Second Ponds Creek EarthCache EarthCache
Hidden : 2/12/2010
Difficulty:
2.5 out of 5
Terrain:
1.5 out of 5

Size: Size: other (other)

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Geocache Description:



Note: Colorado and Oregon users: The information on this page is fairly lengthy and may not be completely displayed on your GPS. You should print this page before attempting the EarthCache.

This EarthCache is located on Second Ponds Creek in Rouse Hill. The aim of this EarthCache is to teach geocachers about weirs, water, pollution, sediment and erosion controls. When you arrive at ground zero you will need to examine the weir and waterway to complete the EarthCache.


Pollution, Sediment and Erosion Controls


Waterways and wetlands are one of the best ways to naturally filter out pollutants from our environment and to control erosion. Four separate methods listed below have been used extensively within the area to filter pollutants, toxins and sediments from the waterways. You will need to read each method below to answer the final questions.   

1 - Gross Pollutant Traps

Pollutant Removal Estimates for Gross Pollutant Traps

 Expected removal (mean annual load)
 Comments
Litter and organic matter
 10%-30%
 Depends on effective maintenance, specific design (hydraulic characteristics, etc). 10% where trap width is equal to channel width, 30% where width is 3 or more times channel width.
Total Suspended Solids
 0-10%
 Depends on hydraulic characteristics; will be higher during low flow.
Total Nitrogen
 0% (negligible)
 Transformation processes make prediction difficult
Total Phosphorus
 0% (negligible)
 TOTAL PHOSPHORUStrapped during stormflows may be re-released during inter-event periods, due to anoxic conditions.
Coarse sediment
 10-25%
 Depends on hydraulic characteristics; will be higher during low flow.
Oil and grease
 0-10%
 Majority of trapped material will be that attached to organic matter and coarse sediment.
Faecal coliforms
 unknown
Heavy metals
 0% (negligible)


2 - Vegetated Swales and Filter Strips

Swales are open vegetated (generally grass) drains, which provide some stormwater filtration prior to discharge to downstream drainage systems or receiving waters. Whilst a traditional feature in rural environments (due to lower infrastructure cost, and available space), swales are increasingly being used to reduce impacts of urban stormwater. A buffer or filter strip is aligned perpendicular to the direction of flow, and is used to filter particulate matter and associated pollutants prior to entry to the receiving water. With a relatively short flow path length through the buffer, treatment performance relies on having well-dispersed flows .Effectiveness will therefore be reduced in situations where flow channelisation occurs.


Pollutant Removal Estimates for Gross Pollutant Traps

 Expected removal (mean annual load)
 Comments
Litter and organic matter
 Very high (>90%)
 Should be almost 100% removal, provided there is adequate vegetation cover, and flow velocities are controlled (below 0.5m/s).
Total Suspended Solids
 60-80%
 Assumes low level of infiltration. Will vary with varying particle size distribution.
Total Nitrogen
 25-40%
 Dependent on speciation and detention time.
Total Phosphorus
 30-50%  
 Dependent on speciation and particle size distribution.
Coarse sediment
 Very high (>90%)  
 Assumes re-suspension and scouring is prevented, by controlling inflow velocities to <0.8m/s, and maintaining dense vegetation.
Oil and grease
 n/a
Faecal coliforms
 n/a
Heavy metals
 20-60%
 Highly variable: dependent on particle size distribution, ionic charge, detention time, etc



4.3 Infiltration and Bioretention Systems

This category of treatment measure is unified by the use of a filtration medium (e.g. loam, sand, gravel) to treat urban stormwater. Filtration systems may include sand filters, rain gardens, bioretention basins, etc. Similarly, infiltration systems may take many forms, including trenches, or basins (dry or wet). The distinction between the two systems is the destination of the treated water:
-    Infiltration systems remove water from surface flow, allowing it to infiltrate below ground, and ultimately to groundwater
-    Filtration and biofiltration (also called bioretention) systems detain water, and discharge it back to receiving surface waters.



Pollutant Removal Estimates for Gross Pollutant Traps

 Expected removal (mean annual load)
 Comments
Litter and organic matter
 100
 Expected to trap all gross pollutants, except during high-flow bypass.
Total Suspended Solids
 65-99
 Pre-treatment required to reduce clogging risk.
Total Nitrogen
 50-70**
 Dependent on speciation and state (soluble or particulate).
Total Phosphorus
 40-80
 Dependent on speciation and state (soluble or particulate).
Coarse sediment
 95-100
 May pose a clogging risk. These systems should have pre-treatment to remove coarse sediment prior to entry into the filter media.
Oil and grease
 n/a
Faecal coliforms
 n/a
Heavy metals
 50-95
 Dependent on form (soluble or particulate).


4.4 Ponds, Wetlands and Sediment Basins

Ponds, wetlands and sediment basins operate using similar mechanisms (flow attenuation, sedimentation, and in some cases, filtration), to remove contaminants from urban stormwater. The variation observed in wetland performance can be explained in part by relationships between key factors (e.g. hydraulic loading and input concentration), which vary greatly in the highly dynamic processes influencing stormwater flow and quality.




Pollutant Removal Estimates for Gross Pollutant Traps

 Expected removal (mean annual load)
 Comments
Litter and organic matter
 Very high (>95%) (s,p,w)
 Subject to appropriate hydrologic control
Litter and coarse organic matter should ideally be removed in an aerobic environment PRIOR to a pond or wetland, to reduce potential impacts on BOD.
Total Suspended Solids
 60-85 (p)
65-95 (w)
50-80 (s)
 Depends on particle size distribution.
Total Nitrogen
 30-70 (p)
40-80 (w)
20-60 (s)		 Depends on particle size distribution.
Total Phosphorus
 50-80 (p)
60-85 (w)
50-75 (s)		 Depends on particle size distribution.
Coarse sediment
 Very high (>95%)
 Subject to appropriate hydrologic control.
Oil and grease
 n/a
 Inadequate data to provide reliable estimate, but expected to be >75%
Faecal coliforms
 n/a
 Inconsistent data.
Heavy metals
 50-85 (p)
55-95 (w)
40-70 (s)		 Quite variable: dependent on particle size distribution, ionic charge, attachment to sediment (vs. % soluble), detention time, etc

* Summary of Expected Pollutant Removal by Ponds (p), Wetlands (w) and Sedimentation Basins (s).




Weir Dams

A weir dam is a small overflow-type dam commonly used to raise the level of a creek or river. Weir dams are used to create mill ponds, fishing ponds, river crossings, decorative areas, to control erosion and pollution. Water flows over the top of a weir. Since the weir is the portion where water is overflowing, a long weir allows a lot more water with a small increase in overflow depth. This is done in order to minimize fluctuation in the depth of the river upstream with changes in the flow rate of the river. Weirs also give hydrologists and engineers a simple method of measuring the rate of flow over the weir. There are different types of weirs. It may be a simple metal plate with a V notch cut into it or it may be a concrete and steel structure across the bed of a creek or river.


Sharp Crested Weir

A sharp-crested weir allows the water to fall cleanly away from the weir. Sharp crested weirs are typically thin metal plates





Broad Crested Weir
Broad crested weirs are large structures that are generally constructed from reinforced concrete and which usually span the full width of the river. 





Crump Weir
 
A Crump weir is a fixed weir dam with water flowing over it and usually it has a trapezoidal shape while being made out of concrete.If the down-stream level below the weir crest is about the same as the up-stream it can be known as an underwater weir
 




Proportional Weir or "V" notch weir

A specially shaped weir in which the flow through the weir is directly proportional to the head.





Combination Weir

For accurate flow measurement over a wider range of flow rates, a combination weir combines 2 or more types of weirs. Below a V-Notch weir with a crump weir






Terms associated with weir dams.




Nappe: The flow or discharge after the crest.
Head: The level above the crest
Crest:  The width of the top of the weir
Approach:  The level of the river below crest also know as the datum.
 



To log this EarthCache you will need to email me answers to the following questions and upload a photo with your log.

1)    What type of pollutant and sediment control (Choose 1 of the 4 listed above) is being used at the EarthCache location ?
2)    Close to a GZ a sign describes a sepcial type of pollution control methods used here. This special name is..." ____"
3)    In the immediate area (100 meters upstream & downstream from GZ) do you see the use of any other pollutant, sediment and/or erosion control? If so, which type? (There could be a variety of answers for this question so do the best you can)
4)    Is the pollution and sediment control working effectively? Explain your findings
5)    Besides pollution and sediment control, is the weir/s performing other functions? E.g. Wild life refuge, erosion control, decorative, fish pond, etc. Explain your answer.
6)    Of the weir types listed above, which is the closest type that matches the weir at the EarthCache location?
7)    Take a photo showing yourself and/or party holding your GPS in front of the waterway.

You MUST attend the EarthCache location and message me answers to all of the questions and uploaded the required photos to claim a find. Any logs without ALL of these will be deleted, no exceptions!!

There is no need to wait for a confirmation message to log this earthcache. I read all emails to verify the correct information was sent and will contact you if there are any problems with your answers. Likewise, there is no need to email me photos. Just upload any photos with your log. If both tasks are not completed within a timely manner of logging your cache online your log will be deleted.


References:
 Australian Water Conservation and Reuse Research Program (CSRIO and Australian Water Assosiation) -
 A Review of Stormwater Sensitive Urban Design in Australia  January 2004

Additional Hints (No hints available.)



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