Corps answers to our Questions - Still leaves questions

Park View Terrace Questions for Army Corps of Engineers (Rock Island)
Friday, January 09, 2009


1. What is the Corps of Engineers doing/going-to-do to minimize the chances of another flood in PVT in Spring 2009?

RESPONSE: Flooding in Park View Terrace will continue to be a possibility dependent on snowmelt and rainfall amounts within the 3,115 square-mile watershed flowing into Coralville Reservoir and below the Reservoir.

Coralville Reservoir will always reduce peak flows on the Iowa River below the reservoir, regardless of the size of a flood, which will minimize flooding in PVT, Iowa City and areas downstream of the reservoir. The highest outflow during any given event will always be less than the peak inflow, even when water is well over the top of the spillway. The dam stores water when its pool elevation is increasing, meaning that the inflow is greater than the outflow. A few days after the peak inflow has occurred, the pool elevation will crest when the inflow equals what is being released in the outflow.

In 2008, we coordinated releases from Coralville Reservoir with Iowa City officials to provide ample time for emergency responders to remove property from anticipated flood areas, sandbag city infrastructure and personal property, and to provide the public with the maximum amount of time possible to implement flood protection for their personal property or evacuate if needed. During the 2008 flood, Coralville Reservoir successfully reduced flows on the Iowa River below the dam by 17,500 cubic feet per second, which reduced the River’s flood stage by 5.0 feet.

Prior to, and during, the 2008 flood, the Corps deployed flood-area engineers to Iowa City, Des Moines, Cedar Rapids, the Quad Cities, and throughout the state of Iowa advising emergency officials of the National Weather Service flood forecasts and our operations of reservoirs.

We will implement all of these actions again in 2009 if needed.

In late winter and early spring, the Corps will again work closely with the National Weather Service and the U.S. Geological Survey to monitor ground conditions, snowmelt and flood potential. During that time, we will maintain the Reservoir according to its approved Regulation Manual.

In the spring, the reservoir pool levels are maintained to allow for snow melt runoff, and for predicted and actual rainfall, to prevent downstream flooding. The pool levels will occasionally fluctuate to prepare for such runoff and for National Weather Service rainfall predictions. Pool levels are also maintained to ensure minimal bank erosion which contributes to sedimentation on the reservoir floor, adequate summer water supply, continued river flow below the reservoir, conservation purposes, and for Iowa and surrounding areas recreational opportunities.

During flood control operations, weather parameters are evaluated on an hourly basis to consider rainfall in the drainage area above the reservoirs; rainfall below the reservoirs; and National Weather Service rainfall predictions over a 24-hour period. This information is used by the Corps to anticipate inflows to the reservoirs and make adjustments to release rates to conserve flood storage capacity and minimize both up-river and down-river flooding.

2. Instead of waiting until the level at the reservoir reaches 700 feet to get active about moving water out of it, why not move it out sooner, say, at about 680 feet? It seems like waiting that long is almost too late and if any unforeseen rain comes in from the north, there isn’t enough wiggle room. Is there a possibility of changing the outflow numbers?

RESPONSE: As you know, the Coralville Reservoir is operated according to its approved Regulation Manual. All of our reservoirs are operated to conform to a strict, standard regulation plan that is coordinated by the Corps of Engineers for review and approval by local, state and federal agencies with water resources responsibilities. This standard includes regulation of releases during flood events. The latest revision occurred in January 2001 and was subject to public review and comment. A copy of the manual is available on the CD-ROM provided at this meeting (Note: The manual on the CD-ROM does not include plates and diagrams of the reservoir for security purposes).

Outflow modifications during flood emergencies are considered at the request of public officials. If outflow modifications are warranted, approval from our higher headquarters is required. We do not modify outflows during normal operating conditions.

To modify outflows on a permanent basis would require a revision of Coralville Reservoir’s operations manual. Revising the manual requires a request from the state of Iowa and a cost-sharing of 50 percent of the study. The Corps would also require appropriations from Congress for our cost share of the study. The cost of the study would have to be determined once the scope of the study was developed.

3. What is the minimum level of water that must be retained in the Coralville reservoir for:

a) protection of wildlife,
b) move sewage downstream, and
c) for recreational boating?

RESPONSE: These issues were considered as well as others when the following lake levels were determined, but there is no specific level for each.

The current approved operating levels are essential in order to protect fisheries within the reservoir and provide a minimum 150 cubic feet per second outflow as required by the state to meet downstream water quality targets during droughts. The current approved operating pool levels are:

15 February – 20 March: 683 to 679 National Geodetic Vertical Datum (NGVD) *
20 March – 20 May Hold @ 679 NGVD *
20 May – 15 September Hold @ 683 NGVD
15 September – 15 December Hold 683 to 686 NGVD **
15 December – 15 February Hold @ 683 NGVD

Notes:
* Variable draw down based on snow cover, ice, and 30-day climatic conditions coordinated with IDNR
** Dates and elevation of fall pool raise coordinated with the IDNR

4. Communications and the Corps

a) How does the Corps coordinate communication in times of flooding? Does it give directives for local councils regarding mandatory evacuation and other actions, or does it leave all these decisions to each city and township? (Could this info be shown on a diagram or in a written document).

RESPONSE: During periods of predicted and actual flooding, the Corps dispatches flood-area engineers to communities that may be affected by, or are affected by, flooding to alert communities to the flood projections and to provide technical flood-fighting support. Our Emergency Operations Center at Rock Island, Illinois, is activated and we are in regular communication with officials from affected communities, State emergency operations staff, and the Department of Homeland Security.

In addition, Corps water management and reservoir staff conducted daily teleconferences each morning (and sometimes more frequently)with Iowa City, the University of Iowa, the city of Coralville, and the Iowa Department of Transportation to aid them in the their decision-making process with regard to flood fighting, evacuations and road closures. This process will be followed during all future floods.

The Corps can only advise officials of what might happen and provide our professional opinion of a flooding situation. We do not have the authority to require evacuations or any other mandatory actions from local officials.

b) Will the Corps be communicating with Iowa City in the future to advise us of high water and how it will impact Park View Terrace?

RESPONSE: As in the past, and during the 2008 flood, if flooding is a concern, the Corps will dispatch flood-area engineers to Iowa City to ensure communities are aware of flood impacts and to provide technical flood-fighting support as needed. The Corps will continue to advise city officials of what might happen and provide our professional opinion of a flood situation.

Due to lessons learned during the 1993 and subsequent floods, and improved technology, we believe we had much better communication with affected communities during the 2008 flood. This will only continue to improve with additional lessons learned and better technology.

c) We have found the Corps forecasts of flood levels at the hydraulics lab gauging station less than helpful. The problem is that the gauging station is in a choke-point in the river valley and it is immediately downstream of a dam, so a 4-foot rise there does not translate to a 4-foot rise in areas where the floodplain is wider and dams are distant (as in our neighborhood). Could the Corps offer river-level forecasts for developed areas along the river such as ours?

RESPONSE: The Corps does not forecast river levels for Iowa City as the National Weather Service (NWS) is the agency responsible for issuing all weather and river forecasts to the public. The Corps does provide a 7-day outflow forecast from Coralville Reservoir to the NWS. The NWS incorporates the outflow information along with flows on Rapid Creek and Clear Creek to develop a river forecast for Iowa City.

The stream gaging network in place today is a mix of gages funded by the Corps, the USGS and other cooperators. Each agency operates and maintains their gages as resources allow. Together, the network provides the necessary data for the NWS to model stream and river conditions to provide the best-available river level forecasts. These forecasts are available on the internet @ http://www.nws.noaa.gov/ and at www.rivergages.com.

While additional gaging stations along rivers and tributaries are always useful, the Corps is not funded at this time to install and maintain additional gauges. However, it should be noted that the USGS gage at the hydraulics lab has a long period of record and is an excellent location with regard to maintaining a stable stage versus flow relationship which is essential to providing an accurate forecast. In lieu of installation of an additional gage, Park View residents can relate actual flooding that has occurred on their property historically to Iowa City gage readings.

5. Do Corps personnel ever come "in person" checking rivers downstream of Coralville Reservoir? Because it was clear for us riverside residents that river was very high since March 2008, and then, once or twice, it went down almost eerie low in April, then the flood came. Something was amiss, something that the computers probably got wrong, but human eyes could easily recognize.

RESPONSE: The low river levels that were observed in April were due to a temporary outflow reduction required to reduce flooding downstream at Wapello and Burlington and not a gage malfunction. If a gage is not functioning properly, the Corps and USGS deploy technicians that will inspect the gage in person and make any repairs needed.

The Corps of Engineers relies on our system of gages to operate all of our reservoirs, including the Coralville Reservoir. Gage data is provided via satellite to provide real-time flow information which allows us to operate our reservoirs to the best of our abilities.

6. Since Hurricane Katrina levee collapse and the Minneapolis I35 bridge collapse, we are hearing a lot about many US infrastructure failures -- out of date facilities, poor maintenance, and recurring human errors. Therefore,

a) What, frankly, is the state of the Coralville Dam currently?

RESPONSE: The U.S. Army Corps of Engineer’s dams are managed through the Dam Safety Program, which includes routine inspections and continual evaluations in accordance with the Federal Guidelines for Dam Safety issued in 1979 and 2004. The primary objective of the Dam Safety Program is to improve public safety by ensuring that Corps-owned and operated dams are structurally sound and operated according to the intended purpose; and that risks to the public are minimized.

There are no structural or other operating concerns at Coralville Reservoir. The Reservoir received a thorough inspection in August 2008 following the flood. Prior to that in August 2006, the Screening Risk Portfolio Analysis team that assesses dam safety rated Coralville Dam as being in good overall condition.

Corps dams are designed to withstand enormous pressures and water levels. All Corps reservoirs are built to stringent engineering standards to ensure they will withstand record flood events. Each reservoir is under observation to ensure its structural integrity and safety.

Reservoirs are also visually inspected on a regular basis under normal operating conditions and are visually inspected several times a day during flood events. Minor erosion adjacent to the outlet works can occur during major flood events but does not impair the structural integrity of the dam. The dam was thoroughly inspected after 1993 and 2008 and no movement or deterioration has been noted.

b) What is the REAL lifetime of the reservoir (we've heard everything from 50 years to 100 years)? What are the factors for determining the reservoir's lifetime, how does silting-in factor? What capacity has been lost due to silting-in and how does that relate to water upstream and the altered retention capability of the reservoir.

RESPONSE: Any sedimentation below the conservation pool does not impact flood storage. As an example, take two cups of equal size. One cup is half full of water and the other cup is half full of saturated silt, both cups still have the same amount of water storage volume left in them.

Sedimentation impacts are mostly recreational and environmental within the conservation pool. While the deposition of sediment continues to occur, the majority of sediment deposition has been in the conservation pool. For example, Coralville reservoir still retains approximately 89% of its original flood storage capacity, in comparison to only 55 percent of its original conservation storage capacity. Major flood events deposit sediment in the flood control pool, but on a day to day basis, sediment deposition is in the conservation pool.

Over many years the sediment dropping out in the conservation pool will fill the pool forming more of a “dry reservoir” with a river running through it. The river will reach a point where the water velocity will keep suspended sediment from falling out according to the release rates from the dam. The preponderance of flood storage will still remain; however, there may no longer be a deep pool of water for recreational purposes.

c) What is the Corps doing to address these problems?

RESPONSE: We continue to perform periodic sedimentation surveys at our reservoirs and assess flood-storage capacity issues.

d) Can the capacity of the Coralville reservoir dam be increased through de-silting or raising the level of the dam?

RESPONSE: As noted in 6 (b), above, the preponderance of flood-storage capacity still remains despite sedimentation build up.

The capacity of the reservoir can be increased by dredging or emptying the reservoir to remove material to return it to its original design standards; however, dredging and issues related to disposal prove to be extremely costly. Raising the height of the dam would likely not be physically possible from an engineering and topography perspective.

7. Were all the flood gauge sensors in good working order prior to June 2008 flooding? If not, how is the Corps addressing this problem?

RESPONSE: Yes. All river gages needed to run models to develop flood forecasts for the spring and summer 2008 were in working condition. If a gage is not functioning properly, the Corps and the USGS have a team of technicians that will inspect the gage in person and make any repairs needed.

8. Regarding the definition of the 100 year flood, how has the expected 100 year flow (at the Coralville Dam’s tailwaters) changed from the time the dam was constructed 50 years ago until today? Is there a trend in the data. That is, can we anticipate that the 100 year flood, as defined in 50 years will be greater than the current definition by about the same amount as the current definition is greater than that offered when the dam was built?

RESPONSE: The Corps plans to conduct an updated flow frequency analysis for the Iowa River from Coralville Reservoir downstream to the confluence with the Mississippi River which will include the 2008 flood event. Until the revised analysis has been completed, it will not be possible to examine trends in the data.

9. Does the Corps operate on the assumption that global warming is a present reality and one that will shape meteorological conditions in the coming decades? If so, how does the Corps incorporate long-term predictions of significantly more precipitation for the upper Midwest and increasingly unpredictable weather conditions into its models for operating the dam?

RESPONSE: There are many disparate views by climatologists regarding global warming. As global warming science and trends are developed and verified, the Corps will consider their implications when developing it projects and operating plans.

Whether or not global warming has an impact on current or future meteorological conditions, the Corps will continue to work closely with the National Weather Service and the U.S. Geological Survey to monitor ground conditions, snowmelt and flood potential and operate our reservoirs accordingly.

10. We had the impression last June that the reservoir release rates were being set largely on the basis of water already in the Iowa River basin, or even on the basis of water already in the reservoir, as many of the public pronouncements from the Corps were stated in terms of "if no more rain falls, this is what we expect." How much does the corps look at weather forecasts? The weather bureau's short term forecasts seem to give fairly reliable (on the scale of the Iowa River basin) estimates of expected rainfall a day or two in advance, and useful estimates up to about a week in advance.

RESPONSE: All National Weather Service river forecasts include runoff from rain that has fallen over the previous 24 hours and runoff from rain that is forecasted to occur over the next 24 hours. The statement, “If no more rain falls,” meant that if no more rain falls above and beyond what is predicted by the NWS over the next 24-hour period.

During flood control operations, weather parameters are evaluated on an hourly basis to consider rainfall in the drainage area above the reservoirs; rainfall below the reservoirs; and National Weather Service rainfall predictions over a 24-hour period. This information is used by the Corps to anticipate inflows to the reservoirs and make adjustments to release rates to conserve flood storage capacity and minimize both up-river and down-river flooding.

11. How do cities rank among the Corps' priorities for flood protection?

RESPONSE: Reducing flood risk to property and the public is the primary purpose of all of our flood risk management projects. We take that responsibility very seriously and have constructed more than 100 projects within our 78,000-square-mile area of operations. Since their construction, these projects have cumulatively prevented more than $8.4 billion in property damages.

Coralville Reservoir was constructed at a time when there was little development in the floodplain. As cities and towns grow, so does development in the floodplain. This continued development places additional constraints on the operation of the reservoir and the current regulation manual attempts to take this growth into consideration for all properties below the reservoir, not Iowa City alone.

Coralville Reservoir was constructed at a cost of approximately $15,750,000, in 1958. Since then, the reservoir has prevented an estimated $167.5 million in property damages.

In 2008, the reservoir successfully reduced flows on the Iowa River below the dam by 17,500 cubic feet per second, which reduced the River’s flood stage by 5.0 feet. An estimated $99 million in damages were prevented due to the river stage reduction in Iowa City and downstream.

The three reservoirs (Saylorville, Red Rock and Coralville) built and maintained by the U.S. Army Corps of Engineers, Rock Island District, are operated as multi-purpose dams. The primary purpose authorized by Congress is for flood damage reduction for public and private property below the reservoirs. Other purposes include recreation and conservation. Corps reservoirs also maintain a conservation summer pool to augment low flows during drought and an additional fall pool raise to provide habitat for migrating bird species.

12. What can the City (and other entities in the Iowa City metro area) change to allow the Corps to release more water at the beginning of the spring flood season when the river is at a lower level?

RESPONSE: City officials could make a request to the state to have the reservoir’s operations manual reviewed for possible revision. To modify outflows on a permanent basis would require a revision of the Coralville Reservoir operations manual. Revising the manual requires a request from the state of Iowa and a cost-sharing of 50 percent of the study. The Corps would also require appropriations from Congress for our cost share of the study. The cost of the study would have to be determined once the scope of the study was developed.

13. Farmland downriver from Iowa City:

a) How much farmland south of Iowa City is in danger of flooding after May 1st of each year?

RESPONSE: All public and personal property below Coralville Reservoir is at risk of flooding. Flooding can occur at any time due to excessive snowmelt and rainfall in the spring, and excessive rainfall in the summer.

b) Would buying up farmland downriver to create a larger flood plain reduce risk of flooding in Iowa City?

RESPONSE: The purchase of agricultural land downstream would allow for higher reservoir releases. However, higher release rates at the reservoir would also create flooding in Iowa City.

To determine if additional farmland could be purchased and flooded, and what impact it would have on Iowa City, would require a cost-shared study with the Corps receiving appropriations from Congress for our share of the study. The cost of the study would have to be determined once the scope of the study was developed.

Additionally, an authorization and appropriation from Congress for the Corps to purchase farm land below the reservoir would be required.

c) Would it be legally possible to buy up this farmland?

RESPONSE: While it is legally possible to purchase farmland above and below Coralville Reservoir from willing sellers, the Corps does not have the authority, or the funding to do so.

d) Would it cost less to buy this farmland than other mitigation options in Iowa City?

RESPONSE: To determine if the cost of purchasing farmland is greater or less than the cost of other mitigation options in Iowa City, would, again, require a cost-shared study to review all available alternatives and their associated costs. The Corps would need to receive appropriations from Congress for our share of the study. The cost of the study would have to be determined once the scope of the study was developed.

Additionally, an authorization and appropriation from Congress for the Corps to purchase farm land below the reservoir would be required.

14. What are the costs and benefits to the Park View Terrace Neighborhood of Coralville building their proposed flood wall?

RESPONSE: This question would be best answered by Iowa City officials as it is not within the purview of the Corps of Engineers.

15. What impact would raising Dubuque Street have on Park View Terrace?

RESPONSE: This question would be best answered by Iowa City officials as it is not within the purview of the Corps of Engineers.

16. If the University of Iowa builds walls on both sides of river from the Park Road Bridge to the Burlington Street bridge (and the power plant south of it), what impact would they have on Park View Terrace? We understand that narrower channels invariably seem to have steeper gradients, while the gradient decreases when the river is allowed to spread. Again, we worry that Park View Terrace residents could become the victim of aggressive flood control measures elsewhere in the area.

RESPONSE: This question would also be best answered by Iowa City officials as it is not within the purview of the Corps of Engineers. The Iowa Department of Natural Resources Flood Plain Development Program department would also be a more appropriate agency to contact regarding this question.

Questions pertaining to the Flood of 2008

17. What impact did the Park Road Bridge have on flooding in Park View Terrace? What impact would redesigning the Park Road Bridge have on our neighborhood?

RESPONSE: As above, this question should be addressed to Iowa City officials as it is not within the purview of the Corps of Engineers. The Iowa Department of Natural Resources Flood Plain Development Program department would also be a more appropriate agency to contact regarding this question.

18. The University of Iowa has a coffer dam across the Iowa River, north of the Burlington Bridge. This dam has been in place for two or more years.

a) What impact did this coffer dam have on flooding in Park View Terrace?

RESPONSE: Without detailed study, it would be difficult to determine the impacts of the coffer dam on flooding in Park View Terrace. At this time, the Corps has no knowledge or information to suggest the cofferdam had an impact on the flooding at Park View Terrace.

The city had a consulting firm perform backwater analyses to monitor the effects of the cofferdam at different flows. This question should be addressed to the city or the University as it would be more appropriate for them to respond.

b) When did the Corps become aware of the Coffer Dam?

RESPONSE: The Corps received an application to install two chilled water mains under the Iowa River from the University of Iowa and their agent, NNW, Inc., on August 18, 2006.

On August 21, 2006, the proposed utility project with associated cofferdam was routed for comments through the Corps’ Engineering and Operations offices and the Iowa Department of Natural Resources (IADNR). Our reviewed resulted in no concerns; the IADNR required a mussel survey.

Eventually, the site was cleared for state of Iowa threatened and endangered species and the Corps issued a nationwide permit verification letter on October 5, 2006. In our letter we notified the permittee that ". . . the contractor's progress may be impeded by high flows in the late winter, spring, and early summer months, and the Corps of Engineers does not adjust reservoir releases at Coralville Lake for contract work."

On January 28, 2008, NNW, Inc., requested an extension of time to complete the project under the new series of nationwide permits which were issued on March 19, 2007. The Corps verified that the project under construction met the conditions of the new nationwide permits, and a permit verification letter was issued on February 14, 2008.

The Iowa Department of Natural Resources issued Sovereign Lands Construction Permits on September 27, 2006 and September 05, 2008.

c) Who issues permits for Coffer Dams, and do you know if the University obtained such a permit?

RESPONSE: The U.S. Army Corps of Engineers issues permits for any construction in navigable waters or the discharge of dredged or fill material into waters of the United States. The Iowa River is classified as a navigable waterway from its mouth to mile 3.0 near Toolesboro, Iowa.

We have a joint application process in place where copies of the application are simultaneously sent to the Corps and the Iowa Department of Natural Resources for review. The DNR issues Section 401 Water Quality Certification, Sovereign Lands Construction Permits and Floodplain Construction Permits in coordination with the Corps but independently with their own process.

The Corps issued a nationwide permit verification letter on October 5, 2006, for the project. On January 28, 2008, NNW, Inc., requested an extension of time to complete the project under the new series of nationwide permits which were issued on March 19, 2007. The Corps verified that the project under construction met the conditions of the new nationwide permits, and a permit verification letter was issued on February 14, 2008.

The Iowa Department of Natural Resources issued Sovereign Lands Construction Permits on September 27, 2006 and September 05, 2008.

19. Some engineers have estimated that had the Corps released 18,000 cfs starting May 23rd or so then water may have not gone over the spillway in 2008. Is that correct?

RESPONSE: The Corps ran a simulation of the 2008 flood using an 18,000 cubic feet per second release rate beginning May 23. Results of that simulation indicate the reservoir level would have still exceeded the crest of the spillway and that an 18,000 cfs release could not have been maintained due to physical limitations with regard to outlet capacity.

20. FEMA informed Park View Terrace residents in July 2008 that they knew by March 2008 that there could be a flood this year. Did the Corps have similar knowledge?

RESPONSE: We are unable to comment on what statements a representative from FEMA might have said in March 2008.

The National Weather Service provides flood forecasting information. Our first notification of potential flooding on the Iowa River basin and throughout the Midwest was provided to us near the end of May 2008. At that time, we sent our flood area engineers into the field to advise local communities and municipalities of the flood potential and offer any Corps assistance available. The National Weather Service forecasts are available on the web @ www.nws.noaa.gov and at www.rivergages.com.

21. Did the Corps know how high the crest might be in IC earlier than June 11, 2008? If Yes, did the Corps advise the City?

RESPONSE: No, we did not. It was not possible to model and forecast the height of the crest until after the heavy rains in the basin the night of June 12.

Beginning in early June, Corps Water Management staff provided daily and sometimes more frequent briefings on reservoir releases and forecasts to city, county and university officials. At times, we delayed increasing releases from Coralville Reservoir to provide ample time for emergency responders to remove property from anticipated flood areas, sandbag city infrastructure and personal property, and to provide the public with the maximum amount of time possible to implement flood protection for their personal property or evacuate if needed.

The District responded during the 2008 flood by deploying nearly 300 employees throughout the Midwest to work closely with state and local emergency responders to inspect, advise and assist communities with professional engineering expertise and materials during flood fights.

In all, the Corps provided nearly 13 million sandbags, 100 pumps, and more than 30 miles of plastic to assist local communities and levee districts in their flood-fight effort.

We deployed Corps engineers to Iowa City, Des Moines, Cedar Rapids, the Quad Cities, and throughout the state of Iowa advising emergency officials of the National Weather Service flood forecasts and our operations of reservoirs.

22. Had the Corps been able to release 12,000 cfs in the spring of 2008 instead of the 10,000 permitted under current rules, how much would this have reduced the peak flood release on June 15? We note that, at 10,000 CFS, northbound Dubuque Street was only inches above water. The point of this question is to help us evaluate the importance of elevating northbound Dubuque Street, since we suspect that this would have allowed both increased drawdown prior to the flood.

RESPONSE: The Corps ran a simulation of the 2008 flood using a 12,000 cubic feet per second release rate instead of the current 10,000 cfs maximum release rate stipulated in the reservoir regulation plan. Results of that simulation indicate the maximum reservoir release during the flood would have only been 1,000 cfs lower.