Derek M. Heeren

USING RAPID GEOMORPHIC ASSESSMENTS TO ASSESS STREAMBANK STABILITY IN OKLAHOMA OZARK STREAMS

High streambank erosion and failure rates on streams in the Ozark ecoregion of Oklahoma may be attributed to land use change and degradation of riparian areas. Numerous benefits may be achieved from streambank stabilization, but methods are needed to determine the most critical reaches for investing limited funds. Rapid geomorphic assessments (RGAs) have been used to aid in prioritizing stream reaches. This research (1) applied an existing RGA, the channel sta- bility index (CSI), on several reaches along the Barren Fork Creek and Spavinaw Creek, and (2) modified the existing RGA to create an ecoregion-specific RGA called the Oklahoma Ozark streambank erosion potential index (OSEPI) for larger-order streams in the area. Aerial photography (2003 to 2008) was used to document recent lateral bank retreat for evaluating the RGA scores. Whereas the CSI provided a relatively simple, inexpensive way to identify reaches that should be further evaluated for stability, it failed to disaggregate unstable stream reaches. Limitations included not considering the streambanks cohesion and the difficulty in assessing some metrics. The OSEPI, which included parameters to account for the streambanks cohesion and stream curvature, had higher correlation (R 2 = 0.29 for all reaches; R 2 = 0.45 for reaches with similar soils) with recent streambank erosion. These results indicate promise for its use in prioritizing reach- es for future stabilization projects in the Ozark region of Oklahoma. Additional research is needed to further test the ge- neric and ecoregion-specific RGAs and to determine the conditions that necessitate ecoregion-specific indices.

In Situ Soil Pipeflow Experiments on Contrasting Streambank Soils

Abstract. Soil piping has been attributed as a potential mechanism of instability of embankments and streambanks. Limited field work has been conducted on quantifying and modeling pipeflow and internal erosion processes in the field with either natural or artificially created soil pipes. This research utilized an innovative constant-head trench system to conduct constant-head soil pipe experiments in two contrasting streambanks: Dry Creek in northern Mississippi and Cow Creek in northern Oklahoma. Experiments included open pipes, in which the soil pipe was directly connected to the constant-head trench and open at the streambank face, and clogged pipes, which involved plugging the outlet of the soil pipe using soil excavated adjacent to the pipe. A tensiometer network was used to measure soil water pressures surrounding open and clogged pipe outlets on the streambank face. When pipeflow occurred, flow and sediment samples were collected using flow collection pans to quantify sediment concentrations. Flow and sediment data were used with an existing turbulent pipeflow and internal erosion model to estimate erodibility and critical shear stress properties of the soils, which were subsequently compared to similar properties derived from jet erosion tests. Clogged soil pipes resulted in pore water pressure increases in the soil adjacent to the pipe, which generally remained below saturation during these experimental periods, except at locations close to the plug. Depending on the density of the plugged soil material, the clogged soil pipes either burst, resulting in turbulent pipeflow, or were manually punctured to establish pipeflow. Calibrated critical shear stress from the turbulent pipeflow and internal erosion model matched that observed from jet erosion tests for the less erodible soils on the Dry Creek streambank, where sediment concentrations were consistently below 2 g L -1 even with fairly large hydraulic gradients on the pipe (0.3 m m -1 ). Calibrated erodibility coefficients were much smaller than those measured with jet erosion tests. For the more erodible streambank soils of Cow Creek, sediment concentrations approached 40 g L -1 . There is a need for improved pipeflow modeling that accounts for rapidly changing pipe geometries, partially filled soil pipes, and pipeflow/soil matrix interactions.

Evaluation of a Stream-Aquifer Analysis Test for Deriving Reach-Scale Streambed Conductance

Extracting groundwater from pumping wells located adjacent to streams can reduce streamflow, a result that is known as alluvial well depletion. Numerous analytical solutions have been developed for alluvial well depletion that vary in their mathematical complexity. Predicted drawdown by the analytical solutions can be matched to observed drawdown from a stream-aquifer analysis (SAA) test (i.e., a pumping test adjacent to a stream) to simultaneously estimate aquifer and streambed hydrologic parameters. However, only a few SAA tests have been documented in the literature and compared to field-measured streambed parameters. Therefore, the objective of this research was to perform an SAA test for the purpose of evaluating the ability of analytical solutions, when applied to the SAA test data, to estimate reach-scale streambed conductance. The SAA test was performed at a well site located adjacent to the North Canadian River in central Oklahoma. Observation wells were installed between the stream and the pumping well and were instrumented with automated water level loggers. The pumping well, located approximately 85 m from the North Canadian River, discharged at a constant rate (2180 m3 d-1) for 90 h. Predicted drawdown by an analytical solution was fit to the observed drawdown to inversely estimate the transmissivity (790 to 950 m2 d-1), specific yield (0.19 to 0.28), and streambed conductance (600 to 1500 m d-1), which was compared to values derived from in-stream measurements (i.e., grain-size analyses on streambed sediment samples and in-stream falling-head permeameter tests). Estimated streambed conductance from the in-stream measurements and the SAA test were both on the order of 1000 m d-1. The similarity in estimates supported the use of SAA tests to derive reach-scale streambed conductance. Both the SAA test and in-stream conductivity measurements suggested minimal streambed hydraulic resistance. Therefore, for this and other streams, simpler analytical solutions may be adequate to inversely estimate the aquifer and streambed hydrologic parameters.

Berm Method for Quantification of Infiltration and Leaching at the Plot Scale in High Conductivity Soils

Measuring infiltration and leaching at the plot scale is difficult, especially for high hydraulic conductivity soils. Infiltration rate has been indirectly calculated at the plot scale by comparing surface runoff to rainfall. Direct measurement of infiltration and leaching beyond the point scale is typically limited to locations where land forming has been performed, e.g. infiltration ponds and fields with basin irrigation. The standard method for field measurement of infiltration is a double ring infiltrometer, which is limited in size (typically 30 cm diameter). In this research, a new method is proposed that uses a temporary berm constructed of a water filled 15 cm diameter vinyl hose with the edges sealed to the soil using bentonite. The berm is capable of confining infiltration plot areas of various sizes (e.g. 1 m by 1 m and 3 m by 3 m areas in this research). Water tanks (0.8 m3 and 4.9 m3) and gravity flow were used to supply water and tracers to the plots. A constant head was maintained within the plot automatically using float valves for lower flow rates and manually with a gate valve for higher flow rates. Observation wells were installed 0.5 m outside the plot to monitor for water table rise and tracers that leached into the groundwater. The procedure was tested on soils ranging from silt loam to coarse gravel with measured infiltration rates ranging from 5 to 70 cm/hr. Guidelines are provided for tank size and refilling frequency for field experiments. In addition, numerical simulations were performed to estimate time of response in wells for various soil and experimental design conditions.

Development of Deficit Irrigation Strategies for Corn Using a Yield Ratio Model

Competition for water is increasing while a growing world population requires more food production. It is critical to develop and implement efficient deficit irrigation strategies and to predict the impacts of deficit irrigation on yield. South Dakota State University (SDSU) Management Software, which simulates evapotranspiration and soil water contents, was originally designed as an on-farm decision support system capable of fully automating center pivot irrigation. A simple yield model was developed for the software in order to extend its use for evaluating deficit irrigation strategies. Yield ratio (i.e., actual yield/potential yield) was predicted based on a normalized transpiration ratio (i.e., seasonal transpiration normalized with daily reference evapotranspiration/normalized potential transpiration), requiring only daily transpiration data. Results from the updated software compared favorably with field data for corn under deficit irrigation, indicating that the yield model accounts for yield reductions due to water stress. SDSU Management Software was used to simulate center pivot irrigation and corn yield at seven locations across the Great Plains with historical weather data. Thirty irrigation strategies were evaluated across three soil water holding capacities and three pumping rates. Strategies with high water use efficiencies performed well across all treatments and locations. The recommended maximum yield strategy is 30-60-30 (strategies were defined by the minimum available soil water (%) for early, middle, and late season), which used 4% to 14% less irrigation water than a traditional strategy with negligible or positive impacts on yield. Recommended limited water supply strategies are 15-50-0, 0-30-0, and 0-15-0 for minimal, moderate, and severe water restrictions, respectively. Annual variation in yield was greatest when water was most limited. Reduced pumping rates substantially limited maximum yields for arid locations.

Impact of Preferential Flow Paths on Stream and Alluvial Groundwater Interaction

A better understanding of stream-aquifer interactions is needed both for water policy and for quantifying its impact on stream chemistry and water quality. Assuming homogeneity in alluvial aquifers is convenient but limits our understanding of stream-aquifer interactions. Previous research in the Ozark ecoregion, which is characterized by cherty soils and gravel bed streams, identified subsoils with hydraulic conductivities of 140 to 230 m d –1 and showed non-uniform groundwater flow. In a preferential flow path (PFP), even a sorbing contaminant, such as phosphorus, was found to be transported and not significantly attenuated through the subsurface. The objective of this research was to document the impact of flow heterogeneity (i.e., PFPs) on groundwater flow patterns, which will strengthen current understanding of contaminant interaction between streams and alluvial aquifers. Long term monitoring was performed adjacent to the Barren Fork Creek and Honey Creek in northeastern Oklahoma. Based on results from subsurface electrical resistivity mapping, observation wells were installed both in PFPs and in non-PFP subsoils. Water levels in the wells were recorded real-time using pressure transducers. Plots of the water table elevation, streamlines, and water level divergence were generated using six weeks of data including multiple high flow events. Divergence was used to quantify heterogeneity in hydraulic conductivity. The activity of PFPs depended on the elevation of the water table and the interaction between the stream and the groundwater. It appeared that PFPs acted as divergence zones, allowing stream water to quickly enter the groundwater system, or as flow convergence zones, draining a large groundwater area.

Heterogeneity influences on stream water–groundwater interactions in a gravel-dominated floodplain

ABSTRACT Floodplains are composed of complex depositional patterns of ancient and recent stream sediments, and research is needed to address the manner in which coarse floodplain materials affect stream–groundwater exchange patterns. Efforts to understand the heterogeneity of aquifers have utilized numerous techniques typically focused on point-scale measurements; however, in highly heterogeneous settings, the ability to model heterogeneity is dependent on the data density and spatial distribution. The objective of this research was to investigate the correlation between broad-scale methodologies for detecting heterogeneity and the observed spatial variability in stream/groundwater interactions of gravel-dominated alluvial floodplains. More specifically, this study examined the correlation between electrical resistivity (ER) and alluvial groundwater patterns during a flood event at a site on Barren Fork Creek, in the Ozark ecoregion of Oklahoma, USA, where chert gravels were common both as streambed and as floodplain material. Water table elevations from groundwater monitoring wells for a flood event on 1–5 May 2009 were compared to ER maps at various elevations. Areas with high ER matched areas with lower water table slope at the same elevation. This research demonstrated that ER approaches were capable of indicating heterogeneity in surface water–groundwater interactions, and that these heterogeneities were present even in an aquifer matrix characterized as highly conductive. Portions of gravel-dominated floodplain vadose zones characterized by high hydraulic conductivity features can result in heterogeneous flow patterns when the vadose zone of alluvial floodplains activates during storm events. EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR X. Chen

Quantification and Heterogeneity of Infiltration and Transport in Alluvial Floodplains

In order to protect drinking water systems and aquatic ecosystems, all critical nutrient source areas and transport mechanisms need to be characterized. It is hypothesized that hydrologic heterogeneities (e.g., macropores and gravel outcrops) in the subsurface of floodplains play an integral role in impacting flow and contaminant transport between the soil surface and shallow alluvial aquifers which are intricately connected to streams. Infiltration is often assumed to be uniform at the field scale, but this neglects the high spatial variability common in anisotropic, heterogeneous alluvial floodplain soils. In the Ozark ecoregion, for example, the erosion of carbonate bedrock (primarily limestone) by slightly acidic water has left a large residuum of chert gravel in Ozark soils, with floodplains generally consisting of coarse chert gravel overlain by a mantle (1 to 300 cm) of gravelly loam or silt loam. The process of alluvial sediment deposition is highly variable, and can cause gravel layers to outcrop on the soil surface at various locations within a floodplain. The objective of this research was to quantify heterogeneity in infiltration rates at three floodplain sites in the Ozark ecoregion of Oklahoma and Arkansas. Innovative field studies, including plot scale (1 by 1 m and 3 by 3 m) solute injection experiments along with geophysical imaging, were performed on both gravel outcrops and non-gravel outcrops. Plots maintained a constant head of 3 to 10 cm for up to 48 hours. Infiltration rates varied from 0.8 to 70 cm/h, and varied considerably even within a single floodplain. Electrical resistivity imaging was used to identify zones of preferential flow as well as characterize subsurface soil layering. Fluid samples from observation wells outside the plot (0.5 m from the boundary) indicated nonuniform subsurface flow and transport. Phosphorus was detected in the groundwater for 6 of the 12 plots and was positively correlated to the presence of gravel outcrops. Results indicated that flow paths are sub-meter scale for detecting infiltrating solutions. Tension infiltrometers showed that macropore flow accounted for approximately 85% to 99% of the total infiltration.

A New Technique to Improve the Emission Uniformity for Trickle Irrigation Systems

The trickle irrigation method is a relatively new watering technique which has proven to be a progressive, successful development all over the world. Benefits of using this method in vast areas of Iraq are obvious, especially in parts of drought areas where development and reclamation necessitate the use of trickle irrigation. Previous field research has improved the emission uniformity ( EU ) of trickle irrigation to 100% by individually elevating emitters above the lateral line. In this research, a simpler procedure was proposed for improving EU . This procedure raises the inlet of the lateral pipe to a desired height above ground level. The increasing energy due to elevation drop along the lateral compensates for friction loss, resulting in a more consistent pressure distribution in the pipe. The objective of this research was to improve the resulting EU and to provide a method for determining the optimum inlet height. If tension is placed on the lateral such that its slope is zero at the end of the lateral, its profile becomes a catenary (a hyperbolic cosine function). A hydraulic analysis was performed to estimate flow for each emitter and the resulting EU . Setups that were used in the previous research were simulated. Lateral elevations at the emitters were similar to the elevations of the raised emitters in the previous research, since both approaches were based on the same hydraulic idea. While 100% was not achieved, all EU s were over 99%. The hydraulic analysis was also used to evaluate the effects of inlet elevation and emitter exponent on EU . It was found that the EU increases when the height of the inlet lateral pipe increases up to a maximum EU , correlating to an optimum design inlet elevation, before it starts to decrease again. Raising the inlet to the optimum elevation caused the EU to increase from 95 to 99.5% compared to leaving the lateral pipe on the ground. The emitter exponent had a negative correlation with the estimated EU , indicating that emitters with lower emitter coefficients may be preferable when designing trickle irrigation systems for maximum EU . The developed procedure for trickle irrigation systems can be used to execute designs of lateral pipe lines that maximize EU .

Streambank Erosion and Instability Induced by Groundwater Seepage

Excessive sediment is one of the most common surface water pollutants. It diminishes water quality and destroys aquatic habitat. Streambank erosion is known to be a major source of sediment in streams and rivers, contributing as much as 80% of the total sediment load in some watersheds. Little work has been done to study the effects of seepage on streambank erosion and failure. Prior research, primarily in the laboratory under well-defined and controlled conditions, has examined seepage as a mechanism for bank erosion, but more needs to be done to validate conclusions derived from the laboratory with field data. This project studied a streambank on Dry Creek (a tributary to Little Topashaw Creek) located in Chickasaw County, Mississippi. The bank was previously observed to produce seepage even during dry summer months. This creek is a deeply incised stream in the Yalobusha Watershed with near 90 degree banks. The creek flows through alluvial plains under cultivation and surrounded by forested areas. Excess sediment has been identified as the main water quality issue in the watershed with gullies and banks being the main sources. Watershed geology is characterized by silt loam and clay loam with a more conductive loamy sand between the loam and an underlying cohesive layer. The site was initially instrumented with a network of tensiometers and observation wells. Groundwater conditions and bank erosion were monitored for several weeks, followed by an induced seepage experiment. A trench installed 2.8 m from the edge of the bank and approximately 2 m below ground surface was used to provide a constant head for groundwater flow in the near-bank area. The bank face was outfitted with a seepage collection device that measured seepage flow rate and sediment transport. Groundwater conditions were again monitored by the tensiometer and observation well network. Experiments consisted of a trench injection at a constant head and observations of flow rates, erosion rates, soil-water pressures, and water table elevations. Flow rates varied from 0.004 L/min to 1.16 L/min at different locations on the bank. It was observed that the seeps experienced ‘self-healing’ erosion in which upper layer cohesive soil failures blocked further particle mobilization. One experiment simulated fluvial erosion removing the failed material, thereby, resulting in combined erosion rates of over 6000 g/min. Seepage erosion could be a dominate mechanism of streambank failure where the self-healing process is not occurring.