Evaluation of the function of Vertical drains.

Similar documents
Evaluation Report Teluk Chempedak Oct 2005

BEACH NOURISHMENT COMBINED WITH SIC VERTICAL DRAIN IN MALAYSIA. Claus Brøgger 1 and Poul Jakobsen 2

PRESSURE EQUALISATION MODULES FOR ENVIRONMENTALLY FRIENDLY COASTAL PROTECTION

SAND BOTTOM EROSION AND CHANGES OF AN ACTIVE LAYER THICKNESS IN THE SURF ZONE OF THE NORDERNEY ISLAND

MODELING OF FLOW THROUGH A VERTICAL PERFORATED PIPE IN THE BEACH, AND THE MORPHODYNAMIC INTERPRETATION: THE PRESSURE EQUALIZATION MODULE SYSTEM

Simulation of tidal effects on groundwater flow and salt transport in a coastal aquifer with artificial drains (Pressure Equilibrium Modules)

LAB: WHERE S THE BEACH

Label the diagram below with long fetch and short fetch:

Ocean Motion Notes. Chapter 13 & 14

INTRODUCTION TO COASTAL ENGINEERING AND MANAGEMENT

Chapter. The Dynamic Ocean

The Composition of Seawater

OECS Regional Engineering Workshop September 29 October 3, 2014

Imagine that you can see a side view of a wave as it approaches a beach. Describe how the wave changes as the wave approaches the beach.

Chapter 22, Section 1 - Ocean Currents. Section Objectives

Chesil Beach, Dorset UK High energy, shingle coastline. Brighton Beach, Sussex UK Pebble beach

Figure 4, Photo mosaic taken on February 14 about an hour before sunset near low tide.

Coastal Change and Conflict

Deep-water orbital waves

FOR PERSONAL USE. Shoreline Erosion BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN ACTIVITY ASSESSMENT OPPORTUNITIES. Grade 4 Quarter 1 Activity 9

Exemplar for Internal Assessment Resource Geography Level 3. Resource title: The Coastal Environment Kaikoura

Using sea bed roughness as a wave energy dissipater

Figure 1. Schematic illustration of the major environments on Mustang Island.

Volume and Shoreline Changes along Pinellas County Beaches during Tropical Storm Debby

CHAPTER 134 INTRODUCTION

INTRODUCTION TO COASTAL ENGINEERING

CHAPTER 8 ASSESSMENT OF COASTAL VULNERABILITY INDEX

Earth Science Chapter 16 Section 3 Review

Low-crested offshore breakwaters: a functional tool for beach management

4/20/17. #31 - Coastal Erosion. Coastal Erosion - Overview

Shoreline Evolution Due to Oblique Waves in Presence of Submerged Breakwaters. Nima Zakeri (Corresponding Author), Mojtaba Tajziehchi

TITLE: COASTAL EROSION AND LANDFORMS.

The ocean water is dynamic. Its physical

Shoreline Response to an Offshore Wave Screen, Blairgowrie Safe Boat Harbour, Victoria, Australia

Field trip Information folder

Cross-shore sediment transports on a cut profile for large scale land reclamations

Modeling Beach Erosion

Among the numerous reasons to develop an understanding of LST are:

Khosla's theory. After studying a lot of dam failure constructed based on Bligh s theory, Khosla came out with the following;

DUNE STABILIZATION AND BEACH EROSION

Natural Bridges Field Trip Activity

CHAPTER 132. Roundhead Stability of Berm Breakwaters

/50. Physical Geology Shorelines

Follets Island Nearshore Beach Nourishment Project

HYDROSPHERE, OCEANS AND TIDES

Physical Modeling of Nearshore Placed Dredged Material Rusty Permenter, Ernie Smith, Michael C. Mohr, Shanon Chader

Cove Point Beach Restoration: Utilization of a Spawning Habitat by Horseshoe Crabs (Limulus polyphemus)

Currents measurements in the coast of Montevideo, Uruguay

The evolution of beachrock morphology and its influence on beach morphodynamics

Before we start. Copyright William C Cromer 2015

Activity #1: The Dynamic Beach

Columbia River Plume 2006 OSU Ocean Mixing Nash, Kilcher, Moum et al. CR05 Cruise Report (RISE Pt. Sur, May )

Julebæk Strand. Effect full beach nourishment

Inventory of coastal sandy areas protection of infrastructure and planned retreat

Overview. Beach Features. Coastal Regions. Other Beach Profile Features. CHAPTER 10 The Coast: Beaches and Shoreline Processes.

OCEANS. Main Ideas. Lesson 2: Ocean Currents Ocean Currents help distribute heat around Earth.

Section 1. Global Wind Patterns and Weather. What Do You See? Think About It. Investigate. Learning Outcomes

General Coastal Notes + Landforms! 1

Constructive waves build beaches. Each wave is low. As the wave breaks it carries material up the beach in its. material will then be deposited as

IMPACTS OF COASTAL PROTECTION STRATEGIES ON THE COASTS OF CRETE: NUMERICAL EXPERIMENTS

Lecture Outlines PowerPoint. Chapter 15 Earth Science, 12e Tarbuck/Lutgens

Available online at ScienceDirect. Procedia Engineering 116 (2015 )

TITLE: North Carolina s Changing Shorelines. KEYWORDS: erosion - shorelines - mapping - sustainability

Anatomy of Coastal Regions

Wave Breaking and Wave Setup of Artificial Reef with Inclined Crown Keisuke Murakami 1 and Daisuke Maki 2

Nearshore Sediment Transport What influences the loss of sediment on Beaches? - Waves - Winds - Tidal Currents - River discharge - Runoff

Beach Profiles: Monitoring Sea Level Rise. Student Activity Sheet. Name Date Class

Lecture 8&9: Construction Dewatering

COASTAL ENVIRONMENTS. 454 lecture 12

3.9 FROM ISLANDS TO ATOLLS

consulting engineers and scientists

SHOREHAM BEACH LOCAL NATURE RESERVE

PARAMETRIZATION OF WAVE TRANSFORMATION ABOVE SUBMERGED BAR BASED ON PHYSICAL AND NUMERICAL TESTS

The Impact on Great South Bay of the Breach at Old Inlet Charles N. Flagg School of Marine and Atmospheric Sciences, Stony Brook University

Lesson: Ocean Circulation

Directed Reading. Section: Ocean Currents. a(n). FACTORS THAT AFFECT SURFACE CURRENTS

Beach profile surveys and morphological change, Otago Harbour entrance to Karitane May 2014 to June 2015

Name Class Date. Use the terms from the following list to complete the sentences below. Each term may be used only once. Some terms may not be used.

Construction Dewatering

Operating Principle, Performance and Applications of the Wave Mill

Beach Profiles. Topics. Module 9b Beach Profiles and Crossshore Sediment Transport 3/23/2016. CE A676 Coastal Engineering

Shoreline changes and reef strengthening at Kavaratti island in Lakshadweep Archipelago - A case study

TRANSPORT OF NEARSHORE DREDGE MATERIAL BERMS

R E M I N D E R S. v Two required essays are due by April 9, v Extra Credit: Think Geographically Essays from any five of the textbook s

CORTEZ GROINS RECONSTRUCTION PROJECT FEASIBILITY STUDY AND 2012 HURRICANE SEASON IMPACTS

Experiment of a new style oscillating water column device of wave energy converter

Geology 10 Activity 8 A Tsunami

Examples of estuaries include bays, sounds, salt marshes, mangrove forests, mud flats, swamps, inlets, and sloughs.

CHAPTER 21 VARIABLE DISPERSION AND ITS EFFECTS ON THE MOVEMENTS OF TRACERS ON BEACHES

Welcome to Paddle for the Edge!

LAKKOPETRA (GREECE) EUROSION Case Study. Contact: Kyriakos SPYROPOULOS. TRITON Consulting Engineers. 90 Pratinou Str Athens (GREECE)

Estuarine Shoreline Stabilization

Real Time Surveying GPS and HYDRO Software for Tide and Swell Compensation

Tidally influenced environments. By Alex Tkaczyk, Henrique Menezes, and Isaac Foli

Identify one factor which influences wave strength (1 Mark) Factors which affect wave strength

An experimental study of internal wave generation through evanescent regions

Building with Nature: Systems Description of Krogen

EVALUATION OF BEACH EROSION UP-DRIFT OF TIDAL INLETS IN SOUTHWEST AND CENTRAL FLORIDA, USA. Mohamed A. Dabees 1 and Brett D.

Request Number IR1-12: Flow Passage. Information Request

170 points. 38 points In your textbook, read about modern oceanography. For each item write the word that meets the description.

Transcription:

International Coastal Symposium ICS2007 Gold Coast Australia. C. Brøgger and P. Jakobsen SIC Skagen Innovation Center Skagen 9990 Denmark sic@shore.dk SIC Skagen Innovation Center Skagen 9990 Denmark sic@shore.dk ABSTRACT BRØGGER,C and JAKOBSEN,P., 2007.. ICS2007 (Proceedings of the 9th International Coastal Symposium), Gold Coast, Australia. ICS 2007 International Coastal Symposium. Gold Coast, Australia The PEM system is used for beach erosion control and involves the principle of vertical draining. Scientists generally agree that a well drained beach is robust and accrete, but beaches with a high water pressure will erode. On this background a field test was performed on the Danish west coast with DIVER water level instruments. The test with the Diver sensors was carried out over 2 weeks, where the PEM modules with sensors were placed between the wells with sensors in week nr. 2. All the Divers in the wells and PEM modules were time locked and registered the water table for every 2 minutes. The effect of the PEM modules corresponds to the theory from (Glover and Todd, 1975) about fresh water outflow in Coastal zones. Additional index words: Beach dewatering, SIC, PEM. INTRODUCTION Scientists generally agree that a well drained beach is robust and will generally favour infiltration and onshore sediment transport. The position of the water table in beaches is mostly controlled by tidal waves. The effects of vertical drains on the water table in beaches are investigated in this report. The drains are called Pressure Equalizing Modules (PEM). The vertical drains consist of a 1.0 m long screen drain on a 0.75m tube with a diameter of 0.06m. The functioning of the PEMs is that the effective permeability of the beach is increased. A two-week experiment was conducted at a beach near Holmsland on the west coast of Denmark in order to investigate the hydraulic functioning of the PEMs (Fig 1). Two different experiments were meant to be investigated. 1. A beach-scale experiment where tidal dynamics influence on the water table were monitored in rows with normal observation wells and PEMs. 2. A close-in scale experiments, where the pressure distribution around a drain was continuously monitored. The close-in test failed due to installation failure. The experiment was divided into two periods. Period one where all the wells were installed with pressure sensors DIVERs ( fig 5 ) Measurement every 2 minutes and. Period two where PEMs were installed, also with pressure sensors. Three rows were established. One row with just wells and no PEMs, which then acted as a control site. One row with both wells and PEMs. One row with a few wells and mostly PEMS, which was designed primarily for the close-in-scale experiment. The idea was to make a before-and-after comparison, where the tidal response in the wells during period two could be compared with the tidal response in period one. Unfortunately due to a dramatic change in the weather conditions resulting in higher water level in week two compared with week one (Fig 2), we found the before-after evaluation not useful. We then decided to use data only from week two and only from the center ( C ) row as it was found that the beach geology in the north ( N ) row differed to much.

Figure 1. Test site Figure 2. ( C ) Center row / Beach profile Field site The field site is located 5 km south of Hvide Sande on the West coast of Denmark, ( Fig 3 ). Figure1 show the location of the installed wells (small circle) all with DIVERs measuring the water level and the Pressure Equalizing Modules (big double circle) also with DIVERs. The North row was meant as a control row, where no PEMs were installed. The Center row includes wells, and with PEMs centrally located in between two wells (Fig 2). There are 5o meters between the rows and 10 meters between the wells. Between the wells and PEMs there are 5 meters. The South row has only four wells, three nearest to the sea, and one at the other end, and five PEMs. All wells were installed starting on 8:00, March 20, 2006. The PEMs were installed on March 26, 2006 The test ended on April 02 2006. The MSL are shown on Figure 7. The center row (C) (fig 2) only is used in this evaluation. Fig 3 Test site location (Skodbjerge) Fig 4 DIVER sensor

Fig 5 Fig 6 Conditions Fig 5 illustrates the water pressure at the beach and outflow zone. According to (GHYBEN HERZBERG) we know that for every meter the groundwater stays over the sea there is 40 meters down to the saline water. However this is not the case in the outflow zone where according to (CLOVER and TODD D.K ) the conditions are stated in the equation: Weather During the first period the wind was easterly with small wave activity. At the start of the second period the weather shifted to westerly wind with wind speeds between 14 and 19 m/sec, which resulted in a water level rise of 0.40 meter (Figure 7). X=q/2(Ps-Pf)K Where X= outflow zone in meter q = freshwater flow pr. meter Ps = density of saline water Pf = density of fresh water K = hydraulic conductivity The outflow zone (X) moves with the tide and is an important factor in the function of the drains as the positive change of the hydraulic conductivity in the beach will broaden the area of outflow and increase the outflow thereby lower the water pressure in the beach. Vertical drains Vertical drains connect different permeable layers in the beach and increase the outflow. The water may move up or down in the tubes depending on the water pressure in the beach and the swash zone (figure 6). The pressure drop in the beach will increase the saline water circulation and accretion will take place creating a sand groin which catches the long shore sediment transport (fig 8). The vertical drains acts like a starter that keeps the process going. When more or less impermeable layers has been penetrated or/and when several permeable layers has been connected by the drain, the draining process starts washing out fine material and in that way becomes more and more effective. Fig 7 Fig 8

International Coastal Symposium ICS2007 Gold Coast Australia Fig 9 Fig 10 Impermeable layers The presence of more or less impermeable layers in a beach is well known. They may consist of very fine material. The material could be particles of clay or organic material coming from rivers and municipality sewers (Fig 10). These layers we also found at the test site (fig 6, fig 9) where the drain pipes penetrates the impermeable layers and connects the permeable layers. Pressure sensors This field test use DIVERs as pressure sensors in the beach. This model was chosen because it is robust and accurate, it has no external wires. The measurements are easily transferred to a PC via a docking station. The DIVER ( Fig 4 ) measures the groundwater level with an accurate pressure sensor. The weight of the water Colum above is the determining factor. The DIVER sensors were submerged in the wells / drains and their X Y Z coordinates were logged with GPS. All DIVERs were synchronized in time and the logging intervals were set to 2 minutes. (fig 12, fig 13)The data from the DIVERs shows that in PEM 1 and PEM 2 the water level is well above the calculated average value (C1+C2)/2, (C2+C3)/2. Indicating an upward draining flow as expected in the outflow zone. Method The draining effect is illustrated by comparing the water level inside the drains with the water level in the beach as recorded of the sensors inside the wells (C1+C2)/2, (C2+C3)/2, (C3+C4)/2, (C4+C5)/2, (C5+C6)/2. C1 and C2 water pressure The difference in C1 and C2 is reduced to 5-6 cm after draining in period two. Without draining the level difference is between 4 and 19 cm indicating the drains has equalized the pressure (fig 11). Fig 11 Fig 12 Fig 13

Conclusion The hydraulic effect of installing pressure equalizing modules ( PEM ) was investigated. The test showed that on a dry beach the water level inside the PEM was significant lower than in the neighboring wells, indicating effective downward draining of the beach. PEM modules in the swash zones that were submerged due to high tide, showed a higher water level than in the neighboring wells. This indicates that the outflow of water is increased by the drain. Fig 14 (fig 14, fig 15, fig. 16) PEM 3, PEM 4 and PEM 5 data shows, that the water level is below the calculated value (C3+C4)/2, (C4+C5)/2 (C5+C6)/2 indicating an downward draining flow as expected in the dry zone. The effect of the drains acts as trigger starting the process and thereafter the system is self sustained. Effective draining of a beach will increase the beach s capacity to absorb water from the incoming waves. The sediment they contain will be deposited on the shore. Gradually a sand groin will develop picking up the long shore sediment adding sand to the beach. Fig 15 References. Jakobsen, P. Pressure Equalisation Modules For Environmentally Friendly Coastal Protection.Conference Yamba 2000 Jakobsen, P. SIC- systemet løsningen på den globale vandstands-stigning. Geologisk Nyt. AarhusUuniversity 1/07 page 4-8. Jakobsen P. Trykudligningsmoduler skaber brede ligevægtsprofiler. Geologisk Nyt. Aarhus University 1/07 page 10-17. Fig 16 Jakobsen, P. and Brøgger, C. Coastal protection based on Pressure Equalization Modules (PEM). Conference ICS 2007.