Grantee Research Project Results
Final Report: Establishing Correlations Between Upland Forest Management Practices and the Economic Consequences of Stream Turbidity in Municipal Supply Watersheds
EPA Grant Number: R825822Title: Establishing Correlations Between Upland Forest Management Practices and the Economic Consequences of Stream Turbidity in Municipal Supply Watersheds
Investigators: Hulse, David , Niemi, Gerald J. , Grant, Gordon
Institution: University of Oregon
EPA Project Officer: Chung, Serena
Project Period: October 1, 1997 through September 30, 2000 (Extended to September 30, 2001)
Project Amount: $320,000
RFA: Decision-Making and Valuation for Environmental Policy (1997) RFA Text | Recipients Lists
Research Category: Environmental Justice
Objective:
The objectives of this project were to: (1) prepare an analytical framework for estimating the downstream costs from increased sedimentation caused by land and reservoir management activities; (2) employ this framework to improve understanding of the sediment costs incurred by the City of Salem, Oregon, and its water users from such activities in the Santiam watershed; and (3) coordinate with key stakeholders to identify alternatives for managing these costs.
Summary/Accomplishments (Outputs/Outcomes):
Salem, OR, a city of 125,000 people, has long relied on the North Santiam River, flowing out of the Cascade Range into the Willamette Valley, as a municipal source of nearly pristine water (Figure 1). From February 5-9, 1996, northwestern Oregon was inundated by a series of intense storms. These storms, originating in the subtropics, brought a combination of record-breaking rain and warm temperatures. River flood stages in the first week of February 1996, were comparable in magnitude to the December 1964 flood, the largest in Oregon, since flood control reservoirs were built in the 1940s and 1950s. With the heavy rainfall and flooding, the Army Corps of Engineers flood control reservoirs and the North Santiam River received large amounts of sediment-laden water.
The February 1996 storm produced extremely high turbidity throughout the North Santiam River during and following the storm event. Turbidity readings as high as 140 nephelometric turbidity units (ntu) were measured at the City of Salem's Geren Island water treatment plant intake, which is designed to treat water at less than 10 ntu. Because the river water is normally of extremely high quality, the city uses a slow-sand filtration system that can treat pathogens and moderate turbidity and has low operating costs relative to conventional filtration systems. High turbidity, however, may damage the slow-sand filters.
The turbidity experienced in February 1996, overwhelmed the filtration capability of the city's water-treatment plant, forcing the city to close the plant for 8 days. After initiating unprecedented measures to curtail customer water use, and after building emergency pretreatment facilities, the city reengaged the treatment plant before serious water shortages materialized. However, turbidity exceeded drinking water standards set by the Environmental Protection Agency (EPA) through mid-July, and levels of turbidity remained unusually high for 5 months thereafter.
The high turbidity triggered diverse economic consequences. Damage from clogging of the filters, plus other short-run costs to the city's water utility, totaled $1.4 million (Table 1). Additional, but undocumented costs of $20-$45,000 occurred as political leaders and staff were diverted from normal activities. Some industrial water customers incurred costs of $2-3 million. Lost revenues were incurred primarily because they responded to the city's request to curtail operations during the crisis. Workers at the plants experienced a loss of $56,000 in wages during the temporary layoffs. Although the city issued an alert when the treatment plant was closed, asking all residential and commercial customers to limit non-essential uses, the overall impact apparently was no more than an inconvenience, and the alert may have triggered some water hoarding.
Table 1. Short-Run Damage to the City's Water Utility (1996 Dollars)
Category | Damage |
---|---|
Damage to Filter #1 | $1,000,000 |
Cost of alternative water supplies | $204,467 |
Installation and operation of emergency pretreatment system | $184,320 |
Repairs and cleanup | $4,755 |
Lost revenue associated with forgone sales | $17,000 |
Diversion of managerial attention | Unquantified |
TOTAL | $1,410,542 |
Source: ECONorthwest with information from the City of Salem.
Table 2. Long-Run Costs (estimated) to the City's Water Utility (1996 Dollars)
Category | Costs |
---|---|
Pretreatment facility | $1,200,000 |
Additional monitoring | $300,000 |
Water treatment | $56,000 |
New well for industrial supply | $80,000 |
TOTAL | $1,636,000 |
Source: City of Salem.
The city, at a long-run cost of $1.6 million, subsequently increased its ability to cope with future pulses of high turbidity by expanding an early-warning monitoring system, increasing its treatment capacity, securing back-up supplies from other sources, and increasing storage of treated water (see Table 2). Industrial customers also apparently incurred costs of about $80,000 to reduce the risk of future disruptions by securing back-up supplies and increasing onsite filtration capabilities. Ironically, however, this unprecedented occurrence of high turbidity clarified the value of having a watershed that usually delivers extraordinarily pure water; on average, it allows the city to avoid $2-4 million in annual treatment costs.
Figure 1. North Santiam Watershed and surrounding area
In the weeks and months following the February floods, controversy raged over the causes of the water supply problem. The media reported that much of the sediment that caused problems for the Salem water treatment facility was derived from logging activities in the basin's headwaters. This reflected a widely held view of a direct causal link, such as shown in Figure 2a, between land use (especially forestry) and sediment production and delivery to streams, causing downstream turbidity. Despite the intrinsic appeal of such a simple syllogism, this study confirms a more complex relationship among land use activities, sediment production, and transport, and turbidity. In a real sense, the flood's muddy waters revealed the complex and often contradictory web of management objectives among the agencies and parties responsible for water management in the Santiam. It specifically highlighted how management for one narrow set of objectives might exacerbate problems in another sector. For example, decades of logging in the North Santiam Basin targeted the most unstable piece of ground, thereby potentially exacerbating production of sediment causing persistent turbidity during storms. The operation of dams for flood control captures and prolongs the release of persistent turbidity downstream, causing problems for municipal water users. Relying on the normal behavior of a watershed to produce clean water under all circumstances exposes societal vulnerability to inherent geological hazards and their interactions with land and water use decisions. Trade-offs involved in reducing persistent turbidity turned out to be much more complex in space, in resource management decisions, and in time than was hypothesized. Some background on causes of turbidity in water is useful. Turbidity is a measure of the clarity of water in relation to its concentration of light-scattering material. Turbidity in water is typically the result of dissolved and suspended fine organic and inorganic particulates, with the inorganic fraction primarily made up of clays.
In the western Cascade mountains of Oregon, this and other studies, following both the 1996 flood and earlier floods, consistently show that water exhibiting persistent turbidity contains high concentrations of a type of clay termed smectite, along with lesser amounts of other amorphous clays. Smectitic clays are widely but not uniformly distributed throughout the western Cascades. Using x-ray diffraction techniques and clay mineralogy, the source of persistent turbidity can be tied to various landforms and soils that have high quantities of smectite. This relationship among landforms, clay mineralogy, and persistent turbidity can be represented as a triangle (Figure 2b), with each leg defining a causal linkage, as indicated by the arrows, and supported by independent data. In this relationship, land use is not the cause but a contributing factor through its effect on increasing the rate of native erosion processes.
Figure 2. Two conceptual models of the sources of persistent turbidity
A more detailed look at the relationships among landforms, turbidity, and clay mineralogy reveals that earthflows overwhelmingly are the dominant source of smectitic clays producing persistent turbidity in the Santiam Basin. Samples from diverse landforms, including stream terraces, landslide deposits, earthflows, and glacial deposits show that smectitic clays comprise between 70 and 90 percent of the clay fraction from earthflows. We found smectite concentrated in only one other landform, soils derived from a debris flow that initiated above an earthflow and traveled through it en route to a stream below. Debris flows traveling through earthflow complexes may incorporate smectitic clays, and thereby provide another source of persistent turbidity. Another potential source for smectite are terraces immediately downstream from earthflow complexes that store smectite-rich sediments derived from the earthflows upstream. Although our limited sampling did not reveal smectite in such terraces and thus did not reveal the extent to which such terraces represent long-term sources of smectite, to be conservative, we included them in subsequent analyses.
Forest Land Use Effects on Sources of Persistent Turbidity
Although our analysis revealed that weathered volcanic landscapes, such as the North Santiam watershed, naturally produce clays that cause persistent turbidity, and that upstream land manager's role in causing sedimentation was less clear than originally hypothesized, we considered how forest land use activities, including logging and road construction, might accelerate or increase natural production rates of smectite and related clays. Our focus was on land use activities that accelerate sediment production or delivery processes in smectite-rich areas of the landscape (i.e., earthflows). Land use activities that we hypothesized as likely to increase sediment production or delivery from earthflows, listed in rough order of decreasing effect, include:
- Forest harvest directly on earthflows themselves, which can accelerate erosion due to compaction, soil disturbance, or changing onsite hydrology resulting in accelerated earthflow movement.
- Harvest in steep unstable areas prone to landsliding upstream from earthflows, where tree harvest can reduce root strength, leading to landslides and debris flows that pass through earthflows.
- Road construction resulting in road-stream crossings upstream of earthflows; such crossings or nodes have a much higher likelihood of failure as slides or debris flows during storms.
- Forest harvest and roads on terraces located immediately downstream of earthflows; soil compaction, disruption, and road failure in these sites might deliver smectite-rich stored sediments into stream channels.
We conducted a geographical information systems (GIS) analysis to evaluate the spatial distribution of sites where land use activities might potentially increase sediment production leading to increased persistent turbidity during storms. The maps from this analysis reveal several important conclusions about the distribution and potential land use impacts on sources of persistent turbidity within the North Santiam watershed. First, the primary sources of smectitic clays are not uniformly distributed over the basin, but are concentrated in certain areas, some of which are more active than others. In particular, most active earthflows are concentrated in the Blowout Creek sub-watershed, with lesser amounts in the Breitenbush and main North Santiam watershed. No earthflows are found within the upper North Santiam and wilderness areas that make up the eastern third of the basin. The reasons for this highly patchy distribution of earthflows are not fully understood, but likely result from the age, composition, and weathering history of the rocks in the western Cascade volcanic pile. The younger rocks making up the High Cascade region have not had sufficient time to weather to produce the high clay concentrations necessary for earthflow evolution.
Focusing in on the Blowout Creek sub-watershed reveals relationships among active earthflows, streams, and landslide trigger sites. Steep unstable zones surround many earthflows; some of these steeper areas are likely headscarps and bluffs formed as earthflows flowed downhill, leaving harder rock behind. Instability leading to landslides in these areas occurs as the underlying exposed rock along the headscarp is eroded and sapped. Most of these unstable headscarp areas are not likely to fail as true debris flows, because they typically do not concentrate water.
A more likely source of debris flows that can travel through earthflow complexes entraining smectite are steep unstable headwater areas and road-stream crossings upstream of earthflows. Not all road crossings are potential failure sites; hillslope position (i.e., upper, middle, or lower), size of stream, type, age, and dimensions of culvert are all factors determining failure potential during storms. Further, GIS analysis including these and other factors could potentially target the highest risk sites.
On the other hand, a much higher number of road crossings that could be potential trigger sites are present if both active and dormant earthflows are considered. The large areas in these older complexes coupled with dense road and stream networks mean that many more road crossings are present above old, now dormant, earthflows. A much closer look at the potential for these dormant earthflows contributing smectite should be a component of any management strategy intended to reduce land use effects on turbidity.
Conclusions:
With respect to forest and reservoir management within municipal watersheds, care must be taken to ensure that human activities superimposed on intrinsic geological conditions do not exacerbate existing erosion processes or introduce new ones. Specifically, land and water managers should recognize how watershed processes are coupled in both time and space. In the North Santiam, decades may elapse between flood events capable of producing extreme turbidity. During those decades, the combination of land use and geomorphic processes may progressively increase downstream risk. There is a nonuniform spatial distribution of landforms producing turbidity within a watershed. Different types of landforms produce different types of turbidity, as landforms and geological processes interact with each other. Consequently, an understanding of the spatial relationships and change over time among sediment production and transport processes is essential to guide land and water use and restoration activities.
More generally, human systems, including institutions, which develop with a narrow sense of time and space, become more vulnerable. The lessons of the North Santiam show that cogent watershed planning must recognize time and space scales, tradeoffs, and the imperative that what you do, and when and where you do it matter, in land and water management. A proper, more sophisticated accounting of watersheds in space and time gives more options the next time a crisis occurs. Such an accounting will provide for the correct association of public concern with those land and water management decisions that have a credible cause/effect relationship on water quality problems. New directions for the watershed that have emerged since the 1996 flood include: an early warning monitoring scheme, the prospect of higher resolution spatial planning for the U.S. Forest Service, and a broadened multi-agency dialog regarding water management; as well as a heightened public awareness of the fact that all urban residents of the Willamette River Basin live downstream from earthflows, forests, and reservoirs.
Our investigations of the 1996 flood brought to light additional, previously unseen or underappreciated interdependencies among the three agencies' (U.S. Forest Service, U.S. Army Corps of Engineers, City of Salem Public Works) use of the basin and clarified the spatial and temporal dimensions of intrinsic sediment production and turbidity, and the ways human activities may exacerbate turbidity. Trade-offs involved in reducing persistent turbidity turned out to be much more complex in space, time, and resource management decisions of institutions than was previously assumed. This complexity led, in the Santiam, to increased cooperation among the involved agencies for addressing research and monitoring, as well as land and water use decisions. In addition, the hazards presented by muddy waters will require new approaches on the part of each of the agencies involved. Our interactions with these and other stakeholders identified 10 key issues, options, and questions relevant to future land and water management in the Santiam watershed:
1. Hazard profile of increased sediment from forest lands in the basin increases with time from last major storm event.
2. Earthflows need to be viewed within their geographic context:
a. Are they downstream of potential debris flow initiation sites?
b. Do they deliver directly to stream channels?
3. Roads may interact with earthflows to change movement patterns; a sound management principle would be to not increase supply of water to earthflows via roads and perhaps reduce water supply via road/culvert re-engineering or removal.
4. If climate changes, hazard profile for persistent sediment delivery downstream may change as well (e.g., snow changing to rain).
5. Dams should be re-engineered to accommodate outflow from different pool elevations out of concern for turbidity and not solely stream temperature.
6. Flood protection equals occasional high turbidity.
7. Influence others upstream whose actions effect water quality.
8. Substitute alternative water supplies.
9. Substitute for watershed services.
10. Manage water demand.
The 1996 Salem/Santiam flood offers insights into several important watershed-management issues emerging across North America and elsewhere, with special emphasis on three domains of issues: economic, geologic, and watershed planning domains. In particular, this case study demonstrates the potential consequences of relying on a watershed to provide high-quality source water for municipal-industrial use, and the economic and institutional adjustments that must be confronted as the demand for high-quality source water rises relative to the demands for timber, flood control, and other goods and services derived from the watershed. This event indicates that the actions of land managers, river managers, and municipal water utilities are interconnected in ways not previously anticipated. Furthermore, the importance of this flood's impacts on turbidity, rather than on more conventional concerns about flood inundation, highlights the necessity for watershed managers to have a deeper understanding of a watershed's geology, looking beyond topography's impacts on the hydrograph to see how soil composition and geological processes, such as deep earth movements, interact with human activities and infrequent precipitation events influencing water quality. The 1996 Salem/Santiam flood also offers lessons for capitalizing on floods and flood-response planning to shape long-run, watershed management strategies that explicitly recognize these geological characteristics and their impacts on the supply of high-quality source water and other goods and services.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 11 publications | 3 publications in selected types | All 2 journal articles |
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Type | Citation | ||
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Grant G. Dam removal: panacea or Pandora for rivers? Invited commentary. Hydrological Processes 2001;15(8):1531-1532. |
R825822 (Final) |
Exit |
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Hulse D, Ribe R. Land conversion and the production of wealth. Ecological Applications 2000;10(3):679-682. |
R825822 (2000) R825822 (Final) R825797 (2000) |
Exit Exit |
Supplemental Keywords:
watersheds, sediments, Pacific Northwest, OR., RFA, Economic, Social, & Behavioral Science Research Program, Scientific Discipline, Water, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Water & Watershed, Hydrology, Ecosystem/Assessment/Indicators, Ecosystem Protection, State, Forestry, Ecological Effects - Environmental Exposure & Risk, decision-making, Pacific Northwest, Drinking Water, Watersheds, Economics & Decision Making, ecosystem valuation, logging, ecological exposure, risk assessment, community involvement, Oregon, Willamette River Basin, human population growth, forest ecosystems, other - risk assessment, municipal supply watershed, economic incentives, environmental values, flood management, watershed land use, environmental policy, aquatic ecosystems, forests, public values, stream turbidity, upland forest management, water quality, municipal sopply watersheds, public policy, OR, cost effectivenessProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.