A MODEL FOR THE DETERMINATION OF THE NATURAL STREAMFLOW OF VENISON CREEK R.W. Irwin W.T. Dickinson W. Lammers Member CSAE School of Engineering Hydrologist School of Engineering University of Guelph Water Resources Division University of Guelph Guelph, Ontario Ministry of the Environment Guelph, Ontario Toronto, Ontario INTRODUCTION model, the basin characteristics being model that the effects of groundwater suitable for the study, and hydrometric takings on streamflow, observed at an Water takings for the irrigation of and observation well data being available inventory point at a downstream gauge, tobacco in Ontario reduce streamflow (3). will lag the actual takings by several days. during the months of July and August in Initially, there will be local adjustments most years. Yakutchik and Lammers (5) in the water table. Additional takings at estimated streamflow reduction for Big MODEL DEVELOPMENT the same or nearby sites will result in Creek at Delhi in the order of 70% for the additional water-table adjustments. The period July 30 to August 1, 1964, due to For this study, the natural discharge of effects of these takings are cumulative, irrigation takings in that basin. These a stream is defined as the discharge because each additional groundwater reductions affect the natural functions of generated in the basin under existing land taking will add to the existing effects of streams, and cause water use conflicts use. A large number of man-made ponds previous takings. Therefore, the effects of between stream users. are part of the existing land-use pattern groundwater takings on streamflow will of Venison Creek and have increased the be of little significance during the start of For the management of water total free water surface of the basin. the irrigation period but will increase resources in such basins, knowledge is Their effects are incorporated in the steadily as the irrigation period progresses required regarding (i) the amount of natural discharge as defined. until groundwater takings cease. water available during peak water demand periods; (ii) the amount of water likely to The model is based on three assump A basic relationship for natural stream- be used from various sources; and (hi) the tions regarding the effects of various flow determination may be expressed: relative effects of water takings from types of water takings on streamflow different sources on streamflow. Informa reduction: (1) tion regarding the natural flows available (i) Takings from streamflow have a for use is often scarce, since streamflow direct effect on streamflow reduc where records for many of the streams in tion, Southern Ontario began after the practice (ii) Takings from surface-water storage Q = natural streamflow; of tobacco irrigation was established in areas not located on the stream (i.e. M = measured streamflow; D = direct streamflow losses due to stream- the early 1950's. Therefore, there is a farm ponds) do not affect stream- flow takings; and need for a method to estimate natural flow, / = indirect streamflow losses due to ground streamflow patterns in order to evaluate (hi) Takings from groundwater resources water takings. the effect of water takings. Such have an indirect effect on streamflow information is important to the develop reduction. For a consideration of mean daily ment of improved water management streamflow values, the D and / terms may systems in the region. Assumption (i) is readily apparent. be expressed as: Assumption (ii) is valid for the case A streamflow determination model has involving intermittent streams, but is not (2) been developed for the generation of strictly true for permanent streams. ^L-(r-i)5' estimates of natural mean daily stream- Assumption (hi) considers that ground flow. Input for the model includes water takings, whether from wells or and records of existing daily streamflow, and ponds dug to below the water table, n - b water takings from ground and surface reduce the rate of groundwater discharge U =AR2 Gtfoin<m+b, .... (3) water sources. Venison Creek basin has to the streams, due to locally reduced n t = 1 been used as a verification site for the hydraulic heads and gradients of the water table to the streams. Such reduc or tions remain until the aquifers from which the water has been withdrawn have Presented July 7, 1971 CSAE Conference, It =ARcln-(m+b)]x Gtfom>m+b been recharged to their capacity. This n t = 1 Lethbridge, Alberta. normally occurs only during the spring (4) recharge period, about 200 days after the water taking occurs. where RECEIVED FOR PUBLICATION JULY 4, 1972 It has further been assumed in the Dm =mean daily streamflow loss due to 12 CANADIAN AGRICULTURAL ENGINEERING, VOL. 17 NO. 1, JUNE 1975 direct streamflow takings, on the «th TABLE I STATISTICS ON IRRIGATORS AND WATER-TAKING RECORDS day following the commencement of irri gation in the basin for a selected year understudy; Year: 1967 1968 1969 P = scale factor to convert reported daily streamflow takings to total daily stream- Total irrigators 102 102 105 flow takings; Irrigators holding permits * 99 99 102 T = travel time, in days, of streamflow from Permitted water sources* 108 108 113 farthest water-taking site on the stream Irrigators submitting suitable to the inventory station at downstream records (%) 65 61 54 gauge; n = day number following the commence * Certain irrigators are exempted. ment of irrigation in basin; * Certain irrigators use more than one water source. t = time, in days; S( = reported daily streamflow taking on day t\ crops was estimated from water-taking records satisfactory for analysis. Statistics Itn ~ mean daily streamflow loss on the «th records3 on file with the Ministry of the on irrigators and water-taking records are day due to takings from groundwater; Environment for the 1967, 1968 and shown in Table 1. A- constant, characteristic of the study basin; 1969 irrigation seasons. This estimation R = scale factor to convert reported ground was carried out by: Figure 2 reveals a histogram of the water takings to estimated total ground 1. Compilation of a list of permits issued number of irrigators reporting water water takings; by the Ministry to tobacco growers in takings and the histogram of the total b = average delay time, in days, before the the study basin. reported daily takings. These histograms effects of groundwater takings on previ 2. Compilation, assessment, and classifi portray three patterns of water use. The ous days are felt in streamflow reduction cation of water-taking records submit histogram for 1968 shows a period of at the inventory station; ted to the Ministry by the permittees intensive water use as compared to 1967 Gf = reported groundwater taking on day t; C = constant, characteristic of the study for the three irrigation seasons. and 1969. basin; 3. Determination of daily totals of m = day number, counted from first day of reported water takings from each of Water is withdrawn from three main irrigation, for last day of water takings the categories and sources of supply. sources in the basin: groundwater, from groundwater. streamflow, and surface-water storage. Classification of these records was Figure 3 shows histograms of water use Equations (2), (3) and (4) were substi based on the following types of with by source for 1968. tuted into equation (1) to form: drawal sites utilized: 1. Withdrawal from groundwater re n-S The following assumptions were used Qtn =Mtn +^ [Stn - 1+Stn] +AR X Gt sources through water takings from to estimate total daily and seasonal L f = 1 wells and sandpoints and from dugout irrigation water use in the study area: ponds not connected to a stream or (i) All irrigators possessing permits to for located in a streambed of an intermit take water would have submitted tent stream. «<m + 5 water-taking reeords when they had 2. Withdrawal from surface-water re taken water, and sources through water takings from: (ii) Irrigators whose takings are exempt (i) Streamflow, on-stream dugout under water-use legislation would Qtn=Mtn+?[Stn- 1+Sr„] + ponds and dugout ponds con have irrigated according to the same nected to streams; or ratio as the irrigators having permits ARC[n - (m +5)] g G (ii) Surface-water storage behind dams to take water, r = l on permanent or intermittent (iii) Irrigators who submitted unsuitable streams. water-taking records would have for irrigated in the same manner and on The accuracy of water-taking records the same days as those submitting «>m + 5. depends on the irrigator. Information is suitable records. submitted annually by the irrigator regarding dates of taking, duration and The scale factors used to convert STUDY BASIN AND TEST DATA time of operation, and details of the reported water takings to estimated water irrigation system (4). Water use is takings are presented in Table II. Venison Creek, a tributary of Big calculated on the assumption that the Application of these scale factors to the Creek, lies on the Norfolk sand plain, average irrigator operates his irrigation reported annual amounts of irrigation north of Lake Erie. The basin is about 19 system at the recommended pressure water use yields estimates of total annual km long and 5 km wide, and has an area specified by the sprinkler manufacturer. amounts of irrigation water use. of about 90 km2. The location of the basin and observation sites are shown in Figure 1. WATER USE ASSESSMENT GROUNDWATER STAGE VS. GROUNDWATER DISCHARGE The watershed above the Water During the period 1967 to 1969, only RELATIONSHIPS Survey of Canada hydrometric gauge on 54-65% of the known irrigators submitted Venison Creek was selected as the study Relationships were established be area. The area above the gauge is about tween the mean daily groundwater stage 78 km2 and represents about 82% of the a Ontario Water Resources Commission.