Subsurface Return Flow Research Articles

A mathematical concept of runoff prediction model for small tropical catchment areas

After the Horton overland flow concept became legend until the early 1960s, new findings then revised this concept for implementation in several catchment area conditions. Runoff processes in tropical regions seem to have specific characteristics such as thick humus on the top layer of the catchment area and non-uniformity of hydraulic conductivity vertically and horizontally across the stream. To overcome the runoff problems in tropical regions, a reasonable model needed to be developed to predict generated runoff. Based on the concept that saturation condition in a catchment generates non-uniformly during the course of a rainfall, and that the storage capability of top layer in intercepting rain-water leads to subsurface and return flow, the water balance in a segment of the catchment area is calculated. The mechanism of flow in the model is that subsurface flow and return flow, which are a function of hydraulic conductivity, and surface runoff on a segment are integrated for the whole areas. The generation of flow using the model seems to indicate that runoff peaks will commence after each segment is saturated starting from the valley bottom. The lag time for initial flow to alter significantly depends on the data on stream-flow before the storm began that indicate the soil moisture and depth of the temporary water table. Generally, though, the model is very flexible, so that data on each segment subject to the wide variety of physical conditions of the catchment area characteristic of tropical regions can easily be implemented.

Retention and Transport of Nutrients in a Third-Order Stream in Northwestern California: Hyporheic Processes

Chloride and nitrate were coinjected into the surface waters of a third—order stream for 20 d to examine solute retention, and the fate of nitrate during subsurface transport. A series of wells (shallow pits) 0.5—10 m from the adjacent channel were sampled to estimate the lateral interflow of water. Two subsurface return flows beneath the wetted channel were also examined. The conservative tracer (chloride) was hydrologically transported to all wells. Stream water was >88% of flow in wells <4 m from the wetted channel. The lowest percentage of stream water was 47% at a well 10 m perpendicular to the stream. Retention of solutes was greater in the hyporheic zone than in the channel under summer low—flow conditions. Nominal travel time (the interval required for chloride concentration to reach 50% of the plateau concentration) was variable by well location, indicating different flow paths and presumably permeability differences in subsurface gravels. Nominal travel time was M 24 h for wells <5 m from the wetted channel. Coinjected nitrate was not conservative. Two wells were significantly (P < .05) higher in nitrate—N than would be predicted from chloride, while four were significantly lower. Wells 2.0—4.0 m from the wetted channel tended to have higher nitrate concentration than predicted, whereas nitrate sink locations tended to have transport distances >4.3 m. The capacity of the hyporheic zone for transient solute storage and as potential biological habitat varies with channel morphology, bed roughness, and permeability. A conceptual model that considers the groundwater—stream water interface as the fluvial boundary is proposed. Emerging paradigms of the riverine network should consider the hyporheic zone and associated nutrient cycling as an integral component of fluvial structure and function.

IRRIGATION SUBSURFACE RETURN FLOWS AND WATER USE IN LYSIMETERS CONTAINING APPLE TREES

For 9 yr, subsurface return flow measurements from irrigated lysimeters containing "Macspur McIntosh" apple trees (Malus domestica Borkh.) on MM 111 rootstocks were collected. Water use with and without a grass cover crop was calculated as irrigation plus summer precipitation minus drainage. Drainages were consistently and significantly lower, and therefore water use higher, under grass than under bare soil but the differences were not large. The times of irrigation and drainage events were not closely linked. Drainage followed irrigation anywhere from a day to many days, stretching at times into weeks or months. By far the largest drainages, however, occurred during the irrigation season. Irrigation amounts provided most of the water for return flows with summer or winter precipitation contributing little to the drainage. At the higher irrigation levels the return flow quantities and calculated water use quantities clearly indicate that sprinkler design flow quantities are too high for the area and that improvements in irrigation efficiencies are possible. Key words: Drainage, irrigation, lysimeters, water use, apple trees

National Water Quality Goals and Irrigated Agriculture

The 1972 Federal Water Pollution Control Act Amendments (P.L. 92-500) have an important but often overlooked impact on the irrigated agricultural community of the western United States. The specific goals of P.L. 92-500 are unrealistic because of the lack of both knowledge and funds to develop effective control technologies in regard to irrigation return flows. Surface and subsurface return flows should be differentiated for purposes of study, treatment, and management. Treatment and salt disposal require expensive and complicated technologies. Some states have been granted the authority to oversee the issuance of National Pollution Discharge Elimination System permits; irrigation entities in both California and Washington have formed large return flow groups to facilitate the collection of water quality data and to assist the farmer in developing the best practical control technology. The agricultural user also needs information on the relationship between crop yield and irrigation water quality; the ASCE Task Committee was formed to study the salinity hazards faced by the irrigator.

SHALLOW AQUIFERS RELATIVE TO SURFACE WATER, LOWER NORTH PLATTE RIVER VALLEY, WYOMING1

ABSTRACT. The occurrence of ground water in the lower North Platte Valley, Goshen County, Wyoming, was studied to determine safe yield within the alluvial aquifer under varying discharge and recharge conditions. The alluvium of the North Platte is extensively developed for irrigation purposes and the effects of large‐scale pumpage are of major concern. Actual withdrawals are estimated to be 46,000 acre‐feet. Should pumping reach potentially higher levels an overdraft is expected. Effect of ground water withdrawals are established from projections of the flow regime within the alluvial aquifer. A time dependent, numerical model was employed to predict aquifer response to increased withdrawals. The results suggest that more efficient use of surface waters and/or increased use of ground water will reduce the annual subsurface return flow to the North Platte River and its tributaries by an amount equal to the reduced ground water recharge increment. Alternatives are available for management of the lower North Platte alluvial aquifer. The preferred course is to correlate surface and subsurface water rights, in light of convenience, economics, and best means of storage for maximum utilization of the single water resource.

On the currents over the shelf off cap blanc in the northwest African upwelling area

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.

The Effect of Bathymetry on the Coastal Upwelling of Homogeneous Water

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 direction of the longshore wind component and exceeds the surface layer longshore movement in mass flux.

Relationship between the Hake Fishery and a Southerly Sub-surface Return Flow below the Peru Current off the Chilean Coast

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.