Designing and Evaluating the Quality and Cost-effectiveness of Saturated Sediment Permeameters

Many simulations require accurate measurements of saturated hydraulic conductivity, a sediment property that governs the speed at which water flows through sediments relative to head differences. The goal of our project is to design and build an inexpensive permeameter capable of producing accurate hydraulic conductivity values. We tested four permeameters; a standard research grade constant-head permeameter, a falling-head permeameter modeled off of an in situ stream method, a constant-head permeameter made out of 4” PVC pipe, and a similar constant-head permeameter made out of 2” PVC pipe. Our custom-built constant-head permeameters both utilized a U-shaped design, two tubes which form a manometer, and multiple output overflows. Despite significant differences in design, method, and cost, we found that all four of the permeameters yielded relatively consistent mean hydraulic conductivities with low standard deviations (0.004-0.019). We also compared the attributes: price, weight, and number of parts. Our conclusion is that because the average K-value and standard deviation of each design is within reason, the best choice depends on the practitioner’s situation and intention.Faculty Sponsor: Susa H. Stonedah

Designing and Evaluating the Quality and Cost-effectiveness of Saturated Sediment Permeameters

Many simulations require accurate measurements of saturated hydraulic conductivity, a sediment property that governs the speed at which water flows through sediments relative to head differences. The goal of our project is to design and build an inexpensive permeameter capable of producing accurate hydraulic conductivity values. We tested four permeameters; a standard research grade constant-head permeameter, a falling-head permeameter modeled off of an in situ stream method, a constant-head permeameter made out of 4” PVC pipe, and a similar constant-head permeameter made out of 2” PVC pipe. Our custom-built constant-head permeameters both utilized a U-shaped design, two tubes which form a manometer, and multiple output overflows. Despite significant differences in design, method, and cost, we found that all four of the permeameters yielded relatively consistent mean hydraulic conductivities with low standard deviations (0.004-0.019). We also compared the attributes: price, weight, and number of parts. Our conclusion is that because the average K-value and standard deviation of each design is within reason, the best choice depends on the practitioner’s situation and intention

Analyzing and Designing an Arduino Controlled System to Study the Effect of Changing Water Levels on Water Flow Through Sediments

The hyporheic zone is the region of sediment under a stream where water from the stream flows before returning to the stream itself. Many studies focus on steady water flow through this region, however, in natural systems, water levels and water flow rates change due to storms, tides, dams, or melting snow. To investigate flow under unsteady conditions, we built a system that allows us to control the water level and thus the flow rates. We used a pressure sensor that is connected to an Arduino board to measure the water level. The Arduino board uses the measured pressure value to control a water pump. When the water level is lower than desired, the pump will turn on and when it is higher than desired, it will turn off. This allowed us to hold the water level constant or tell it to oscillate. We then evaluated our system by comparing our desired water level functions to those measured with our pressure sensor, those measured by a pressure transducer connected to a separate Arduino, and those we extracted from videos of our system

Hydrogeomorphology of the Hyporheic Zone: Stream Solute and Fine Particle Interactions With a Dynamic Streambed

Hyporheic flow in streams has typically been studied separately from geomorphic processes. We investigated interactions between bed mobility and dynamic hyporheic storage of solutes and fine particles in a sand-bed stream before, during, and after a flood. A conservatively transported solute tracer (bromide) and a fine particles tracer (5 μm latex particles), a surrogate for fine particulate organic matter, were co-injected during base flow. The tracers were differentially stored, with fine particles penetrating more shallowly in hyporheic flow and retained more efficiently due to the high rate of particle filtration in bed sediment compared to solute. Tracer injections lasted 3.5 h after which we released a small flood from an upstream dam one hour later. Due to shallower storage in the bed, fine particles were rapidly entrained during the rising limb of the flood hydrograph. Rather than being flushed by the flood, we observed that solutes were stored longer due to expansion of hyporheic flow paths beneath the temporarily enlarged bedforms. Three important timescales determined the fate of solutes and fine particles: (1) flood duration, (2) relaxation time of flood-enlarged bedforms back to base flow dimensions, and (3) resulting adjustments and lag times of hyporheic flow. Recurrent transitions between these timescales explain why we observed a peak accumulation of natural particulate organic matter between 2 and 4 cm deep in the bed, i.e., below the scour layer of mobile bedforms but above the maximum depth of particle filtration in hyporheic flow paths. Thus, physical interactions between bed mobility and hyporheic transport influence how organic matter is stored in the bed and how long it is retained, which affects decomposition rate and metabolism of this southeastern Coastal Plain stream. In summary we found that dynamic interactions between hyporheic flow, bed mobility, and flow variation had strong but differential influences on base flow retention and flood mobilization of solutes and fine particulates. These hydrogeomorphic relationships have implications for microbial respiration of organic matter, carbon and nutrient cycling, and fate of contaminants in streams

Hydrologic controls on the accumulation of different sized microplastics in the streambed sediments downstream of a wastewater treatment plant (Catalonia, Spain)

Wastewater treatment plants (WWTPs) act as a point source of microplastics (MPs) to freshwater ecosystems. Although MP abundance has been linked to high-density population areas, the mechanisms of how river hydrodynamics and particle size influence MP accumulation in streams are still largely unknown. This study investigated the spatial distribution of MPs within streambed sediments downstream of a WWTP effluent in Cànoves stream (Montseny, Catalonia) during baseflow conditions. MP concentrations from an upstream control site were compared to the WWTP bypass that added untreated wastewater at times when stream discharge exceeded capacity. The 450 m section investigated downstream of the WWTP consisted of three geomorphically altered sub-reaches interspersed between three unaltered buffer sub-reaches, each ∼75 m that provided a range in hydrologic conditions. Measurements of MP characteristics, hydrogeomorphic variables, and fine particles were simultaneously taken. MPs were quantified following the Nile red fluorescence method for large (>64 µ m) and small (10–64 µ m) particles. MPs in sediment samples downstream of the WWTP were mainly fragments with a higher abundance of small MPs (85 particles/g of sediment) vs large MPs (9 particles/g of sediment). While the abundance of large MPs in streambed sediments decreased with distance from the WWTP point source, the abundance of small MPs increased. Furthermore, the area of small MPs decreased with distance from the WWTP. MPs were most abundant at the WWTP bypass, suggesting these infrequent inputs during storm events represent an important source of MPs to the stream. Higher MP abundance coincided with increased organic matter content and smaller sediment grain sizes. Overall, our results present significant findings that could help explain differences in transport and accumulation patterns of MPs that influence their retention times in streambeds, suggesting a combination of preferential filtration in the streambed sediments, and fragmentation of larger particles