Field Hydrology Research Articles

MODIFICATION AND USE OF DRAINMOD TO EVALUATE A LAGOON EFFLUENT LAND APPLICATION SYSTEM

Traditionally, lagoon design has considered waste inflow, sludge accumulation, individual event rainfall associated with the 25-year, 24-hour storm, and sufficient temporary storage to handle excess rainfall during non-irrigation periods. Excess rainfall was defined as the “average” or “normal” rainfall in excess of evaporation during the non-irrigation (drawdown) period. North Carolina experienced a series of tropical storms and hurricanes in 1995 that resulted in several lagoon overtoppings; however, none of the storms individually satisfied the 25-year, 24-hour criterion. These storms raised questions as to whether the 25-year, 24-hour criterion presented the appropriate design constraint to prevent lagoon overtopping or whether the cumulative impact of prolonged rainy periods (referred to herein as “chronic” rainfall) was a greater threat. To evaluate the validity of existing lagoon design criteria and emergency action measures proposed by the North Carolina Soil and Water Conservation Commission, the irrigation component of the field hydrology model DRAINMOD was modified to consider animal waste lagoon constraints of chronic rainfall, crop nitrogen utilization, and emergency lagoon operational measures. The modified DRAINMOD was used to evaluate lagoon design and operational guidelines in effect in eastern North Carolina at the time of the 1995 lagoon breaches and the proposed 1999 emergency measures. Model simulation results showed that prolonged wet periods in the winter that result in high moisture surplus are the most likely cause of excessively high lagoon stage or overflow. To minimize the occurrence of elevated lagoon stage and eliminate the risk of overflow, model results also showed that the design temporary storage criterion should be increased to account for chronic rainfall excess between drawdown periods. Intense storms with short durations, such as the catastrophic design (25-year, 24-hour) storm, mainly occurred in the summer and usually posed no risks to lagoon overflow because these events typically occurred at a time when lagoons were traditionally drawn down to their lowest allowable stage. Using a constant average nitrogen concentration for lagoon wastewater resulted in fewer irrigation applications, which in turn resulted in more frequent high lagoon stage and more overflows. Lagoon spills resulting from extreme weather conditions could be avoided by applying wastewater more frequently and temporarily suspending the crop nitrogen limit in wet years without exceeding soil hydraulic limits.

Effects of long-term winter wheat, summer fallow residue and nutrient management on field hydrology for a silt loam in north-central Oregon

In a region where water is the primary limiting factor of crop production, loss of water from fields by overland flow represents an economic loss to producers. Traditional crop management practices in north-central Oregon have led to crop water loss by overland flow. In 1931, a long-term experiment was begun near Pendleton, Oregon, in a Walla Walla silt loam (coarse-silty, mixed, mesic Typic Haploxeroll—US; Kastanozems—FAO), to examine the influence on soil fertility and crop production by nutrient amendments and crop residue management practices. This experiment provided the opportunity to evaluate the influence of a several traditional farming practices on field hydrology. Tillage in all treatments consisted of moldboard plowing and multiple passes with secondary tillage equipment to smooth the surface for planting and for weed control. The treatments were combinations of nutrient amendments (0.90 kg N ha −1 commercial fertilizer, and 145 kg N ha −1 from manure) and residue management (fall-burn, spring-burn, and no-burn), whose soil organic carbon increased with increasing nutrient amendments. These treatments were in a winter wheat–fallow system and represent a set of past and current cultural practices. Overland flow from these treatments was measured. Lister furrows separated the plots of 12 m×40 m (≈0.05 ha) to prevent overland flow from treatment to treatment and were instrumented with weirs to capture and measure overland flow. To determine if hydrologic differences existed between treatments, we tested the overland flow to precipitation ( Q/ P) ratio. The Q/ P ratio ( P<0.15) was greatest within crop year/low soil fertility (0 kg N ha −1, burn) whereas the high fertility (145 kg N ha −1, no-burn) treatment crop year plots Q/ P ratios were similar to fallow, standing stubble plots. Most notably, the manure amendment plots in crop, produce significantly less overland flow than the other residue and nutrient management practices, and marginally less overland flow than treatments in stubble. This research demonstrates that overland flow was greater from low fertility and stubble burned treatments. Increased overland flow increases the risk of soil erosion and loss of water to overland flow is potentially a loss of needed soil water for crop growth and production.

PREDICTING FIELD HYDROLOGY IN COLD CONDITIONS WITH DRAINMOD

The field hydrology model DRAINMOD was modified for cold conditions, where soil freezing, thawing, and snowaccumulation affect the hydrologic cycle. Field observations of water table depth and subsurface drainage from Carsamba,Turkey; Truro, Nova Scotia; and Lamberton, Minnesota, were used to test the modified DRAINMOD. At Carsamba, Turkey,the modified DRAINMOD correctly predicted the timing and magnitude of drainage events resulting from snow accumulationand subsequent snow melt. Although the variable weather pattern and nature of rain/snow mixture at the Nova Scotia sitemade it difficult to describe hydrology during winter months, the modified DRAINMOD predicted the timing and magnitudeof most drainage flow events more accurately. Continuous longterm model simulations at Lamberton, Minnesota, weregenerally in good agreement with drainage measurements. The temperaturebased approach used in the model caused someunusual rainfall events to be missed during winter. Errors from snow event predictions contributed to errors in hydrologicpredictions. Overall, the modified DRAINMOD gave reasonable predictions of field hydrology. The simplified snow algorithmprovided a timely prediction of snow accumulation and melting.

DRAINMOD MODIFICATIONS FOR COLD CONDITIONS

The field hydrology model DRAINMOD was modified to include freezing and thawing, and snowmeltcomponents. Based on daily hydrologic predictions of the original model, the modified DRAINMOD numerically solvesthe heat flow equation to predict soil temperature. When freezing conditions are indicated by below zero temperatures, themodel calculates ice content in the soil profile and modifies soil hydraulic conductivity and infiltration rate accordingly.Recorded precipitation is separated as rain and snow when daily average air temperature is above or below a rain/snowdividing base temperature. Snow is predicted to accumulate on the ground until air temperature rises above a snowmeltbase temperature. Soil surface temperature is recalculated when snow cover exists. Daily snowmelt water is added torainfall, which may infiltrate or run off depending on soil freezing condition. The modified DRAINMOD predictions ofsoil temperature agreed well with field observations at Plymouth, North Carolina, Truro, Nova Scotia, and Lamberton,Minnesota. Assuming air temperature as the soil surface boundary condition increased the variability of soil temperaturepredictions at shallow depths, agreement with field measurements was still good. The method of using average airtemperature as an indicator to separate snow and rain worked very well for Carsamba, Turkey. At Truro, Nova Scotia,however, the method was not as successful, and several snow events were predicted as rainfall and vice versa. Comparedwith the original version of DRAINMOD, the modified version predicts fewer drainage flow events in winter monthsbecause of snow accumulation on the surface. Subsurface drainage and/or surface runoff resulting from snowmelt arepredicted when air temperature rises, the snow melts, and the soil begins to thaw.

Field Hydrology in Tropical Countries: A Practical Introduction

Hydrology is not only a highly mathematical science but also, and mainly, a practical science of measurement of main elements needed to address questions such as water balance in a basin. It is also a matter of commitment for those involved in the everyday task of taking data from instruments and providing that data to national meteorological and hydrological services. It is a highly skillful science for those who aim to understand the water cycle and its contribution to sustainable development of the environment.Having served in a national meteorology and hydrology service in a tropical country, and having experienced the difficulties that observers go through in the field, far away from the central office, I find very familiar much of what Henry Gunston says in his book Field Hydrology in Tropical Countries: A Practical Introduction.The author himself has spent a great deal of time in the field and has a good understanding of the difficult situations that observers in tropical countries go through every day Field hydrology in many places, the tropics included, is a very difficult task because of both the lack of economic support and the lack of prepared people in the country to do the job. Most of the observers do their job because the enjoy it, hoping the next field team may bring them not only payment but also new logs to record the data and good news from the city.

CropSyst, a cropping systems simulation model: Water/nitrogen budgets and crop yield

In agriculture, water and nitrogen are two critical resources for growing a crop. However, their management cannot be analyzed independently of weather, soil characteristics, field hydrology, crop characteristics, crop rotation, and management factors. This paper describes the water, nitrogen, and crop growth components of CropSyst, a comprehensive cropping systems simulation model, and provides preliminary verification of these components. The water budget of the model properly describes crop water use. Predicted nitrogen contents throughout the soil profile did not exactly match the measured values from leaching experiments, but they did follow the general trends of the data. The agreement between simulated and observed biomass and yield of corn, winter wheat and spring wheat grown in two locations with a total of 77 data points was good as shown by several statistical indicators. Based on this preliminary validation, CropSyst appears promising as a tool to analyze management practices for water and nitrogen. Additional validation of model components, including a wide range of crops and conditions, should be conducted in the future.

A Coupled, Field Hydrology – Open Channel Flow Model: Theory

A coupled, field hydrology and stream routing model is presented. It simulates field hydrology and routes field outflow through a canal network. Water levels in the canal can suppress field drainage. Backwater conditions and flooding in the stream are simulated. Sensitivity analysis for runoff events with one-half- to two-year return periods found watershed outflow to be sensitive to (in order of importance) time of concentration in the fields, bottom slope of the main channel, hydraulic conductivity of the soil, subsurface drain spacing in the field, and channel roughness. The simulated outflow was only moderately dependent on surface storage and was not dependent on channel depth and width, rooting depths or drainable porosity. The model can make multiple year simulations and can be used to analyze hydrologic effects of water management systems, changes in land use practices, tidal effects, and channel constrictions such as weirs or partial ditch blockage.

Petrology of Philippine geothermal systems and the application of alteration mineralogy to their assessment

Abstract Philippine geothermal systems occur in the vicinity of large Holocene calc-alkaline volcanic complexes. Wells drilled in these areas encountered multiple intrusions; the latest dikes are the subsurface manifestations of the youngest heat source. Commonly, at least two hydrothermal regimes are juxtaposed in a single area, with the latest being in equilibrium with the present temperature and chemical regime. Alteration by neutral-pH water is pervasive and abundant. A contact-metamorphic aureole also occurs near intrusives. Alteration due to acid-sulfate fluids is generally confined to permeable structures. Neutral-pH alteration is divided into four zones on the basis of key clay minerals, and two subzones are defined by calc-silicates. These are the smectite (ambient to 180°C), transition (180–230°C), illite (230–320°C) and biotite (270–340°C) zones. Subzones are defined by epidote (250–340°C) and amphibole (280–340°C). The four main zones of acid alteration are: kaolinite (ambient to 120°C), dickite ± kaolinite (120–200°C), dickite ± pyrophyllite (200–250°C), and pyrophyllite ± illite (230–320°C). Where relict high-temperature alteration reaches the surface, the area being drilled is usually the outflow zone of the present system. These hydrothermal mineral assemblages are used: (1) as geothermometers; (2) to assist in determining the depth at which the production casing will be set during drilling; (3) to estimate fluid pH and other chemical parameters; (4) to predict possible corrosion and scaling tendencies of the fluids; (5) as a measure of permeability and possible cold water influx into wells; (6) as a guide to field hydrology; and (7) to estimate roughly the thickness of the eroded overburden.

Evaluating Peat‐Mining Hydrology Using Drainmod

A process that uses the field-scale model DRAINMOD to simulate the hydrologic response of a watershed to peat mining is presented. An eastern North Carolina watershed has been proposed as the site of a peat mining project. Within the watershed are several distinct soils, land uses, and drainage characteristics. Land use, drainage, and even soil characteristics change as peat soil is mined and reclaimed. The hydrologic response of this watershed is determined for each year of the proposed mining project by combining the field hydrology model with a simple reservoir model, a spreadsheet program, and a statistical program. Results show that peat mining alone increases the annual runoff volume and peak outflow rates. However, by mining land in small sections, by reclaiming the land for agricultural and forest uses, and by installing water retention reservoirs, the annual runoff and peak daily flows from the watershed can be reduced to the magnitude of those presently occurring on the unmined site.

Evaluation of Six Rice Genotypes in Relation to Field Hydrology

Evaluation of Six Rice Genotypes in Relation to Field Hydrology