The 2010 River Dam Inventory Provides a Snapshot of Vital Information for Developing a Mitigation Plan for Major Rivers
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ams, like the rivers and 22 The 2010 River Dstreams in which they are built, are not a constant. Dam Inventory Some are wiped out in floods, never to return. Some are re-constructed with a new design or a new height, while others are patched. Others gradually fall into disrepair. A few remain stable long beyond their original design lifespans. Periodically, major data updates will be needed. The 2010 river dam inventory provides a snapshot of vital information for developing a mitigation plan for major rivers. 17 Why is this inventory 2a. Inventory Background different from the National Inventory of Dams? The 2010 inventory of low-head dams in Iowa began with the Rock dams: Human-made structures of loose rock. The U.S. Army Corps of Engineers’ Iowa Conservation Commission’s 1979 Inland Dams Inventory. Minor low-head: Low-head dams with 1-foot or less of head For five years, additional data was added via the water trails 2009 National Inventory of Dams was that are known to submerge at relatively low river discharge used to document dams from a list of program. When this plan was initiated, a review of existing GIS levels. data and aerial photos was conducted in the study area. The 3,374 dams. The purpose of this listing list was reviewed against the National Inventory of Dams kept Rubble dams: Human-made structures that often include relates to hazard potential for structural by the Iowa DNR floodplains program. waste concrete, rebar, rocks, bricks, and other waste build- failure, what the consequences of that ing materials. would be, and inspect to avoid a catas- Study area: Major rivers Seasonal wetland low-head: Adjustable height dams that trophe. Out of the total, 210 are listed The study area was narrowed to streams that are clearly public are used seasonally by wildlife management authorities to as “significant” and 101 are listed as resources (Code of Iowa, Chapter 462A.2.20; 462A.69). “Major seasonally flood floodplain wetlands. Not a planning priority. “high” hazard if failure would occur. rivers” for the purposes of this plan means: Lake outflow structure: Outflow structures on natural lakes • any flowing water with a watershed greater than 50 that manage lake levels; not a planning priority. The highest hazard dams do not relate square miles While rubble, rock dams, and lake outflow structures were to the number of actual deaths at the identified as obstructions during the process of evaluating • in urbanized streams, a more conservative criteria of 25 dam, and no deaths have occurred square miles of watershed was used structure types, they were not included in the analysis, as they were considered out of scope of this study. due to dam failure to date. For the Direct staff and volunteer observations, a survey of dam own- purpose of documenting the types ers, additional calls to public managers, and intensive data of dams where deaths are actually entry, review, and updating led to the final inventory. Table 2-a occurring in Iowa, and which create Categories of dams the primary barriers for aquatic spe- Quick statistics: The 246 cies, the National Inventory of Dams To aid policy decision making and generalized priorities for structures on major rivers provides little overlap, as it does not public purposes, dams were categorized into the following: require reporting for dams under 6 feet Low-head dams: A river-wide dam that is normally over- Types Ownership in height. topped by the entire river’s flow; gates may or may not be (# dams / category) (# dams / category) present to reduce upstream flooding effects. Height is less than 30 feet. Low-head dams: 177 Private: 28 Breached low-head dams: A low-head dam with a breached Breached low-head dams: 6 Cities: 77 portion at some point across the width. These may be rela- Minor low-head dams: 4 State: 47 tively low-hazard at low flows, but may have long portions that re-circulate at higher flows. Fish passage may or may Large impoundment dams: 18 County conservation: 34 not be consistent. Stream Crossings: 8 Federal: 17 Large impoundment dams: Earthen dams that create a recreational lake upstream with a concrete chute or piped Seasonal wetland dams: 4 Unknown: 15 spillway, usually accompanied by an emergency overflow Rock and rubble dams: 29 spillway. Height is 30 feet or greater. Figure 2-a: Iowa’s 2009 National Inventory of Dams. 18 2b. Social considerations Figure 2-b. Reported Openess to Modification, Dam Owners Survey Very Open Somewhat Open Probably Not Open 1 Definitely Not OpenPerceived Benefits, Dam Owners Survey Don’t KnowRiver Crossing Stream Channel Stabilization I Need MoreUtility Info/Pipeline Protection Hydropower Generation Upstream Impoundment OtherAgricultural Purposes Hunting Fishing Visual Interest 1 0 10 20 Historic Valu3e0 40 50 60 Fish & Aquatic Habitat Wildlife Habitat Aeration Enhanced Water Quality Figure 2-c.RepFolorotde Cdo Cntruorl rent Stream Uses, Dam Owners Survey Water Supply Other Don't Know None Boating Table 2-b 0 10 20 30 40 50 60 70 80 Fis9h0ing 100 Stakeholder groups and the public were surveyed or Dam Owners’ Most Agricultural Purposes otherwise contacted about their views on dams. This Other Land-based Recreation data was used to determine planning direction. Common Responses Perceived Benefits, Dam Owners Survey 1 PercHeuivnetindg Benefits, Dam Owners Survey Most % of total Swimming Question frequent River Crossing Dam owners responses River Crossing answer Other Stream Channel Stabilization Utility/Pipeline ProtectioSntream Channel Stabilization Important among stakeholders in any discussion How open are you to Utility/Pipeline Protection Very open 34 Don'tH Kyndorowpower Generation considering a modification? Hydropower Generation Upstream Impoundment about dam mitigation are the owners of the dams. Current Stream Use Upstream Impoundment Fishing 71 AgriculturaNl oPnuerposes Benefits Dam Provides at AgriculturalH Puunrtpinogses Dam owners, including state and county manag- Fishing Area of Stream 56 Hunting Fishing Fishing Why was the dam originally Visual Interest ers, municipal officials, and corporate or individual Mill / business Visual Interest constructed - What was its 24 1 0 20 40 60Historic Val8u0e 100 120 140 function 1 Historic Value Fish & Aquatic Habitat landowners were surveyed by mail in 2009, and 54 purpose? Fish & Aquatic Habitat Wildlife Habitat What problems may Upstream Wildlife Habitat percent responded. Surveys were not sent to rock or 45 Aeration exist with your dam? siltation Aeration Enhanced Water Quality Enhanced Water Quality How acceptable is the Somewhat Flood Control rubble dam owners. Tallies of responses to various FloRode pConrttroeld Problems, Dam Owners Survey condition of the dam? acceptable 31 Figure 2-d. Water Supply questions are included in this section and provide OWthaeterr Supply Do you believe your dam... Don't KnoOwther Don't Know insight into views reported by the owners. Their most educated... is a barrier toabout fish benefits, they can become None Yes 57 None passage? Stream and/or Channel Erosion common reported problem (Figure 2-d) was upstream a... mitigation is a barrier to project’s strongest proponents. 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 siltation. Majorities of respondents believed their dam Aboutnavigation 50 and avid recreat streamion anglersYes responded50 uses? Debris Collection at High Water ... reduces biodiversity in the was a barrier to navigation and fish passage, but a to the internet survey. OfNo those, 9659 percent stream? Upstream Siltation majority believed the dam had no role in reducing fished... affects nea10rb yor w atemorer table days per year, 44 percent No elevation 54 1 Perceived Benefits, Dam Owners Survey biodiversity (Figure 2-h). A majority of responses also reported fishing streams below river dams, Other indicated they would be “very open” or “somewhat and 20 percent reported fishing below lake River Crossing Don't Know Stream Channel Stabilization open” to a modification on their dam. dams. They spent 43 percent of their angling Utility/Pipeline Protection Hydropower Generation time wading, 22 percent at the stream edge, None Upstream Impoundment Agricultural Purposes Anglers and 13.2 percent in non-motorized boats. A Hunting Fishing Dam owners reported fishing as the most common majority believed in balance mitigation ap- Visual Interest 1 0 10 20 30 Histo4ri0c Value 50 60 70 80 dam use. Anglers are often the most resistent to proaches, whereas as 16 percent thought all Fish & Aquatic Habitat Wildlife Habitat change at dams. After being listened to, and being dams should be removed. Aeration Enhanced Water Quality Flood Control 19 Water Supply Other Don't Know None 0 10 20 30 40 50 60 70 80 90 100 Figure 2-e. Perceived Benefits, Dam Owners Survey River Crossing Stream Channel Stabilization Utility/Pipeline Protection Hydropower Generation Upstream Impoundment Agricultural Purposes Hunting Fishing Visual Interest 1 Peerrcceeiivveedd BBeenneeffiittssH,, is DDtoaarmicm V OOawluwenneerrss S Suurrvveeyy Fish & Aquatic Habitat Wildlife Habitat River CrossingAeration River Crossing Stream Channel Stabilization Stream ChEannhnaenl cSetda bWiliaztaetrio Qnuality Utility/Pipeline Protection Utility/PipFelolionde PCroonttercotlion Hydropower Generation HydropoweWr aGtenr eSrautpiopnly Upstream Impoundment Other Upstream Impoundment ADgroiicnu't lltKtunrraollw Puurrppoosseess Hunting None Hunting FFisishhiningg Visual Interest 0 10 20 30 40 50 V6is0ual Inter7e0st 80 90 100 1 HHisisttoorricic VVaaluluee FFisishh & &