Regional Strategic QUARTERLY. Getting from Push to Pool An Alternative Starting Point in the Water Quality Debate Summer. Essay Three of Six

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1 2018 Summer Regional Strategic QUARTERLY Essay Three of Six Getting from Push to Pool An Alternative Starting Point in the Water Quality Debate Mark Imerman, Eric Imerman When we think of water quality issues in an agricultural state, we generally think of agricultural nutrient pollution. Several years ago, the big issue was manure from livestock confinement facilities. For the past couple of years, it has been nonpoint nutrient runoff from farm fields. While these are different problems, they have something in common. The first issue in addressing them is generally a choice between pushing water off the site (push-first tiling farm fields or releasing manure into streams) or pooling the water for controlled release and treatment (poolfirst). In the case of field run-off, we have opted for push-first. In the case of livestock manure, we have we opted for pool-first. While we have good intentions of treating farm field runoff as we push it downstream, a substantial increase in investment is needed to make meaningful treatment a reality. Even with increased investment, the various bioreactors and saturated buffers being implemented invariably get bypassed when flows are high. This means we treat the water only when the flow is not very large. This is a problem inherent in choosing to push runoff rather than pooling it. In addition to bypassing treatment during high flows, pushing runoff also does nothing to alleviate (and in many cases exacerbates) flooding problems downstream. This doubles-up the problems with a pushfirst solution. It increases the volume and velocity of water flooding downstream areas at precisely the times when that water is bypassing the facilities put in place to remove nutrients. When rivers are flooding, most of the water is untreated. Page 1

2 Finally, a push-first solution requires the continued expenditure of substantial funds downstream to alleviate flooding and pay flood damages. Runoff treatment in a push-first environment requires substantial new investments in a resource-scarce environment. If we could successfully pool runoff upstream, we could reallocate downstream investments in flood control towards upstream pooling and treatment. This would take time, but it would transform much of the combined nutrient and flood control issue from a political funding problem to a design and allocation problem involving funds we have already committed. Des Moines River Watershed Flows We don t need to be experts to understand the issues. Download annual discharge rates for the Des Moines River at Keosauqua (data on the Iowa River reveal a similar story) and annual rainfall rates at the Des Moines airport. A few things quickly become apparent: Ten-year averages of annual discharges have increased 38.5% over the past 30 years (from approximately 0.71 acre-feet per watershed acre to approximately 0.98 acre-feet) The ten-year annual average discharge ending in 2016 was approximately billion cubic feet or 9.3 million acre-feet of water per year 1 Ten-year averages of annual precipitation at the Des Moines airport have increased 12.1% over the same 30 years (from inches per year to inches per year) The increase in discharge (0.27 acre-feet per watershed acre per year) is less than the increase in precipitation (0.36 acre-feet per watershed acre per year) Increasing the Floodcontrol Efficiency of Existing Reservoirs Sequestering water upstream in the Des Moines River watershed could facilitate more effective utilization of Saylorville and Red Rock reservoirs. The reservoirs have combined capacities of nearly 2.1 million acrefeet. Over 1.8 million acrefeet of this is flood storage capacity (the normal pool capacities are 262,600 acrefeet). When extended events like 2008 and 2010 begin, we cannot know if they will last 2 days or 200 days. Reservoirs starting with full standing pools begin holding water almost immediately. Extended events quickly fill the reservoirs flood capacities, forcing them to release water as fast as they take it in and flood the areas downstream they are meant to protect. Sequestering water The increased discharge equals 3,565 cubic feet per second (cfs) upstream extends every second of the year flowing past Keosauqua planning horizons. As water begins pooling upstream and weather patterns appear problematic, reservoirs Des Moines River Discharge Rates at Keosauqua can proactively release a Cubic Feet Per Second portion of their standing pools downstream and marginally increase exit flows because they know water exists upstream to 5000 replenish the pools. This extension of the planning Annual Average Cubic Feet Per Second 10-year Average Cubic Feet Per Second horizon would increase their flood-control capacity and leverage investments 1 An acre-foot of water is enough water to cover an acre (43,560 square feet almost the size of a football field) with one foot of water. in upstream sequestration. Page 2

3 Rainfall and discharge do not come as annual averages. They come in bursts. Daily Des Moines River discharge levels at Keosauqua from January 1, 2007 through December 31, 2016 illuminate the size of those bursts: The average of daily flows over the ten years is about 13,000 cfs The lowest daily average is 196 cfs (one acre-foot every 3 minutes and 42 seconds) The highest daily average is 105,000 cfs (2.4 acre-feet per second) 924 days (about 25% of all days over the ten years) had average flows of 20,200 cfs or more These days accounted for 59% of the water flowing past Keosauqua 925 days had flows of 3,370 cfs or less These days accounted for only 2.5% of the water flow past Keosauqua The upper and lower flow levels are problematic. High flows cause flooding. High flows also invariably bypass nutrient treatment facilities upstream. Low flows cause water deficiencies for communities that depend upon the river and reduce the recreational value of streams, parks, and other improvements on the watershed Rainfall Reports at the Des Moines Airport Annual Rainfall 10-year average rainfall Change in Rainfall Relative to Change in Discharge (moving 10-year averages) Increasing Treatment Efficiency Through Pooling First Sequestering runoff upstream also pools water containing nutrients and sediments that challenge downstream water quality. Passive wetland sequestration may be enough to resolve nutrient challenges in some portions of the watershed. Simply holding water and averaging rates of flow over time might significantly reduce peak nutrient parts per million in some situations. Where active treatment remains necessary, sequestered pools provide venues for active interventions such as algae farming, bioreactors, aeration, or chemical intervention. Variable runoff rates create substantial barriers to effective waterway nutrient reduction in a push-first runoff system. Upstream sequestration can make that process more efficient and cost effective. Index of Annual DM Rainfall Index of DM River Discharge Page 3

4 Smoothing the Flow These flows could be smoothed, however. Using a simple spreadsheet model with daily flows at Keosauqua over ten years, we can theoretically sequester (pool) all flows exceeding 20,200 cfs, hold the water, and release it back into the river when flows fall below 20,200 cfs 2. The model holds water for portions of every year. Challenging scenarios appear in 2008 and In 2008, the model holds pooled water on 281 days. The 2008 pool size peaks at approximately 3.6 million acre-feet in August. In 2010, the model holds pooled water on 301 days. The 2010 pool size peaks at approximately 7.1 million acre-feet in October. On December 31, 2010, the model still has 4.9 million acre-feet in the pool. That water does not completely clear the system until November 27, It may not be reasonable to hold 7 million acre-feet of water in the Des Moines River basin, but simple variations in the model illustrate substantial trade-offs. If the pool-release trigger is moved to 25,000 cfs, peak pools in 2008 and 2010 fall to 2.8 million acre-feet and 5.1 acre-feet, respectively. A trigger of 30,000 cfs yields peak pools of 2.2 million acre-feet and 3.1 million acre-feet. More detailed models utilizing variable thresholds and data from multiple points on the watershed could more accurately tune these results. Costs of Pooling First Costs are not out of reach, and if runoff sequestration reduces downstream flooding substantial funds can be reallocated from other flood-related efforts over time. Suppose for every million acre-feet of sequestration capacity we need 250,000 acres that can be intermittently flooded to an average depth of 4 feet. We could conceivably develop 50,000 acres of permanent wetlands surrounded by 200,000 acres that could be intermittently flooded. Individual wetland size need not be defined at this point. Different wetland sizes may be advantageous for different portions of the watershed, but each wetland acre is surrounded by 4 acres of floodable capacity. Partially controlling fill and release will require some type of holding structure or dam. This could be purpose-built for small wetlands. This could be a modified country-road bed in some cases. In a simple scenario without active treatment of the sequestered runoff, variable release might be accomplished by a simple spillway with several through-tile or small culvert pipes at various levels. Where active treatment requires a metered release, this could be accomplished with electric pumps or spillway controls (solar and wind power might be options). 2 20,200 cubic feet per second was selected to affect the 25% of days when 59% of water is discharged. The analysis could easily be done with other thresholds. Potential Flood Reduction Due to Pooling 1 Million Acre-feet of Water During peak weather (flooding) events, every million acre-feet of runoff pooled upstream would prevent about 1,562.5 square miles of downstream flooding at a depth of 1 foot 781 linear miles of downstream flooding 1 mile wide and 2 feet deep 208 linear miles of downstream flooding 1.5 miles wide and 5 feet deep at any point in time. Bear in mind, however, that floods move downstream. 208 linear miles of flooding on any given day does not disappear at the end of the day. It moves downstream to the next 208 linear miles until it reaches a large enough body of water to absorb it. Water pooled above Emmetsburg and Algona will, over time, reduce flooding by these levels in Humboldt, Fort Dodge, Boone, Des Moines, and Ottumwa. Water pooled above Nashua and Iowa Falls will reduce flooding in Waterloo, Cedar Falls, Cedar Rapids, Marshalltown, Tama, Page 4

5 The 50,000 acres in permanent wetlands equal about 0.5% of the watershed area. The 200,000 intermittently flooded acres equal about 2.1% of the watershed area. Suppose it costs $10,000 per acre to select and acquire the 50,000 acres of core wetland An average of $2,500 per acre to make all 250,000 acres suitable for sequestration $150 per acre per year to cover flood damages to crops on the 200,000 acres of cropland in the wetland basins (regardless of how ownership is handled, net cost for these acres should approximate the cost of intermittent flood losses due to sequestration) Up-front investments would be approximately $1.125 billion. Production flood insurance would cost $30 million per year. There would also be annual maintenance and flow-control costs, but the system would provide employment, wildlife habitat, and recreational opportunities while substantially reducing flood control investments and damage costs downstream. Simply moving flood control and damage costs from high-value urban land to low-value rural land would generate economic value that could help finance the necessary investment. Funding and Reallocation Iowa makes substantial investments in flood control, paying for flood damages, and treating nutrient-laded drinking water. No attempt is made here to generate and exhaustive accounting of those expenditures. It is enough to simply show that Iowa s flood-related expenditures dwarf the funds needed to change our runoff perspective from push-first to pool-first. To put this in perspective, Iowa has had 26 flood disasters with damages exceeding $1 billion since Events in 1993 and 2008 caused damages of $15.4 billion. At a bare minimum, these total $39.4 billion over 39 years slightly over $1 billion per year. This would pay up-front costs (outlined above) for sequestering 890,000 acre-feet of runoff every year. At this rate, it would take about 8 years to finance the pooling capacity needed for the maximum (7.1 million acre-feet) scenario described above for the Des Moines River. The Iowa River watershed might require 10 years-worth of the flood damage money. Figure another 10-years for other Iowa watersheds, and there is still $11 billion of the original $39.4 billion in major-event damage costs that can be available for operating costs, improvements, or savings. This would be entirely possible with the damage costs from 26 major flood disasters. This does not account for the continuous stream of Iowa flood events causing less than $1 billion in damages. That money could also be reallocated or saved. Iowa City, Columbus Junction, and Wapello. Pooling a million acrefeet of water upstream with one investment will pay for itself in reduced flooding costs in every downstream community on the watershed. 1 While it would be possible to sequester enough water to virtually eliminate downstream flooding, even modest capacity could make a substantial difference. We could largely eliminate small flood events that regularly occur, and we could substantially reduce the severity (in both water depth and event duration) of major intermittent flood events. The design objective is to pick initial pooling investments that provide substantial immediate reductions in flood damages and flood control investment needs. These reductions can then be partially invested in additional pooling capacity. The cycle continues until we have optimized upstream pooling with respect to downstream flood damage and control expenditures. 1 The benefits of this are not exclusive to urban residents. Downstream flooding affects both urban and rural areas. A push-first solution to agricultural runoff disproportionally benefits upstream farmers while imposing flooding costs on downstream farmers as well as downstream consumers. Page 5

6 Pooling upstream would also eliminate or substantially reduce flood control investments downstream: Des Moines spent over $140 million on flood-related projects between 1993 and 2015 (about $6 million per year) and intends to spend at least $100 million over the next ten years ($10 million per year) Cedar Rapids is currently pursuing a system of flood-control projects projected to cost $750 million over 20 years (about $37.5 million per year) The 2016 Iowa Flood Mitigation Board Annual Report lists ten cities the board has made commitments to. Total funding for the projects listed equals nearly $1.5 billion. Most of the projects are spread over 20 years for an average of about $75 million per year for just ten communities in Iowa This all comes from a brief internet search of flood control and damage expenditures. It, by no means, captures the total that local, state, and federal governments are spending on flood control or emergency flood expenditures in Iowa. Even on this basis, the funds identified dwarf the funds needed over time to implement a pool-first strategy for managing Iowa s agricultural runoff and nutrient challenges. Regional Strategic, Ltd. PO Box 36534, Des Moines, Iowa mark@regionalstrategic.com Page 6