The Environmental Impacts of Flooding and How to Manage the Post-Flood Phase (Clean-up Stage)

About one tenth of Nigerian towns and villages have just been ravaged by flood and brought untold, unprecedentedly widespread hardship to millions of people, as loss of lives, livestock and property and crops renders it a national disaster.

However, the flooding has an expiry date. It is very important to understand what has occurred, what to do just after it subsides and how to mitigate the situation during any predicted, potential recurrence.

”The environmental impacts of flooding can be quite wide-ranging, from the dispersion of low-level household wastes into the fluvial system to contamination of community water supplies and wildlife habitats with extremely toxic substances. On the other hand, flood preparedness activities, such as forecasting and warning systems, can help to avoid some of these impacts. Indeed, actions undertaken prior to the event will have repercussions on the level of damages accruing from the flood. Effective remedial actions, such as sandbagging, can significantly reduce losses, and with planning, prevent some of these secondary environmental impacts. Specifically, the removal of fuel tanks and attention to hazardous wastes would eliminate some of the potential problems. In contrast, inadequate attention to these components of the flood hazard will invariably lead to additional problems and intensify adverse environmental impacts. Similarly, during a flood, variables such as depth of water, velocity of flows, and duration of inundation, in combination with land-use attributes, all contribute to the relative severity of flood impact (Tobin and Montz, 1994). Floods of greater depth are likely to result in greater environmental damage than floods of lesser magnitude, in part because more area has been flooded. Long duration floods will exacerbate environmental problems because clean-up will be delayed and contaminants may remain in the environment for much longer time. The argument is the same for other flood traits; extreme conditions are likely to precipitate additional environmental problems.

During the post-flood phase, that is the clean-up stage, many other environmental impacts can become apparent. The volume of the debris to be collected, the extent to which public utilities such as water supply systems and sewage operations have been damaged, and the quantity of agricultural and industrial pollutants entering fluvial systems might present pressing problems. These findings, then, should be incorporated into long-term restoration and reconstruction programs to eliminate unacceptable environmental impacts from subsequent flooding.

Environmental evaluation of the flood hazard, therefore, sets the stage for the strategic assessment of redeveloping flood prone areas. Specifically, recurring losses and negative intrusions into environmen- tal systems could be avoided, or at least minimized, by identifying, measuring, and interpreting the magnitude and significance of environmental impacts associated with flooding.

Currently, there is a tendency to re-analyze the economics of redevelopment in the aftermath of an event, and rebuild with future losses in mind, assuming the provisions of the NFIP are met. It follows that a similar approach regarding environmental impacts would provide a comparable basis for decision-making. The guiding principle in this instance would be reducing costs related to environmental clean-up and providing additional protection.

Strategic environmental assessment (SEA) has been defined as “the formalized, systematic and comprehensive process of evaluating the environmental impacts of a policy, plan, or program, and its alternatives . . . and using the findings in publicly accountable decision-making” (Therivel et al., 1992). The application of this definition to flooding is apparent. Reconstruction of floodplains is a policy that is enabled through federal and state disaster relief funding and private money. Traditionally, this has followed the simple economic model discussed above. However, strategic assessment of floodplain reconstruction permits a comprehensive analysis of policy decisions, prior to the emergency phase immediately following a flood event. Since this is usually a period of chaos and confusion, such planning is essential if meaningful policies are to be implemented.

Estimates of flood damage were put at $17 to $18 million (St. Maries Gazette Record, 1996a). Perhaps the most significant losses occurred when the dry kiln of Potlatch was inundated, closing production of green cedar products for about three weeks, and the whole Potlatch complex for two days during the peak of the flood. It was suggested that, although only 10 to 20 people worked in the dry kiln area, over 40% of local jobs hinged on the operation of the dry kiln (Coeur d’Alene Press, 1996). The long-term consequences for the community, therefore, could be serious. Federal aid to area residents and business persons came from federal agencies such as the Federal Emergency Management Agency (FEMA) and the Small Business Administration (SBA). FEMA provided $1.5 million dollars to hire displaced workers to help with the clean up. Another, $500,000 was provided to extend unemployment benefits, while $6 million came from federal transportation funds to fix roads and bridges in northern Idaho (Idaho Spokesman-Review, 1996). Additional expenditure came from the Environmental Protection Agency (EPA) in monitoring some of the environmental impacts.

Power was lost for a time, and the city sewage works was also damaged (St. Maries Gazette Record, 1996b). The sewage plant was flooded relatively early, and wastewater came over the top of the levee (Currier, pers. comm., 1996). Flood water entered the primary treatment area and excess wastes were pumped into the ground and river. Most of the city residences are connected to the city sewer system, although there are a few septic tanks in the Riverdale area. These, however, are connected to the main system through a series of pumping stations (Municipal Public Works Foreman, pers. comm., 1996). However, city authorities reported no major contamination associated with flooding of the sewage works, although no testing was undertaken.

A boil water order was issued by the Department of Environmental Quality on the basis that sewage, petroleum products, and micro-organisms could have contaminated supplies (St. Maries Gazette Record, 1996a). There was some criticism of this order, since St. Maries uses surface water brought from eight miles upstream at Rochat Creek and only utilizes a local well if surface supplies are short (Municipal Public Works Foreman, pers. comm., 1996). However, high turbidity levels, not unusual for this location, were used to argue for the order.

The Environmental Protection Agency collected approximately 260 containers that had been inundated and were either floating around in flood waters or were under water. Of these, 241 had been recovered from the Meadowhurst district, 17 from Riverdale, 59 from north of the town, and 5 were brought in by residents. Many of these had been used for home fuel, such as kerosene; for the storage of lubricants, hydraulic oils, grease, petroleum products, and other waste oils; and for heavy duty cleaners and household chemicals. Some of the barrels were punctured and their contents had leaked out, while others were open. It was thought that most of these had come from residences and businesses located in the Meadowhurst and Riverdale areas. In fact, there are numerous small businesses which would use such materials, including automobile repair operations and activities associated with wood products. In addition, Potlatch had a 1,000 gallon fuel tank in the flood waters and several other fuel tanks were floating around the airport (Rodin, pers. comm., 1996).

It appeared that no serious contamination had resulted from the flood, although some materials were tested to see if they were hazardous. Of the 238 samples tested, 107 proved positive. Chemical testing revealed primarily oils, grease, and some household chemicals, along with some agricultural pesticides, acids, and paints. Quantities were variable, with containers ranging from 1 to 55 gallon drums. Not all of these were full; many had clearly leaked into the surrounding environment. Barrels were stored temporarily at a landfill during the flood, eventually to be sent to a RCRA facility if hazardous. Visible evidence of contamination was not high. In places there was a thin film on the top of the flood water from petroleum and hydrocarbons, most of which was expected to dissipate or mix into soils. There was a possibility that such products could get into groundwater depending on the depth and condition of wells. Some of the contaminated areas had been boomed and absorbent materials used to soak up the wastes (Rodin, pers. comm., 1996).

The barrels discussed in the previous section represent only one source of environmental impact. There are others, which can act singly and in combination to create the overall environmental impact of the flood. The matrix in Figure 1 provides one means of identifying and analyzing the nature and range of impacts and serves as the first step in the strategic analysis of the environmental impacts of flooding.

The vertical axis of the matrix includes those environmental parameters that are expected to be affected by flooding, no matter what the location. The horizontal axis includes the activities or characteristics associated with flooding that are expected to cause an impact on one or more environmental parameters, whether positive or adverse. Those cells with a checkmark indicate a relationship between the activity and the environmental parameter. A more in-depth analysis of a flood event would allow for some measurement, if only relative, of the magnitude of these impacts. While this is preferred over the identification of impacts in Figure 1, sufficient data are not available for reliable measurements. Additional long-term research is required to develop measures of anticipated magnitudes. Nonetheless, some observations can be made from the matrix.

The range of impacts from different flood characteristics can be determined by reading down from a given category of activity. For instance, the existence of opened and leaking barrels in the flood area may have potential impacts on surface water and groundwater quality, on aquatic habitat and species, and on different land uses, depending on the amount and type of contaminants involved. In addition, the number of flood-related characteristics or activities that affect a given environmental parameter can also be identified. For example, surface water quality will be adversely affected by the velocity, depth, and duration of flooding as well as by flooding of the sewage treatment plant, by the tanks and barrels in the flooded area, by household hazardous wastes in the flooded area, and by debris and mud removal. As a result, water quality is subject to numerous intrusions, which, both separately and in various combinations, can be significant depending upon the contaminants released. Costs of dealing with this can be high, in terms of real dollars as well as environmental costs if contaminants move through ecological systems. And surface water quality is just one parameter affected.


Given the data available immediately following the flood in St. Maries, it is difficult to determine even relative measures of the magnitude of environmental impacts. Reports by local officials suggest that the impacts were small and not significant. The EPA’s data show hundreds of barrels and containers in the flood water, with small quantities of household chemicals, oils, and grease being the main constituents found in the containers. For such a small community the number of barrels was astounding. Of further concern was the fact that many barrels were either unmarked or contained foreign substances, making clean-up operations more difficult. This lack of knowledge, therefore greatly complicated the task of the EPA. It also suggests that the environmental impacts from flooding in larger communities, especially where there is heavy industry, might constitute a significant problem. This is supported by examination of the matrix in Figure 1 which illustrates the large number of impacts that are likely to have occurred.

This study indicates that some refinement in the ability to measure environmental impacts is needed. The overall approach appears to have merit and provides a useful framework for identifying potential environmental problems. Certainly the elements included in the matrix have relevance to St. Maries, as well as to other floodplain areas. As mentioned previously, however, the magnitude of impact could not be assessed, given the data available at the time of this research. Additional work is required. Nonetheless, the utility of the matrix in post-flood St. Maries suggests that it has the potential for wider application in pre-flood communities, where the exposure of environmental parameters to flood characteristics can be estimated prior to an event.

In the final analysis, therefore, assessment of the environmental impacts of flooding involves consideration of a range of interactions that do not usually enter floodplain management decisions, at least in any systematic way. It may be argued that flooding at a place is a rather rare event, and as a result, associated environmental impacts are equally rare and generally insignificant in the short-term. Yet, when we consider the flood hazard in the United States as a whole, environmental impacts are devastating. Losses from flooding are estimated to be up to $3 billion per year, a considerable proportion of which is spent by local, state, and national agencies on clean-up operations involving environmental problems (Federal Interagency Floodplain Management Task Force, 1992).

Because of recurring and ever increasing economic losses due to flooding, new policies have been implemented, most notably the NFIP, which to some extent account for flood risk. Consequently, there are now restrictions on floodplain development in over 18,000 participating communities (Emergency Information Public Affairs, 1995). A similar strategic approach, based on nature, magnitude, and significance of impacts, is recommended with environmental losses. To date this has not been done, in part because it has not been of sufficiently high priority to merit consideration. However, as the environmental impacts of the St. Maries indicate, environmental impacts and risks can be considerable.


ASSESS FLOOD HAZARDS Click here to view


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