Subsurface Outflow Research Articles

Groundwater in a coral island

Freshwater aquifers in small coral islands usually occur as thin lenses which are significantly influenced by stresses such as groundwater pumping, sea tides, etc. Kavaratti, a coral island, is one of the 36 such islands in the Arabian Sea off the western coast of India. Detailed hydrogeological investigations were carried out to determine the quantity of freshwater that could be pumped in addition to the present usage. Salinity of groundwater must remain within permissible limits and a 2-D solute mass transport model with a vertical section of the island was constructed by the computer code SUTRA. The model was calibrated by obtaining a match of computed and observed values of the water table, tidal efficiency, and salinity of groundwater at the water table. The model analysis showed that the salinity of groundwater continues to increase unless groundwater pumping is kept below a certain rate. Groundwater potential can be augmented by reducing the subsurface outflow to the sea and by raising the water table by a subsurface dam.

Impact of climate change on the water resources of Awash River Basin, Ethiopia

An attempt was made to investigate the sensitivity of water resources to climate change in the Awash River Basin in Ethiopia. The climate of the basin varies from humid subtropical to arid. The basin was divided into 3 subcatchments for better resolution in calibration and simulation. Station- based meteorological data were processed to obtain areal averages necessary for the simulation. Different sets of temperature and rainfall scenarios were developed using GCM (both transient and CO2 doubling) and incremental scenarios. The IIASA integrated water balance model (WatBal) was used to estimate runoff under a changed climate. The model represents the water balance among sur- face outflow, subsurface outflow, and evapotranspiration. The model was calibrated using a 10 yr period (1971 to 1980), validated with the next 6 yr period (1981 to 1986), and then applied for different climate scenarios. Results of the impact assessment over the basin showed a projected decrease in runoff, which ranged from -10 to -34%, with doubling of CO2 and transient scenarios of CO2 increase (GFD3, CCCM, GF01). Sensitivity analysis based on incremental scenarios showed that a drier and warmer climate change scenario results in reduced runoff.

An experimental study on the burrowing activity of river crabs on subsurface water movement and piping erosion

Abstract The effects of the burrowing activity of river crabs on subsurface water movement and piping erosion were studied through a flume experiment. Cohesive field soil was used and constant fluvial head was applied. During the experiments with river crabs, burrows were excavated downwards under the groundwater level. At the outlet of each burrow, the crabs excavated pellets of soil and stacked them in piles, in the form of cone mounds. These mounds acted as effective dams for subsurface outflow, but they sometimes collapsed. The roofs of the burrows also caved in occasionally, whereby the crabs would excavate new burrows. The burrowing activity of the crabs led to marked erosion. In contrast, no marked erosion was observed in experiments without crabs, indicating that piping erosion occurs through the assistance of burrowing activity. It was observed that burrowing activity and piping erosion was pronounced when the hydraulic head was not significantly high (0.21–0.25). Analysis of the potential distribution of the soil mass indicated that the head loss close to the burrow was small in the case of experiments with crabs. This suggests that the burrow enhances rapid discharge of subsurface water. Consequently, burrowing activity was found to play an important role in piping erosion and rapid discharge of subsurface water.

Separating preferential and matrix flows using subsurface tile flow data1

Preferential flow is primary mechanism for faster movement of agricultural chemicals to groundwater. Subsurface tile flow data were used to quantify the contributions of preferential flow and matrix flow at the field scale over time. Tile flow hydrographs were constructed using hourly tile flow data related to rainfall events that were equal to or greater than 25.4 mm. A hydrograph separation technique was applied to separate preferential and matrix flow components of the subsurface tile flows. On the average, preferential flow was found to contribute about 13% of the total subsurface tile outflow for all the rain events, and an annual contribution of 10–20% is reasonable approximation. However, considerable spatial and temporal variability was observed, even among contiguous plots. Preferential flow for some rain storms was found to be as high as 60% of the total subsurface tile flow. This study also indicated that for storms greater than or equal to 25.4 mm, the subsurface tile outflow, on the average, was about 16% of the total rain water. However, it was observed that some of the subsurface tiles could drain as much as 80% of the rainfall depending upon the initial water table and soil moisture conditions.

Magnetic anomalies associated with high temperature reservoirs in the taupo volcanic zone (New Zealand)

Abstract Distinct magnetic total force anomalies are associated with many, but not all, liquid-dominated geothermal reservoirs in the Taupo Volcanic Zone, which stand in thick, young (

Mass balance of major solutes in a rainforest catchment in the Central Amazon: Implications for nutrient budgets in tropical rainforests

A solute mass balance for a 23.4 ha catchment of undisturbed rainforest in the central Amazon Basin was computed from detailed measurements of water and solute fluxes via rainfall, streamflow, and subsurface outflow over an annual cycle. Annual atmospheric deposition fluxes are lower than previously reported among mass balance studies conducted in the Amazon. Nutrient export fluxes are lower than previously reported for the Amazon, despite the fact that export fluxes via flow paths not previously measured were included. Given that climatic conditions were representative of a one in 10 wet year, the ecosystem was expected to show a net loss of nutrients rather than net gain. Instead, an excess of nutrient inputs via rainfall over ecosystem outflows was detected, ranging in annual quantities from 0.30 to 0.50 of the measured input. Among several mechanisms that could reconcile this budget, two are supported by the information presently available while two others cannot be evaluated without further research. Interannual variability in the amount of water available for runoff at the spatial scale of small catchments varies by a factor of two, in contrast to rainfall variability of ±20%, and may be a critical control on the apparent changes in ecosystem storage detected by annual-scale nutrient budgets in rainforests. Entrainment of materials from the terrestrial ecosystem to the atmosphere, including particulates containing elements which do not exist as gases, may be a particularly important loss pathway in rainforests existing on deeply weathered or nutrient poor soils.

Estimation of mountain front recharge to regional aquifers: 1. Development of an Analytical Hydroclimatic Model

This paper addresses the hydroclimatic modeling of mountain front recharge to regional aquifers. An analytical relationship between the mean seasonal precipitation and runoff is obtained based on a conceptualization of the hydrologic processes occurring in hard rock mountainous terrain and a derived‐distribution approach where the input variables are considered to be stochastic and their probability distributions are transformed into the probability distribution of the output variable by using the deterministic physical process. In a first‐order approximation a relationship between the seasonal values of precipitation and runoff is obtained. An analytical model of the seasonal streamflow is then developed where initial abstraction and the long‐term effective subsurface outflow, or mountain front recharge, are viewed as unknown model parameters. In addition, a procedure that combines the water balance equation with a relationship provided by the so‐called “vegetal equilibrium hypothesis,” and which enables the estimation of effective soil‐related parameters jointly with the mean seasonal evapotranspiration and surface runoff, is introduced. This procedure is applied to a mountainous watershed in southern Arizona.

Radar altimetry: A new concept in monitoring lake level changes

Remote sensing of closed and climatically sensitive open lakes can provide useful information for hydrological applications and, through long‐term monitoring, for climatic change. One new method that offers a unique way of providing relative lake level data in areas where ground gauge measurements are unavailable uses satellite radar altimetry.Global measurement of climate‐related variables will help to detect and monitor climate changes as they occur and validate climate models and related process studies. Because lake volumes respond to changes in precipitation integrated over their catchment basins [Street‐Perrott et al., 1986], they can act as important indirect indicators of climatic change. This response is particularly marked for closed lakes which have no significant surface or subsurface outflow.

Export of nutrients and major ionic solutes from a rain forest catchment in the Central Amazon Basin

The relative roles of base flow runoff versus storm flow runoff versus subsurface outflow in controlling total export of solutes from a 23.4‐ha catchment of undisturbed rain forest in the central Amazon Basin were evaluated from water and solute flux measurements performed over a 1 year period. Solutes exported via 173 storms during the study were estimated from stream water samples collected during base flow conditions and during eight storms, and by utilizing a hydrograph separation technique in combination with a mixing model to partition storm flow from base flow fluxes. Solutes exported by subsurface outflow were estimated from groundwater samples from three nests of piezometers installed into the streambed, and concurrent measurements of hydraulic conductivity and hydraulic head gradients. Base flow discharge represented 92% of water outflow from the basin and was the dominant pathway of solute export. Although storm flow discharge represented only 5% of total water outflow, storm flow solute fluxes represented up to 25% of the total annual export flux, though for many solutes the portion was less. Subsurface outflow represented only 2.5% of total water outflow, and subsurface solute fluxes never represented more than 5% of the total annual export flux. Measurement errors were relatively high for storm flow and subsurface outflow fluxes, but cumulative measurement errors associated with the total solute fluxes exported from the catchment, in most cases, ranged from only ±7% to 14% because base flow fluxes were measured relatively well. The export fluxes of most solutes are substantially less than previously reported for comparable small catchments in the Amazon basin, and these differences cannot be reconciled by the fact that storm flow and subsurface outflows were not appropriately measured in previous studies.

Water balance and hydrologic characteristics of a rain forest catchment in the Central Amazon Basin

The water balance and hydrologic characteristics of streamflow and subsurface outflow were measured for a first‐order catchment draining a 23.4‐ha stand of undisturbed terra firme rain forest in the central Amazon Basin over a 1 year period. Total rainfall during the study period, representing a 1 in 10 wet year, was 2870 mm of which 1650 mm and 42 mm respectively were exported from the catchment as streamflow and subsurface outflow. A hydrograph separation technique applied to the entire streamflow record distinguished 173 storms. The storm flow volume was 88 mm, which represented only 5% of overall streamflow and less than 3% of the rainfall. The 20% of least frequent, large‐volume storms accounted for 75% of the rainfall volume and 80% of the storm flow volume. The fraction of the catchment that could account for the volume of storm flow runoff in a given storm as overland flow never exceeded 4%, even for the largest storms. The change in soil water storage from the previous year was equivalent to about 57 mm of water. Evapotranspiration, estimated as the water balance residual, was equivalent to 1120 mm per year with an uncertainty, estimated by propagating measurement errors, of ±16–21%. Evapotranspiration is significantly less than values previously reported from catchment‐scale water balance studies in the central Amazon, and is slightly lower than recent estimates derived from micrometeorologieal techniques, though differences in the latter case are within measurement error.

Vegetative Filter Treatment of Dairy Barnyard Runoff in Cold Regions

AbstractA vegetative filter strip was installed to treat barnyard runoff from an active dairy farm in Vermont. Runoff from a concrete surfaced barnyard flowed through a detention pond, then onto a vegetative filter strip measuring 22.9 m by 7.6 m with a 2% slope. The water input and surface and subsurface outputs for the strip were continuously monitored from December 1984 through May 1986. Of the total barnyard runoff entering the strip, 65% left as surface runoff and 27% was measured as subsurface outflow. The average hydraulic loading rate was 14.7 cm wk−1 and the average overland flow detention time was 15 min. The filter strip did not significantly (P < 0.05) reduce solids, P, N and bacteria concentrations in the surface output. Over the period of study the mass retention was 33% total suspended solids, 12% total P and 18% total Kjeldahl N. Mass retention was highest during the growing season and was poorest during snowmelt periods. It was concluded that poor filter strip performance was due to an excessive hydraulic loading rate resulting in an inadequate detention time for proper treatment. A preferential flow path from the level lip spreader to the subsurface drain tiles may have contributed to the poor subsurface treatment performance.

Annual mean surface heat fluxes in the Arabian Gulf and the net heat transport through the Strait of Hormuz

Abstract An attempt is made to assess the climatological air‐sea fluxes in the Arabian (Persian) Gulf using meteorological observations. The annual mean values of upward heat transfer due to solar radiation, sensible heat, latent heat and infrared radiation fluxes are ‐212, ‐1, 168 and 66 W m−2, respectively. Based on the surface inflow and subsurface outflow through the Strait of Hormuz, the annual average heat transport into the Gulf is 25 W m−2. This is in fair agreement with the resulting upward flux of 21 W m−2 at the sea surface in the Gulf.

Physical and chemical controls of preferred path flow through a forested hillslope

Investigations of the physical and chemical characteristics of macropores and mesopores at two forested sites established for subsurface transport research are summarized. The hydrologically active macroporosity (pores larger than 1 mm diameter) is a very small fraction of the total soil porosity but is sufficient to conduct a large proportion of ponded infiltration. Mesopores (pores less than 1 mm diameter that are generally drained at field capacity) are sufficient to conduct total infiltration during the majority of rain events and have a much higher surface area than macropores. The cation adsorption coefficient of macropore walls was similar to bulk soil for mineral coatings but was higher for organic linings derived from roots. The subsurface outflow from a 0.46 ha subwatershed generated by two precipitation events displayed two contrasting patterns of chemical concentration. At the time of peak discharge, the concentration of Na, K, Mg, Ca and S was close to maximum (high supply); and for Al, Fe and Mn, chemical concentration was highest prior to peak discharge (low supply). A pathlength-supply hypothesis is proposed, based on (1) changing proportions of mesopore flow path lengths with stage of the subsurface hydrograph and (2) the ability of mesopore surfaces and adjacent micropores to continue supplying chemicals to percolating soil water. Macropores are viewed as being important physical conduits in convergent flow zones of watersheds but as having little influence on water quality.

Indirect detection of subsurface outflow from a rift valley lake

Abstract Naivasha, highest of the Kenya (Gregory) Rift Valley lakes, has no surface outlet. However, unlike other Rift lakes it has not become saline despite high potential evaporation rates, which indicates that there must be some subsurface drainage. The fate of this outflow has been the subject of speculation for many years, especially during the general decline in lake water level during the 1980's. Particularly to the south of the lake, there are few opportunities to obtain information from direct groundwater sampling. However, the stable isotopic composition of fumarole steam from late Quaternary volcanic centres in the area has been used to infer groundwater composition. Using a simple mixing model between Rift-flank groundwater and highly-evaporated lakewater, this has enabled subsurface water flow to be contoured by its lakewater content. By this method, outflow can still be detected some 30 km to the south of the lake. Stable isotope data also confirm that much of the steam used by the local Olkaria geothermal power station is derived from lakewater, though simple balance considerations show that steam use cannot alone be responsible for the fall in lake level observed during the 1980's.

THE INFLUENCE OF SUBSURFACE DRAINAGE PRACTICES ON HERBICIDE LOSSES

ABSTRACT Atrazine and metolachlor were applied preemergent on 22 April 1987, to silage corn on high watertable fields which were either subsurface drained (104 mm drain tubes 1 m deep) or surface drained only. Surface runoff and subsurface outflow were sampled and analyzed for atrazine and metolachlor from 22 April to 31 August 1987. Subsurface drainage reduced atrazine and metolachlor losses by 55 and 51%, respectively. Two-thirds of the losses occurred within 30 days after the application of the herbicides, and most of the losses were in the surface runoff. The edge-of-field average atrazine concentrations, 12.5 and 9.0 ug/1, for the non-drained and drained fields, respectively, were four and three times greater than the U.S. Environmental Protection Agency advisory of 3 ug/1 for drinking water. The edge-of-field average metolachlor concentrations were near the U.S. EPA advisory of 10 ug/1.

Hydrology of a wetland in the continuous permafrost region

Abstract This study examines the hydrological system of a northern wetland in the continuous permafrost region. Water balance computation quantifies the relative importance of various hydrological processes including snowmelt, rainfall, inflows, evaporation, surface and subsurface outflows. The existence of this wetland is closely related to a lake upslope which provides the bulk of the water input. The ability of northern wetlands to absorb water input is limited by the frozen ground and the high specific retention of the peat, rendering the wetland a poor regulator of streamflow. Storage capacity increases in summer as evaporation reduces the moisture content of the peat. Subsurface flow remains insignificant because of the low hydraulic gradient and conductivity. Thus, when the water table lies within the peat layer, there is little wetland contribution to streamflow but when the water table lies above the ground during some intense storms, streamflow is rapidly increased by surface flow on the wetlands.

Hydrology and Chemical Quality of Flow from Small Pastured Watersheds: I. Hydrology

AbstractSurface runoff, soil loss, and subsurface flow were measured from four rotationally grazed summer pastures. One of these pastures was also used as a winter‐feeding area. Surface runoff volumes and peak rates from the three pastures used only for summer grazing were generally less as compared with values for earlier years when the fields were in meadow and fight pasturing; however, runoff from the winterfeeding area was markedly increased. Both before and after the initiation of grazing, the areas used only for summer grazing had but a trace of soil loss. More soil was lost from the winter‐feeding area, particularly during the dormant season. Water‐balance studies indicated that during the growing season surface runoff and subsurface outflow were higher and evapotranspiration (ET) was less from the winter‐feeding area than from areas summer‐grazed only. During the dormant season, surface runoff was higher and subsurface outflow was lower from the winter‐feeding area than from the summer‐grazed areas, whereas ET was similar.

The conservation and utilization of water

There is a need for a quantitative assessment of the factors that determine the water balance of each part of an area, cultivated or under natural vegetation, and of their variability in time and space. These factors are rainfall, soil physical characteristics, potential evaporation and topography, the latter acting on surface and/or subsurface inflow and outflow. Knowledge needs to be assembled as to how to handle the rainfall received in an area. This aspect covers infiltration rates, methods to temporarily impound water on the field, knowledge about rates of water use and water recovery in small-scale storage reservoirs. The next step is to ensure a careful use of water through a judicious choice of the cropping and farming systems and by methods of land preparation and of the timing and choice of farming operations. It is important to increase the efficiency of water use through the choice of crops and varieties, by elimination of non-water factors limiting optimal growth and development of crops, by adequate crop protection and by adopting suitable harvest procedures. Energy inputs into the farming system are to be adjusted to the desired level of production. Among the socio-economic factors that affect the economic use of water, are matters of land ownership and availability of credit for low volume investment. The definition of the correct level of water conservation during a given cropping season is dependent on the requirements of other components of the cropping system, notably of the production of crops on adjacent low lying lands, usually cultivated from the end of the rainy season onwards. Out of season (November-February) irrigated crops on relatively small areas may contribute very significantly to agricultural production during a period when water requirements are relatively low.

Studies on the water balance of a small natural catchment area in southern Sweden

A water balance study is made on a small natural catchment area in flat sandy agricultural country in southern Sweden. Relevant simultaneous data concerning precipitation, evapotranspiration, surface run-off and ground moisture content are obtained from measurements over a period of at least six years. Complete balance between precipitation, evapotranspiration and surface run-off is obtained from the six-year period as a whole. The results show a significant and very pronounced pattern of seasonally influenced subsurface inflow and outflow. When represented as running 12-month means, the surface run-off and ground water level curves show a high degree of correlation to long term variations in precipitation. The ground water is found to lag 6 months behind the precipitation and the run-off 2 or 3 months. The running 12-month mean for evapotranspiration is found to vary only slightly and does not appear to be related to the precipitation. DOI: 10.1111/j.2153-3490.1968.tb00405.x