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There are plenty of reasons to green your business, from a legitimate concern for the planet to the money that using fewer resources can save. The (e,2e) spectrometer vacuum chamber (figure 1) is manufactured from 304 grade stainless steel, the construction being carried out by Vacuum Generators using a design of Jones, Read and Cvejanovic, full details of which may be found in T. 3mm thick mu-metal magnetic shielding is placed both internally and externally to decrease extraneous external magnetic fields to less than 5mG at the interaction region.
All inputs and outputs to the spectrometer pass through the vacuum chamber via feedthroughs on the top flange. The top flange of the vacuum system is a 25mm stainless steel flange with 11 conflat CF70 flanges arranged around a central 200mm flange designed for locating a hydrogen source. Two flanges are used for the high voltage channeltron and photomultiplier tube inputs and pulse outputs.
Three rotary motion feedthroughs allow the analysers and electron gun angles to be changed externally via stepper motors for both analysers and for the electron gun. The ionisation gauge is placed at right angles to the main flange to prevent light from the thoriated iridium filament entering the vacuum system, which would increase noise on the photomultiplier tube.
The ionisation gauge feedthrough is sooted, and a loose cover is placed over the entrance in the chamber flange to prevent stray light from the ion gauge entering the vacuum system. The target gas enters the system via a CF70 flange which has two 6mm stainless steel tubes welded into the flange.
The other gas feed is connected to a hypodermic needle set at 90A° to the incident beam for measurements in other geometries. The gas jet which is not currently used in the interaction region can be used to non-locally fill the chamber with gas for background counting measurements. The final CF70 flange is used when the photomultiplier tube is cooled, usually during baking of the system following exposure to atmosphere. The tube is cooled by passing vapour from a liquid nitrogen source through expansion coils wrapped around the photomultiplier tube housing. The electron gun is a two stage non-selected gun designed by Woolf (Ph.D thesis, University of Manchester) (see figure 3). The gun consists of a filament, grid and anode source which is focussed using a triple aperture lens through two 1mm defining apertures in the centre of the gun. The apertures define the electron beam pencil and beam angles, and are focussed onto the interaction region using a second triple aperture lens located between the apertures and interaction region.
The electron gun is shielded using advance (constantin) sheet which is grounded to the body of the gun mounting. The gun is mounted onto an x-y translation table to allow placement of the electron beam as accurately as possible to the centre of rotation of the analysers and electron gun rotation axis.
The gas jet is mounted from the electron gun using a narrow support of 310 stainless steel, and the Faraday cup can be attached to this support. The original unselected electron gun built by Woolf was completely rewired and a custom built PTFE 25 way inline wire-wrap plug and socket was placed between the 52 way vacuum electrical feedthrough and the electron gun. The wiring from the 52 way feedthrough to the inline plug is shielded colour coded 30 awg PTFE coated advance wire, and the inline plug and socket connectors are non-magnetic gold plated wire wrap pins.
The electron analysers are constructed from molybdenum and are mounted from two rotating gear plates controlled externally via the rotation feedthroughs on the top flange (see figure 2). The input electrostatic lenses for each analyser are three element cylindrical lenses as shown in figure 4.
The interaction region is focussed onto the entrance aperture of the hemispherical energy analysers with a beam angle of around zero degrees, the image of the analyser entrance aperture being larger than the size of the interaction region. Field gradients around the input and exit apertures are corrected using standard Jost correctors.
The energy selected electrons passing through the exit apertures are finally collected by Mullard X919BL channel electron multipliers which amplify the single electron to produce a current pulse at their output. A principle source of noise on the signal pulses arises from the turbo-molecular pump motor. The noise from the turbo pump is reduced to ~ 5mV using these techniques, and as the average pulse height from the saturated multiplier is around 20-40 mV, this allows adequate discrimination following amplification. The pre-amplifiers located external to the vacuum system are commercial 100X preamplifiers with 400pS rise-times, manufactured by Phillips Scientific. The NIM signals produced by the discriminators drive two ORTEC 437 Time to Amplitude Converter's via appropriate delay cables and an ORTEC pulse delay unit. The main TAC output feeds an ORTEC Multichannel Analyser card located in the PC controlling the experiment, whereas the second monitor TAC drives an external MCA, allowing convenient monitoring of the coincidence signal as the experiment progresses.
The high voltage supplies to the electron multipliers are two Brandenberg 5kV supplies controlled by the main PC via serial DAC's. Principally the filter is used to reduce pickup noise from entering via the HT cable onto the multiplier output. Secondly, the filter has a slow response time for high voltage spikes, and reduces the probability of damage to the pulse electronics should the EHT supply suddenly turn on or off. Capacitor C2 decouples the 1kW load resistor to earth for high frequency pulses from the CEM's, and the voltage appearing across this load is connected via the capacitor C3 to the input of the 6954 preamplifier.
Since the input impedance of the preamplifier is 50W and the CEM is effectively an ideal constant current supply, most of the current passes through to the preamplifier.
Finally, the 10M resistor prevents the output to the preamp from rising above ground when the preamp is disconnected from the circuit and is therefore a safety device for the preamplifier when initially connected. The original design placed the atomic beam nozzle and Faraday cup on the same support structure fixed to the body of the electron gun, with the atomic beam direction being in the detection plane when the perpendicular plane geometry is chosen (see figure 2).
A second configuration is adopted for exclusively perpendicular plane coincidence experiments, the atomic beam nozzle being oriented at an angle of 45A° to the detection plane so that the gas effusing from the nozzle does not fill the analysers when they oppose the nozzle (see figure 6). In this configuration the support strut for the atomic beam nozzle is terminated lower than the detection plane, as is the nozzle itself. For non-perpendicular plane measurements the Faraday cup is once mounted from the support strut and the gas effuses perpendicular to the electron beam direction. One difficulty when aligning an (e,2e) coincidence experiment lies in the focussing the incident electron beam and analysers onto the interaction region. The throughput of electron current as detected by the Faraday cup is insensitive to both position and focusing of the electron beam, since the cup opening is usually made quite large (in this case 6 - 10mm) and the bias voltage applied to the cup to prevent electrons returning to the interaction region allows all electron trajectories within this opening to be detected.
Conventionally, following maximisation of the Faraday cup current, the beam is steered and focussed onto the gas jet as detected by counts in the analysers. This has the disadvantage that the overlap volume is maximised for both atomic and electron beam density, which tends to place the interaction volume as close as possible to the output of the atomic beam nozzle, which is almost certainly not in the centre of the detection plane. To eliminate the need for time consuming iterative techniques and the associated errors due to detection geometry, a separate method for tuning the electron gun is adopted that does not depend upon the analysers.
The interaction between the target and the electron beam not only produces ionisation, but the valence states of the target also are excited with various probabilities depending upon the incident energy of the electron beam.
These photons are detected by the photomultiplier tube, by placing a 450nm A± 50nm optical filter in front of the photocathode.
The interaction region is therefore defined where an aperture in front of the photocathode is focused by the lens.
The plano-convex focussing glass lens is covered by a grounded fine tungsten mesh to eliminate surface charging.
The photomultiplier tube may be cooled by circulating nitrogen gas boiled off LN2 through copper coils encircling the photomultiplier tube housing. The photomultiplier tube used in the experiment is a 9789QB EMI photomultiplier tube with a bi-alkali photocathode peaking in the blue region of the optical spectrum. As with the electron multiplier circuitry, it is important to optimise the load of the photomultiplier tube so that reflections along the feeder line to the counting electronics are minimised. The 1nF 6kV capacitors across the dynodes close to the output stage are used as charge storage pumps that quickly refurbish the surface charge on the dynodes, allowing increased counting rates.
The dynode resistors are 1% tolerance metal film resistors as these are more stable with temperature.
The EHT supply to the photomultiplier tube is a Brandenberg 2kV supply operating at 1500V for this tube. The negative going output pulses from the tube measure typically 200-500mV in height, and therefore are able to directly drive an ORTEC 473A constant fraction discriminator located in one of the NIM crates.
All resistors and capacitors for the dynode chain are soldered to the photomultiplier tube base internal to the vacuum system, using standard 5-core solder. Typical pulse heights from the electron multipliers in saturation mode are 25-40mV, whereas the typical height of the photomultiplier tube pulses is of the order of 250mV. The electron multiplier pulses are obtained from the multiplier supply circuitry as explained above.
The amplified pulses from the 6954 amplifiers pass along doubly shielded RG-58 cable to the input of the ORTEC 473A discriminators.
The two analyser discriminators are located in separate NIM crates to increase isolation and reduce common mode pickup. The slow rise-time positive outputs from the 473A discriminators pass to three ORTEC 441 rate-meters which allow counting and monitoring of the pulses.
The fast NIM pulses from the analyser 473A CFD's pass through appropriate delay lines to two 437 TAC's.
This second multichannel analyser allows the operator to monitor the total accumulated coincidence signal during operation.
The lens supplies that control the voltages impressed onto the lens elements and deflectors in the experiment were developed over a number of years, and therefore take different forms.
Three of these supplies feed the deflectors in the electron gun, the other two supply the input deflectors in the analysers. In a second 19" crate is located the gun lens high voltage supplies together with the high voltage supplies for the Faraday cup. In a third 19" crate is located the analyser voltage supplies together with a set of serial loading supplies that control the electron multiplier EHT supplies. A further supply controls the current boost circuitry located in the filament constant current supply unit (see below). The outputs of each computer controlled supply that drives an individual lens element or deflector are connected to a 70 relay switching board. The Digital voltmeter is in turn accessed via an IEEE-488 interface which is addressed by an 8086 slave PC which converses with the central PC which controls the experiment. The outputs from the relay board connect to the spectrometer via shielded multicore cables which take the gun voltages to the 52 way feedthrough and the analyser voltages to the two 19 way feedthroughs located on the vacuum flange. The gun supply multicore also carries the filament supply current to the 52 way feedthrough. The Faraday cup current is measured by the Keithley Digital voltmeter when under computer control but this can also be measured by an external pico-ammeter. In addition to the analyser electrostatic lens and deflector voltage connections, the 19 way CF70 feedthroughs are used to control signals from internal sensing opto-isolators which control the stepper motor interlocks.
The stepper motors that drive the analysers and electron gun around the detection plane are five phase motors with integral 10X reduction gearboxes driving the rotary motion feedthroughs. The intelligent stepper motor drivers are addressed via a serial port located on the controlling PC bus. An additional interference problem was traced to the RS232 serial line from the controlling PC.
The PC bus was found to be poorly earthed due to very little copper being used for the bus earth. This was cured by decoupling the 0V RS232 line from the main 0V line for the stepper motors, as is shown in figure 10. The analyser stepper motor supplies have a facility for halting the motors using limit switches which are optically coupled to the internal 68000 logic circuits driving the supplies. The SD5443-3 phototransistor normally illuminated by the TEMT88PD photodiode during operation ensured a fail-safe mechanism should any of these components fail (this automatically prevent the motors from running). Should the analysers move into a position as defined by the four criteria (a) - (d) above, a shutter located on the analyser turntables moves between the appropriate photodiode and phototransistor, shutting off the light and thereby shutting down the stepper motor current. Only motion in the opposite direction is allowed by controlling logic, allowing the analyser to move away from the point of imminent collision but no closer. The six pairs of optocouplers that prevent the analysers moving into the Faraday cup, electron gun and gas jet support are located on the mounting struts supporting the main body of the spectrometer. Two optocouplers are located on the side of analyser 2, and two shutters are located on the sides of analyser 1 to prevent the analysers colliding with each other.
Finally a ninth optocoupler is located over the electron gun counterweight which monitors when the gun is at an angle less than 65A°, where the sweep angle around the detection plane is reduced. The current boost circuit operates from a serial driven supply card as detailed previously. The main filament drive is through six power diodes that feed the current from the constant current supply to the filament. The Darlington transistor T1 feeds additional current to the filament via three parallel 10 turn 100W trim resistors through a 1N4007 diode. As the constant current supply acts as an infinite resistance source, the boost circuit supplies additional current only when the voltage at the anode of the feed 1N4007 exceeds the output voltage of the constant current supply. Finally, the filament bias voltage (and hence energy of the electrons) is set to the midpoint of the filament by two 100W balancing resistors located across the terminals. In addition to the ADC buffer card, three independent isolated regulated supplies drive REF01 voltage reference sources for measurement of the positions of 10 turn potentiometers located on the analyser and electron gun rotary drive shafts.
The angular position of the electron gun and analysers is calibrated when the system is opened using visible laser diodes that define these angles to an accuracy of A±0.2A°.
Figure 13 shows an overall block diagram detailing the computer control and high speed pulse interfacing to the spectrometer. Q- Would removal of the dam help alleviate upstream flooding problems suffered by residents of the Family Farm neighborhood in Woodside? A- Searsville Dam was not designed to provide any flood protection benefit downstream and has caused flooding upstream. A- While the dam was well built, the average age for a dam is reported, by Stanford, to be 40 years and Searsville Dam is 120 years old. Q- Stanford currently uses the reservoir for non-potable water use, such as irrigation, landscaping and fire-fighting.
A- As with other completed dam removals, this project design would maintain or replace existing owner needs with improved facilities and ease of operation. A- Recent studies and completed dam removal efforts have shown that dam removal is almost always less expensive than eventual dam safety retrofitting, installation of required fish passage facilities, and ongoing maintenance costs. A- Fortunately, there are many sources of funding for dam removal and ecosystem restoration projects of this kind.
A- The existing ecosystem has emerged around an artificial and unsustainable reservoir that is filling in with sediment.
Q- What effects would removal -- including possible flushing of sediment -- have on the recovering population of steelhead elsewhere in the watershed? A- The dam has held back sediment for over a century and altered the natural flow of gravels and beneficial sediments downstream creating a a€?hungry watera€? situation that has impacted bank erosion and the native habitat for steelhead. Corte Madera Creek and the many tributary streams (above) contain excellent habitat and continues to support wild, rainbow trout (below), which are the descendants of sea-run steelhead.
Q- The current wetlands support a rich bird habitat and foraging ground for bats a€“ would this be protected with the removal?
A- Some of the recently established wetlands and habitat utilized by birds and bats can remain with dam removal and design plans would maximize the protection of sensitive areas in a manner similar to other successful dam removal efforts. Stanford officials have often wondered about the impacts of dam removal on vegetation established on the reservoir and possible negative impacts to neotropical migrant birds that have been observed here in high abundance. Searsville Dam removal would restore miles of currently buried streams, riparian forests and thick border habitats, and increase the amount of highly productive fringe wetland habitat that these riparian zones provide.
Overall, the project could trade in the unsustainable, artificial, reservoir habitat for a net gain in stream habitat, riparian forest habitat, fringe wetland habitat, historic wetland ponds, and upland habitat. A- Dam removal will eliminate the artificial reservoir habitat that currently allows for the breeding and dispersal of several exotic and invasive species that prey upon and compete with the native species. A- Dozens of large dams have been successfully removed and hundreds of medium and smaller dams have been taken out over the past couple decades.


A- Over 500 dams have been removed in the United States in recent years and several dams that were about the size of Searsville, and larger, have recently been removed from rivers around the country. The mouth of San Francisquito Creek (above) is near several wetland restoration projects in need of sediment. Q- How would the removal of 60 feet of concrete blocks affect the biological preserve and surrounding communities? A- Removal of the concrete blocks would be a short-term disturbance to the Jasper Ridge Biological Preserve and surrounding communities.
A- Doing nothing at the dam and reservoir is not an option that any stakeholders are currently considering or embracing due to the imminent negative impacts of such a non-action.
Q- How will you work with Jasper Ridge Biological Preserve and other watershed stakeholders to ensure their concerns are being met?
A- Members and supporters of the Beyond Searsville Dam Coalition have been collaborating with Jasper Ridge Biological Preserve, Stanford University, San Francisquito Joint Powers Authority, San Francisquito Watershed Project, local jurisdictions, government agencies, community groups, and other non-profit groups for several decades on a variety of watershed related projects. Jasper Ridge Biological Preserve Director, Philippe Cohen (green cap), and Stanford Engineering Professor, David Freyberg (at right), atop Searsville Dam talking to a group from the Salmonid Restoration Federation conference who were interested in dam removal. 1) What is a dam?a€?There are a number of technical and legal definitions of a dam but generally it is any structure that impounds or diverts water.
However, this inventory only covers dams that meet minimum height and impoundment requirements, so an unknown number of small dams are not included in the inventory. 3) Which state has the most dams?a€?According to the NID, Texas has the most dams of any state at 6,798. 4) Who regulates dam operations?a€?A number of state and federal agencies are responsible for regulating dams. 5) How many dams actually produce power?a€?FERC regulates approximately 2,300 hydroelectric producing dams. 7) Why are some dams being removed?a€?There has been a growing movement to remove dams where the costs - including environmental, safety, and socio-cultural impacts - outweigh the benefits - including hydropower, flood control, irrigation, or recreation - or where the dam no longer serves any useful purpose.
8) How are dams removed?a€?Because dams and rivers vary greatly, physical removal strategies and techniques may also vary on a case by case basis. 9) How many dams have been removed to date?a€?Currently, American Rivers is aware of more than 600 dams that have been removed over the past 50 years in this country.A  We are still in the process of gathering this data, so that figure is likely to increase as more information becomes available.
10) How much does it cost to remove a dam?a€?Because the size and location of dams vary so greatly, the cost to remove an individual dam can range from tens of thousands of dollars to hundreds of millions of dollars. 11) Who owns the dams that are being removed?a€?Private businesses, federal agencies, state agencies, local governments, or public utilities may own dams.
12) Who pays for dam removal?a€?Who pays for the removal of a dam is often a complex issue. 13) Who decides that dams should be removed?a€?The decision to remove a dam is made by varying entities, depending on the regulatory oversight of the dam.
14) Can rivers be restored through dam removal?a€?Although most rivers cannot be completely restored to historic conditions - simply because of the amount of development that has occurred on and along them - dam removal can often recreate conditions that move the river towards those historic conditions.
15) What benefits do dams provide?a€?Dams may provide a variety of benefits, including water supply, power generation, flood control, recreation, and irrigation.
16) How can the benefits of a dam be replaced when it is removed?a€?While dams serve a number of human needs, society has developed ways to address many of these needs without dams.
Rather than plugging rivers with multiple hydropower dams, a cheaper and less environmentally harmful solution is to use existing energy efficiency technologies. 17) Is it cost effective to remove a dam?a€?Dam removal can be expensive in the short term, but in most cases where dams have been removed or are being considered for removal, money is actually saved over the long term. 18) Will the removal of a dam matter if other dams in the system are not removed?a€?Some rivers are so heavily developed and dammed that removal of one dam on that river will only return flows to a small portion of the river. 19) Are we going to decide in twenty years that we need to start building dams again?a€?We have learned a lot in the past twenty years about the many impacts dams have on rivers, and we have learned many alternatives to damming rivers. 21) What are the potential downsides to dam removal?a€?Dam removal does result in fundamental changes to the local environment. How quickly do rivers recover after dam removal?a€?Rivers are very dynamic and resilient systems.
1) What is a dam?There are a number of technical and legal definitions of a dam but generally it is any structure that impounds or diverts water. 3) Which state has the most dams?According to the NID, Texas has the most dams of any state at 6,798. 4) Who regulates dam operations?A number of state and federal agencies are responsible for regulating dams.
5) How many dams actually produce power?FERC regulates approximately 2,300 hydroelectric producing dams.
7) Why are some dams being removed?There has been a growing movement to remove dams where the costs - including environmental, safety, and socio-cultural impacts - outweigh the benefits - including hydropower, flood control, irrigation, or recreation - or where the dam no longer serves any useful purpose. 8) How are dams removed?Because dams and rivers vary greatly, physical removal strategies and techniques may also vary on a case by case basis. 9) How many dams have been removed to date?Currently, American Rivers is aware of more than 600 dams that have been removed over the past 50 years in this country.A  We are still in the process of gathering this data, so that figure is likely to increase as more information becomes available.
10) How much does it cost to remove a dam?Because the size and location of dams vary so greatly, the cost to remove an individual dam can range from tens of thousands of dollars to hundreds of millions of dollars. 11) Who owns the dams that are being removed?Private businesses, federal agencies, state agencies, local governments, or public utilities may own dams. 13) Who decides that dams should be removed?The decision to remove a dam is made by varying entities, depending on the regulatory oversight of the dam. 14) Can rivers be restored through dam removal?Although most rivers cannot be completely restored to historic conditions - simply because of the amount of development that has occurred on and along them - dam removal can often recreate conditions that move the river towards those historic conditions.
15) What benefits do dams provide?Dams may provide a variety of benefits, including water supply, power generation, flood control, recreation, and irrigation. 16) How can the benefits of a dam be replaced when it is removed?While dams serve a number of human needs, society has developed ways to address many of these needs without dams.
17) Is it cost effective to remove a dam?Dam removal can be expensive in the short term, but in most cases where dams have been removed or are being considered for removal, money is actually saved over the long term. 18) Will the removal of a dam matter if other dams in the system are not removed?Some rivers are so heavily developed and dammed that removal of one dam on that river will only return flows to a small portion of the river. 19) Are we going to decide in twenty years that we need to start building dams again?We have learned a lot in the past twenty years about the many impacts dams have on rivers, and we have learned many alternatives to damming rivers. 21) What are the potential downsides to dam removal?Dam removal does result in fundamental changes to the local environment. 22)How quickly do rivers recover after dam removal?Rivers are very dynamic and resilient systems. Then there is the fact that going green and telling the world about it can win you both accolades and new customers. One of these is internally connected to a gas jet which can be set at 45A° to the incident electron beam and is used in the perpendicular plane experiments. These stainless steel feeder tubes are connected to the nozzle using grounded shielded PTFE hose. One follows the anode, another corrects the beam direction between the apertures and a third steers the beam onto the interaction region. This shield is coated with aerodag colloidal graphite to reduce patch fields on the surface of the metal, and is made as small as possible to allow the analysers to approach the gun as close as is feasible when non-perpendicular plane geometries are selected (see figure 2). The XY translation table is mounted from the rotating yoke, to which is attached the photomultiplier tube. This allows the gun to be dismounted from the system without the need for rewiring of the feedthrough when the need arises (filament changes, cleaning etc).
The wiring between the gun and inline socket is also shielded colour coded PTFE coated advance wire facilitating spot welding to the electrostatic lens elements of the gun. The analysers are mounted onto x-z translation tables that allow them to view the interaction region accurately over the full range of angles accessible.
These lenses have a capability for energy zooming of around 10 : 1, and have a maximum entrance acceptance angle of A±3A° as defined by the entrance apertures. This ensures that the overlap volume accepted by each analyser encompasses the interaction volume for all detection angles as the analysers move in the detection plane. These devices use an activated lead glass internal surface which has a high coefficient of secondary electron emission when a high voltage (around 3000V) is applied across the multiplier. This noise may be picked up by the channel electron multiplier and the high voltage feed to the multiplier, and is generated internally in the vacuum system. The CFD's are operated in NaI mode as this has a 2ms dead time following the initial pulse, thus reducing the possibility of false triggering due to any mismatching impedance reflections along the delay cable. These EHT supplies are connected via VERO 200 high voltage couplings to high voltage cable connecting to the pickoff circuitry located on the high voltage feedthroughs.
This allowed the analysers to roam the detection plane over a complete 360A° angular range. The configuration of the target source hypodermic when perpendicular plane measurements are conducted. The common procedure is to initially maximise the current from the gun onto the Faraday cup, then onto analyser counts as the electron beam is moved through the gas jet. Maximising the Faraday cup current is therefore only a crude preliminary alignment of the incident electron gun beam.
This therefore assumes that the analysers are initially focused onto the interaction region, and a slow iterative technique must be adopted where the analysers and electron gun are tuned so as to maximise the signal from both analysers. In this case a true differential cross section is not obtained, since the scattered and ejected electron trajectories lie in a different plane than defined in the initial experimental alignment. An EMI 9789QB reduced photocathode photomultiplier tube is installed in the vacuum system together with optical focussing and defining elements (figure 2).
A group of these excited states decay back to lower valence states with the emission of visible photons at wavelengths around 450nm for both helium and argon targets.
Tuning of the electron gun to PMT counts therefore guarantees that the electron gun is steered and focussed to the point at the centre of the detection plane independent of the analysers or gas beam density.
This is mainly used when the vacuum system is baked at temperatures above 55A°C, since the photocathode is rapidly damaged by temperatures exceeding this. The tube is a venetian blind dynode construction, and has a reduced photocathode to decrease the noise on the output of the tube to less than 20Hz. The photomultiplier tube base was thoroughly cleaned in an ultrasound following location of these components, to displace any flux residue from the solder joints. It is therefore necessary to amplify the channeltron pulses prior to transmission to the discriminators, whereas the photomultiplier tube pulses are sufficiently large to not require further amplification. These pulses are amplified by Phillips Scientific 6954 100X amplifiers located external to the EHT feedthroughs connected by 10cm lengths of RG-58 cable. These crates are further decoupled from the AC mains supply using filter circuitry on each supply line. Internal to these rate-meters buffer 7400 TTL chips have been added to send to 32 bit counters located in the main PC via RG-58 cable.
These supplies are fully floating, their mid-point voltage being equal to the lens element voltage in which the deflectors are housed.
All these supplies are fully computer controlled isolated units with low output impedance to reduce noise and eliminate current loops. This relay switching unit allows either the voltage or the current on each lens element to be measured by a Keithley Digital voltmeter. This drive is further reduced internally by 10X reduction gears, resulting in a reduction ratio of 100:1. This led to the ground line of the RS232 serial line moving around with respect to the 0V stepper motor reference as drive current to the motors returned along the ground line. The optocoupler logic circuit circuit that controls the stepper motors and avoids collisions between the analysers, the electron gun, the Faraday cup and the hypodermic support. Added to this filament supply is a computer controlled current boost circuit that can be used to increase the filament current during electron gun tuning. The additional current then returns to the 12V DC regulated supply via a second 1N4007 diode. This therefore depends upon both the current driving the filament, as well as the resistance of the filament when hot (typically 4W - 6W). This supply feeds current to the filament without changing the characteristics of the main constant current supply used while operating the spectrometer.
These high stability reference sources ensure that the analyser and electron gun positions are accurately measured with time. A datalogger internal to the controlling PC establishes a cubic spline relationship between the measured angles and the corresponding ADC conversion from the potentiometers. This PC also controls the selection of the relay motherboard for measurement of the required lens element either in voltage or current mode when a request is sent from the controlling computer via an RS232 serial line. As the elevation of the reservoir and trapped sediment were lowered, upstream flooding issues caused by the dam are expected to be eliminated. The dam removal design plan can maximize flood protection benefits to downstream communities.
Searsville Dam provides a moderate amount of water that can easily be replaced with a less harmful water diversion facility that allows for improved functionality to Stanford.
Federal, state, local, private, and non-profit entities are all providing large grants and donations to dam removal efforts nationwide. Some of the current vegetation and habitat that has grown up on the upstream end of the reservoir can be maintained with the dam removal design. Dam removal would provide additional spawning gravels below the dam for steelhead as well as more natural water flow regimes and anticipated improvements to water quality. These native trout are genetically isolated by the dam and their survival is at risk due to inbreeding and loss of genetic diversity. It is critical to understand that while the artificial, and disappearing, open-water reservoir habitat will be reduced, the historic and ecologically unique habitat buried by the dam and reservoir will be restored. In addition, much of the established riparian vegetation at the upper end of Searsville Reservoir could remain with theA  dam removal design.
The historic map below shows what this habitat looked like before the dam and what it can look like again with dam removal and ecosystem restoration. Several species of non-native bass, sunfish, and panfish as well as bullfrogs occur in the warm, artificial, flat-water of Searsville Reservoir. Much more complicated dam removals have been completed that involved hydro-power replacement, polluted sediment disposal, adjacent development, and other challenges that this project would not have. There are also several dams that are planned for removal over the next couple years that are many times larger in size and in the amount of stored sediment.
A portion of the sediment can be transported for other uses, including the stated desire for it at planned San Francisco Bay wetland restoration projects or nearby agricultural sites. We will continue to work with all of these stakeholders to address their concerns, as we feel that the safety and ecosystem issues are in our mutual interest and that the most effective project will occur when shared goals are best addressed. While many progressive leaders at Stanford acknowledge the potential benefits of dam removal and the need for comprehensive studies to analyze specific dam removal alternatives, many watershed stakeholders are concerned that several individuals at Stanford are misrepresenting the issue and standing in the way of productive collaboration and investigation on this critical watershed decision that impacts all stakeholders. There are approximately 75,000 dams in the US Army Corps of Engineers' (Corps) National Inventory of Dams (NID), which is the most comprehensive inventory of dams nationwide. Of the 75,000 dams in the database, approximately 66,000 are located on rivers (the remainder impound water off-river). Generally, the process involves drawing down the reservoir, potentially removing the sediment built up behind the dam, removing the structure, and mitigating for downstream effects of increased flow and sediment re-suspension. Most of the dams removed to date have been owned privately, by local government, or by public utilities. In past cases, removal has been financed by the dam owner, local, state and federal governments, and in some cases agreements whereby multiple stakeholders contribute to cover the costs. In most cases, the dam owner itself is the decision-maker, often deciding that the costs of continuing to operate and maintain the dam are more than removing the dam.
For example, fish are returning to historic stretches of river that had been previously obstructed on Butte Creek in California, theA Souadabscook River in Maine, and the Clearwater River in Idaho, as a result of dam removals.
For instance, flood control can often be accomplished more effectively and for less money by restoring wetlands, maintaining riparian buffers, or moving people out of the floodplain.


Removal eliminates the expenses associated with maintenance and safety as well as direct and indirect expenses associated with fish and wildlife protection (e.g. The reservoir will be eliminated, and with it the flat-water habitat that had been created. Experience has shown that natural river systems can be restored relatively rapidly after dam removal. Whatever reasons you have for reducing your office's carbon footprint, know that there are lots of ways that businesses at every size can minimize their environmental impact. Remanufactured ink and toner cartridges not only save money, they also help save the earth by reducing manufacturing energy consumption. The purchase price of these bulbs may be higher but they're going to last practically forever and they use hardly any energy.
Many utility companies now offer the option to specify where your electricity comes from, with wind and solar power being the most popular alternatives. When choosing vendors and other business partners look for those that proudly set and live up to sustainability guidelines. The spectrometer is shown configured in the perpendicular plane, the electron gun being placed in the vertical position with respect to the analysers which span the horizontal detection plane. The electron source is a heated tungsten hairpin filament heated by passing around 2A of DC current through the filament. The saturated gain of these devices yields around 1E8 electrons in the output current pulse for a single electron which enters the input cone. This allows the analyser to roam over a complete 360 degrees of the detection plane when in this geometry (apart from the position where the analysers would clash wth each other).
The analysers are then adjusted for maximum signal count and the procedure is iterated until a maximum is found.
The dark noise count is also reduced when cooled, however since the reduced cathode PMT only produces dark counts of less than 20Hz at room temperature, this is not necessary during routine operations.
The 1.82M resistor was chosen to optimise the single photon counting efficiency of the tube. It is not found that these solder connections significantly affect the ultimate vacuum pressure in the system. Isolated DC supplies to these amplifiers is obtained from a standard +15V supply, the circuit diagram being given in figure 8. The power supply to these TTL buffers is derived from the rate-meter supplies via 7805 5V regulators located internally.
This supply boosts the current without changing the main supply, thus ensuring supply stability before and after the electron gun is tuned. The valley and historic wetlands that are buried beneath Searsville Dam and Reservoir once provided natural flood protection benefits by filling and absorbing winter rains and then slowly releasing flows following the peak flow event. Large cracks that remain on the dam were observed by the dam caretaker immediately after the 1906 earthquake.
The shrinking reservoir provides a fading amount of storage capacity that can be replaced with existing off-stream reservoirs, expanded storage areas, new off-stream storage, and possible dredging of the remaining upper Searsville Reservoir areas.
Almost all dam removal studies and construction efforts are being partially or fully funded with these available grants. In addition, miles of historic stream, riparian, and wetland habitat currently buried can be revived and restored with the dam removal.
The existing downstream steelhead population is able to migrate up all other existing spawning and rearing tributaries in the watershed and away from any potential short-term disturbances from the dam removal.
Several miles of stream habitat and associated riparian forests, comprising over 6 different tributary streams, can be reestablished. These species are able to breed in this artificial habitat and spread downstream of the reservoir were they can prey on and compete with threatened steelhead trout, other native aquatic species; including amphibians and even small birds and mammals. Habitat restoration of this size has been successfully completed at hundreds of locations and many dam removal projects have enabled stream habitat and native wildlife to restore themselves quickly. See our Dam Blog page and American Rivers website for more information on completed and planned dam removal projects. Noise abatement methods, scheduled use of roads by trucks, use of cleaner burning biodiesel in equipment operation, working around Preserve activities and research, and other determined actions could be implemented to reduce impacts. Dredging the reservoir and maintaining some open water has also been considered, but has limited benefits and most of the existing ecosystem and safety problems with the dam would remain.
We firmly believe that a collaborative, well-designed dam removal effort can be in the best interest of Stanford University and the entire watershed community.
Non-federal dams that produce hydropower are regulated by the Federal Energy Regulatory Commission (FERC). According to the NID, Oroville Dam, on the Feather River in California, is the tallest dam in the United States, measuring in at 770 ft. State dam safety offices can often order a dam to be removed if there are major safety concerns. Updating antiquated irrigation systems and replacing inappropriate crops can dramatically reduce the need for dams and reservoirs in the arid West. Many dams that have been removed no longer had any beneficial use or that use was very limited. In some cases, this additional section of river is enough to sustain crucial populations of endangered or threatened species of fish, mollusks, and other wildlife. In the next twenty years we are likely to learn even more about alternatives to dams and the impacts of dams on rivers.
Wetlands surrounding the reservoir will also be drained, although new wetlands are often created both in the newly restored river reach above the former dam site and in the river below.
For example, spawning fish returned to theA Souadabscook River in Maine only months after a dam was removed, and the flushing of the sediment from the Milwaukee River in Wisconsin following the Woolen Mills Dam removal took only six months.
Offices that aren't ready to go paper free can still make an effort to cut down on pointless printing and start a paper recycling program.
LEDs also don't contain the mercury and other toxic gases found in CFLs and incandescent bulbs.
Make work from home policies optional, though, because research has shown that telecommuters can actually use more resources in some cases.
Ask about vendors' commitments to both the environment and the health of their employees during initial interviews and let them know that environmental consciousness is part of your company culture. Or there are plenty of gizmos out there that can handle minimizing nighttime power drain automatically. The electron gun is a two stage non-energy selected gun that produces an incident electron beam current of up to 4 microamps at an incident energy from around 30eV to 300eV.
The 470k resistors bias the dynodes to achieve saturation of the current pulse at the output of the tube, hence biasing the tube for single photon counting applications. This was found to be necessary to eliminate problems associated with current loops from the 20A peak motor current feeding the common point of the logic circuitry. All over the nation, restoration projects are being constructed that restore historic wetlands and adjacent riparian overflow areas to provide the dual benefits of ecosystem restoration and natural flood protection.
It is not known what the current structural condition of the dam is because it has been 43 years since the Division of Safety of Dams (DSOD) has inspected the foundation, toe, and groins of the dam.
New diversion facilities can tie into existing storage facilities, irrigation, and landscaping pipelines and improve water delivery. One state agency, the Department of Water Resources, already offered to study alternatives at Searsville Dam, including removal, at no cost to Stanford. The artificial reservoir ecosystem also currently harbors many exotic species of fish and frogs, which would be eliminated or drastically reduced in numbers, benefiting native species. As observed with other dam removal efforts, such as the Marmot Dam removal in Oregon, wild salmon and steelhead migrated upstream of the removed dam within several days of it being removed and reestablished themselves into historic habitat, expanding their distribution and improving their population health.
Biologically-rich wetland ponds and seasonal overflow wetland areas that are currently covered by the reservoir can be restored along with acres of transitional and upland habitat. Dam removal and ecosystem restoration plans can minimize the risk of additional exotic species becoming established during the restoration effort and help to minimize future exotic introductions.
Other sediment alternatives such as slurry piping and controlled sediment transport can be utilized to design the best plan to address project complexities. As with so many other recently completed dam removal efforts, project stakeholders decided that the long-term gains to the ecosystem, dam owner, and surrounding communities warranted the short-term disturbance of dam removal. Only dam removal has the combined benefits of eliminating the safety liability of the dam, providing a free flowing stream, restoring historic habitat (wetland, stream, riparian), eliminating or reducing non-native species, providing unimpeded steelhead migration, and providing natural flood protection features. Non-federal dams that do not produce hydropower are regulated by the state in which they reside. The dam with the largest impoundment is Hoover Dam, on the Colorado River in Nevada, which stores approximately 30 million acre-feet of water.
The Federal Energy Regulatory Commission can order a hydropower dam under their jurisdiction to be removed for both environmental and safety reasons. In addition, removal often generates income from newly available recreation opportunities - including fishing, kayaking, and rafting - which may actually result in a net economic benefit.
Sediment that collects behind a dam, sometimes over hundreds of years, may contain toxics such as PCBs, dioxide, and heavy metals.
BYOD policies promote fewer devices overall, fewer desktops, and more electronics recycling means less pollution.
Offer bonuses to employees who travel to and from work in alternative fuel or hybrid vehicles.
The analysers are identical, and consist of a 3-element electrostatic lens focussing the interaction region onto the entrance of a hemispherical electrostatic energy analyser. The Anode deflector pair corrects for any misalignment of the filament emission point with respect to the axis of the electron gun.
In addition, dam removal efforts nationwide are being awarded funding to precede the dam removal with major downstream flood protection projects to increase channel capacity, replace undersized bridges, improve levee systems, and ensure that flood risks are reduced with the project. Many earthquakes and several decades have past since this last detailed foundation inspection. The remaining upper reservoir, west of Portola Road, is an historic wetland pond that preceded the construction of Searsville Dam. Water quality and habitat conditions downstream are expected to improve with dam removal, as has been the case elsewhere. Dam removal projects have consistently shown a strong benefit to salmon and steelhead populations in watersheds across the world.
An amazing and diverse array of habitat types and species will be restored for birds, bats, steelhead, and the full array of native species. Most of the non-native species utilizing Searsville Reservoir cannot thrive in the natural flowing stream environment.
A combination of multiple sediment options has been used in other dam removal efforts and may provide the best way to deal with the sediment.
The dam that provides the most hydroelectric power in the United States is Grand Coulee Dam, on the Columbia River in Washington, which generates 6180 megawatts (MW) of power. Re-suspension of these toxic-laden sediments in the process of dam removal has the potential to damage downstream water quality and threaten the health of fish and wildlife and water users.
The Chamber is lined internally with 3mm thick mu-metal, and a mu-metal cylinder encloses the chamber externally as shown.
The electrons selected in angle and energy are amplified using Mullard 919BL channel electron multipliers.
The defining apertures limit the pencil and beam angles of the electron beam following focussing by lens 2 onto the interaction region. The load is set by the 50W resistor across the anode to the HT feed, the pulse being decoupled to ground via the 1nF capacitor. This is an unprecedented opportunity to get massive funding and ease of permitting to reduce flooding, restore ecosystem health, and rebuild Stanforda€™s out-dated water supply facilities to a modern and sustainable state. Stanford is responsible for coordinating this inspection that DSOD has identified in the above 2007 inspection report as a a€?prudenta€? measure that should be taken.
This pond can be maintained and continue to provide fire-fighting needs as well as water storage capacity and open-water wetland habitat benefits. Dam removal would also allow for the resurgence of annual steelhead trout runs to the watersheda€™s largest tributary for the first time in 120 years, bringing back a critical keystone species to the ecosystem. Removal of Searsville Dam would open up over ten miles of historic spawning and rearing habitat in the largest tributary of the entire watershed, where high quality habitat and native rainbow trout persist. In addition, the dam removal will reestablish critical wildlife migration routes at this confluence of riparian corridors currently blocked by the dam and submerged by the reservoir. A detailed Dam Removal Alternatives Analysis study would identify the many options available. Short term impacts of the dam removal itself can include increased water turbidity and sediment buildup downstream from releasing large amounts of sediment from the reservoir, and water quality impacts from sudden releases of water and changes in temperature. This reduces the magnetic field at the interaction region to less than 5mG, an acceptable level for the electron energies used in this experiment. The interaction region defined by the interaction of the gas target beam and the electron beam is focussed onto the photocathode of an EMI 9789QB photomultiplier tube via a lens, 450nmA±50nm optical filter and defining aperture. Placement of the apertures ensures that the beam angle is close to zero degrees at the interaction region over a wide range of energies, whereas the aperture opening reduces the pencil angle to around A±2 degrees over this energy range.
Beyond Searsville Dam requested that the DSOD require this study and they have informed Stanford that the study should happen before the end of 2012. As part of the larger Searsville Dam removal and ecosystem restoration project, Stanford has an unprecedented opportunity to upgrade their water delivery and storage facilities with the benefit of available grant funding, eliminated safety liability, and ease of permitting.
The altered and artificial ecosystem would be transformed to a self-sustainable and native one. The remaining, and historic, upper pond located west of Portola Road can continue to provide open-water wetland habitat. The target gas effuses from a 0.6mm ID hypodermic needle constructed from platinum iridium alloy. The 10MW safety resistor prevents the output charging up to a high voltage if the feed is disconnected.
The deflectors between the apertures correct for space and surface charge beam variations inside the field free region, whereas the final deflectors allow the beam to be steered onto the interaction region defined by focussing a 1mm aperture in front of the photomultiplier tube onto the gas target beam. As the dam and concrete continue to age, experience additional earthquakes, and as the reservoir fills in and transported sediment potentially scours the dam, the structural integrity is expected to be reduced over time. In addition, the upgraded water diversion and storage facilities can be designed to serve a critical secondary function of reducing flooding downstream by diverting and storing peak storm flows into collection basins as is being considered by the Joint Powers Authority in the watershed.
The electrons passing through the interaction region which are not scattered are collected in a Faraday cup opposite the electron gun.
The active San Andreas Fault run adjacent to Searsville Reservoir, which can be seen as the oval blue shape near the center of the map, adjacent to the highest a€?Very-Violenta€? shaking severity level on the above image.
Such multi-objective funding and permitting opportunities are being jumped at by dam owners across the country. The gun, photomultiplier tube, gas hypodermic and Faraday cup all rotate on a common yoke with an axis through the centre of the horizontal detection plane, allowing all geometries from the perpendicular plane to the coplanar geometry to be accessed.
Dam removal can eliminate the dam failure risk identified by San Mateo County and extensive downstream inundation. Searsville Dam is listed as a a€?High Hazarda€? dam by the US Army Corps, State of California, and San Mateo County (pg. As noted in the above document, a High Hazard dam is defined as a dam whose failure would result in a€?probable loss of lives and significant property damagea€?.
Stanforda€™s own report, SPEAR3, cites an analysis that determined failure of Searsville Dam could release a a€?catastrophica€? flow of 60,433 cubic feet per second, or a€?about 6 times the 500-year peak flow of 10,500 cfsa€? (Section 7.1 Page 7).
Stanforda€™s own report, SPEAR3,A  cites an analysis that determined failure of Searsville Dam could release a a€?catastrophica€? flow of 60,433 cubic feet per second, or a€?about 6 times the 500-year peak flow of 10,500 cfsa€? (Section 7.1 Page 7). In addition to geologic, aging, and seismic considerations, the dama€™s limited spillway design and operation and bypass flow drain pipe present additional safety challenges for dealing with dam overtopping during flood events and the ability to quickly drain the reservoir during an emergency.



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