The Iowa Flood Center (IFC), established following the 2008 record floods, has developed a real-time flood forecasting and information dissemination system for use by all Iowans. The system complements the operational forecasting issued by the National Weather Service, is based on sound scientific principles of flood genesis and spatial organization, and includes many technological advances. At its core is a continuous rainfall–runoff model based on landscape decomposition into hillslopes and channel links. Rainfall conversion to runoff is modeled through soil moisture accounting at hillslopes. Channel routing is based on a nonlinear representation of water velocity that considers the discharge amount as well as the upstream drainage area. Mathematically, the model represents a large system of ordinary differential equations organized to follow river network topology. The IFC also developed an efficient numerical solver suitable for high-performance computing architecture. The solver allows the IFC to update forecasts every 15 min for over 1,000 Iowa communities. The input to the system comes from a radar-rainfall algorithm, developed in-house, that maps rainfall every 5 min with high spatial resolution. The algorithm uses Level II radar reflectivity and other polarimetric data from the Weather Surveillance Radar-1988 Dual-Polarimetric (WSR-88DP) radar network. A large library of flood inundation maps and real-time river stage data from over 200 IFC “stream-stage sensors” complement the IFC information system. The system communicates all this information to the general public through a comprehensive browser-based and interactive platform. Streamflow forecasts and observations from Iowa can provide support for a similar system being developed at the National Water Center through model intercomparisons, diagnostic analyses, and product evaluations.

Abstract:The State of Iowa, located in the Midwestern United States, has experienced an increased frequency of large floods in recent decades. After extreme flooding in the summer of 2008, the Iowa Flood Center (IFC) was established for advanced research and education specifically related to floods. IFC seeks to improve Iowa's flood hazard awareness through the development of easily accessible, high-quality mapping products. Mapping initiatives consist of two model development approaches: (1) statewide floodplain delineation using one-dimensional (1D) models, and (2) urban flood mapping using detailed one-dimensional/two-dimensional (2D) coupled models. The statewide floodplain project will benefit Iowans through the creation of a comprehensive set of floodplain maps developed under a single consistent methodology. These will be important tools in evaluating flood risk, regulating floodplains, and participating in the National Flood Insurance Program. Detailed urban flood analyses are used to develop inundation map libraries. These map libraries are meant to supplement National Weather Service river stage flood forecasts by providing a visual representation of potential flood extent according to predicted river stage at stream gage locations.

Many of the Upper Missouri River dikes have been notched to create additional shallow water habitat (SWH, operationally defined as areas in the stream with depth < 1.5 m, and velocity < 0.75 m s À1 ) for fish populations. The goal of this study was to quantify the additional SWH gained from notching these dikes and to evaluate their performance under different flow conditions. A coupled field and numerical study was performed on a reach of the Missouri River, near Nebraska City, NE, which contains a number of dikes notched in 2004. The numerical simulations showed that the SWH criterion for depth was more difficult to satisfy in the study reach than the SWH criterion for velocity. Notching the dikes resulted in a slight shift of the bankline due to local erosion in the vicinity of the dikes and the formation of scour holes downstream of the notches. Results from the study suggested that notching the dikes had limited impact on the SWH because the area gained from the bankline shift was offset by the area lost from the scour holes formation. The performance of the notched dikes in sustaining the minimum habitat suitability conditions for the Missouri River ecosystem was also investigated. These conditions corresponded to discharges < 709 m 3 s À1 for the period from mid-July to mid-August, or equivalently SWH areas > 5225 m 2 dike À1 during the same period. Analysis of the Missouri River annual discharge records at the study site showed that the dikes can provide the minimum required SWH for mean annual discharges < 667 m 3 s À1 . For mean annual discharges > 667 m 3 s À1 , new alternative structures or restoration facilities were needed, in addition to the existing dikes, to sustain the minimum required SWH. The dikes were not effective in providing any SWH for mean annual discharges > 2000 m 3 s À1 .

Research Impact Statement: Agricultural best management practices (BMPs) can reduce flood risk, providing a co-benefit to nutrient reduction.ABSTRACT: Best management practices (BMPs) play an important role in improving impaired water quality from conventional row crop agriculture. In addition to reducing nutrient and sediment loads, BMPs such as fertilizer management, reduced tillage, and cover crops could alter the hydrology of agricultural systems and reduce surface water runoff. While attention is devoted to the water quality benefits of BMPs, the potential cobenefits of flood loss reduction are often overlooked. This study quantifies the effects of selected commonly applied BMPs on expected flood loss to agricultural and urban areas in four Iowa watersheds. The analysis combines a watershed hydrologic model, hydraulic model outputs, and a loss estimation model to determine relationships between hydrologic changes from BMP implementations and annual economic flood loss. The results indicate a modest reduction in peak discharge and economic loss, although loss reduction is substantial when urban centers or other high-value assets are located downstream in the watershed. Among the BMPs, wetlands, and cover crops reduce losses the most. The research demonstrates that watershed-scale implementation of agricultural BMPs could provide benefits of flood loss reduction in addition to water quality improvements.(

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Anthropogenic development of floodplains and alteration to natural hydrological regimes have resulted in extensive loss of off-channel habitat. Interest has grown in restoring these habitats as an effective conservation strategy for numerous aquatic species. This study developed a process to reproducibly identify areas of former stream meanders to assist future off-channel restoration site selections. Three watersheds in Iowa and Minnesota where off-channel restorations are currently being conducted to aid the conservation of the Topeka Shiner (Notropis topeka) were selected as the study area. Floodplain depressions were identified with LiDAR-derived digital elevation models, and their morphologic and topographic characteristics were described. Classification tree models were developed to distinguish relic streams and oxbows from other landscape features. All models demonstrated a strong ability to distinguish between target and non-target features with area under the receiver operator curve (AUC) values ≥ 0.82 and correct classification rates ≥ 0.88. Solidity, concavity, and mean height above channel metrics were among the first splits in all trees. To compensate for the noise associated with the final model designation, features were ranked by their conditional probability. The results of this study will provide conservation managers with an improved process to identify candidate restoration sites.

Water quality sensors deployed on boats, buoys, and fixed monitoring stations along rivers allow high frequency monitoring at dense spatial and temporal resolutions. Research characterizing nitrate (NO3–N) delivery along extended reaches of navigable rivers, however, is sparse. Since land use and stream biogeochemistry can vary within agricultural watersheds, identifying detailed spatial patterns of stream NO3–N can help identify source area contributions that can be used to develop strategies for water quality improvement. Identifying spatial patterns is especially critical in agricultural watersheds that span multiple landscapes and have dynamic hydrological regimes. We developed and tested a new method that quantifies NO3–N delivery to streams at a high spatial resolution by continuously measuring stream NO3–N using a boat-deployed sensor. Traveling up the Iowa and Cedar Rivers (located within agricultural Upper Mississippi River Basin) and their major tributaries with the system, we automatically measured NO3–N concentrations every 15 s during four excursions spanning the months of May to August, 2018, and characterized stream NO3–N both laterally and longitudinally in river flow. Iowa River NO3–N concentrations were highest nearest the headwaters and gradually declined as the river flowed toward the Mississippi River. Conversely, Cedar River NO3–N concentrations increased from the headwaters toward the mid-watershed areas due to elevated NO3–N delivery from tributaries of the Middle Cedar River; NO3–N concentrations declined in the lower reaches. Our results confirm that NO3–N mitigation efforts should focus on level and intensely-farmed subwatersheds. Data collected with our sensor system compliments permanently deployed sensors and provides an option to support NO3–N removal efforts.

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