Search

There probably were a few raised eyebrows about AWWA's theme for its 94th Annual ConferenceWater Reuse: Resource of the Future. The author, however, greeted the theme with a great deal of enthusiasm. For too long the water-utility industry and its associated regulatory agencies have avoided the issue of water reuse, while, at the same time, the industry has been fully aware that increasing amounts of return flows from wastewater-treatment plants have been entering the streams and lakes from the municipalities located on watersheds or along rivers. It is encouraging to see that this issue is out in the open, that the water industry acknowledges the presence of returned flows in water sources, that reuse is a reality, and that it is a very important part of the future. No responsible manager would fail to seek the best possible raw-water source for his municipality. The truth of the matter, however, is that pristine waters are rare and diminishing. Even those few cities that own the major part of their watersheds are finding it increasingly difficult to police those watersheds and to maintain their absolute pristine quality. Other cities that measure the area of their watershed in thousands of square miles have never been able to control growth on their watersheds and therefore have faced growing amounts of return flow in their raw-water sources. A glance at the 1973 population of the first 85 SMSA in the US indicates some 110 million people are residing in these urban and semiurban areas. Allowing a 100-gpc return flow as an average for the group would indicate that 11 bil gal of return flow per day enter the bays, estuaries, streams, and lakes below these cities. This is no drop in the bucket. The industry has been

The Samoan Passage at about 10S, 169W appears to be the major channel through which the deep and abyssal waters flow northward from the South Pacific. The northward flow, Postulated from the distribution of characteristics, is confirmed by direct measurements of the currents. The density field and the water characteristics are consonant with an intensified deep western boundary current, whose quasi-geostrophic balance requires the densest water to lie shallowest on the western side of the Samoan Basin, and from which it appears to cascade suddenly into the deeper waters of the North Tokelau Basin. The density field and the water characteristics are also consonant with a southward flowing western boundary current lying immediately above the abyssal flow. It is proposed that this shallower flow, at depths somewhere between about 2000 and 3500 m, represents a return flow of water from the deep North Pacific, with high nutrient and low oxygen content.

Irrigation return flows are agricultural wastes of major significance in the western states. Irrigated agriculture is the largest consumer of water in the U.S., and return flows from irrigation constitute a large portion of the flow in many western streams. The necessity for leaching salt concentrated in the root zone by evapotranspiration concentrates salt in return flows and causes damages downstream. Numerous engineering control measures can be applied to restrict and reduce water pollution from irrigation. These control measures present institutional constraints, and potential management concepts applicable to this agricultural waste are described briefly. In general, present water laws contribute to irrigation return flow quality problems. Irrigators use their full water rights, else they will lose them. Irrigators generally have a negative incentive to internalize the external diseconomies associated with their excessive use of water.

The three-dimensional circulation of a steady, frictional, homogeneous ocean forced by a wind stress varying sinusoidally in the northward direction is examined, with reference to the effects of continental slopes. It is found that the local circulation pattern is considerably altered by the presence of slopes, although the global pattern is not. Moderately strong eastern boundary currents, of order 1–3 cm sec−1, are predicted, flowing in the same direction as those observed. Areas of secondary up- or downwelling are found near the bottom of the continental slope, even in the absence of a local long-shore wind stress, again agreeing qualitatively with observations. The northward, intense (linear) return flow on the western boundary is again modified. It consists of a wide weak flow over the slope, and a narrower strong flow over the flat bottom; both flows have a northward flux of the same order, however.

Whether the goal is minimizing water quality degradation in receiving streams or maximizing agricultural production on existing croplands; the solutions are identical - improved water management practices. Technology has succeeded in developing feasible solutions to improving irrigation water management, but the law has been slow to encourage or direct implementation. The villain of the western United States water problem is the property right concept of the appropriation doctrine. Improving water management also implies organizational improvements. Also, the so-called “human factor” involves questions of inefficiency and ineffectiveness, that when examined under the criteria of efficacy, may dictate a policy of continuing present practices in certain localities or regions with little technological intervention. The present effort for improving water quality management implies, therefore, a manyfold attack aimed at increasing project irrigation efficiency and effectiveness, under the larger rubric of efficacy and the achievement of larger social goals.

Horizontal transports in a rotating parabolic basin are found for three elementary steady stress fields. For a uniform stress, the circulation consists of two vortices so arranged that the inshore transport is more or less in the direction of the surface stress, with a return flow in the interior. For a stress with constant curl, the interior transport is a large symmetric vortex, with possibly a weak countercurrent near the shore; for a stress with constant divergence, a weak vortex occurs in the interior, with weak countercurrents occurring near shore. For a combined surface stress, the transport in the interior is dominated by the curl component; near shore the uniform stress component may be equally important.

When the use of austenitic materials called for a revision of the start-up devices for once-through Benson boilers, a system using water return flow to one stage of the feed pumps was recalled. The development of glandless recirculation pumps, which made it possible to adopt this system for the highest pressures, is discussed. The paper describes how the system can be adapted to meet more exacting requirements by suction line dimensioning and by cooling the return flow water.

A linear three-dimensional model of the wind-driven ocean circulation is treated by boundary-layer methods. The interior flow, below the Ekman layer, differs from the classical gyres of Munk (1950). There is a north-eastwards transport of fluid from the western boundary current of the southern gyre across the latitude of zero wind stress curl into the northern gyre. A return flow in the Ekman layer preserves continuity.

Four summer seasons of field work near Mt. Rainier have shown that a well-developed valley wind system tends to have the following features: Airflow within a valley is up the valley during the day and down it at night and is compensated by a return flow (anti-wind) at a higher level. The layers occupied by the two flows are of approximately equal thickness, and the boundary between them is generally at, or somewhat below, ridgeheight. Above the anti-wind, the flow depends on the large-scale synoptic situation. Horizontal wind speed in these two layers is greatest slightly below the center of each layer. Speeds reach a maximum in early afternoon and just beforce sunrise. The reversal between day and nighttime flows is almost simultaneous everywhere in the valley, about an hour after sunnet and sunrise. Vertical transport of air between the two layers appears to be localized, mainly in the neighborhood of the ridges. Slope winds apparently feed the vertical currents. Speed fluctuations, having a period of about 20 minutes, were observed in drainage winds near the surface at night. When a well-developed wind system occured in one valley, well-developed systems tended to occur in other valleys in the same area.

A study of irrigation return flow in the Yakima River Basin showed that return flow was the major factor influencing Yakima River water quality. The increase in the quantity and composition of salts in the return flow is due more to leaching than to evapo-transpiration. Water quality changes occurring during irrigation are examined together with techniques and objectives for return flow quality studies. Data are presented on water and salt budgets together with the ion concentrations in the applied water, the subsurface, and the surface drainage water. Salts leached and exchanged from the soil and released to the parent river in the irrigation and nonirrigation seasons are reported on a weight-per-acre basis. The impact of domestic sewage and industrial effluents on river chemical quality is shown to be but a small fraction of that due to return flow. Sixty-one percent of the lower river salt content by weight was contributed by return flow in the irrigation season and 49% in the nonirrigation season.

The derivation of irrigation water requirements and an explanation of their use for project planning work in Texas is presented in which effective precipitation, consumptive use, farm waste and deep percolation losses, canal and lateral losses, return flows, and diversion requirements are discussed. The steps used in developing diversion requirements and return flows are described and an explanation of their use and of land inventory data is given. Cultural practices used in the production of rice are such that the application of effective precipitation and the computation of diversions for other crops are not applicable. Thus, diversion requirements for rice are explained separately. Several references are cited that contain valuable information on the acreage irrigated from surface and from ground water sources, lands suitable for future irrigation, land classification studies, consumptive use data, typical cropping patterns, and farm budget studies. Although the material pertains only to Texas, the methods for calculating detailed water requirements for the various sub-areas can be used elsewhere.

Hydrological data from a number of cruises in the waters near Southern africa have been used in this study. The areas of the Agulhas and Benguela currents provided much new information. In addition to the normal water mass in the subtropical zone, a much less saline water of similar temperature was identified. This was concentrated mainly in the Mozambique Current and Agulhas main stream but other areas were also found off the coast of South West Africa and in the Agulhas return flow north of the Subtropical convergence. A divergence region was found well north of the Subtropical convergence where Central Water upwells at the surface. Vertical displacement of Central Water occurs along both the east and west coasts but an active system of wind upwelling is only developed near the Atlantic shores. Some suggestions are put forward to account for this.

An analytical method for computing return flow or drainage from irrigation applications is presented and discussed. Computations consider aquifer properties, drain spacing, and deep percolation. A graph for determining the fractional part of percolation remaining in transient storage is included. By using the graph and simple digital procedures, realistic estimates of irrigation return flow can be determined. The method was used to determine monthly quantities for 13 yr of return flows in the Mesilla Valley, New Mexico-Texas. This study is reported.

The management of irrigation systems entails not only the design and construction of physical works for supplying water and removing drainage, but considers the impact of these operations on water quality. The behavior of irrigation systems that may be represented as controlled hydrologic entities is examined. A systematized approach for predicting the quality response of these systems to changes in irrigation practice is proposed, and a series of mathematical models through which river system operation may be simulated on a digital computer is suggested. These models are described, and results obtained by simulation of the Sacramento River System are compared to the quality response of the prototype.

When a channel discharges fresh water into a basin filled with salt water an arrested saltwater wedge will develop. If the fresh water is discharged by an outlet-structure that is situated close to the basin, the salt wedge cannot develop its full length. The salt water is then mixed up with the discharged water close to the outlet-structure. A return current of salt water develops from the basin to the mixing region. The theory of two-layer flows is applied to determine the maximum return current. It is shown that this happens when both in the mouth and in the mixing region the flow pattern is internal critical, i.e., when one of the velocities of propagation of internal waves is zero. Nondimensional graphs are given and measurements in nature and in models show good agreement. Conclusions are drawn for the design of outlet channels, cooling water channels, and pneumatic barriers against saltwater intrusion.

Summary Refering to numerous ratings of screw type current-meters and to the results of laboratory-experiments the author studies successively the degree of accuracy of measurements in very shallow water, the disturbing influence of a beam on which several current meters are fixed and finally the behaviour of current meters in return flow and in unsteady flow conditions.

Overflow of free-flowing materials into a fluidized bed from an upright channel in countercurrent gas filtration is investigated. Equations for calculating the weight rate of flow of the free-flowing material and the critical counterpressure are proposed.

Numerical calculations were made to determine the steady state features of the wind-driven circulations in Lake Ontario. It is assumed that the water in the lake may be represented by an incompressible homogeneous fluid layer, a condition that is typical of a winter situation. The linearized mass transport equations are then solved for an imposed wind stress on the surface of the lake. Effects of bottom friction, bottom topography, lateral boundary configuration are taken into account Effect of rotation is represented by a constant Coriolis parameter. Circulation patterns were calculated for the cases of uniform and spacially variable wind stress. It was shown that bottom topography strongly influences the circulation features. The dominant feature of the circulation is a two-cell pattern with a small counter-clockwise circulation cell in the southern part of the lake and a large clockwise cell in the northern part with an intense west-ward return flow in the interior of the lake.

An interpretation of current measurements yields, as a typical feature of the cross-component over the upper slope, two circulation cells with opposite rotation. Here coastal upwelling has been assumed to be mainly a two-dimensional phenomenon. Over the upper continental slope the core of the subsurface onshore return flow (∼+10 cm s−1) occurs at intermediate depths of 60 m to 70 m and above the bottom over the shelf. This flow causes a convergence just beneath the actual relatively shallow upwelling layer. A great part of the water masses of the return flow feeds the Ekman flux in the surface layer. Another minor part, however, sinks down the slope contributing to a weak offshore component above the bottom. It is suggested that the strength, the thickness and the depth of the onshore compensation flow increase with the intensity of upwelling.

Experiments on currents in which processes of long duration are involved, e.g., on slowly depositing, eroding, or decelerating suspensions, cannot be carried out in normal, straight flumes. Einstein and Krone therefore used a channel with a narrower and faster return flow. The disadvantage is the turbulent mixing during this return, but they nevertheless obtained noteworthy results. I employ a circular flume with vertical paddles moving horizontally in a circle along the axis. Centrifugal force and differences in velocity along the inner and outer wall are troublesome, but turbulence due to the drive is uniform and slight. The experiments described here are concerned with the origin of horizontal lamination as shown by nearly all turbidites of finer grain than coarse sand. The origin has been attributed to various causes, but usually to current pulsations of different kinds. Lamination is quoted as evidence for, but also against, deposition by a turbidity current. However, current pulsations are so numero...

the 3,200,000 acre-ft of fresh water withdrawn annually by municipal and industrial water users in Texas, approximately 60 per cent is returned directly to the surface waters of the state. Within the next 50 years, withdrawals may conceivably increase 11,000,000 acre-ft annually, and return flows may increase to about 6,000,000 acre-ft per year.1 Effective utilization of this increasing quantity of return flow will not be feasible unless a work

The results of six cruises of S.A.S. Natal, two during the I.G.Y. and four during 1962–1963 in the Agulhas Current area are examined. These are supplemented by the results of one of the Africana II cruises to Marion and Crozet Is. The results show a marked seasonal variation in the Agulhas Current, which is strongest in April and weakest in October. A strong return flow in 25°–30°E, 35°–40°S is observed in all cases. Examination of the data taken simultaneously by Natal and Africana II shows that the return flow merges with the west wind drift and also indicates the areas of the Agulhas and Sub-tropical convergences. Numerous large eddies are seen to be contained in the current system, particularly in the area east of Durban. The current system appears to be modified only very little by the local winds and is affected mainly by the variations in the South Equatorial Current and the west wind drift. Oxygen and phosphate determinations were obtained during the cruises and their distribution is discussed and compared with that of the water temperature.

The agricultural production from the Lower South Platte Basin in Colorado represents a significant portion of the state economy. Until the early 1950's the production had developed almost exclusively by use of river water. Drought conditions combined with improved well technology resulted in an inordinate amount of well development in the valley during the period 1952-56. These wells were used for supplemental supply in many cases, but the application of sprinkler irrigation brought many acres of here-to-fore dry land into irrigated production. As a result of the vast amounts of groundwater withdrawal by the newly developed wells, senior surface appropriators found a decreasing amount of water available for use in the streams. The legislature, observing the doctrine of prior appropriation, ruled that all surface and ground water in a tributary would be treated and administered as one resource. This, of course, spelled doom for the well-oriented segment of the economy. Analysis of a segment of the river on an inflow-outflow basis was made with careful determination of all inflow-outflow in the study reach to include correlations required to determine ungaged side-channel in-flow and unmetered irrigation wells. Results indicate that wells have intercepted normal return flows to the river resulting in a decreased amount of surface water during the irrigation season. Stream depletion appears to equal the expected consumptive use of well water which ranged between 40% to 50% of the groundwater extraction.

The influence of bathymetry upon the wind-driven, steady-state coastal upwelling motion of homogeneous water is investigated. The motion occurs in two principal layers, a divergent surface Ekman layer and a subsurface return flow. The restriction that the surface layer depth be always a small fraction of the total depth permits the retention of the surface layer solution developed in a previous paper by the author where bathymetry was not treated. The subsurface motion is affected by bathymetry, but the governing equations can he simplified for bottom topographies of slopes characteristic of continental slopes and shelves. The velocity and pressure fields are deduced by a combination of analytic and numerical means. The principal physical effects of bathymetry are two-fold. Shoaling uplifts and compresses the streamline field in the return flow. The resulting acceleration of the flow toward shore induces a jet in the longshore velocity field for the subsurface layer. This motion occurs in the dir...

The lake-breeze circulation on the Great Lakes is often as vigorous as its oceanic counterpart. This paper shows that lake breezes frequently exert drastic control on mesoscale air pollution patterns in urbanized shore-line areas, in this case, Chicago, Ill. Observational data were gathered from a surface mesonetwork, surface and satellite cloud photography, a chain of pilot balloons normal to the shore, optically tracked constant-level balloons, and aircraft measurements of suspended particulate concentrations in several size ranges. On the 2 late summer days studied, the lake breezes were extremely well developed. Inflow depths ranged from 500 to 1000 m, with peak inflow velocities of 6–7 m/s. Beginning at the shore-line between 0800 and 0900 LST, the breezes penetrated inland over 40 km. Clearly defined return flow layers were present both days. Eulerian wind field measurements from serial pilot, balloon releases were used to make cross sections of the u wind component. Computed one-dimensiona...

Intense daytime heating in an interior valley and cold upwelled water offshore combine to produce a strong horizontal temperature gradient and the development of a baroclinic field. This leads to an onshore component of the wind in the lower layers with the main features guided by the local topography. Penetration rates of 5 m/s were found. A layer of winds with an easterly component was also found between the low-level westerlies and an upper level westerly current. This easterly current showed signs of being a return flow and was found to have higher small-particle concentrations over the shore than either layer above or below it.

Return flow from a 82,030-ha (202,700-acre) tract of calcareous silt loam soils irrigated with water diverted from the Snake River in southern Idaho increased the downstream total soluble salt and NO?-N loads, but decreased the downstream PO?-P load. Under the existing water management practice, 50% of the total input water returned to the Snake River as subsurface drainage. Net total soluble salt output was 2.4 metric tons/ha (1.0 English ton/acre) and, on the average, was considerably greater than necessary to maintain a salt balance. Net NO?-N output was 33 kg/ha (30 lb/acre). Only about 30% as much PO?-P left the tract via drainage water as entered the tract in irrigation water. As water passed through the soil, PO?-P was removed by chemical reactions in the soil, thus decreasing the concentration in the subsurface drainage water and decreasing the downstream PO?-P load. Applied P fertilizer was not leached into the drainage water.

A two-day field program in Chicago studied mesoscale pollution transport during typical lake breezes. Streamlines calculated from serial pibal data suggest that a nearly closed circulation cell traps pollutants emitted near a shore line. Optically tracked tetroons confirm the helical trajectory of air within the lake breeze regime. Pollutants released within the inflow layer move inland, rise in a narrow zone of updrafts (100 cm/sec) at the lake breeze front, advect lakeward in the return flow layer aloft, and then subside back down into the inflow layer. Pollution then fumigates back to the surface as the air returns inland a second time causing concentrations higher than would otherwise be expected. Spectral aerosol measurements (0.5-3.0 and 7.0-9.0 micrometer size ranges) made by an instrumented aircraft reveal a marked particle size sorting.

Ground water in the arid coastal area of Peru occurs in more than fifty alluvial aquifers. The aquifers are limited to river valleys and to nearby sedimentary plains. The coast is rainless and the river valleys serve as the drainage outlet of the western slopes of the Andes. The coastal alluvial aquifers are located below the lower limit of the active catchment areas, and are not recharged directly by precipitation. The long igneous batholith and the volcanic formations of the Andean Cordillera form an impermeable barrier which prevents the replenishment of the aquifers by underflow from the Andes. The main source of replenishment of the aquifers in the Peruvian coastal zone is river water. The water infiltrates through the river beds and irrigation canals and migrates laterally within the alluvial deposits. Another important source of recharge is return flow from irrigation. Water also enters the aquifers through boundary faults.

tip of Texas, its mineral content has been increased by irrigation return flow, and various types of nutrient substances that would not otherwise be present are available. The towns of McAllen, Mission, Harlingen, Weslaco, and San Benito, together with a number of villages also located in southern Texas, obtain their water supplies from canal systems off the Rio Grande. In this area, citrus fruits, vegetables, and other crops are produced with the aid of irrigation. For some time these cities have had to

This study was undertaken to determine the physical and dynamical characteristics of the lake breeze wind system at a site on the eastern shore of Lake Michigan. Lake breeze development and progress inland were observed by hourly pilot balloon ascents in a vertical plane perpendicular to the lake shore. The fields of moisture and temperature in this vertical plane on a day when a clearly defined lake breeze occurred were obtained using an instrumented aircraft. Observations were made during periods when prevailing external meteorological conditions would exert minimum influence on the local thermal circulation. Over the land the depth of the layer of onshore flow is approximately 750 m and a maximum velocity of 5–7 m sec−1 is observed within 250 m of the surface directly over the lake shore. Above the lake breeze current a well defined return flow is apparent by midafternoon. The layer of return flow is about twice as deep as the lake breeze and velocities in the return flow axe proportionately l...

A study is made of the records of polar magnetic sub-storms recorded at Lerwick and two neighbouring temporary stations with a view to determining the associated ionospheric current system. The measurements of the horizontal and vertical components of the disturbance vectors and their gradients in the direction of the horizontal component are compared with theoretical values computed for a band of current with a parabolic distribution of intensity across the width, taking into account the effects of induced currents and of return flow at a lower latitude. The main conclusion is that on the average the sub-storms can be accounted for by a system in which the primary current is a polar electrojet flowing westward and it is this intense westerly electrojet which causes the negative bays of the sub-storms occurring between 22 hr and 05 hr U.T. whereas the positive bays of the sub-storms occurring between 15 hr and 20 hr are due to the weaker easterly return flow. Estimates of the height, latitudinal extent and strength of the current are obtained.

According to the mantle convection theory, mantle materials come up to the surface of the Earth at the mid-oceanic ridge system, go off in two horizontal directions, and finally at the trench and orogenic belt system they return to the interior of the Earth. We assume no return flow in the deeper part of the mantle and calculate the change of products of inertia of the Earth due to the above mass transfer. The polar wandering thus calculated is towards the direction of about 90° east and its absolute value is about 0.9 × 10−2 s/yr.

This report presents data which are, in general, supplementary to those the surface-water investigations made in the past by the U. S. Geological Survey. Those have been essentially investigations of the operation of the many gaging stations on the Rogue River and tributaries. The data presented were obtained from a detailed field investigation of the various factors resulting from man-mad* structures that influence the quantity or regimen of the flow at the gaging stations. These factors include diversions from the stream, bypass channels carrying water around the gaging stations, return flow from irrigation'or other projects, storage and release of flood waters, and other similar factors. Where feasible, the location, size, effect upon the streamflow, periods of use, method of operation,, and similar information are given. The information is divided into sections corresponding to areas determined by the location of gaging stations. An index of streamflow records is included. A section dealing with the adequacy of available water-resources data and containing location and period of record also is included. This information is given in general terms only, and is portrayed mainly by maps and graphs.

This report presents data which are, in general, supplementary to those of the surfacewater investigations .made in the past by the Geological Survey. Those investigations have consisted essentially of the operation of the many gaging stations on the Plathead River and tributaries. The data presented were obtained from a detailed field investigation of the various manmade devices that are factors influencing the quantity or regimen of the flow at the gaging stations. These factors include diversions from the stream, bypass channels carrying water around the gaging stations, return flow from irrigation or other projects, storage and release of flood waters, and other similar factors. Where feasible, the location, size, effect upon the streamflow, periods of use, method of operation, and similar information are given. The information is segregated into sections corresponding to areas determined by the location of gaging stations. An index of streamflow records is included. A section dealing with the adequacy of .available water-resources data, including location and period of record, also is included. This information is given in general terms only, and is portrayed mainly by maps and graphs.

Study of the hydrology of the south end of the island of Bonaire indicates that flow of fresh sea water onto the land takes place through permeability conduits in the underlying rock and emerges as numerous springs. Reflux of some heavy brine is probably continuously taking place because of gravitational instability. In addition, evidence suggest a major annual reflux event in early summer that causes a significant loss of heavy brine. This annual event is controlled by the total pressure of the brine exerted at the level of an impermeable clay layer within the Recent sediments being greater than the pressure exerted by the sea water at equivalent level. This annual return flow of brine moves through some of the same permeability conduits that supply fresh water through most of the ye r. Dolomite formed by such a hydrology should be confined to the permeability paths underneath an evaporitic sediment in older rocks. This pattern of rock-selective or permeability-controlled dolomitization may be common in ancient rocks.

THE general arrangement of the wind tunnel shown in Figs. 1 and 3 does not differ materially from the tunnels built up to the present on the plans of Professor Prandtl in Germany, England, America. It is an open jet tunnel with single return flow and two large elliptic nozzles of different design. A single stage helicoidal fan in the return flow provides the air stream. The fan is driven by a synchronous motor across an oil gear, Thoma‐Waldrich type, consisting of two pumps and a motor.

A COMBINED hydrographic and biological investigation has been launched jointly by the Department of Fish and Game of the Ministry of Agriculture of the Republic of Chile and the Technical Foreign Aid Program of the Federal Republic of Germany in order to find possible relationships between the migration and behaviour of fish and the changing hydrographic conditions off the Chilean coast.

Economists now know something about why people migrate. Adequate models have been developed to analyze migration as an investment in human capital and as a result of maximizing behaviour [11]. We still have little to say about a significant portion of geographic mobility, namely return migration.1 And yet, if migration is explainable for example in terms of income differentials, it is clear that people also climb down the income differential ladder and return to their region of origin. Our lack of knowledge in this area becomes more pressing the greater the quantitative and qualitative importance of return migration. Both conditions hold for homeward migration of Canadians in the U.S. Reverse migration of Canadians who migrated to the U.S. has been estimated at anywhere between one in eight to seven in eight, certainly a wide knowledge gap [10, 57]. There also appears to be a tendency for the more highly trained to remain in the U.S.; in other words, the return flow has a lower skill composition [10, 57]. In what follows, we analyze some data on Canadian scientists, engineers and economists in the U.S. to see if any light can be shed on determinants of return migration.

RIP currents have been measured at Holywell in West Cornwall, where a sandy beach is open to waves and swells from the Atlantic. A rip current is a narrow streak of water which flows seawards from the beach; it carries the return flow of the general shorewards transport of water produced by the breaking of waves. Such currents cause many bathing fatalities each year.

In order to make irrigation of a colostomy as easy as possible for the patient, a new piece of equipment has been devised. The story of the evolution of the apparatus helps explain its mechanism and value. At first an aluminum stewpot, with a hole in the center, and a piece of metal pipe attached to it, was used; then a stainless steel emesis basin was substituted for the stewpot. A member of the nursing staff suggested the addition of the flange to prevent the return flow from splashing on the patient. A patient suggested moving the hole from the center to an eccentric position, since his colostomy was not in the midline. Figure 1 is a photograph of the apparatus. The stainless steel basin, 11½ by 5 by 2 in. (31.24 by 12.70 by 5.08 cm.) costs $4.00. The work shop charge for the flange and pipe, both of

In many irrigation-districts where the supplies of surface-water from a stream nave been entirely appropriated, pumping from wells has been resorted to in order to supplement the surface-supply. Where the pumps are near a stream that has a flow during the irrigation-season, either because of normal ground-water flow or because of return flow from surface-water irrigation, the pumping is likely to diminish the stream-flow. Conversely, diversions of water from a stream may diminish the supply of wells that were formerly supplied indirectly by seepage from the stream, but the problem involved is of a different nature than its converse and will not be discussed here.