Part II: Let’s Look at This 20+ Yrs Assumption! How Does Stokes’ Law Help Define Dimensions of a Sediment Basin? (Fifield 2004)

Part II: Let’s Look At This 20+ yrs Assumption!
How does Stokes’ Law help Define Dimensions of a Sediment Basin? (Fifield 2004)
This paper highlights challenges within the Equatorial Rainforest Region of high rainfall, erosive soils and developments of large areas of deforestations. The combination of natural hazards, economic “lack-of-will” and appreciation of appropriate site practices has led to high impact on water quality, sedimentation of rivers, estuaries and flooding of communities.

Primary Objective is to replicate (Fifield 2004) hypothesis on an Alternative Design Approach to Sediment Basin with Application of Stokes’ Law Terminal Velocity under laminar flow conditions.
Secondary objective shall provide erosion and sediment control specialists with “baseline” technical data for sediment basin design, for specific conditions. Project proponent shall be able to evaluate various options and compare applications of effective BMPs for optimum cost and space savings, time constraints and environmental considerations.

Learning Objectives: At the conclusion of presentation, attendees shall have:
• Visited the trials & tribulation of this fundamental research journey, lab techniques and equipment were “reinvented” eg “Uniform Flow Box with built-in Sluice Gate Controls”, experiments at limited resources,
• Introduction to a “Modified 20+years Alternative Design Approach” for an Efficient Sediment Basin for targeted soil particles based on experiment findings,
• Visit “easy-to-use” charts & graphs for Sediment Basin designs approach.

Full Abstract: Part II: Let’s Look At This 20+ yrs Assumption!
How does Stokes’ Law help Define Dimensions of a Sediment Basin? (Fifield 2004)

This paper highlights challenges in the Tropics with high rainfall, erosive soils and developments of large areas of deforestations. The “lack-of application of appropriate site practices has impacted on water quality and sedimentation of rivers.
Sediment Containment Systems (SCS) are critical for construction site’s “first and last defense” best practices for safe-guarding downstream water quality from degradation. Development sites (SCS) when engineered appropriately, shall provide sufficient time for targeted soil particles in suspension to “settle-out” and be captured.
Therefore, it is imperative to determine target particle travel distances to relate to (SCS) dimensions.
It has been taught a sequential design approach using Stokes’ Law Equation to determine sediment basin dimensions (Fifield 2004).

Initial physical experiments were conducted to address the primary objective which is to replicate (Fifield 2004) alternative approach to SCS design. Findings of both physical experiments and theoretical investigations cannot substantiate Dr Fifield’s hypothetical design approach of SCS. However, with modifications to the Fifield’s approach, experiment results demonstrated the relationship between sediment sieve sizes (75 – 355) μm and particle distance traveled per flow discharge velocity, under constant water temperature.

Primary objective of this research is to replicate the (Fifield 2004) hypothesis accuracy and modify design approach with research experiment findings.
Secondary objective was to provide professionals with “baseline” technical data for sediment basin design. This is achieved with graphical presentation that provides project proponent the ability to assess and compare various BMPs for optimum cost and space savings, time constraints and environmental considerations.

There is limited research material on this subject except for sophisticated computational fluid dynamics modeling addressing application of Direct Numerical Simulation “Turbulence analysis of a rectangular sedimentation basin using numerical simulation” performed with Incompact 3d code” Lucchese E et.al to practical application researches that references Stokes’ Law, conducted at Auburn University, “Optimization of Sediment Basin Configurations” by Armstrong, Megan L, Perez, Michael A, and Donald, Wesley N., which have provided good scholarly guidance. However, there is lack of resources on fundamental research on particle travels in sediment basin with application of Stokes’ Law, to determine SCS dimensions other than the Fifield (2004) hypothesis, with calculations and assumptions.

As it rains frequently in Malaysia, research experiments were conducted at the REDAC-USM Hydraulics laboratory at the flumes channel at 5m(L) x 30cm(W) x 25cm(D) and subsequently at the larger flume #2 at 20m(L) x 1.5m(W) x 1m(D). Flume channel although different from an outdoor SCS however, provided good environment to study partial flow path.

Methodological work procedures started with “sediment harvesting” (Sieving British Standard Methods BS1377: P2:1990 Soil Test) from acquired bulk quartz sediment particles of (63-600) μm of high cleanliness and free of organics. 1500g samples were sieved repetitiously to harvest sediment of narrow sieve size ranges at (14) sieve size trays (45–500) μm. The bulk of sediment sizes harvested falls within the larger sizes (300-425) and (180-212), thereby prolonging sieving work.
Preliminary experiments were conducted to determine particle mixing affinities and flow behavioral characteristics. It was found that the finer Stokes’ particles ( <100μm) tend to “clump together” cohesively when wet, exhibiting poor disbursement qualities. This was overcome with several experimental hydraulic premixing of water-soil mixture. Experiment observation with “Green” food dye showed “vertical dropped-down” whilst a portion travels at suspension.

Initially, physical experiments were conducted at calculated Stokes’ Law terminal velocities for specific particle sizes. Experiment findings from both physical and theoretical investigations could not substantiate (Fifield 2004) SCS design approach. However, with modifications to the Fifield’s approach, results from subsequent experiments at the main flume 20m(L) x 1.5m(W) x 1.1m(D) demonstrated the relationship between sediment sieve sizes (63 – 355)μm and particle distance traveled per flow discharge velocity, under constant water temperature.
100+ physical experiments were conducted in flume #2 where 2-compartments were developed with the installation of a metal weir in mid-flume. Water is pumped from the 1st compartment(upstream) to the 2nd compartment(downstream) through a modified “uniform flow box” (UFB), secured on top of the metal weir. The (UFB) provides temporary water storage and uniform discharge through a “built-in” calibrated sluicegate.

Conclusions and discussions: Analysis of experiment results conducted demonstrates high successive consistency between (6 sets) of sediment particle sizes (75-90), (90-125), (150-180), (180-212), (212-300) & (300-355) μm and its travel distances per flow velocities (3 sets) at V1 (0.408 m/sec), V2 (0.566 m/sec) & V3 (1.26 m/sec). Tentatively, “easy-to-use” design charts and graphs shall be: i) Particle distance traveled vs Size, ii) Particle distance traveled vs Velocities per Particle size and iii) Particle distance traveled vs Reynold’s Number, with (R² = high %) regression analysis.