost can range from practically nothing, if you regrade the yard yourself or build a berm with local fill, to $10,000 for a concrete floodwall three feet high with an underground drain and sump pump.

Dry Floodproofing

This term covers several techniques for sealing up a building to ensure that floodwaters cannot get inside it. All areas below the flood protection level are made watertight. Walls are coated with waterproofing compounds or plastic sheeting. Openings (doors, windows, and vents) are closed, either permanently, with removable shields, or with sandbags. A sewer backup protection measure is installed (see page 19). Many dry floodproofed buildings do not look any different from those that have not been modified.

Dry floodproofing is only appropriate for buildings on concrete slab floors (without basements) with no cracks, and subject to less than three feet of water. To ensure that the slab is watertight and sound, an engineering analysis is recommended. A subsurface drainage system with a sump pump is needed in areas where waters will stay at flood stage for more than a few hours.

       Precautions.   A building should not be dry floodproofed if floodwaters may be more than three feet deep or move faster than five feet per second. It is very tempting for the owner of a dry floodproofed building to try to keep the flood out if floodwaters get deeper than two or three feet. This can result in collapsed walls, buckled floors, and danger to the occupants.

Dry floodproofing is only appropriate for buildings with slab on grade foundations. It is difficult to waterproof a crawl space to protect it from underseepage. Basements should not be dry floodproofed to protect them from surface flooding because of the water pressure on the walls and floors. Basement walls can be waterproofed to protect them from groundwater as long as a footing drain is installed to keep the water pressure from building up.

Many commercial waterproofing compounds are made to protect wood from rain, but they will not withstand the pressures of standing water. Some deteriorate over time, so check with the supplier to be sure the waterproofing compound is appropriate for sealing your basement walls from water. Closing openings depends on having enough warning and having someone at the building who knows what to do.

A dry floodproofing project may require a City building permit. Check with the Building Inspection Division (303-431-3032) to be sure that your project does not violate any code requirements.

        Cost.    0-$20,000. An owner can install a dry floodproofing approach for very little money. The cost ranges from $100 when the handyperson simply applies a waterproofing compound to $20,000 for a more secure and attractive approach that works even when no one is home.

Wet Floodproofing

If floodwaters in your yard are touching the house, they are probably also seeping down between the soil and the exterior of the basement walls. Even if the outside water is only a few feet deep, it is putting pressure on the basement walls and floor equal to that of a standing body of water seven or more feet deep-750 pounds of pressure per square foot. (Dry soil exerts less than 100 pounds per square foot.)

Most walls and floors are not built to withstand that kind of pressure. As a result, waterproofed basement walls and floors can be cracked, buckled, or broken by the pressure of floodwater. Instead of just a wet basement, you may end up with a wet basement and broken walls.

One way to deal with this is to let the water in and remove everything that could be damaged by a flood. This is called wet floodproofing. There are several ways to modify a building so that floodwaters are allowed inside, but minimal damage is done to the building and its contents. These techniques range from moving a few valuable items to rebuilding the floodable area.

In the latter case, structural components below the flood level are replaced with materials that are not subject to water damage. For example, concrete block walls are used instead of wooden studs and gypsum wallboard. The furnace, water heater, and laundry facilities are permanently relocated to a higher level. In the illustration below, these items are relocated to a small room added onto the house. Another approach is to raise these items on blocks or platforms where the flooding is not deep.

Wet floodproofing is not feasible for one-story houses because the flooded areas are the living areas. However, many people wet floodproof their basements, garages, and accessory buildings simply by relocating all hard-to-move valuables, such as heavy furniture and electrical outlets. Light or moveable items, like lawn furniture and bicycles, can be moved if there is enough warning.

Another approach is to wet floodproof a crawlspace. If your crawlspace has a furnace in it or is used for storage, these items could be moved to the first or second floor. Vents should be placed on the foundation walls to ensure that floodwaters can get into the crawlspace to equalize water pressure.

Wet floodproofing has one advantage over the other approaches: no matter how little you do, you will reduce your damages. Thousands of dollars in damage can be prevented by simply moving furniture and electrical appliances out of the flood-prone area.

        Precautions.    Moving contents is dependent on adequate warning and the presence of someone who knows what to do. Flooding an area where there is electricity, paint, gasoline, pesticides, or other hazardous materials creates a safety hazard. There will still be a need for cleanup, with its accompanying health problems. Moving water lines or furnaces requires a building permit from the City's Building Inspection Division (303-431-3032).

        Cost.    0-$20,000. You can accomplish some wet floodproofing with an hour of your time, just by moving valuables out of the floodable area. The out-of-pocket cost can range from $3,000 for relocating the furnace, water heater, etc., to as high as $20,000 to rebuild a floodable area with water-resistant materials and to relocate all utilities. This cost can be minimized if the work is done as part of other building improvements or during reconstruction after a flood.

Elevation

Short of removing it from the floodplain, the best way to protect a house from surface flooding is to raise it above the flood level. The area below the flood level is either filled in or left with openings to allow floodwaters to flow under the building, causing little or no damage. Elevation is required by law whenever a new house is constructed in a floodplain.

Many qualified house-moving contractors know the techniques for elevating a building. It is jacked up and set on cribbing while a new foundation is built underneath. The foundation walls are raised to the flood protection level and the house is lowered onto the new foundation. Utility lines are extended and reconnected, steps built, and, in some cases, the perimeter is backfilled or landscaped to mask the change. If the lower area is not filled in, it must have openings to allow water to flow under the building. This keeps the water pressure from endangering the supporting walls.

Where floodwaters are not very deep, the appearance of the elevated house is similar to that of a house on a two- or three-foot crawlspace (see illustration on the next page). If the house is raised two feet, the front door would be three steps higher than before. If the house is raised eight feet, the lower area can be wet floodproofed for a garage or for storage of items not subject to flood damage.

Lighter, wood frame buildings on crawl spaces or basements are the easiest to elevate because jacks can readily be placed under them. Masonry buildings on crawlspaces can be elevated but the cost is higher because of the weight and the care needed to keep the brick or stone from cracking or falling off. Buildings on slabs can be elevated slab and all, but not many contractors know how to do this.

        Precautions.   If you raise your building eight feet, you may be tempted to put materials subject to flood damage, such as furniture, in the "new" lower area. Structural modifications such as elevating a building require a building permit from the City's Building Inspection Division (303-431-3032).

        Cost.    Crawlspace: $15,000-$25,000. Slab with brick walls: $25,000-$50,000. Costs do not include design or permit fees. Projects managed by the property owner have cost as little as $5,000. This is the only floodproofing project that will lower your flood insurance premiums.

Relocation

The surest and safest way to protect a building from flooding is to move it to high ground. If your house is subject to deep flooding or high velocities, you should seriously consider relocating out of the floodplain. There are several federal programs that are interested in acquiring buildings that have been substantially damaged by a flood. The City may have funds for other properties, particularly if they are adjacent to parks or other public land.

Smaller, wood frame buildings on crawlspaces are easiest to relocate. Larger buildings, those on slabs, or those built of masonry may be too expensive to move, and are usually demolished after they are purchased by the City or other entity. The land is then kept open for public or open space use. If you are interested in pursuing this approach, contact the City's Engineering Division (303-421-3033).

Chapter 5:  During the Flood

Storms and floods can occur very quickly in our area. You should be on the alert when you see storms brewing. When in doubt, turn on your radio or television and listen for weather information.

Flash floods can occur at any time along the Front Range. In Arvada, we have a flood warning system that should give you time to react. If you see flooding, please report it to the City so we can have a better picture of what is happening. Call 303-431-3041 during business hours (7:30 a.m. to 4:00 p.m.). After hours, call 303-431-3087 or 303-279-5746.

Flood Warnings

The National Weather Service issues three types of flood notices:

The City of Arvada, Jefferson County, and the Urban Drainage and Flood Control District work with the National Weather Service to share rain and stream flow data and monitor conditions as they develop. If flooding is likely to occur, these agencies will issue warnings through the following ways:

The flood status will be updated on the radio and television stations. Once the agencies are sure that the danger has passed, they will issue an "all clear" message. Remember: You may not get a flash flood warning before flooding actually begins. Play it safe in stormy weather, and read the next section.

What You Should Do

Once you hear a flood watch or warning, you should take the following steps:

Turning Off the Utilities

If your house or basement could get flooded, turn off your utilities to prevent greater damage. This section provides directions on how you can do this safely. If you are unsure of how to do these things, ask a friend or neighbor to help you, or don't do them at all. If your house is in danger of a flash flood, it's more important that you get to safety quickly.

        Electricity.    The most important utility to turn off is electricity. You have a fuse box or a breaker box in the house. The breaker box is more common in newer buildings or if you have had some electrical work done in the last 10 years. The illustration below shows how to turn off the power.