Relating Design Storm Events to Ordinary High Water Marks in Indiana

Hydraulic design and environmental permitting are heavily dependent upon Ordinary High Water Marks (OHWM) because they define the active river channel. The United States Army Corps of Engineers (USACE) use OHWM for regulation of the “Waters of the United States” as well as for flood and drought management. Current methods to determine OHWM are based on detailed on-site surveys to identify physical characteristics like scouring, deposition around the banks, absence of vegetation and water staining. These characteristics are site specific so there are fluctuations in measurements based on the water body, weather conditions, channel morphology, slope, fluvial patterns and size of the channel. A more reliable way to estimate this variable for hydraulic design is required that is based on storm return periods. This study uses hydrologic and hydraulic modeling to relate OHWM to storm return periods by analyzing hydraulic and hydrologic parameters corresponding to design streamflow events for 26 watersheds in Indiana. The results show that the OHWM corresponds to discharges that have return periods ranging from 0.7 – 1.1 years. These results also suggest that that OHWM correspond to channel discharges much smaller than bank-full discharge, which typically has a return period of 1.5 – 2 years. The OHWM discharges are then related to 100-year discharges to enable the use of this relationship in approximately estimating the OHWM discharge when the 100-year discharge is known. For Indiana, it is found that ratio of OHWM discharge and 100-year discharge has an average value of 4.99% for the northern part, 3.60% for the central part, and 5.49% for the southern part

Determination of Unit Hydrograph Parameters for Indiana Watersheds

Regression equations predicting Clark Synthetic Unit Hydrograph (SUH) parameters for time of concentration (tc) and storage coefficient (R) are developed for small watersheds across Indiana [drainage areas = 3-38 square miles (mi2)]. The state is partitioned into three regions: North, Central, and South, with consideration for past regionalization studies of Indiana and geomorphology. The equations are derived using multiple linear regression analysis for 30 watersheds with 90 observed rainfall-runoff events. Clark SUH parameters are optimized using Hec-HMS to match the observed rainfall-runoff events. The optimized Clark SUH parameters are related to geomorphologic parameters estimated using geographic information system (GIS) applications. An extensive list of 29 geomorphologic parameters is considered including parameters related to depression storage, slope, drainage area, basin shape, and stream network. Separate regression equations for tc and R are developed for each region and the entire state. Values for tc and R are predicted using the regression equations and used to model 7 new rainfall-runoff events in HEC-HMS for comparison to the NRCS SUH method

Implementation of surface soil moisture data assimilation with watershed scale distributed hydrological model

This paper aims to investigate how surface soil moisture data assimilation affects each hydrologic process and how spatially varying inputs affect the potential capability of surface soil moisture assimilation at the watershed scale. The Ensemble Kalman Filter (EnKF) is coupled with a watershed scale, semi-distributed hydrologic model, the Soil and Water Assessment Tool (SWAT), to assimilate surface (5 cm) soil moisture. By intentionally setting inaccurate precipitation with open loop and EnKF scenarios in a synthetic experiment, the capability of surface soil moisture assimilation to compensate for the precipitation errors were examined. Results show that daily assimilation of surface soil moisture for each HRU improves model predictions especially reducing errors in surface and profile soil moisture estimation. Almost all hydrological processes associated with soil moisture are also improved with decreased root mean square error (RMSE) values through the EnKF scenario. The EnKF does not produce as much a significant improvement in streamflow predictions as compared to soil moisture estimates in the presence of large precipitation errors and the limitations of the infiltration–runoff model mechanism. Distributed errors of the soil water content also show the benefit of surface soil moisture assimilation and the influences of spatially varying inputs such as soil and landuse types. Thus, soil moisture update through data assimilation can be a supplementary way to overcome the errors created by inaccurate rainfall. Even though this synthetic study shows the potential of remotely sensed surface soil moisture measurements for applications of watershed scale water resources management, future studies are necessary that focus on the use of real-time observational data

Application of data assimilation with the Root Zone Water Quality Model for soil moisture profile estimation in the upper Cedar Creek, Indiana

Data assimilation techniques have been proven as an effective tool to improve model forecasts by combining information about observed variables in many areas. This article examines the potential of assimilating surface soil moisture observations into a field-scale hydrological model, the Root Zone Water Quality Model, to improve soil moisture estimation. The Ensemble Kalman Filter (EnKF), a popular data assimilation technique for nonlinear systems, was applied and compared with a simple direct insertion method. In situ soil moisture data at four different depths (5, 20, 40, and 60 cm) from two agricultural fields (AS1 and AS2) in northeastern Indiana were used for assimilation and validation purposes. Through daily update, the EnKF improved soil moisture estimation compared with the direct insertion method and model results without assimilation, having more distinct improvement at the 5 and 20 cm depths than for deeper layers (40 and 60 cm). Local vertical soil property heterogeneity in AS1 deteriorated soil moisture estimates with the EnKF. Removal of systematic bias in the forecast model was found to be critical for more successful soil moisture data assimilation studies. This study also demonstrates that a more frequent update generally contributes in enhancing the open loop simulation; however, large forecasting error can prevent more frequent update from providing better results. In addition, results indicate that various ensemble sizes make little difference in the assimilation results. An ensemble of 100 members produced results that were comparable with results obtained from larger ensembles

RWater – A Cyber Enabled Tool For Hydrologic Modeling And Analysis

Existing distributed hydrologic models are complex and computationally demanding for using as a rapid-forecasting policy-decision tool, or even as a class-room educational tool. In addition, platform dependence, specific input/output data structures and non-dynamic data-interaction with pluggable software components inside the existing proprietary frameworks make these models restrictive only to the specialized user groups. RWater is a web-based hydrologic analysis and modeling framework that utilizes the commonly used R software within the HUBzero cyber infrastructure of Purdue University. RWater is designed as an integrated framework for distributed hydrologic simulation, along with subsequent parameter optimization and visualization schemes. RWater provides platform independent web-based interface, flexible data integration capacity, grid-based simulations, and user-extensibility. RWater uses RStudio to simulate hydrologic processes on raster based data obtained through conventional GIS pre-processing. The program integrates Shuffled Complex Evolution (SCE) algorithm for parameter optimization. Moreover, RWater enables users to produce different descriptive statistics and visualization of the outputs at different temporal resolutions. The applicability of RWater will be demonstrated by application on two watersheds in Indiana for multiple rainfall events

A Laboratory Study of Apron-Riprap Design for Small-Culvert Outlets

The present study investigated primarily the appropriate stone-sizing of on-grade riprap aprons, and more specifically whether the current INDOT design policy may be overly conservative especially within the context of smaller culverts. In the study, laboratory experiments were performed with two pipe diameters, D = 4.25 in (0.35 ft) and 5.75 in (0.48 ft), and four stone sizes, median diameters estimated to be d50 = 0.61 in, 1.22 in, 1.73 in, and 2.24 in, for a range of discharges and tailwater depths. Video records were made of the laboratory apron to detect stone-mobilization events, and stable and unstable cases were distinguished. Logistic regression was then applied to develop equations delineating the boundary between stable and unstable regions for different riprap size classes in terms of d50/D. These regression equations were then modified to ensure that they formed an ordered system in that each equation was more conservative than the next, to include a safety factor, and to set a minimum size for each size class consistent with the applicability of each equation. Procedures for applying the proposed equations are described. Compared to the current INDOT design policy, the proposed approach typically predicts a smaller standard riprap class required for apron stability. In an application to a sample of actual culverts, the proposed approach, including the recommended safety factors, yielded a smaller required standard INDOT riprap class in 75% of cases, but, in a small number of cases with very low relative tailwater depths, did recommend a more conservative design. Of the other two main approaches to stone sizing for riprap aprons, the HEC-14 model was rather restricted in its range of application, but where applicable it was found to be somewhat more conservative in its stone-size recommendation, though in practice the recommended riprap class largely agreed with the proposed approach. The results of the other main approach, that due to Bohan (1970), were more erratic, with the maximum-tailwater equation being too lax and the minimum-tailwater equation being generally too stringent. Both the HEC-14 and the Bohan models tended to be less conservative than the proposed approach for larger values of d50/D. A secondary aim of the study was an examination of the velocity field downstream of the outlet, and the possible implications for scour downstream of the apron. Point velocity measurements were obtained for four cases, all with the same 4.25-in diameter pipe, three of which involved the largest (d50 = 2.2 in) stone, and one over a smooth bed. In the three cases with a stone apron, the apron extended a distance of ≈9D downstream of the outlet. In all four cases, substantial velocities (maximum velociites greater than 70% of than the average outlet velocity) were observed beyond 4D (which is the minimum specified by INDOT design guidelines) and even beyond 8D (which is the largest apron length specified in HEC-14). A comparison between rough-bed and smooth-bed results indicated a measurable effect on maximum velocity due to the rough apron, but the reduction in maximum velocity is still likely insufficient to prevent scour downstream of the apron in most practical cases even if the apron extends to 9D

Assessment of HY-8 and HEC-RAS Bridge Models for Large-Span Water-Encapsulating Structures

Current INDOT policy requires that culvert-like structures with spans greater than 20 ft be treated for purposes of hydraulic analysis as a bridge, and hence mandates the use of software such as HEC-RAS for predicting the headwater, rather than the culvert-specific software, HY-8. In this context, culvert-like structures are assumed to have a standard inlet geometry (e.g., such as those already modeled in HY-8) and a constant barrel geometry. The present study examines the technical basis of this policy, and whether the policy could be revised to allow the application of simpler culvert-hydraulics analysis and HY-8 to culvert-like structures with spans greater than 20 ft. Laboratory experiments were performed with model box culverts of span 1.5 ft and two streamwise lengths, 2.1 ft and 8 ft, and performance curves describing the variation of headwater with discharge were obtained. The effects of bed roughness, the presence or absence of a cover (if present, the rise was 0.5 ft), and a range of tailwater levels, were investigated. The laboratory observa­tions were compared with predictions by HY-8 and HEC-RAS models, and the model performance assessed. In general, HY-8 predictions were found to be as good as, and in some cases superior to, the HEC-RAS predictions, for both long and short culvert-like structures. This was attributed to the empirical information in HY-8 being more tailored to the specific standardized geometry of culvert-like structures, and the automatic inclusion of roughness effects, whereas HEC-RAS, at least when used with default coefficients and settings, relied on generic coefficients and neglected roughness effects. It was therefore recommended that a change in INDOT policy allowing large-span culvert-like structures to be analyzed using conventional culvert hydraulics would be technically justified for problems where the structure could be considered in isolation and accurate input data are available

Water Resources Policy Development Using Hydrologic And Systems Dynamics Modeling – A Case Study For East Africa

Drought is a natural disaster that affects millions of people across the globe. Lack of rainfall reduces crop yields and livestock productivity and in turn, food availability and income. In developing countries, these effects are even more detrimental. As droughts become more frequent, adaptation is a fundamental concern for countries and their policy makers. Hydrologic and system dynamics models were developed for a region in East Africa, focused on the Horn of Africa (ie. a region bordering Kenya, Somalia, and Ethiopia), an area well-known for frequent droughts due to unpredictable rainfall and high temperatures. The models simulate the interdependencies between water availability, land degradation, food availability, socio-economic welfare and the impact new adaptation policies can have on the region over a 10 year simulation. It was found that a combination of increased hydraulic infrastructure and innovative agricultural practice policy can reduce domestic water deficits by 54-100% while increasing the income per capita up to 285% over the 10 years. By innovatively combining hydrologic and system dynamics modeling, realistic simulation of the effects water scarcity has on natural systems can be observed. Implementation of policies within the model aids the selection process by evaluating multiple options, quantifying the effectiveness the policies have on individual stakeholder livelihood, and analyzing the overall outcome to ensure equitable costs and benefits